Brakes sticking when warm (solved - pedal interference)

[luxuryrules]

New to me 06 XLR-V just arrived. From what I can tell of this car, it’s been sitting in various dealer lots and auctions for the past 9 months, and previous owners were snowbirds who left it parked for part of the year, so I’m expecting gremlins from it sitting.

When I drive it farther than a few miles, the brakes lock up, like a sticking caliper but at all four corners. From taking a 4 miles drive into town (at sub-35mph speeds), ok for the first few blocks, then really have to get on the gas to get the car moving and as soon as I let off the gas it stops in like 20 feet. As soon as I got home, I could feel the heat radiating from each of the four wheels.

I have new flex hoses, pads, and rotors to do the brakes at all four corners as they’re pretty spent already, along with replacing the fluid that looks like coca-cola. I notice that once the car sat overnight the brakes stopped sticking.

Question is, should I be looking at something like a master cylinder too?

Edit: tl;dr: problem was a kick panel that wasn't secured, blocking the brake pedal from returning to home position

 

[mickeytee]

All four at one time would be pretty rare unless they are really rusted up.

 

[luxuryrules]

Exactly. I changed the fronts last night and I didn’t encounter any sticking hardware, siezed pins or bolts, etc; so unless the fluid is contaminated enough to do this I’m wondering if I need to suspect a failing brake booster or master cylinder.

 

[mickeytee]

Highly doubt it. Fluid is not going to be that cantaminated . if the pistons pushed back into the housings then the fluid is not the problem. Neither will the master cylinder as its split front and back so no way all four are sticking. If the abs module is not working it would set a code. So you may have other problems. If they are sticking enough to have to press the accelerator hard they would be boiling in a mile or so and so hot the lugs are popping and making cracking sounds . use an actual thermo gauge to find out the heat. plus once you get the car moving take your foot off the gas and see if it rolls. If the brakes are locking it will stand you on your head.

 

[luxuryrules]

. use an actual thermo gauge to find out the heat. plus once you get the car moving take your foot off the gas and see if it rolls. If the brakes are locking it will stand you on your head.

I don’t have a thermo gave but all four wheels get too hot to touch after a half dozen 20-0 stops and about one mile of driving around neighborhood. You are correct, flushing out the contaminated fluid did not fix either. And can confirm when driving as soon as i let off the gas the car immediately slows down as if im applying pressure to the brake pedal.

The forums are full of frustrated stories about people like me with all four corners dragging, and people having replaced calipers, master cylinders, and brake boosters to no avail. Found a couple spots where someone suggested backing off the master cylinder retaining nuts by a few turns as a diagnostic test, to confirm that the brake booster output was indeed pushing too hard against the master cylinder by relieving it slightly. That relieved my symptoms. So when I pulled the master cylinder away from the brake booster, I discovered that the splines against which the bore of the master cylinder rest, were worn in by probably 1/16".

Current workaround is using a washer on each of the master cylinder mounting studs, although I suspect the long term "correct" fix is to actually put a shim where the master cylinder bore contacts the brake booster. I've got one of those H shaped measuring tools on the way with the sliding center rod so I can measure this out correctly, but with the thing being non-adjustable what's the perspective on the shim strategy?

 

[mickeytee]

Well you are a first to me. Ive been working on these cars a long time and have a friend even longer since new. He also works on the corvettes . never ran across a master cylinder problem on any car.likje you claim. I dont know whst forums you are reading with lots of problems but i dont think its xlr. Ive also not found your problem on the c6. When master cylinders go they usually go to the floor with no brakes from excesive wear. . Not locking all four . the design alone would prevent that from happening as the pressure fom the mastercylinder would have to somehow lock the fluid underpressure in pace. The abs coud fail and lock a wheel but not the master cylinder applying presdure and somehiw holding it to all wheels enough to hold the brakes. Thats hundreds of pounds if force. It sounds like what you are doing is decreasing travel which could get you killed when the brakes fail.. They are designed by engineers with a whole lot more knowledge than i have or you will Find on the internet. I reccomend you taking it to a professional shop.

 

[justdennis]

I agree with Mickeytee, brakes are nothing to "experiment" with when you really don't know what's causing the problem. Your temporary/ permanent fix sounds questionable, this may be a time to bite the bullet and leave it to the professionals. Safety first.

 

[luxuryrules]

What do you two believe a professional shop is going to do that we can't? Can one of you suggest what part may have failed?

Replace a brake booster with a used one since they're discontinued?

Replace the master cylinder?

I can do either of those things but I'm asking for some help on the diagnostics so I'm not just randomly throwing parts at the issue. I agree this isn't an XLR specific concern which is even weirder, there's nothing special about this braking system.

For reference - I didn’t mean to imply XLR forums were full of this problem, just enthusiast forums in general.
All 4 brakes dragging - Ford Truck Enthusiasts Forums - replaced MC and brake booster only to discover output shaft of the brake booster was adjustable and needed adjustment. It's not adjustable on the XLR which is why I am looking at shims instead.

