Thank you for taking the time to read this post! I need some help! I'm having an issue with my rear calipers locking up, usually after driving for 20-30 minutes. The brake pedal begins to stiffen up and then it's as if I'm holding down the brake pedal...but only the rear brakes!? I had an evaluation done and was told my the shop that my rear calipers needed to be replaced, which I've done and after changing them out and bleeding the brakes, I let the car idle for about 30 mins, brakes seemed fine....I went for a test drive through the neighborhood and seemed like a vast improvement! I drove for about 15-20 mins, pulled into a friends house up the street to take him with me on a joy ride, never turned the car off and as soon as I tried to back out of his driveway, my rear calipers were tight again! Anyone else had this issue? I havesearched and read all kinds of pages and posts and I have a couple of other ideas, but I have yet to discover anyone talking about this same issue! I need some advise!

 

when you replaced the caliper, did you replace the whole caliper and braket assembly, or just the caliper? I'm assuming you don't have brembos?

If you didn't replace the caliper, i'd bet your slide-bolts are corroded and binding.

 

I replaced the caliper, the mounting bracket and the guide pins. They were lubed and tourqed to 21 lbs. Thecalipers themselves are working great, until this pressure issue happens. I'm thinking it's something either with the master cylinder or inside the brake line. I am going to try the master cylinder check test on the rear lines first and then the front just for assurance sake and if that passes I'll try a cleaner/flush and a double bleed of fluid!

 

Do you have an ABS light?

 

I've never had any lights for the brake unless I pull the E brake and get the standard brake light.

 

Jack stands , and time. I'm very interested in the outcome. Wish it was closer, I would live to be directly involved in the troubleshooting.


Thinking something to do with underwood heat, master or ABS unit. I would start with a master rebuild , maybe a sticking piston.

 

just it to a mechanic. I learn that here at a forum people taking guesses at your problem will solve nothing.

 

...I am the MECHANIC! HaHa! I completely understand where you are coming from, I agree people guessing at your problems does solve nothing! However, being mechanically inclined and trusting my own work and respect for my wallet I am looking for someone who has eitherencountered the same problem before...or...Someone that sparks something that I myself had not yet thought of!
....Don't get me wrong...If I had posted a question and replaced the first part someone mentioned or just started spending money with wreckless abandon and had absolutely no mechanical skills...I would definitely take it straight to the shop! ....but in reality...it's a hydraulic braking system it's not rocket science...just time consuming and definitely could be expensive if you just start replacing everything!

 

Btw is it one or both rear calipers ?

Sounds like drive it till it happens, get it on jack stands and play with it . See where the pressure is building up.m

 

What is the vehicle history? Agree prob master or abs.

 

I'm hoping to get a chance before Friday to have it figured out. I bought everything I need to check the master cylinder specifically and also more brake fluid and have everything I need for a brake flush...hopefully one of those will solve the riddle!
It is both rear calipers, But I have another trick up the ol sleeve that might help out as well! I will keep the progress and the final diagnosis posted!
....except for the walkthrough and the revealing of the mystery culprit *LIVE!* on PAY PER VIEWWWWWWWW! ...HaHa!

 

Both would make me lean on the master.

2 lines out of the master, front and rear and go to the abs controller. Then 4 seperate lines from the controller to the calipers.

If it is the controller, it would have to effect both circuits to the rears.

Ebrake , can't completly rule it out. But I don't see anything straight mechanical getting effected by heat or time while running.

 

That's what I want to check out next, but I may have found a solution...hopefully no rain and enough time this afternoon to know for sure!

 

So.....after all the horrible weather, the time, money effort so far (Lack of free time making it tough!) I'm still having an issue...however...I am updating my entire braking system which is a great thing! I started out small, removed everything (calipers, pads, rotors and parking brake) cleaned EVERYTHING, replaced parking brake shoes and adjusted, brake line flush, replaced rear calipers, all new stainless steel/braided flexible brake lines, adjusted the brake pedal and still having an issue, which pretty much narrows down the culprit to the infamous master cylinder and hopefully not ABS related. (Which I had leaned toward before and a couple guys actually mentioned, but when your married and you need to budget in upgrades, you ALWAYS go with the process of elimination!) Haha! But thanks for all of the feedback! Love my Z and its die hard fan club!