Technical Brakes barely work, changed/read all, need help!

[gatoslocos]

Hello all, I have a new to me 1982 Fiat Spider. Beautiful! Brakes were good but brake booster had vacuum leak. Installed new brake booster, and while I am there, changed master cylinder, 4 calipers and pads, brake lines, and brake compensator. Brakes are VERY WEAK. With engine on, I can push pedal to the floor (with some effort). I have changed the master cylinder twice now. In both cases, I bench primed and then primed in place as well. I have used multiple schemes to ensure no air in the system (push from the reservoir and pull from the bleed valves).. Beautiful clean liquid comes out the caliper bleed plugs. I originally did not change all the above, but in the process of trying to make it work again, I have progressively changed more and more, with new parts from Midwest Bayless.

Help!!!! I do have car experience and have restored some cars before but of course plenty of you know more than I do.

Some details/symptoms:

I did have to regulate the brake booster piston length to a very low amount to match the original one. I know if I "make it longer" then I cannot pass liquid through the front brakes. Now, it is just barely pressed when I fasten the master cylinder over it. All four calipers can be bleed very nicely.

When I press the pedal, it has maybe 1 or less of "Free play" (seems ok). The whole brake pedal travel is around 10 cms. At around slightly less than half the brakes are strong enough that I cannot push the car, but I should not be able to push the pedal all the way down (which takes some effort but still that is not correct). Again, I have primed the master cylinder several times and I can see no bubbles at all.

Somebody please take pity on me and tell me the obvious thing I am doing wrong...

-Frustrated,

D.

 

[bugsymike]

Hello all, I have a new to me 1982 Fiat Spider. Beautiful! Brakes were good but brake booster had vacuum leak. Installed new brake booster, and while I am there, changed master cylinder, 4 calipers and pads, brake lines, and brake compensator. Brakes are VERY WEAK. With engine on, I can push pedal to the floor (with some effort). I have changed the master cylinder twice now. In both cases, I bench primed and then primed in place as well. I have used multiple schemes to ensure no air in the system (push from the reservoir and pull from the bleed valves).. Beautiful clean liquid comes out the caliper bleed plugs. I originally did not change all the above, but in the process of trying to make it work again, I have progressively changed more and more, with new parts from Midwest Bayless.

Help!!!! I do have car experience and have restored some cars before but of course plenty of you know more than I do.

Some details/symptoms:

I did have to regulate the brake booster piston length to a very low amount to match the original one. I know if I "make it longer" then I cannot pass liquid through the front brakes. Now, it is just barely pressed when I fasten the master cylinder over it. All four calipers can be bleed very nicely.

When I press the pedal, it has maybe 1 or less of "Free play" (seems ok). The whole brake pedal travel is around 10 cms. At around slightly less than half the brakes are strong enough that I cannot push the car, but I should not be able to push the pedal all the way down (which takes some effort but still that is not correct). Again, I have primed the master cylinder several times and I can see no bubbles at all.

Somebody please take pity on me and tell me the obvious thing I am doing wrong...

-Frustrated,

D.

First are you 100% sure there is at least a small amount of freeplay at brake pedal, otherwise when using car in future brakes can gradually lock on?
Next, are you 100% sure no air anywhere in system?
Next, you don't mention new brake discs? I have had vehicles where new pads or shoes replaced all round and due to a small wear ridge on disc or drums I have had a terrible pedal on starting a road test, but after a few miles of working the brakes (not over heating them though) gradually the pads/shoes overcome the wear ridge and align fully with the contact area.
If that is the case , do not over heat the brakes trying to bed them in , do it gradually and allow them to cool otherwise the disc/drums will be damaged/distorted.
If new discs were fitted at same time as pads then disregard this advice as surfaces should meet evenly and give normal travel, although still may firm up as bed in.

 

[124BC1]

I agree with 'bugsymike' ^^ .

Brake booster (servo) pushrod adjustment should be set so that the tip of the pushrod protrudes 1.05 to 1.25mm ( 0.041 to 0.049 inch) beyond the surface to which the master cylinder is mounted on the brake booster, see diagram (disregard that it shows a single circuit master cylinder) below:-

To check servo is functioning normally, with engine off, press brake pedal several times to expend any vacuum, pedal should then be hard, hold the brake pedal down while starting the engine - as vacuum is built up in the servo, the brake pedal should drop a little but still be firm but probably a bit less so than before.

