Brakes Locking Up

[Pescado]

Sooooo…. A couple of days ago I introduced myself and my new 1979 Spider to you all, today I'm reaching out for some help with a break issue. Took the car to work today about a 20 min drive and noticed that my brake pedal was getting stiffer as I travelled. By the time I got to a parking spot the pedal was stiff as could be and the car was locking up. I've had the car for about 4-5 weeks now with no problems and did some long drives...no issues. The master cylinder was changed recently before the sale of the car by the previous owner. After letting the car cool down for about an hour I did a quick inspection under the hood but found nothing that looked like a problem. I then proceeded to put the car in neutral and pushed it back and forth quite easily and heard what sound like some rubbing/light grinding from both front tires. Drove the car home no problem....continued to drive around the neighborhood to try and build up some heat on the breaks to see if this issue would occur again and it certainly did. On the drive way I jacked each corner of the car and tried to spin the tires to see if I could isolate the issue to perhaps one brake caliber but instead found that all four wheels would not turn freely....again once the car cooled down I was easily able to roll the car around in neutral. looks like its time to get may hands dirty....anyone have this experience on their car?

[18Fiatsandcounting]

anyone have this experience on their car?

Yes. The usual cause for this is either:

1) The flexible brake hoses to the individual calipers are collapsing internally due to age/wear, and so you can push brake fluid through them with the brake pedal, but then the collapsed hose holds that pressure until it slowly relaxes (can take several minutes).

2) An issue with the master cylinder, or the wrong master cylinder, or improper adjustment of the actuator plunger that comes from the brake pedal.

Since it appears all 4 of your brakes are locking up, I'm inclined to think issue #2 is the cause. This might not be the issue, but I have heard of previous owners putting in the wrong part. Not that they are evil people, but there are subtle differences in some of the aftermarket master cylinders that can cause issues.

Hope this helps.

-Bryan

[Pescado]

Thanks Bryan….I'm thinking the same thing (master cylinder ) based on your experience and what I've researched so far...plus the fact that this was replaced recently. Question...if the master cylinder is installed incorrectly is it possible for it to operate like normal for over a month and then show issues? I included a picture but not sure you can see enough to comment on whether or not its the correct one. so guys just to let you know I have very little mechanical experience...I am an electrician so I can turn a wrench just not always sure which way LOL. What would be the first thing to trouble shoot?

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[Nut124]

I had this happen to my car on occasion, usually I would feel increasing drag on the highway. Seemed to happen more often in hot weather.

I think this is related to thermal expansion of the brake fluid and the master cylinder being slightly out of adjustment so that the expanding fluid is trapped in the cylinder rather than releasing into the fluid reservoir.

I never fixed nor adjusted mine, but it has not happened in a few years.

[Pescado]

Thanks Nut124

Here's another picture...might be better

[Nut124]

The problem would not be in the plumbing but in the internal adjustment between the brake pedal/booster and the master cylinder piston.

Effectively, when the pedal is at rest, the master cylinder piston is too far fwd blocking the ports that would allow fluid to expand to the reservoir.

I'm not an expert on this, but could one loosen the master cyl retaining nuts, back it out a bit from the booster, and insert shims? At best, this would be a redneck fix?

[18Fiatsandcounting]

I agree with Nut on this. Try backing off the two 13mm nuts that hold the master cylinder to the brake booster, and insert a thin U-shaped shim under each nut. In this way, the master cylinder will be moved slightly further from the brake booster plunger. If nothing changes in terms of your brakes locking up, that wasn't the issue. But, if things improve, then the adjustment of the plunger that goes into the MC is likely the issue.

-Bryan

[Pescado]

I agree with Nut on this. Try backing off the two 13mm nuts that hold the master cylinder to the brake booster, and insert a thin U-shaped shim under each nut. In this way, the master cylinder will be moved slightly further from the brake booster plunger. If nothing changes in terms of your brakes locking up, that wasn't the issue. But, if things improve, then the adjustment of the plunger that goes into the MC is likely the issue.

-Bryan

I agree its a good starting point...do you think one or two cut fender washers would be enough?

[18Fiatsandcounting]

I agree its a good starting point...do you think one or two cut fender washers would be enough?

One on each side should be fine. And by the way, this suggestion was meant to help diagnose the problem, but I wouldn't consider this a permanent fix. If the problem is with the plunger adjustment, that needs to be looked at.

Effective and reliable brakes are something that you want to get right.

-Bryan

[Nut124]

I'd consider regular rather than fender washers in order not to interfere with the piston.

[Pescado]

Ya I agree fenders don't work too big just thought it would be easier to hold on to. The only thing that has me puzzled about trying this is why this adjustment would need to be done if I had no problems with breaks for 4-5 weeks with long drives. If the MC needed adjustments wouldn't this of been an issue right from the installation of the new MC?

I never mentioned this earlier and might sound ridiculous but here we go...the only thing I did recently to the car was wash the rims with a special wheel cleaner...is it possible that the pads are contaminated now and heating up more than normal?

so right now I have the driver side wheel off and when turning the rotor it is definitely dragging...I have loosened up the MC about a 1/4", should this release the pad pressure on the rotors? so far it has not...thoughts?

[Nut124]

The drag at the wheel, when the car is cold, is not likely due to the fluid expansion but a mechanical problem with the caliper or the slides.

Increasing drag while driving can be caused by the fluid heating up and being blocked in by the MC. The heating up can be related to the mechanical drag you can feel when everything is cold.

When the engine is running, the manifold vacuum applies vacuum to the brake booster, this could move the piston forward causing the "blocked" situation.

Assess and fix the mechanical drag. Either the caliper does not slide, or the caliper piston is stuck.

[Pescado]

Thanks for helping me out Nut124 much appreciated...I have this situation on all four tires so I don't think its a caliber issue but then again I don't know much LOL. I got some separation between the MC and the booster using washers tonight, i'll put wheels on and test drive tomorrow to see how this impacts things and report back...thanks again guys.

[Pescado]

ok so did the test drive today...a little bit cooler outside but did an aggressive 45 min drive and happy to say no issues with locking up brakes but the pedal certainly doesn't feel as good as before. I guess now the next step is to make an adjustment to the MC that equivalent to the washers I used. I'll do some research to see what I can find on making this adjustment but if you guys have any info I'll take it. Still curious as to why I'm needing to do this out of the blue...any thoughts on why this adjustment is now needed?

What a great drive today with cooler temps and fall foliage...I love this car, really don't want to put it away. Hope you guys are all enjoying the beauty of fall.

[18Fiatsandcounting]

Yep, took a drive with the dog in the back seat in my '71 just yesterday. Nice time of year!

As for your brakes, my guess is that your master cylinder isn't quite right for this car. There are master cylinders that fit in terms of being able to connect them, but the plunger cup in the open end (next to the booster) doesn't have the right depth for the actuator arm from the booster/brake pedal. Depending which new MC was installed before you bought the car, that could be the issue.

I usually don't just throw parts at a car, but in this case since you don't really know the pedigree of the MC, my advice would be to put another MC in the car from a reputable vendor (Vick's, Midwest-Bayless, AutoRicambi), bleed the brakes thoroughly, and see what this gets you.

Before you install the new MC, there is an adjustment acorn nut on the end of the brake plunger, and there are specs for how that should be adjusted. Let us know when you get to that point and we can guide you through that if needed.

-Bryan