New Master cylinder needed?

[18Fiatsandcounting]

Did you bleed the lines on the rear brakes? If so, did you the raise the car by the rear axle, or by the body? If you raised it by the body, it's possible your rear brake regulator (compensator) did its thing and reduced the flow of brake fluid to the rear calipers, and leaving air in the rear brake lines.

Based on what you've described, it sounds to me like the pistons of the rear brake calipers are not fully extended to be snug against the brake pads (when both the pedal brake and emergency brake are off). This could be because of air in the brake lines, a bad rear brake regulator, or a frozen piston. Your emergency brake moves the pistons outward only a couple of millimeters, so if the piston isn't snug against the pad when the emergency brakes are off, you can tighten the emergency brake adjusting nuts all you want and the emergency brake still won't engage very well.

-Bryan

[profcucchi]

Did you bleed the lines on the rear brakes? If so, did you the raise the car by the rear axle, or by the body? If you raised it by the body, it's possible your rear brake regulator (compensator) did its thing and reduced the flow of brake fluid to the rear calipers, and leaving air in the rear brake lines.

Based on what you've described, it sounds to me like the pistons of the rear brake calipers are not fully extended to be snug against the brake pads (when both the pedal brake and emergency brake are off). This could be because of air in the brake lines, a bad rear brake regulator, or a frozen piston. Your emergency brake moves the pistons outward only a couple of millimeters, so if the piston isn't snug against the pad when the emergency brakes are off, you can tighten the emergency brake adjusting nuts all you want and the emergency brake still won't engage very well.

-Bryan

I raised the car by the pumpkin and had jack stands under the axles. I bled all the brakes farthest to closest, and the brakes work as good as they ever did. How do I test for a bad brake regulator?

Found this:

Just a point of clarification...

It is the brake regulator that necessitates that the rear axle be under load to bleed the rear brakes. Without weight on the rear wheels the regulator will not allow fluid to pass.

However, many have bypassed the regulator. If this is the case, the weight bearing requirement is no more.

So, the tires need to be on for a proper rear bleed?

Thanks!

[18Fiatsandcounting]

It sounds like you did the brake bleeding exactly the right way, and since your main brakes seem to be working fine, some of my previous hunches are incorrect. By the way, removing the tires to bleed the brakes is fine.

So, at this point it seems like the problem is confined to the emergency brake operation only. If you have an assistant, have them pull the handbrake lever up while you're looking at the mechanical arm (lever) on the bottom of each of the rear calipers. That arm should move towards the front of the car about an inch or so when the handbrake lever is pulled.

Once you determine whether those arms on the rear calipers are moving or not, we can further narrow down the problem.

Also, when I think about it, I have had a couple Fiats where the emergency brake barely did anything, but the main brakes worked just fine. I seem to recall it was an issue internal to the rear calipers (the emergency brake self adjustment system). While I'm thinking about this some more, if someone else knows for sure, please add your thoughts.

-Bryan

[rridge]

If the parking brake did work after the last major caliper and pad renewal and then gradually lost effectiveness I'd suspect the cable needed adjustment or the cable itself is seized or partially seized. Go with Bryan's suggestion and see whether pulling the handle moves the parking brake arms on the rear calipers.

[profcucchi]

I changed my oil, first time, and it was interesting. I read the manual and watched videos and it was pretty easy. Took me 2 hours though...slight interruption due to lunch, honest!

Installed a new plug as the old was really chewed up. I have a shield and since I won't change oil for a bit, I'll install.

Next year, the whole area needs a deep clean and maybe new pan and gasket.

[RRoller123]

Try this with the shield! Pretty easy, used some slit rubber fuel hose, held in place with RTV, to cover the sharp edges after hack-sawing the cutout.

[profcucchi]

Try this with the shield! Pretty easy, used some slit rubber fuel hose, held in place with RTV, to cover the sharp edges after hack-sawing the cutout.

Thanks RRoller123

I've seen this before and it makes a lot of sense. The shield I have has the metal bands, but same idea for the cut out.

[profcucchi]

Hello All,

Same issue arising. I bled the brakes, all good, clean.fluid, no bubbles. Reservoir is full.

I start the car and the brake pedal hits the floor. No leaks or puddles on the floor.

Now would it be the master cylinder?

Thanks

[DieselSpider]

Hello All,

Same issue arising. I bled the brakes, all good, clean.fluid, no bubbles. Reservoir is full.

I start the car and the brake pedal hits the floor. No leaks or puddles on the floor.

