Technical 1970 Fiat 500 F Brakes

[Vitesse]

I have to say one man bleed kits and me have never got on very well, I just never seem to get them to work properly. You can't beat the tried and tested two person method.

I am getting my petrol pipes and brake pipes mixed up, the plastic pipe goes to the master cylinder not the centre tunnel. The only step left if you are getting very little pressure is to carry out a thorough check of the copper pipes for possible damage.

 

[looigi]

Years ago, in a previous life, I was a diesel mechanic. We have a pressure bleeder that was a hand pump on a 20L of brake fluid. We used to work on a lot of the old gear with juice brakes like TK Bedford's, Commer, Dodge etc.

We found the best way of getting air out of some of the more 'characteristic' British brake systems was to put the pressure bleeder on the wheel cylinder nipple and backfeed to the master cylinder. You just have to keep an eye on the master cylinder to make sure you don't overflow the reservoir, but it seemed the most effective way of doing it.

Cheers
Chris

 

[Labman]

Years ago, in a previous life, I was a diesel mechanic. We have a pressure bleeder that was a hand pump on a 20L of brake fluid. We used to work on a lot of the old gear with juice brakes like TK Bedford's, Commer, Dodge etc.



We found the best way of getting air out of some of the more 'characteristic' British brake systems was to put the pressure bleeder on the wheel cylinder nipple and backfeed to the master cylinder. You just have to keep an eye on the master cylinder to make sure you don't overflow the reservoir, but it seemed the most effective way of doing it.



Cheers

Chris

Hmmmmm. This sounds interesting. Now how do I get it to backfeed?? The one I have gets attached to a compressor.


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[stevehg]

As per Peter's post, even with the smallest fitment, I couldn't get a good seal on the small bleed nipples used on the 500 cylinders with my vacuum kit. The pressure would drop too quickly.

I found when replacing the master cylinder that it pays to do the fronts first, move to the rears and then back to the front.

To help you eliminate things get a 10mm fine bolt and some Ptfe and take out the rear feed on the master cylinder and use the bolt to block this off. Bleed the fronts. If you can't bleed them properly, strip down and look at each cylinder/joint etc. Until you find the leak.

If you can bleed them ok, strip down the rears and look for the leak. Again if you are struggling to find it, you can use the bolt on the rear bulkhead y piece to isolate one side at a time.

I know it's frustrating, but equally it's a nice simple system, so you will sort it.

cheers, Steve

 

[looigi]

Suck out most of the brake fluid from the master cylinder reservoir.
Put the pressure bleeder hose on the wheel cylinder bleed fitting and open it.
Pump up your pressure bleeder and the fluid will backfeed into the master cylinder reservoir. Be careful not to overflow it!

This procedure goes against the grain a little, but it works amazingly well. Air wants to rise, and the master cylinder is above the wheel cylinders, so it tends to get pushed up towards the reservoir. The traditional method relies on the flow rate of the fluid pushing the air down to the wheel cylinders faster than it can float up.

Let me know how you get on.

Chris

 

[Labman]

Suck out most of the brake fluid from the master cylinder reservoir.
Put the pressure bleeder hose on the wheel cylinder bleed fitting and open it.
Pump up your pressure bleeder and the fluid will backfeed into the master cylinder reservoir. Be careful not to overflow it!

This procedure goes against the grain a little, but it works amazingly well. Air wants to rise, and the master cylinder is above the wheel cylinders, so it tends to get pushed up towards the reservoir. The traditional method relies on the flow rate of the fluid pushing the air down to the wheel cylinders faster than it can float up.

Let me know how you get on.

Chris

This sounds like a good way to do it but my pressure bleeder works with a compressor and always operates under vacuum. I don't think there is a way to pressurize it. I will see if I can get my hands on one of those hand operated ones. I will give all these suggestions a try and hopefully one of them works!

