Technical Fiat 126 Brake Issues

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Technical Fiat 126 Brake Issues

SimpleIsBest

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Hi guys, having some issues with my 126 with brakes. This post ended up being quite long, but the main symptoms right now and questions are listed at the end if you don't want to read through what I've done to lead up to this.

First a bit of background, it's a 1981 Fiat 126 Personal 4 (air-cooled 650cc with the plastic bumpers). There's no Polish badges "officially" on it, but from the number of parts with Polish markings on them I think it's probably a Polish made car sold as a Fiat. I also have a Haynes workshop manual for a Fiat 126 1973-1977, which I thought could cover most of my car but have since discovered a lot of small but important differences.

A while ago I decided to have an inspection of the whole braking system since the car had been sitting for a while before I bought it. There were a couple of stages of what happened, which I'll list below:

Stage 1:
Brake cylinders on the fronts were found to be a bit stuck. I decided to order a whole set of fronts and rears since they seemed to be cheap enough. These ended up coming in as 23.7mm front and 19mm rear diameters. I had them fitted and they worked fine, although I found the brake pedal now had a bit of play at the top. Figured that maybe one of the seals on the master cylinder was going bad (original Fiat stamped part), so ordered and fitted a new one, with no difference.

Stage 2:
Decided it was probably the shoes going out of adjustment. The Haynes manual mentioned that to adjust them one had to reverse and brake suddenly. I tried this but no luck. Tried to squeeze the self-adjustment mechanism spring with a big vice but no luck. Eventually bought a new set of shoes, along with brake springs to refresh the whole system.

Stage 3:
Replaced the shoes and springs. Before this point the braking system seemed to be working with just a bit of play at the top, but after doing this I found that there was no pressure at all within the system, even at the rears which were untouched. Decided that the "new" MC was rubbish and binned it, tried the original Fiat item to find it was leaking through the rear seal into car. Ordered a Akron one which I had heard good things about

Stage 4: Replaced the MC with the Akron unit, rear brakes work great but fronts lack pressure. This is where I currently stand

So right now, the symptoms are:
  • First half of pedal travel is extremely light (front brakes), second half of travel is completely solid (rear brakes)
  • With brake pedal fully depressed and held down, front wheels have small amount of resistance but still turnable with wheel on. Rear wheels are completely locked solid

I went through a measured a bunch of things and found the following weird things:
Cylinder diameter mismatch - the manual states 23.7mm fronts and 15.9mm rears, the ones supplied by the shop are 23.7mm fronts and 19mm rears, the original ones on the car are 19mm all round (???) From what I can tell, the MC size remained identical through the course of production, so would a standard 19mm MC be able to pump enough fluid for all these different combinations?
Brake drum dimensions - manual states 170mm or so, one of the front drums has a stamping that states min diameter of 186mm or so, I measured about 184mm internal diameter with a ruler

I honestly feel lost with a bunch of ideas with regards to what to try next. Does anyone have any advice or clarifications with what I've found so far or what I should do next? I'm at a stage where I feel like I should just buy a full set of shoes, springs, and cylinders again from a more reputable shop and replace everything with the hope that it works out in the end.
 
Hi guys, having some issues with my 126 with brakes.
I honestly feel lost with a bunch of ideas with regards to what to try next

Firstly congratulations on having a very rare car in NZ with only less than 100 being officially imported by Fiat over the years. Which would also account for why your car had the 3/4" wheel cylinders which was standard fitting on the more plenty full Fiat 500 and I imagine more easily available in NZ.
As you say the early 126 up to '76 had 23.8mm front and 15.7mm rear. Rear cylinder size was increased to 19.05 (3/4") after '76.
I can understand your frustration as these things can drive you bonkers sometimes. In my experience assuming there are no faulty components the brake problems stem from the self adjusters not gripping the shoes properly as the springs overcome the friction resistance of the adjusters. So most of the brake pedal travel is just expanding the shoes till they finally make contact with the drum and you get a pedal. Or sometimes the system seems to defy attempts to bleed it.
I had an 850 van that was notorious for this until I was advised to allow the pedal to fly back after the nipple had been nipped up on bleeding.
The fact that your rears lock but not the fronts and you have excessive pedal travel suggests to me that there may be a bleeding problem at the front or that the travel on the shoes is so excessive that they only just touch the drum but lack the pressure.
 
