I desperately needed new brakes on my 1993 Corvette Base, so I ordered the Powerstop Z26 Street Warrior kit from Summit, thinking it would be a quick and easy job, even for someone as inexperienced as me. It has been quite the opposite. I need help from people far more experienced.

My problems consist of what I think is the brakes not releasing pressure throughout the system. Before I started the brake job, everything worked fine just that my pads were completely original (the car has 66k miles purchased Aug 2024). Everything was going smoothly until I couldn't get the calipers back over the new pads and rotors, since they needed compressing. My first error was that I did not know that I was supposed to open the bleeder valve when compressing the pistons. I compressed the pistons anyway, and probably pushed some bad fluid up the system. After reinstalling everything, and pressing the brake a couple of times, I learned the new rotors would no longer move, as hard as I tried. The pads were stuck to the rotor because of the tight fitment.

Disappointed, I did a full brake fluid flush with new dot 3 fluid hoping that was my issue, but to no avail. I then rebuilt all 4 calipers with new seals and cleaned them out. I think this helped a bit, as now the pistons will compress further than they would before, and the calipers fit more happily over the pads and rotors now (in the front at least, the rear is a different story). Once the brake system was bled of air, I pumped the brakes a couple times and the front wheels now move freely, albeit with a little bit of drag on the pads, but I assume that's fine since they are brand new and have yet to have been broken in.

The rears are completely locked up still though. The caliper was an extremely tight fit over the new pads and rotors despite being fully compressed. Even with the wheel on for better leverage I cannot get it to move. From what I've seen online the rotors should be around 20mm, the inner pad 13mm, and outer pad 11.6mm. All of this information seems to line up with what I've installed, but could I be wrong? There is absolutely no room for the caliper to slide side to side via the slide pins as the caliper hits the outer pad before sliding out at all.

As for what the problem could be, I do not know. My theories are that me pushing the fluid back up through the system without opening the bleeder valve could have damaged some seals in the ABS valve, brake booster, or master cylinder, causing the system to act like a one-way valve, allowing pressure in but not out. My confusion here is that why is this not an issue in the front anymore? I am sure it is not the parking brake as the parking brake is down, and the car is in neutral.

I've been struggling with this for a while and I just want to drive my car again, its been out of commission with this problem for weeks. I feel like an idiot.

 

1. I also been dealing with a similar problem.......my 90 drove perfect then I could sense rear brake drag with all the symptoms and fear the ABS mystery ! ? I will follow and hope we both get help??

h get some opinions.....

 

I really hope its not my abs module... sounds complicated haha

 

Hi hopefully be something simple, is normal to use a G clamp to press the caliper pistons back into the callipers. No need to release the bleed screw, anyway always good to bleed the brakes every two years as brake fluid absorbs moisture. Sounds like your issue is now with the rear brake dragging, have attached images from my shop manual to show the calliper handbrake mechanism adjustment. Also the automatic handbrake adjust how to disable and enable it. It may be the auto handbrake adjuster or incorrectly adjusted calliper adjusting screw (23 in rear calliper diagram) causing your rear brake to not release fully.
Hope these images help you 🙂👍

 

Appreciate these images greatly! Will report back.

I just ordered my service manuals today, wishing I had these a while ago.

 

A few hopefully clearer images

 

​​​​​​When at the rear calliper with handbrake cable pulled off the calliper lever, you will know if its the calliper adjuster screw incorrectly set not allowing the piston back fully or the handbrake auto adjuster needing to be reset. Good luck 🙂👍

 

Agreed with the others, compressing the piston without the bleeder screen did not mess up your ABS unit. Doing that with the bleeder screw open isn't a bad idea I guess if you're planning to do a brake fluid flush afterwards. Just means you're dealing with getting air out of the system again.

Did you lube the pad holders up fully? The pads being stuck on the holders can cause this too. It sounds like you got the pads and calipers back over the rotors? If you got them on, they're not an incorrect fitment. You have some sort of other issue causing this.

 

Here are some images.

 

The caliper looks fully compressed, correct me if I’m wrong, but the pads still stick right up against the rotor with a pretty tight fit. I tried to show that as best I could in the images. As for the parking brake does everything look normal? As I’m not engaged? Pic shown below


(I do have the caliper and pads off in this photo)

EDIT: I took the brake line off for better access to the caliper. Both 11 and 23 in the caliper diagram are pushed faints the piston: parking brake. You said to take off the parking brake cable and then I would know if that was the problem? How do I go about doing that

 

I suppose I should have asked this earlier but this isnt normal right? for the brake pads to be smushed up against the rotor like this? i can't rotate the rotors by hand with the caliper and pads on, but i can with them off. I can't imagine this much resistance is good to drive on? Im not making a problem out of nothing right... this is my first brake job.

 

is there a possibility the rotors are thicker than stock?

 

It looks to me like the pistons aren't compressed like at all. I could be misinterpreting that picture, but I see what looks like a lot of piston sticking up out of the caliper.

 

i mean they are thicker than the old rotors that are worn but they are 20mm which is within spec. i was actually considering running the old rotors for a bit to take some pad off so that the new rotors would fit better. need to check if the old rotors are past the discard width though.

