Hello all...long term browser of the site, first time poster.
I have a 1969 L which pulls to the left under breaking. I have renewed the lines, the cylinders, the master cylinder, the shoes and return springs. Bled the system several times. I've set the brakes up by reversing like a nutter and hitting the pedal. Still pulls to the left! Today I swapped the left drum to the right and vice-versa...and the problem follows the drum! Has anyone an idea what is happening here? I need new ones I guess and they are not expensive. Would love to hear some opinions on what is going on? Thanks for listening!

Warped/misshapen drum would be my guess

I would agree with Chris---slight drum warpage. Replace BOTH.

Thanks chaps...I have just ordered a pair. If the drum was warped wouldn't I feel that through the pedal?...a pulsating or some sort of irregularity?
I gave the car a good shake down and really got into the working temperature zone (and out the other side ? )...no change...always a heavy pull. In any case I hope this fixes it...if not then I'm lost and so's my MOT ?

The original drums had a habit of going out of round due to the relatively light construction. Like many things on the original Fiat 500 weight was a consideration in the design but replacements were cheap so they stuck with them until 1972 when the 126 and 500R came on the scene , more power in the engine and more braking power needed so the drums were beefed up to suit. Many of the drums for sale now are of the 500R pattern.

The new ones I ordered are looking quite reinforced judging by the ribs on the inside. The ones on the car look the same mind you...but it's difficult to tell how much service they have done...maybe to the moon and back...who knows!

Well the new drums are on my car now....and it still pulls to the side....deap despair! So...Bled the system again and went out for a proper shake-down. Oddly the lock-up starts at the driver side and occasionally will switch to the other side when hot. Then occasionally I can get both wheels to lock (it's wet out today)....once cooled down the lock goes back to the driver side. Don't know what to do now!?
I think I'm going to strip down both sides and have a good look at the shoes, the springs, the cylinders and ensure that it's all in balance from left to right. It's all new stuff...so it should be fine.
Any further advice (however improbable the potential solution may be) would be greatly appreciated...I'm at the stage where I'll try anything!

mitchw1971 said:

Well the new drums are on my car now....and it still pulls to the side....deap despair! So...Bled the system again and went out for a proper shake-down. Oddly the lock-up starts at the driver side and occasionally will switch to the other side when hot. Then occasionally I can get both wheels to lock (it's wet out today)....once cooled down the lock goes back to the driver side. Don't know what to do now!?
I think I'm going to strip down both sides and have a good look at the shoes, the springs, the cylinders and ensure that it's all in balance from left to right. It's all new stuff...so it should be fine.
Any further advice (however improbable the potential solution may be) would be greatly appreciated...I'm at the stage where I'll try anything!

Click to expand...

Is the car pulling noticeably to one side while braking?
Or has that been cured?

Is the concern now that both wheels don't lock up simultaneously?

Cheers
Jack

Whilst braking yes...it's the last issue I have... and I've had a few! This problem is a good-un mind you, and is defying me to the bitter end! Failed MOT because of it. I need to get it to brake straight before going back for re-test.

mitchw1971 said:

Whilst braking yes...it's the last issue I have... and I've had a few! This problem is a good-un mind you, and is defying me to the bitter end! Failed MOT because of it. I need to get it to brake straight before going back for re-test.

Click to expand...

Which brand of shoes did you fit?

Did you clean the preserving oil off the drums prior to fitting?

One of the problems that has been noted with some of the 'patern' brake shoes is that the lining is slightly thinner than the original, which when added to the problem of 'patern' brake-shoe springs being too short, does cause problems. Speak to Middle Barton Garage---thay have had brake shoes for the 500 (sadly, not the 126) especially made for them by a leading brake manufacturer to the ORIGINAL specifications.