To rule out brake shoe return springs being too strong and overcoming the friction of the auto-adjusters, you could temporarily remove the springs, or even just the upper spring (the lower spring mainly just holds the shoes against the lower pivot point) - then try re-bleeding and adjusting the front brakes.

You might find that it's easier to bleed the front brakes if the brake shoes are levered back as far as they will go. (= less space in the wheel cylinders).
Some people recommend using either pressure or vacuum brake bleeding equipment, but imho, manual bleeding normally works just fine.

Have you tried clamping off the front brake flexible hoses. This will isolate the front brakes and allow you to determine if the master cylinder is ok.

Re:- new master cylinders failing? Fiat used to include a leaflet with genuine master cylinders warning you to strip the new cylinder, clean all parts with isopropyl? alcohol?, then lube all seals with brake fluid and re-assemble if the new master cylinder might have been in storage for some considerable time (6 months?). I came across a couple in which one of the pistons had become stuck in it's bore, thereby preventing bleeding of that brake circuit and a very long brake pedal (the stuck piston wasn't pushing any fluid). Does your master cylinder have a removeable end cap that you could remove in situ to check if the front piston has stuck in the end of it's bore?

Hth,

Al.
 
Thanks for the responses guys!

With regards to bleeding, I think I've done it correctly on the system. I've done it using the manual system as well as a pump (i.e. pushing air from the reservoir through the system) to both the fronts and the rears. Since the rears are working pretty well, I think both should have bled correctly? If doing this car and my other project car is anything to go by, it could well be some weird hydraulic thing I've missed though!

So a friend who knows these cars quite well (has a fully restored one he did in Italy) recommended that I check the diameter of the drums and distance between the shoes as well as the full travel of the shoes. I found that the shoes were moving a small but definitely noticeable amount (see attached images, one is with no brake and one with fully depression). I also took a few measurements:
  • Drum Internal Diameter: ~184-185mm
  • Shoe Diameter (no brake): 182.4mm
  • Shoe Diameter (fully depressed brake): 184.6mm
(Note that these measurements are quite rough, especially the drum internal diameter)
I have tried already to squeeze the automatic adjusters to force them to sit a bit closer to the drum, but I think they're still sitting quite far since there's a good ~2mm of difference between the measured diameters with no brake.


In my experience assuming there are no faulty components the brake problems stem from the self adjusters not gripping the shoes properly as the springs overcome the friction resistance of the adjusters. So most of the brake pedal travel is just expanding the shoes till they finally make contact with the drum and you get a pedal. Or sometimes the system seems to defy attempts to bleed it.
Thanks! Yeah it's a pretty rare vehicle here, especially as a lot of the other imported ones have been sacrificed as engine donors for 500s and stuff (picked up 2 speedos identical to mine from a guy for about $20, sadly the ones they came out of were too bad to save :( )

Have you tried clamping off the front brake flexible hoses. This will isolate the front brakes and allow you to determine if the master cylinder is ok.
What would be the best way to clamp off the hoses? I've seen there's a specific tool people use, unfortunately I don't have one lying around and due to the current global situation the auto shops near me have all closed for the next few weeks.


Does your master cylinder have a removeable end cap that you could remove in situ to check if the front piston has stuck in the end of it's bore?
I've already installed a new MC, but I could have a look and see if it's salvageable. Cheers for the tip!

So I think from all your responses that it's likely that I've still not quite done the perfect bleed job or there's an issue with the automatic adjustment mechanism and the brake springs. If it's an issue with the adjustment and brake springs, what options would I have? I have a feeling it's the most likely cause of the issues, but short of buying a bunch of springs and maybe shoes and hoping they work, is there anything I can really do? Is there maybe some weaker spring made for a 500 or something which would work? I guess one solution might be to buy a new 19mm brake cylinder from a 500 and making it work with the extra piston travel?

Thanks for the responses again and I hope you'll take the time to answer these questions I have!
 

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Re:- How to clamp off a brake hose if you don't have the correct tool?

Many just use a vise grips with something to protect the hose from damage e.g by wrapping a rag/cloth around the hose, or using a piece of old leather belt between the jaw serrations and the hose etc.