 

Hopefully someone has a rear calliper out and can measure the gap between fully retracted piston and calliper end, then you will know your piston is fully back and not held out by the adjustment screw or pushrods . Have replaced the rear pads on my vette a few months ago and had no issue fitting the calliper and brake pads onto rotor, however I did disassemble the calliper and put a new seal kit in. I followed the procedure in manual to ensure the adjuster screw was set correctly, if not it can limit how much room there is for the brake pads. it's a one off only adjustment when calliper is being rebuilt. Hopefully no one had fiddled with it, not knowing there is a separate handbrake lever area auto adjuster as well. Have never had brake pads that were too thick, in my 20+ years of replacing them on my corvettes. Always pushed the piston back fully with a G clamp, pushing fluid into master cylinder. You cannot damage the abs unit, unless there was a lot of rust debris in the calliper. I suggest checking the calliper adjuster screw as per shop manual, to ensure correct clearance and eliminate that being an issue before sanding the pads down to fit. Good luck, perseverance pays off, you will find the problem eventually 👍

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Lucky I have A mold wheels easy to check the rotors with my vernier callipers, measured my rear rotors they are 20.2mm thick. So is not your brake rotor being too thick, one thing you can eliminate. Next pull the handbrake cable off the lever on calliper, then see if the piston and clamp the pads are up against can go back further. In case the handbrake cable attached to calliper does not allow the pushrod back enough. Then check that adjustment procedure. Screw number 23 in diagram, that can limit the clamp rod and actuator collar the pads rest against going back fully if set incorrectly.

 

Gentleman, as always thank all of you for your responses and thoughts and images of course! I thought I would just throw out there what I have done, my car is a Florida car no rust no corrosion calipers and all working cables and such are clean and corrosion free, that being said as mentioned earlier I noticed brake drag in the past couple times I've driven it which is not often so I put it on the rack took off the back wheels & rotors would not turn release the bleeder screws rotors turned close the bleeder screws start the motor in neutral just enough revolution to watch them spin ,rotors spin as expected pull on the emergency brake they stop release the emergency brake they continue to turn as expected then I applied foot break pressure rotors stopped released pedal rotors did not turn! Release the bleeder rotors turned so here we are what is the thoughts amongst you gentlemen ? I have removed the brake lines as that seems to be a popular possibility and have not replaced them yet but have them ready to go on. I had my wife pump the brakes with the brake lines off in the rear flushing clean fluid through the lines I am now at the point of replacing the hoses connecting everything & bleeding out the calipers and crossing my fingers? One other question my sliders seem to be okay they move push them forward and back when I was wondering how much movement I should expect I have not removed the calipers / the emergency brake cable / the sliders or anything ,everything is as it was. Again I thank everyone for their thoughts and opinions based on what I have tried any new thoughts or
ideas as always are greatly appreciated, hope this helps some of you guys as you work through these problems.

 

Looks like there is no problem with the handbrake or callipers adjustment, only leaves a few things like brake hoses swollen up inside causing a restriction or master cylinder issue it is rare to have a big restriction in the hoses though. Have heard people have brake drag issues with not enough air gap in the master cylinder fluid reservoir, enough resistance with cap on to prevent the calliper from releasing. As long as the fluid level has a 1/4" or more air gap to master cylinder cap you should be ok. The only other explanation would be if the booster had an issue with tear in the diaphragm, when starting the car ensure the brake pedal does not drop / pull down slightly? However that would affect front brakes dragging also. The master cylinder has two pistons for front and rear, if there is an issue with the rear brake master cylinder piston not returning fully it would not allow fluid to bleed back into the reservoir when stepping of the pedal. Again a rare failure, even rarer would be an abs pump failure however as you can bleed the brakes it suggests there is no issue there.
Had seen a few reports of people having similar issues on this forum in 2008 of rear callipers not fitting on with new brake pads, the rear locked up and people sanding the pads thinner when searching rear brake issues online.... So you are not alone in experiencing this issue, so check the air gap in master cylinder to reservoir cap and check the brake pedal doesn't drop when starting the car. To eliminate the reservoir over full or booster issue, your latest tests show its only a problem when the brakes have been applied and when cracking the bleed screw open it releases points to a fluid issue not returning to master cylinder reservoir. Be it brake hose restriction, booster applying pressure without effort on pedal or master cylinder issue. Interesting to hear what you find ! 🤔
We never stop learning what can go wrong on our cars, some things are a unique combination of problems... I have been stumped at times by the simplest things, always good to step back and review peoples opinions and take a viewpoint from different perspective. Sometimes the problem suddenly stands out, leaving ourselves cursing how did I not see that. We have all been there done that, keep your chin up you will get find the issue eventually and we will all learn
🙂👍

 

Have a look at the shop manual regarding dragging brakes, has some steps to take what to look at. 👍

 

during the caliper rebuild did you check fit the pistons to ensure no binding? did you wipe them with clean break fluid before final install? Also I have seen rubber hoses inner lining separate and act like a one way valve. Pressure goes to the calipers but cannot return towards the master cylinder.