Short story long:

I set out to change my rear brake shoes and adjust my parking brake last week. After struggling to remove the drums, I pulled them off, with help from this forum. Now, after changing the rear brake shoes and wheel cylinders, I have an issue that is really frustrating me. I have ZERO pressure in the brake pedal despite multiple attempts to bleed the brakes, using multiple means.

Here's what I've done:

1) I bled the brakes, using a vacuum bleeder, starting at the right/rear tire, then left/rear, then right/front, left/front. Although there was much air in the system, I eventually was able to bleed both rear brakes satisfactorily.

2) I cannot get the front brakes to bleed. I cannot even get fluid to flow from the front brakes using the vacuum bleeder or conventional bleeding (someone pushing the brake pedal). No fluid flow and the brake pedal goes to the floor with no increases in pressure, despite any amount of pushing. I made sure the brake fluid reservoir was kept full throughout the entire process.

3) Here's what I'm thinking: I have upset the master cylinder, as a result of me losing pressure in the system, when opening the hydraulic lines, to change the rear wheel cylinders. This condition is prohibiting me from building pressure within the system, and not allowing me to bleed the brake with a vacuum bleeder or, using conventional bleeding. Is there a way to burp/bleed the master cylinder? I haven't seen in in the manual.

I'm pretty close to calling a tow truck and taking it to a shop, as this issue has me really frustrated. Before I do that, I thought I'd ask the experts on this forum for their opinion.

The car is a 1970 500L, with 126 Personal hubs, brakes. Thank you all, in advance.

Very curious--what I do when I am bleeding brakes, initially on my own ('er indoors helps me when I get to the 'pressure required' part) is to just open the bleed valve and let it 'all flow out', obviously keeping a careful check on the reservoir level. One question---have you retained the original 500 'single circuit' master cylinder or have you had the 'dual circuit' master cylinder fitted?

the hobbler said:

Very curious--what I do when I am bleeding brakes, initially on my own ('er indoors helps me when I get to the 'pressure required' part) is to just open the bleed valve and let it 'all flow out', obviously keeping a careful check on the reservoir level. One question---have you retained the original 500 'single circuit' master cylinder or have you had the 'dual circuit' master cylinder fitted?

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That's a good question. I didn't bother to look and verify whether the master cylinder is the single or dual circuit. It appears to be very difficult to reach from underneath the car. I'll verify tonight. I would expect it to be dual cylinder and somehow involved in my troubles getting air out of the system.

It sounds likely to be a dual circuit given the difference between front and rear performance.


On the fiat, and on another car, I have had a master cylinder fail during the cycle of draining the system, replacing a wheel cylinder then re-pressuring.


It is very frustrating because normal fault finding leads you to re-check the connections and pressuring process, but in reality you're trying to diagnose one problem which is actually two!


If you are in the UK I can probably supply you a 500 master cylinder. I don't have any 126 ones though

Yes I agree it will probably have a dual circuit master cylinder . May have been fitted with brake upgrade. Are the rear brakes working ?

MOD500 said:

It sounds likely to be a dual circuit given the difference between front and rear performance.


On the fiat, and on another car, I have had a master cylinder fail during the cycle of draining the system, replacing a wheel cylinder then re-pressuring.


It is very frustrating because normal fault finding leads you to re-check the connections and pressuring process, but in reality you're trying to diagnose one problem which is actually two!


If you are in the UK I can probably supply you a 500 master cylinder. I don't have any 126 ones though

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Frustrating is an understatement. My thoughts are that one stage of the master cylinder is interfering with bleeding the brakes, maybe keeping a pocket of air trapped. Tonight when I get home I’m going to try a gravity bleed, opening the bleeder valves, and allowing them to drain slowly. I’m hoping this will free up any large pockets of air in the system. We shall see. It would be bad luck if the master cylinder failed upon re-pressurizing the system. Thanks for the offer, but I am in Italy. At least there are tons of parts available very inexpensively.

phoenix1 said:

Yes I agree it will probably have a dual circuit master cylinder . May have been fitted with brake upgrade. Are the rear brakes working ?

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None of the brakes are working. The pedal goes all that to the floor with no resistance. No amount of pumping changes this condition.

It looks like I have a single stage master cylinder. So much for my theory about one of the stages malfunctioning. Gravity bleeding is in progress.

You could clamp three of the flexi-hoses and get someone to push the pedal whilst you concentrate on one front wheel. Whilst you're bleeding it, turn the bleed-nipple only a fraction in order to avoid an influx of even more air; I ended up using PTFE tape on the nipple-threads

My brakes were awkward, similar to this, but eventually it was sorted.

fiat500 said:

You could clamp three of the flexi-hoses and get someone to push the pedal whilst you concentrate on one front wheel. Whilst you're bleeding it, turn the bleed-nipple only a fraction in order to avoid an influx of even more air; I ended up using PTFE tape on the nipple-threads

My brakes were awkward, similar to this, but eventually it was sorted.

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I’m not confident this will do much for me. The pedal has no resistance when pressed and is ineffective to move fluid through the system. Last night I left the bleeder nipples cracked open overnight in the hopes I’d be able to get fluid through the front brakes. I read that this “gravity” method can be effective for bleeding brakes that are otherwise problematic. This morning I checked and no fluid drained.

After looking at the brake system diagram, I think that the master cylinder has some of blockage preventing fluid from exiting the front brakes. Am I way off course here?

Master cylinders are cheap enough and I’ve got nothing to lose changing it. Or do I?