 

[Labman]

I did everything as suggested. Still barely any pressure. I even bled the MC just in case there was trapped air then re-bled the whole system. Still the same. Next I'm going to take the front and rear drums off and give a look around. If all ok then I will plug the rear brakes MC outlet then if ok, the fronts as suggested to see if I can isolate a blockage or something. I can't believe how simple this system is and how much grief it is giving me


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[Labman]

So this is what I did. An expert on these cars told me that the pin attached to the brake pedal that pushes into the MC frequently gets worn and creates too much play so the plunger in the MC never fully gets pushed in all the way. It had about 1/2" (1.5cm) of movement before it engaged with the MC. I removed the pin (which had a lot of wear at the attachment point to the brake pedal) and welded on a 1/4" (about 6 or 7mm) piece of metal the to end of the pin thus elongating it. Then I ground it a bit to make the edges smooth. Reinstalled with a new cotter pin and BOOM! Brake pressure came up after bleeding and now I have brakes!
I really think you all should check the wear on this pin if your brakes are marginal.
Thanks for all your help with this matter!




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[fiat500]

Brilliant

 

[malbers]

Hi, Just needed to comment on this 17 yr old thread. I had exactly the same issue as OP - and racking my brain, was getting really frustrated. Turns out, same thing after I replaced the MC, some brake lines, and some cylinders at the wheels. I had a garage do a full bleed, still no dice.

After reading this, did the same thing (I did a test by cutting off a bolt of same width at similar dimensions 5-6mm, inserted it and then put the pin on it). Voila that did the trick! Now I'll be extending/welding the pin to that length, I might visit a friend to fabricate a new pin also.

My guess is that the new MC internal plunger moves way further away, and so the old pin no longer works. So glad I saw this, and hopefully if someone still has one and the same issue. Just wanted to confirm that making the pin longer on a new MC did the trick for me also.

Thanks much!!

 

[the hobbler]

Hi, Just needed to comment on this 17 yr old thread. I had exactly the same issue as OP - and racking my brain, was getting really frustrated. Turns out, same thing after I replaced the MC, some brake lines, and some cylinders at the wheels. I had a garage do a full bleed, still no dice.

After reading this, did the same thing (I did a test by cutting off a bolt of same width at similar dimensions 5-6mm, inserted it and then put the pin on it). Voila that did the trick! Now I'll be extending/welding the pin to that length, I might visit a friend to fabricate a new pin also.

My guess is that the new MC internal plunger moves way further away, and so the old pin no longer works. So glad I saw this, and hopefully if someone still has one and the same issue. Just wanted to confirm that making the pin longer on a new MC did the trick for me also.

Thanks much!!

3 things make it difficult to initially get a good brake pedal after the brakes have been overhauled on a 500---(1) the modern 'pattern' springs are slightly too short, so when they are extended (brakes being used) they have too much 'return' strength and the brake shoes are pulled back too much. (2) the 'pattern' brake shoes seem to have a thinner lining than the original 'Factory' parts---this again means that they have to out further before they start working and, (c) I am not convinced that the self-adjusters that come with the the new shoes are as effective as the original ones were.
The answer to these problems are quite simple---(1) try to use the original springs, but if you have to use new brake-shoe return springs, stretch them slightly so that are the same length as the original and, (2) Tony Castle-Miller at "MiddleBarton Garage" has had Ferodo manufacture some shoes made to the original Factory specifications. Sadly, there is very little one can do with the self-adjusters as they now come with the new shoes; in the old days they were availble as a 'kit of parts' which were fitted with a special spanner (the shoes were supplied 'bare').

 

[malbers]

3 things make it difficult to initially get a good brake pedal after the brakes have been overhauled on a 500---(1) the modern 'pattern' springs are slightly too short, so when they are extended (brakes being used) they have too much 'return' strength and the brake shoes are pulled back too much. (2) the 'pattern' brake shoes seem to have a thinner lining than the original 'Factory' parts---this again means that they have to out further before they start working and, (c) I am not convinced that the self-adjusters that come with the the new shoes are as effective as the original ones were.
The answer to these problems are quite simple---(1) try to use the original springs, but if you have to use new brake-shoe return springs, stretch them slightly so that are the same length as the original and, (2) Tony Castle-Miller at "MiddleBarton Garage" has had Ferodo manufacture some shoes made to the original Factory specifications. Sadly, there is very little one can do with the self-adjusters as they now come with the new shoes; in the old days they were availble as a 'kit of parts' which were fitted with a special spanner (the shoes were supplied 'bare').

Thanks! I actually decided to buy new drums also (before I tried this). I was wondering if they were worn out. But the old springs is a really good comment - it did feel indeed there was too much space and flex. I might out on the old springs to see if that helps.

Thanks!!