A better way, if you happen to have needle-nose visegrips, would be to cut some suitably sized metal/hard plastic hose/pipe/tube and slip these over the jaws of the vise grips to protect the hose.

Another way would be to use some 'G' clamps if you have these.

Please bear in mind that the internal bore of the brake hose is only c. 3mm (1/8 inch), so the brake hose doesn't have to be squashed flat in order to prevent brake fluid from flowing.

Most production car brake hoses have a rubber inner, then a woven fabric layer (which provides the strength to resist the brake pressure), all covered by the outer rubber layer to protect the fabric - you don't want to damage the outer rubber layer, nor the intermediate fabric layer.

It would appear that your problems only really began in earnest after you fitted new brake shoes and return springs....

Could you try re-fitting the old shoes and springs (if you still have them) and see if the brake pedal now has normal travel/brakes work well?

Or maybe just refit the old brake shoe springs and see if this improves matters?

As Toshi 975 (and many others on here have said over the years), the replacement brake shoes springs seem to be too strong and can pull the brake shoes back too far by overcoming the adjusters. I think this is probably what is happening on your car. Your brake shoe to drum clearance figures seem to me to be excessive and this alone would give you a very long pedal travel. You mentioned having a reasonably good pedal (just some initial free movement despite the old master cylinder being about to fail)) after you fitted the new wheel cylinders, so the old brake shoes and springs were probably ok, maybe just re-use them if they're not too worn?
I'd be surprised if it was a bleeding issue, as you've bled brakes successfully before and have tried both manual and pressure methods.

If you have someone to help, maybe have them slowly press the brake pedal and observe the movement of the current (new) brake shoes and springs. The shoes should move outwards and when the pedal is released, the shoes should be kept there. The only movement backwards should be equal to the clearance between the adjuster bore and the pin on which it sits, i.e. maybe c. 1?mm. Given how little your shoes move with one push of the pedal, you'll probably have to press the pedal 2+ times to move the shoes full outwards - just be careful not to pop a piston out of a wheel cylinder (= big mess). If the shoes are being retracted all the way back, then the adjusters aren't holding - usually due to excessively strong springs.

Many either refit the old brake shoe springs, or some here, have stretched the new springs. This can be done by holding one end of the spring in a bench vice and pulling on the other spring end (v. hard work!) or if you have some way of heating metal up to red heat, just heat a couple of coils at one end and extend the spring to achieve the extra length - some say increasing the free-length of the spring by c. 6mm (1/4 inch) should work fine.

I wonder if a previous owner had problems with excessive brake pedal travel and fitted 19mm wheel cylinders to fix the issue?

Al.
 
Could you try re-fitting the old shoes and springs (if you still have them) and see if the brake pedal now has normal travel/brakes work well?

Or maybe just refit the old brake shoe springs and see if this improves matters?
Yeah I think I could give that a go. I think it makes a lot of sense if it's the springs and I think I still have some floating around. I'll give it a shot, at least with the top two since in the earlier response you did mention that the top two do most of the work


If you have someone to help, maybe have them slowly press the brake pedal and observe the movement of the current (new) brake shoes and springs. The shoes should move outwards and when the pedal is released, the shoes should be kept there. The only movement backwards should be equal to the clearance between the adjuster bore and the pin on which it sits, i.e. maybe c. 1?mm. Given how little your shoes move with one push of the pedal, you'll probably have to press the pedal 2+ times to move the shoes full outwards - just be careful not to pop a piston out of a wheel cylinder (= big mess). If the shoes are being retracted all the way back, then the adjusters aren't holding - usually due to excessively strong springs.
Yeah that sounds consistent with what I've seen. I did try exactly that, the shoes moved out the small amount shown above then retracted back completely to the original position, so very likely that the springs are way too strong (also when I took those two pictures, there's a video too but it's probably too big to attach).

Many either refit the old brake shoe springs, or some here, have stretched the new springs. This can be done by holding one end of the spring in a bench vice and pulling on the other spring end (v. hard work!) or if you have some way of heating metal up to red heat, just heat a couple of coils at one end and extend the spring to achieve the extra length - some say increasing the free-length of the spring by c. 6mm (1/4 inch) should work fine.
Yeah looks like that's what I'll be getting up to this Easter Weekend haha. Are old springs generally ok to use for a long period of time? Mine were a bit dirty but looking back there wasn't really any other reason to change (if I can find them...). I do have a propane torch so that could be an option, hope it doesn't come to that though!
 