Now to determine where the problem lies, I'd suggest clamping off all the brake flexible hoses - there are proprietary hose clamps available but if you don't happen to have these, then very careful use of Visegrips or similar using protective padding to protect the hoses will suffice - the inside bore of the hoses is only c. 1/8 inch so no need to clamp them flat, just a gentle squeeze will work. If the brake pedal is now solid with little travel then the problem is downstream of the master cylinder i.e calipers, pipes etc. If the pedal is not firm, problem is in the master cylinder/ brake booster.

If the problem is not in the master cylinder, then release each of the hose clamps in turn and try the brake pedal - this will tell you which brake unit/s is/are at fault. I'd suggest you try releasing the clamps on each of the front brakes first because I suspect the front brakes are o.k. and the problem is most likely in the rear brakes.

If the problem is indeed found to be in the rear brakes, then the rear calipers may not have been set up correctly.
1. If you examine the rear brake caliper piston, you'll see a deep groove that fits over the pin that protrudes from the rear of the brake pad. But there is also a thin groove that looks like a line scratched on the piston. It's important that this thin line is above the deep groove when the caliper is installed - this line corresponds with a cutaway/channel in the piston inner end inside the caliper to allow all the trapped air to be bled out. If the piston is not orientated correctly, you could bleed the brakes multiple times and still not get all the air out (this might be the cause of your problem?). N.B. This info applies to original caliper pistons, idk if it applies to replacement calipers).

Now, as regards adjusting the rear calipers, my approach is to back off the parking brake cable adjustment fully (at the U shaped cable balancer under the transmission tunnel) so that the parking brake operating arms on the calipers are fully off.
Screw the caliper pistons in fully (clockwise both sides), ensure that the thin line on both caliper pistons in uppermost and refit the calipers.
Bleed the rear brakes, (with the engine turned off) ensuring that either the axle is raised or the compensator linkage is disconnected and propped up to keep the compensator valve open - if the axle is left hanging, the compensator valve will be closed preventing proper bleeding of the rear brakes (I assume you already know this as you've managed to get fluid out of the rear brakes).
Next, pump the brake pedal several times, this adjusts the caliper pistons out against the brake pads (will possibly have already happened when bleeding the brakes).
Adjust some of the slack out of the parking brake cable and apply the parking brake, hard, several times - this will adjust the parking brake mechanism inside the rear caliper pistons, then readjust the parking brake cable, if necessary - you don't want it set too tightly, it's important the parking brake doesn't bind at all when released. Iirc the normal parking brake travel is quite long maybe 5 - 7 clicks for fully applied.

(P.S. This ^^ is how I used to set up Fiat 124 rear brakes when I worked as a Fiat Dealership Mechanic in the '70's)

 

[bugsymike]

Excellent advice from @124BC1 and although I always located the pin in pads, I was not aware it could effect bleeding the caliper, I had thought it was to assist the self adjusting mechanism position.
On that note, it is surprising how often people over adjust their handbrake cables as easiest to do, to the point that the handbrake lever on the caliper never returns to it's fully off position thus preventing the self adjusting function from operating, so actually making matters worse.
I was taught from the days of drum brakes to adjust at the wheel where possible and then finish off with the cable finally.
The reason was, as taught by my college lecturer was leverage is strongest at 90 degrees to the fulcrum point, so if cable is over adjusted it starts to lose it's max. efficiency, but even more important on self adjusting calipers.

 

[s130]

Excellent advice from @124BC1 and although I always located the pin in pads, I was not aware it could effect bleeding the caliper, I had thought it was to assist the self adjusting mechanism position.
On that note, it is surprising how often people over adjust their handbrake cables as easiest to do, to the point that the handbrake lever on the caliper never returns to it's fully off position thus preventing the self adjusting function from operating, so actually making matters worse.
I was taught from the days of drum brakes to adjust at the wheel where possible and then finish off with the cable finally.
The reason was, as taught by my college lecturer was leverage is strongest at 90 degrees to the fulcrum point, so if cable is over adjusted it starts to lose it's max. efficiency, but even more important on self adjusting calipers.