Richenrygarcia said:

I’m not confident this will do much for me. The pedal has no resistance when pressed and is ineffective to move fluid through the system. Last night I left the bleeder nipples cracked open overnight in the hopes I’d be able to get fluid through the front brakes. I read that this “gravity” method can be effective for bleeding brakes that are otherwise problematic. This morning I checked and no fluid drained.

After looking at the brake system diagram, I think that the master cylinder has some of blockage preventing fluid from exiting the front brakes. Am I way off course here?

Master cylinders are cheap enough and I’ve got nothing to lose changing it. Or do I?

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I would buy a new one. They're not expensive, and it does immediately rule out several issues.


If gravity feeding isn't working then something is fundamentally wrong. At rest the master cylinder should allow fluid from the reservoir to reach both pipes. If this is not happening:

• both brake pipes are blocked
• reservoir inlet is blocked
• seal issue.

you can check if both pipes are blocked, which is very unlikely and you can check if it's a reservoir issue.
Seals can be damaged if there is no fluid in the system before pressurising.


When I have had this exact same issue before, I went over everything twice. Swore at the brakes (not the car, just the brakes.) then ordered another master cylinder. Don't get sucked into doubting your work once you've already ruled it out, master cylinders can fail during a system bleed.

MOD500 said:

I would buy a new one. They're not expensive, and it does immediately rule out several issues.

When I have had this exact same issue before, I went over everything twice. Swore at the brakes (not the car, just the brakes.) then ordered another master cylinder. Don't get sucked into doubting your work once you've already ruled it out, master cylinders can fail during a system bleed.

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Thank you for the advice. I'm on my way to buy the master cylinder after work today. Do you, or anyone, know whether I need to bench bleed the master cylinder before installing? I've read about this before but the manual does not mention the need to bench bleed before installing the master cylinder.

I've never bench bled one. I've also never been advised to bench bleed on this or any other car.
The 126 Haynes manual tells you to bleed after installation. I don't have the 500 Haynes to hand but I expect it's the same.

Unfortunately I am back to square one. I installed a new master cylinder which cost all of 15 Euro at the local autoricambi. The process was pretty straightforward overall, with little drama. The problem still exists - I am not getting fluid to the front brakes and the pedal is still soft.

I tried multiple times to bleed the front brakes but I am not getting fluid flow. The fluid in the reservoir is not even being depleted as I open the bleeder valve and apply vacuum. In fact, when I crack open the bleed valve with vacuum pressure applied, the vacuum if not losing pressure and neither air nor brake fluid is exiting. I fear I have a blockage somewhere in the front brake lines.

As my next plan of attack, I plan to disconnect the front brake hard lines at the master cylinder and attempt to blow (not sure how yet) the line from the master cylinder to the bleed valve. I'll attempt this with the bleed valve completely off, in the hopes that whatever is clogging the system exits.

Not sure if this will be effective but I am running out of options.

have you visibly checked the lines in case one has been crushed flat or something?

Fayray said:

have you visibly checked the lines in case one has been crushed flat or something?

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This is another good idea. I looked at the hard lines when swapping the master cylinder and they appeared to be OK. A colleague of mine suggested I inspect the flexible brake hose. He says he once had a car with a collapsed brake hose which affected one caliper. Sounds reasonable to me.

If, and this is a big if, I do find two collapsed brake hoses, then this could mean I've been driving with inoperable front brakes for some time. My rationale behind this amateur theory, is that I don't think I've done anything in the recent past to affect the front brake system.

More to follow.

That's a shame, I had hoped the new master cylinder would have sorted it for you. At least it wasn't very expensive.

If the vacuum bleeder won't pull fluid through to the front cylinders, again, I would suggest clamping the rear flexis and rigging-up a means to pressurise at the fluid reservoir. I think there are tools made for this but maybe cut out the part of a cycle inner-tube with the valve attached and clamp it round the top of the fluid reservoir with a Jubilee-clip and then apply a bit of air-pressure with a cycle-pump and see if that forces fluid down to an open slave cylinder?

Hi, the problem started after you replaced your rear brake shoes. The soft pedal and bleeding problems may be caused by the poor quality of some of the self adjusters fitted to the replacement shoes.

When you apply the foot brake, the shoes should self adjust leaving a very small clearance between the brake linings and drums. If the adjusters fail to self adjust the brake wheel cylinder pistons will be pulled all the way back into the cylinders by the shoe return springs. When you apply the brakes all the brake fluid in the master cylinder bore is being sent to the rear brake cylinders as the pistons are having to extend a much greater distance than they should. The pedal will be very soft and may go to the floor. This means that little fluid will pass through to the front brakes. If the adjusters are working correctly, only a small amount of brake fluid is needed to force the linings into contact with the drums. You can check where the problem is by putting brake hose clamps on the rear hoses. If you get a firm pedal, your problem will be the rear brakes. If you still have your old shoes you could reinstall them to prove that your new shoes have faulty self adjusters.

The self adjusters on replacement brake shoes are notorious for failing to self adjust. I had similar problems as you and eventually traced the problems to the new shoes having weak self adjusters with too little friction to resist the shoe return springs. I ended up stretching the shoe return springs by a few millimetres to weaken them. This allowed the the shoes to self adjust and solved the problem.

Thanks all for the assistance thus far. I tried to pressurize the fluid reservoir, in attempts to push fluid to the drums but I couldn’t get any flow. I then disconnected the front brake flexible line at the drum and, again, no fluid flow. But, when I disconnected front brake line flexible line from the hard line, fluid flowed, unlike previously.

On my way to the auto parts store tomorrow morning to get new flexi lines. Hoping this will cure my issues.