Brake shoe springs can last for a very, very long time.

I think many people change them unnecessarily, probably because they just look old or think they might have become weak.

The way I see it, if they were to become weak, they would likely stretch, if they stretch, there will be space between the coils. So, no spaces = no stretch = not weakened, therefore fit to re-use.

Only wear I've seen, on very rare occasions, was a groove worn in the end loops where the spring attaches to the brake shoe spring holes. In this case the spring might fail at some point so should be renewed as a precaution. They should also be renewed if the end loops have started to straighten out.

Another way of 'weakening' a spring might be to grind a flat along it's length, i.e. so that the shape of the wire used is changed from circular to 'D' shaped, a bit like using a spring made from thinner wire, it'll be weaker and won't exert as much force when retracting the brake shoes.

Al.
 
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Brake shoe springs can last for a very, very long time.

I think many people change them unnecessarily, probably because they just look old or think they might have become weak.
I think that sums me up perfectly haha. I found them again (thankfully I have the bad habit of keeping old parts), measured them (see attached pics) and yeah it looks like the old springs are actually a fair bit longer. I also measured the coils to be slightly smaller in diameter (about 11.3mm vs 11.7mm for the newer ones) which may have contributed too.

Anyway, I installed the old springs onto the car and I've finally got my 126 fully up and running again! It seems like there's still a bit of an issue with the springs vs the shoes (when I push out the shoes they keep retracting, so it seems like the springs are still too strong or the shoes springs are too weak), but definitely driveable now with decent brake pressure. I think I might try increase the length of the new springs I took out to see if I can get them to be a bit weaker for the shoes.

Another somewhat unrelated question too, I changed the oil today along with the brakes. When doing that, I stupidly didn't pay attention to how it was filling into the rocker cover and had a fair amount of the stuff overflow. I tried to clean most of it up where I could, but I think there was a decent amount which went behind the engine and down the airbox with the fan. I've left it alone for today, but would it be safe to start with some oil potentially covering parts of the engine and probably around one of the spark plugs too? I've heard of engine oil fires being a thing so thought I would check (especially since taking that cover off seems to be a massive pain)

Again, thanks guys for giving me this advice and reading through my original post! It's crazy how long it took to sort such a simple problem, but it feels so good to finally sort it out (or at least know what was wrong)
 

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That's great news that you've got your brakes working reasonably well again.

When measuring the springs, it would probably be better to measure between the insides of the hooks at either end because in the case of your springs there's a significant difference between the lengths of the coiled sections. Doing it this way allows you to compare the length of the spring with the distance between the holes in the brake shoes where it fits before trying to stretch the new spring.

Point to note about springs. A spring can be regarded as a torsion bar, just in a coiled shape. 2 main factors determine the strength of a torsion bar, length of bar and diameter of bar. The longer the bar, the easier it can be twisted, the shorter the bar, the harder it will be to twist. The thinner the bar, the easier it can be twisted, the thicker the bar, the harder it will be to twist. In the case of a spring, the total length of the wire used (which is not the same as the length of the spring) and the diameter of the wire determine it's strength.

As regards spilling some oil over the engine - to clean this off properly would really require the removal of the sheet metal cowling (cover). Leaving the oil spill as it is will result in some smell and some oil continuing to drip on the ground for some time, there might also be some fumes/smoke emitted depending on where the oil has reached. I doubt the spilt oil would catch fire unless it is on the exhaust system - nothing else on the engine gets hot enough to set the oil on fire.

I can understand your reluctance to remove part of the engine cowling (cover), it can be a bit fiddly. About all you could do without removing it might be to spray some engine de-greaser (anything non-flammable, e.g. Gunk or Jizer are 2 brands over here, don't use petrol/ diesel/ kerosene/ paraffin/ white spirit/ paint thinners etc.) in the area where the oil spilt, leave to soak in, then flush with plenty of water.

If you have access to a steam cleaner or even a hot water/detergent pressure washer, these would be even better than the above de-greaser.

Al.
 
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