Now would it be the master cylinder?

Thanks

It depends on whether you successfully primed the master cylinder first and whether you pumped too low and sucked air back into it while bleeding the wheels. If you pumped the brake pedal to bleed them then the master cylinder is at least pumping some brake fluid.

I can be a more than one rinse, wash, repeat cycle when bleeding brakes. After almost 50 years I finally got myself a MityVac Vacuum Bleeder and now wish I had done that decades ago since it makes the job much easier and increases the first time success ratio greatly.

I thought you mentioned though that they were working fine after you bled them some time ago. Have you been driving it since then or is this the first time its been started since your originally got them bled and moved on to changing oil, adjusting the parking brake, etc?

[18Fiatsandcounting]

I reread this entire post, and I had the same question as in DieselSpider's last sentence in his post right above. At this point, I still think that there is air in the brake system, and probably lots of it since your brake pedal goes to the floor. But, I can also think of four other possibilities, all admittedly remote:

• 1. The brake seals on the calipers are bad. I say this because I once rebuilt all 4 calipers with new seals and for unknown reasons, they didn't seal and the brake pedal went all the way to the floor, starting about 50 miles after I rebuilt the calipers (the brakes were nice and tight during the bleeding process). This was about 30 years ago, but I seem to recall that the brake fluid was leaking past the seals and then being "collected" in the area under the dust caps at the ends of caliper pistons, so no leaks were apparent from just looking at it. The solution was to buy and install new caliper seals from a different manufacturer, and everything worked fine after that.
  2. Your pistons on the rear calipers are stuck in the fully retracted position, so the master cylinder is pumping fluid to the rear brakes, but all it is doing is moving the pistons outward, but not enough to engage the brake pads, so that's why you have no pedal pressure. I have some problems with my answer here, as the front brakes shouldn't be doing this, and you should get some pedal pressure if the rears are goofy but the fronts are OK.
  3. Your brake pads and rotors are so worn that the pistons are at the end of their travel and so when you push the brake pedal, all that you're doing is taking up the slack in the system but not engaging the pads against the rotors. I would think that the piston would just continue to move outward even to the point of pushing it out of the caliper, but I'm not sure if there is a point when the pistons just don't move that much more if they're fully extended and especially with air in the system.
  4. The plunger on the master cylinder is way out of adjustment, so that when you press the brake pedal, all you're doing is moving that plunger until it just starts to engage the pistons in the master cylinder. Enough to bleed the brakes perhaps, but not enough to properly function the brakes. Just racking my brain here trying to think of all possibilities.

One other question: With the wheels off the ground, can you still turn all 4 wheels when you press the brake pedal to the floor?

-Bryan

[profcucchi]

Hey everyone,

I was on vacation and just got back.

I replaced the master cylinder (tight space but a flare nut wrench helped), bled the brakes (I've learned to have extra screws around, as well as PB Blastr and flat vice grips) and... nothing. Same issue of the brake pedal hits the floor with zero tension.

What are my next steps? All help is appreciated!

[DieselSpider]

Ensure the that rod coming out of the brake booster is adjusted properly and engaging the master cylinder completely and that it was actually bled. If its not holding after you bleed it there is a chance too that one of the fittings is not tight or possible was over tightened causing a hairline crack that is allowing air to get back into the system.

Its really hard to say without being able to put hands and eyes on it.

[profcucchi]

Ensure the that rod coming out of the brake booster is adjusted properly and engaging the master cylinder completely and that it was actually bled.

How do I turn the acorn without the whole rod turning? Seated or not it spins as one.

Should I use a padded vice grip? I won't touch a thing until I know better.

Thanks

[SteinOnkel]

That's exactly what I did. There's a tiny locknut too I believe.

Remember, the plastic cup needs to also be in the booster when you install everything. Then you have this absolutely nightmarish to measure spec of 1.0-1.5mm (not 100% on that, check the manual) that it needs to stick out. Try not to get this wrong, as I did bleeding was no problem, but after a mile of driving all four corners were piping hot due to constantly braking. I turned the acorn another 1.5 turns in et voila. Pads and rotors perfectly bedded, brakes feel amazing.

Good Luck

[profcucchi]

Ladies and gents,

I followed all the recommendations you provided as well as local FIAT gurus and there was no change in the pedal. Nothing.

So I brought her to the local Fiat mechanic and he was stumped, too.

And, as expected, I noticed a rad fluid leak from the thermostat tee.

But, no complaints, as I've had fairly worry free driving for a few years.

I'll keep you posted.