Slightly off topic but you mentioned rear drums and fulcrum.

The Strada 130TC is fairly notorious for excessive brake pedal travel. Worse still the excessive travel takes the pedal past the maximum fulcrum point.

Most of the problem (not all) was with the rear drums brakes requiring more fluid to properly get the shoes to brake operation point. Some people used to over adjust the handbrake to reduce required shoe travel. Others used to drive with the handbrake not fully home, up a notch or two, and I even saw suggestions of changing the way the lever that pulls the shoes by welding up some of the shoe to lever notches.

The proper solution was to rectify a design fault. The fault was that the shoe return springs were too strong so that the self adjusting friction pads were being overridden and the shoes retracting too far. In the case of the 130TC one spring is stronger than the other so I replace the stronger one with same spring as the weaker one. This sorted most of the problem.

The rest of the problem was the master cylinder and front brake pots. The 130TC had larger Bendix pots but the master cylinder displacement was not really changed thus resulting in more pedal travel to get fluid into the large pots.

I never resolved this latter problem as I instead fitted Aeroquip stainless braided reinforced hoses which due to their zero/near zero expansion under pressure less fluid was required to get the brakes really hard on for track use.

All fun and games of vehicle ownership and DIY.

 

[bugsymike]

Slightly off topic but you mentioned rear drums and fulcrum.

The Strada 130TC is fairly notorious for excessive brake pedal travel. Worse still the excessive travel takes the pedal past the maximum fulcrum point.

Most of the problem (not all) was with the rear drums brakes requiring more fluid to properly get the shoes to brake operation point. Some people used to over adjust the handbrake to reduce required shoe travel. Others used to drive with the handbrake not fully home, up a notch or two, and I even saw suggestions of changing the way the lever that pulls the shoes by welding up some of the shoe to lever notches.

The proper solution was to rectify a design fault. The fault was that the shoe return springs were too strong so that the self adjusting friction pads were being overridden and the shoes retracting too far. In the case of the 130TC one spring is stronger than the other so I replace the stronger one with same spring as the weaker one. This sorted most of the problem.

The rest of the problem was the master cylinder and front brake pots. The 130TC had larger Bendix pots but the master cylinder displacement was not really changed thus resulting in more pedal travel to get fluid into the large pots.

I never resolved this latter problem as I instead fitted Aeroquip stainless braided reinforced hoses which due to their zero/near zero expansion under pressure less fluid was required to get the brakes really hard on for track use.

All fun and games of vehicle ownership and DIY.

That drum brake friction adjusters has been an issue on many with that design, apart from the Fiats we had it with Ladas in the 70s even with original equipment new parts. As you suggest weaker top springs helped.
I won't mention the Moskvichs which were in a different World again
Master cylinder and wheel cylinder dimensions has been an issue on many makes over the years and even when some had servos and the wrong master was supplied, or in the case of Mk1 Ford Transits the Lockheed wheel cylinders were used on many vehicles 3.5 ton twin wheel pick ups down to 850cc Minis, so the opportunity for mistakes multiplied.
Aeroquip hoses started near us in Totnes so was able to benefit from their knowledge on retro fitting to a 1947 Vauxhall 14 saloon that we dragged out of a lock up when quiet after Christmas one year and got it back on the road.
Incidentally a recent thread mentioned battery life, that one had been sat in lock up for over 25 years and after a charge the Lucas battery was able to start it to our surprise.

 

[gatoslocos]

All,

Many thanks for your input...I think perhaps I got things working. My brake booster is on a bracket and that bracket then fixes to the firewall. However, the four screws on back of the booster (to fasten to the bracket) were slightly too long so it prevented the booster from fastening flush to the bracket and to the firewall so the pedal attachment was maybe 0.25 inches receded. Also, I adjusted the booster piston rod (that pushes against the master cylinder) to 2.5mm sticking out (supposed to be up 1.9 mm). At 2.5, it engages ever so slightly at rest but liquid can still return from all four wheels so there is no brake preload. As soon as I step on the pedal the brakes engage and I cannot spin the wheels by hand (else they rotate freely). However when driving, the first half of the pedal does not "stop the car much" but in the second half I can lock-up wheels. Also, in conversation with some supplies for this car, they remind/think the stock brakes are from the 60s and not "superb" compared to today, so perhaps I was expecting more than what can be delivered by the stock brakes. I did order some EBC brake pads and that supposedly have a little more "bite" but they have not arrived yet.