I got the shoes from https://www.fdricambi.com ... They're no particular brand generic stuff. I could drop the originals back on that do look a bit more substantial and have enough meat still. I did wipe down the braking surface of the new drums...and my test drive got them to the kind of temperature where nothing could survive. I thought giving them a good pounding might bed them in. But that proved fruitless.

mitchw1971 said:

I got the shoes from https://www.fdricambi.com ... They're no particular brand generic stuff. I could drop the originals back on that do look a bit more substantial and have enough meat still. I did wipe down the braking surface of the new drums...and my test drive got them to the kind of temperature where nothing could survive. I thought giving them a good pounding might bed them in. But that proved fruitless.

Click to expand...

Giving brakes a good pounding trying to bed them in is actually counter productive.

With new brake components drive gently for couple of hundred miles, unless you have to brake hard of course.

Generic pattern parts can be a bit rubbish.

Good luck

Let us know

Even if you have been supplied a set of undersized brake-linings, (which I doubt), the difference is not going so be anywhere near as much as if you have used linings (like me) which are approaching the wear limit but which still work; so I don't see this as a problem. Early 126 linings are the same as those for the 500 and although other pattern parts can be really poorly made, it is extremely unlikely that such a critical component, which is used on a variety of other vehicles and has been widely manufactured for decades, will not be within tolerances. In any case, all the linings are the same on your car so any discrepancies are equal on all wheels.

Have you tested the brakes whilst stationary in order to eliminate the possibility of this being related to steering geometry, worn or loose wheel-bearings or other worn or misaligned components?

I would get the car off the ground, get someone to apply the footbrake and attempt to manually turn the wheels. Obviously, you will expect to either be able to turn the driver's side wheels or at least feel a little less resistance. If this is the case, if you are certain that everything inside the drums is correctly assembled, I would be looking at the pipes and the hoses for problems, which may be internal blockages.

With a suspect drum removed it would be useful to have someone slowly apply the brake whilst you have a broad screwdriver or some other tool to wedge each of the shoes against the backplate in turn whilst watching to see if the wheel cylinder pushes the free brake shoe. Prepare them to stop immediately if you see the piston getting pushed too far out of the cylinder.

Doing this may deepen the mystery but might also give you something to work on.

mitchw1971 said:

Whilst braking yes...it's the last issue I have... and I've had a few! This problem is a good-un mind you, and is defying me to the bitter end! Failed MOT because of it. I need to get it to brake straight before going back for re-test.

Click to expand...

So did the brakes fail the MoT on the rollers when they were tested? If so do recall how unbalanced they were both front and back? Was there an obvious difference on just the front or was it unequal on both front and rear? What was it like when they tested the rear brakes using the handbrake? Was that ok?

I assume when you say you have changed both drums, you are talking front? As it is not an split braking system i.e. I doesn’t have an independent system for front and back. It’s quite possible that the rear drums maybe be dragging and causing the car to pull to one side. The natural assumption would be to concentrating of looking for the problem on the front end because that is what you would expect with a modern car with a split system.

With a single system if your car is pulling to the left it could be a problem on the front left but equally it could be a problem on the rear.

It’s some thing worth considering because you seem to have eliminated a lot of components but it’s unclear if you have been concentrating purely on the front end? Which to be fair most people would.

Interesting comments and ideas chaps. This evening I had another crack at it. Took both drums off and compared the 2 sides. I noticed the lock-up side was full of dust and the other side not so much...which figures. I also noticed the upr return spring was shorter on the none-locking side. So I lengthened it by getting pliers in between the coils. Then I decided to take the shoes and springs off and swap sides. Cleaned everything up, wheels back on and off out for a shake down. Now it's better...but the blummin thing likes to pull one way or the other based on i-dont-know-what. Both sides are braking well now for sure but one side always wins out and the car drifts that way. Seems rather random. I know my geometry is a bit awry and I will get that fixed and then risk the MOT again. On that subject...whilst British I live in Belgium...MOT or "keuring" is a government run thing and u are not allowed in because of Covid. And they are notoriously unfriendly and give u no feedback at the end other than the paper which says only "Brakes: more that 50% delta between left and right side". I would really just like to run the new brakes in a bit by using the car before I go back..but if I get caught...?