New Master cylinder needed?

[profcucchi]

Hello All,

My car has run trouble free for a couple of years, so it was bound to happen...

I push the brake pedal and there's no tension or pressure. It just slams down and bounces back.

Am I looking at a new master cylinder and or brake booster? Is there a way to check one or the other, or just replace both?

I drove last week and the brakes seemed a bit off, almost like they were spongy, but I didn't touch the brakes at all, so there wouldn't be air in them.

Thanks

[DieselSpider]

Is the brake reservoir still full or is it now empty?

If its still full then you probably need a new master cylinder while if its empty you might need a new master cylinder or you could have a caliper in need of rebuilding, ruptured brake hose or brake line.

You really need to check the entire system out for leaks. The last item to consider when the brake pedal goes to the floor is the brake booster since that is just a big vacuum diaphragm to assist in pressing the brake pedal and not really a hydraulic part.

How bad did the brake fluid look when the last 2 year brake flush was done? If the brake fluid has not been flushed out and replaced with fresh for a while the metal brake lines could have rotted from the inside out due to absorbed moisture from the air and now be in need of replacement along with any caliper or master cylinder that's had the corrupted brake fluid going through it. Brake fluid flushes are a critical part of brake maintenance and could probably eliminate most premature metal brake line, master cylinder and brake caliper failures.

How old are the rubber brake hoses and calipers?

Did you ever put other than old fashioned DOT3 brake fluid in it? Some of the rubber parts in the brake components sold for the 124 Spider don't react well with the newer types of brake fluid and have been know to fail shortly after one of the new ultra synthetic brake fluids are put in them.

Air can get sucked into the system from a bad seal or a leaking line. You can also get a bubble in the system if the brakes overheated from forgetting the parking brake on or from the calipers getting stuck. When you do the 2 year brake fluid flush its also good to clean and lubricate the sliding wedges on the calipers with a good quality caliper grease to help prevent them from sticking.

[18Fiatsandcounting]

I heartily agree with everything that Dieselspider mentioned above, and I'll just add that functional brakes are very critical and not to be taken lightly.

Based on what you've told us so far, I'd first check the brake fluid level in the reservoir. My first guess (could be wrong of course) is that you've had a slow leak somewhere in the system, and when the fluid got low enough, air was sucked into the master cylinder which is where you are now. If this happens to be the issue, you'll need to find and fix the leak, and re-bleed the system, at a minimum.

-Bryan

[profcucchi]

You guys are awesome!

Today is too beautiful to be in the garage, but tomorrow is troubleshooting day, and maybe ordering parts...

Thanks!

[profcucchi]

Hello all,

I was able to successfully bleed the rear tires. Never done it before and it was very easy.

When I got to the passenger front, the bleeder screw was rounded off. I clamped it, tried tighter closed wrenches. Nothing.

Any idea how to get the bleeder out without causing more damage?

Thankfully, the driver front is in perfect condition.

[Odoyle]

Use PB blaster and wire brush, then pair of vice grips

[samakijoe]

Here's the tool to use. First cut off the end of the fitting so you can use the largest size.
Gets a better grip on the head. Lowes carries this brand of tool.

https://smile.amazon.com/IRWIN-HANSON-B ... ay&sr=8-10

[18Fiatsandcounting]

Frozen brake fittings and bleed screws are challenging, and the above is good advice. Here's what I do: Use a brass wire brush to clean off all the debris around the bleed screw. Heat the bleed screw with a propane torch, just on a low flame, and leave the end of the blue flame tip at the bleed screw for a minute or two. Let cool, and apply Kroil* penetrant around the threads. Let sit overnight, apply some more Kroil, and then use either a flare nut wrench or a pair of vice-grips to remove the bleed screw. Sometimes gently hammering on the top of the bleed screw helps, as does gentle hammering as you twist the bleed screw in the tightening direction, then the untightening direction. Wave some chicken bones over it if needed.

*Kroil, while not cheap, seems much better than WD-40.

If the above doesn't work, drill out the bleed screw and retap. I've never had to do this though, as the above has always worked.

-Bryan

[RRoller123]

Be careful. Brake fluid is incredibly flammable, very dangerous.

[18Fiatsandcounting]

Be careful. Brake fluid is incredibly flammable, very dangerous.

Agreed, caution is urged. Braking systems can certainly get very hot during hard usage, and I've seen stock car rotors glowing cherry red after a hard lap around the track. However, I can't say how hot the calipers are, or the brake fluid within. After doing some Googling, it appears that brakes in normal car usage don't get much over 400 oF, although brakes in racing cars can reach 1000 oF. Again, these are the hottest parts and not necessarily the brake fluid temperature.

I certainly wouldn't advise heating a stuck bleed screw until it glows red (way too hot), but mild heating with a brief low flame or a high powered soldering iron is often used as one tool to remove stubborn bleed screws. Any open flame around a car or its components should be treated with respect.

I'd suggest trying the other (non-heating) methods first.

-Bryan

[RRoller123]

Maybe a hot air heat gun, like for shrinking heat tubing? Tip of a soldering iron sounds like a pretty controllable minimalist approach too.

I was always taught to apply whatever penetrating fluid is being used, and then lightly tap the junction with a small wrench or small hammer. The small impact shocks help the lubricant work down into the joint. It does seem to work.

[18Fiatsandcounting]

Yes, lightly tapping with a hammer is a good approach, and you can do this while applying torque in both the tightening and loosening directions. I've found the primary factor for success is a wrench that fits tightly over the bleed screw, although if it's already rounded, that's not much help. A good six point (not twelve point) socket also works for bleed screws, although again not if the screw is rounded and not if you're looking to remove something with a brake line hose or line attached. A flare nut wrench is very helpful in those situations and helps to avoid rounded screws and nuts in the first place.

For rounded bleed screws, the only approach I know is a pair of vice grip pliers or, in extreme cases, carefully drill out the bleed screw and retap, being careful not to go deep enough to drill into the mating face down at the bottom of the bleed screw hole. Another approach (I've never had to do this) is to remove the caliper and take it to a machine shop, or just buy a new or good used caliper.

For the past few decades, I've put one layer of Teflon tape on the threads before reinserting bleed screws, being careful that the tape covers only the threads and not the mating face at the tip. For me, this has worked well to avoid future problems, and anti-sieze compound on the threads might also work although I've never tried it.

Just yesterday I successfully replaced the rear brake regulator in my '71 Fiat, and the brake lines to that were a mess. A combination of light wire brush cleaning, an overnight dose of Kroil penetrating oil, about 30 second of a low flame from a propane torch, let it cool down, and the connections came right off with a flare wrench.

OK, I've gone on long enough. To the original poster and others with similar problems, good luck!

-Bryan

[profcucchi]

Dear Fiat friends,

I got it done! Heat, PB Blaster, tapping and a flat vice grip got it undone. Local auto shop had one, only one in stock, and I started over from scratch.

Very proud to do it on my own, and more appreciative of all the guidance!

[18Fiatsandcounting]

Hooray for Prof. Cucchi! A job well done, sir.

-Bryan

[profcucchi]

Hello All

Quick one, I hope:

I was adjusting the ebrake, which I've done in the past. When I turn the adjusting nut, the rear tires don't stop spinning. It does feel tighter, but they spin. I turned the nut in so much the hand brake wouldn't lift, so I backed off a bit.

On the ground, with the brake on, the car hardly moves.

Is it stripped? I have a ebrake cable handy so replacing isnt an issue.

Thanks