Thanks for all your help! Will update on that last part when installed...

 

[bugsymike]

All,

Many thanks for your input...I think perhaps I got things working. My brake booster is on a bracket and that bracket then fixes to the firewall. However, the four screws on back of the booster (to fasten to the bracket) were slightly too long so it prevented the booster from fastening flush to the bracket and to the firewall so the pedal attachment was maybe 0.25 inches receded. Also, I adjusted the booster piston rod (that pushes against the master cylinder) to 2.5mm sticking out (supposed to be up 1.9 mm). At 2.5, it engages ever so slightly at rest but liquid can still return from all four wheels so there is no brake preload. As soon as I step on the pedal the brakes engage and I cannot spin the wheels by hand (else they rotate freely). However when driving, the first half of the pedal does not "stop the car much" but in the second half I can lock-up wheels. Also, in conversation with some supplies for this car, they remind/think the stock brakes are from the 60s and not "superb" compared to today, so perhaps I was expecting more than what can be delivered by the stock brakes. I did order some EBC brake pads and that supposedly have a little more "bite" but they have not arrived yet.

Thanks for all your help! Will update on that last part when installed...

I wouldn't put too much stock in "conversation with some supplies for this car, they remind/think the stock brakes are from the 60s and not "superb" compared to today," .
Obviously not ABS etc. but would still expect a firm brake with a good response.
As in, stamp the brakes and lock the wheels without pedal being on the floor.
Little bit concerned about what you are saying about servo mounting and rod adjustment.
If someone applies the foot brake firmly on and off, there should be very little flexing or movement on the mountings under the bonnet for servo etc. Also I would like to see a slight visible freeplay between pedal and master cylinder.

 

[gatoslocos]

No mounting flex. Yes, some freeplay I agree should exist between piston rod and master-cylinder. That extra 0.5mm probably does nothing so I could return it to just under 2mm, but that requires dissassembling everything again for the 100th time. Will get to it later. I also ordered a "rear compensator delete union", just to fact out that issue. All my calipers and the rear compensator are new, but still something could be off...once I get all that I will try change pads first, then try rear compensator delete, etc...

 

[124BC1]

@gatoslocos

I don't know if you read my post (#3 above) but you don't seem to have tried anything I suggested?

Back in the day, if I couldn't achieve a firm pedal with no more than normal travel, I wouldn't even bother taking the car out on roadtest - it's not likely to improve with driving and could even be dangerous.

I don't know how much technical understanding you have but you don't appear to fully understand how a brake booster works (you might check into this especially the operation of the reaction disk) nor the internal workings of a dual type brake master cylinder (especially what happens when the brakes, operated by one of the 2 cylinder circuits, are out of adjustment). In the case of your car, I suspect that the forward master cyl. piston (which afaik operates the rear brakes) is being pushed (not by the brake pedal) but by the fluid in front of the rear m. cyl. piston (which operates the front brakes via 2 outlets) to the end of the cyl. bore while trying to apply the rear brakes, which the front piston can't do due to incorrectly set-up rear caliper pistons. Only when the front m. cyl. piston reaches the end of the bore, can the fluid between the 2 pistons be pushed by the rear piston to apply the front brakes. This will result in a long pedal that only seems to apply the brakes when the pedal is maybe 1/2 way down. Clamping off the brake hoses as I suggested will confirm or refute this.

I'd suggest re-adjusting the booster pushrod to standard specs - I've done this on some Fiats by disconnecting the master cylinder from the booster (2 nuts) and pulling the master cylinder out of the way (leaving all pipes undisturbed and no need to re-bleed). I know space is very tight on lhd cars but you might be able to do it this way (just don't damage any pipes). Iirc, excessive protrusion of the pushrod from the booster can result in excessively sharp servo (booster) action and make it difficult to modulate the brake application (i.e. they're either on or off and sharply so).

I wouldn't bypass the rear compensator valve (it shouldn't affect brake pedal free travel) - it's a safety feature to prevent rear wheel lock-up under heavy braking - if rear brakes were to lock-up, especially in wet conditions, it could cause the car to spin, possibly out of control. You fitted a new valve, so it should be fine (the only problem I've encountered with these valves is becoming seized in the open position). Just set up the operating linkage as per the manufacturer's recommendations and it should be fine.

Changing brake pads to a different brand/type is not going to affect brake pedal travel. You mentioned having fitted new pads and I'd assume new rotors at the same time, but you haven't confirmed this. The original pads and discs worked fine, (back in the day) (at least for the 1st few hard applications, might get a bit of brake fade subsequently). See the brake figures below, the 124 Coupe (a heavier car than the Spider but has same brakes), you'll see it's brakes performed as well as one of the Ford Mustang models :-

I still think your problem is due to the rear brake caliper pistons not having being adjusted up correctly...
(if you don't believe me, try clamping off the rear brake hoses and see how much pedal travel you then have...)

 

[gatoslocos]

I appreciate your information and your stubbornness

What adjustments are to be done for the rear pistons?

0. I have new calipers, compensator, brake lines, pads, master cylinder and brake booster; rotors are not changed but seem ok.
1. bleed with weight on wheels so the brake compensator is letting fluid through; done lots of times; check!
2. ensure the groove on the rear piston is pointing towards the bleed valve; check!
3. hand brake engages with only 3-4 clicks; check!
4. raise the car to see if wheels spin freely; check!
5. press pedal ever so slightly and see if rear wheels cannot be spun by hand; check!
6. I read somewhere that the piston can be screwed in/out to adjust for hand-brake cable but that would seem useless since handbrake engages just fine
7. Disk brakes should be self-adjusting, what else to adjust?

 

[gatoslocos]

Also, I did try clamping off the rear brake hoses and I believe no big difference, but also I am not sure I clamped off fully -- I am a bit hesitant to clamp the hose to strongly.

 

[bugsymike]

6. I read somewhere that the piston can be screwed in/out to adjust for hand-brake cable but that would seem useless since handbrake engages just fine
7. Disk brakes should be self-adjusting, what else to adjust?

Re items 6 and 7 on your list.
With handbrake cable disconnected or very loose, do the handbrake levers at the calipers sit on their stops as they should?
Then with wheels able to turn freely, if you actuate those levers, if caliper self adjustment working correctly, you should only need to move the handbrake lever on the caliper a very tiny amount for the wheel to stop, just from the action of your finger.
Assuming both sides are like that, then I would carry on checking the hydraulics action/issues.

Incidentally I was interested in the Road test Brake comparison chart from @124BC1 as in the mid 1970s I worked for the Mazda dealership and often drove Mazda RX3s and RX4s with the Rotary engine in shall we say "spirited fashion" and found no problem with braking compared with other vehicles of the day, so if the Fiat 124 Coupe was giving the best braking figures, roughly in line with the Ford Mustang of that era and better than the Mazda, then quite fair for those days.

 

[124BC1]

@gatoslocos

I agree with @bugsymike re the importance of ensuring that the handbrake (parking brake) operating levers on the rear calipers need to be able to return to their stops i.e. fully off,to allow the caliper automatic adjusters to work correctly.

Fitting new brake pads to used rotors can cause some issues as @bugsymike has already pointed out but this is unlikely to be the cause of your excessive brake pedal travel, so I'm not suggesting you replace them.

Handbrake cable adjusted to be fully on @ 3-4 clicks - is too tight and can prevent the auto adjusters in the rear calipers from working correctly. Adjusting the cable so that the handbrake works doesn't mean that the rear caliper pistons are now adjusted correctly, things need to be done in the correct order.
The caliper internal adjuster works slowly given the small operating range of movement of the h/brake operating levers, if you adjust the h/b cable before allowing the adjusters to do their work, they may not be able to work at all...One possible giveaway that this has happened is that the brake pedal travel is significantly longer with the handbrake off that when the handbrake is applied (on).

To check if the auto adjusters are working:-
With the caliper removed from it's mounting (no need to disconnect the hose or h/brake cable) operate the caliper h/brake lever, you should see the caliper piston gradually adjust out in small steps. Screw the caliper piston back in fully before refitting the caliper, do not try to screw the piston out to adjust out the pedal travel, instead follow the set-up procedure below.

To adjust the rear calipers pistons :-
1. Back off the handbrake cable adjustment so that the handbrake operating levers are full off, i.e. back against their stops (as @bugsymike has said).
2. Screw in the caliper pistons fully clockwise, ensuring that when you've done so, that the line/shallow groove on each piston is facing upwards.
3. Refit the rear calipers.
4. Press the brake pedal a few times to push the brake pads against the rotors, see what the brake pedal travel is like.

5. *Either* hold the brake pedal down and apply the handbrake several times (this should cause the internal caliper adjusters to adjust up).
Or, press the brake pedal and apply the handbrake simultaneously several times (which should cause the auto adjusters to adjust up)
[* Given that it's c. 40 years since I worked on Fiat rear brakes, I can't remember which method worked best but I think both will work.]

6. Try the brake pedal, see if the pedal travel is now acceptable. It should now be and is iirc, not dependent on handbrake cable adjustment.
7. Finally adjust the handbrake cable to give 5-7 clicks when fully applied, check that when released that there is no binding/dragging, if there is, back off
the adjustment until the wheels turn freely.

A few final thoughts:-
Bleed the brakes with the engine off. (no need for booster assistance and may only cause confusion - pedal may not be fully firm with boost working).

Do not, under any circumstances, shake the container of brake fluid - doing so will introduce air bubbles into the new unused fluid, then into the system you're trying to bleed - I've seen people do this without thinking and then wonder why they can't get a solid pedal, so they start changing parts...Or they bleed the brakes again a few days later and get a glug of air initially out of each caliper because the tiny air bubbles they cause to be entrapped in the can of brake fluid they shook, has now settled out of the fluid in each caliper just below the bleed screw hole...

I'm not a fan of silicone brake fluid (DOT 5), as this stuff can itself cause problems, Dot 4 brake fluid is perfectly adequate.

Bear in mind that any, even quite small, lost movement at any of the brake units will result in a much larger increase in brake pedal movement, due to the leverage ratio of the brake pedal to the brake pushrod e.g. something that causes an extra movement of 1/8inch on the brake pushrod might result in an extra movement of the brake pedal of 3/4 or even 1 inch. All items should be firmly mounted and mountings be devoid of flex e.g. booster mounting to engine firewall (bulkhead) should be quite solid.

Incorrect adjustment of the front hub bearings can 'kick' the brake pads back when the car is driven giving a long pedal when brakes are next applied.

If the rear brake calipers have been adjusted correctly, there should be no significant difference in brake pedal travel between applying the brake pedal only versus applying the brake pedal with the handbrake on (applied fully).

I still maintain that clamping off the brake hoses is the best and quickest way to determine where the problem lies. I can appreciate your reluctance to risk clamping the hoses too tightly but given the bore of the hose is only c. 1/8inch, not much more compression than this is required. The type I use were made by Girling (a major brake component manufacturer) but there are lots of different types available, or use something else with padded jaws or maybe a small C clamp?
To clamp off the rear brakes on the 124 Spider, you only need to clamp the rear brake hose that goes from the metal pipe on the body to the 3 way union on the rear axle.

And, as regards calling me 'stubborn', I'm highly offended

( )

 

[bugsymike]

100% agree with all of @124BC1 comments.
Re the brake pipe clamps, my Girling ones have died a long time ago , so now use this type, which are quick to fit and release.
As an apprentice, I recall my boss loaning a set of brake pipe clamps to a regular customer, but on return the guy was complaining about them damaging his pipe. He had fitted them to the metal pipes!!!

 

[124BC1]

No update from @gatoslocos ?

But for anyone else who might be interested, here's a guide I found showing how to adjust the Brake Booster (Servo) pushrod :-

Brake Booster Adjustment

FIAT 124 Spider and Sport Coupe Brake Booster Adjustment

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