All four brakes dragging similar story, similar result

I’m a little concerned that this is that unique of an issue. If my booster is already pressing the master cylinder then it’s like I’m driving around with the pedal at, say, 20% engagement. By moving the MC out, I’m brining the pedal back to 0% engagement, I still have the full range of engagement. The important detail is I need to make sure I don’t move it to lower than 0% engagement as that would, as Mickey points out, decrease my effective travel as I could never then get it to the full 100%.

 

[mickeytee]

The xlr does not have a design problem neither does the c6 or c7 as millions and millions hof miles have been put on themand they usethe exact dame parts fot over 10 years.. There is no procedure for doing any modification in the factory gm manual to the push rod length. You read in some old c4 forum about the adjustable pushrod problem. Those cars where not made like.ours.they use okd tevhnology and tgat still only applies to front or rear not all four.only a onle line master coukd be made to do what you are claiming and they have been outlawedsince the 50's
You can ridE around all day with your foot touching the pedal and it may heat up the brakes but it will not in no way ever lock up all four brakes when you stop.so maybe in your head you thnk you know what you are doing but the master cylinder by design cannot lock up all four brakes and adjusting it off the brake booster does nothing like you think. Adjustable rods are used in custom builds to change the geometry of the pedal and to adjust bias front to rear on cars with dualmaster cylinders. The gm factory manual says remove old master install new. Thats all there is to it. No adjustment needed and no way to adjust.The only thing that could hold presure is the abs module and since you dont know where it is or have a scanner then you cannot check it.
im glad you have your problem solved but i highly advise anyone to not modify the factory brake master as he described. There is a seal to keep dirt, water and trash from going into the booster. What you did breaks that seal allows moisture into the booster and will allow rust that very well may cause failure in the future. Gm engineers designed the part . there is no wear areas that need to be addressed except the eyebolt and pin.Forums about4 x4 pickups dont apply to our cars. in searching i see you have pOsted on about 4-5 sites so im done with wasting time here.

 

[lextoy]

You need to scan with a tech 2 or clone. Could be some codes that will elucidate what's going on. I agree right now your are guessing it's something mechanical. I'm guessing it's something electrical. There's a lot of modules on this car. I agree with Mick here, the brakes work really good on millions of cars. I doubt it needs a lil tweak. Something else is going on. What's your location, members all over have scanners...

 

[luxuryrules]

If someone in the southeast Michigan area has a tech2, I’m in. Would love to get it scanned and see. Sounds to me like both of you are in the “could be an abs module” camp. Appreciate if there’s anyone who can help with the diag. Or if someone could offer me guidance on what to purchase: I understand I need to invest in one of these things I just want to make sure I’m buying the right thing.

In my defense I only posted on two sites - the other one being a more general Cadillac site that I was already an active member on for another vehicle.

Edit - to be clear, I really do appreciate everyone’s input. Thank you both for the suggestions and ideas so far. I’m not 100% in on shims that’s why I’m still asking questions. I just don’t want to throw parts at it.

Edit 2 - also adding, since you all have experience with these cars, I genuinely trust your diagnostic advice more than a shop who may not have seen one of these in a decade. Again why I’m asking for your ideas rather than throwing it at a shop.

 

[luxuryrules]

Anybody have experience with this unit, using the GM pcmcia card? US$213.00 - GM Tech2 Tech 2 Scanner with CANdi TIS Works for GM/SAAB/OPEL/SUZUKI/ ISUZU/ Holden

 

[justdennis]

You need to identify the real problem, that's why I said a professional or someone that knows these newer systems. I always do it myself when I know what i'm doing but my fear is your problem is the ABS controller or some other module. The last thing I want to do is pretend to know what i'm talking about and make your problem worse. I have a tech2 clone and it has the ability to bleed the ABS brake system but I am not sure what else it can do. I have never needed to try that and I would need to learn more about it before I do.

 

[luxuryrules]

You need to identify the real problem, that's why I said a professional or someone that knows these newer systems. I always do it myself when I know what i'm doing but my fear is your problem is the ABS controller or some other module. The last thing I want to do is pretend to know what i'm talking about and make your problem worse. I have a tech2 clone and it has the ability to bleed the ABS brake system but I am not sure what else it can do. I have never needed to try that and I would need to learn more about it before I do.

Thanks mate - do you mind at least sharing what unit you’ve got? Appreciate any information you have.

 

[justdennis]

It's a Chinese clone and looks just like the original, it came with the GM card, Candi interface and TIS 2000. I purchased it on EBAY, I think it was a company called "cartooldeal", google that and you should find it. I paid $312 total delivered and so far it works fine for what I have wanted to do. The only down side for me is my lack of knowledge on how to use it, some of it is easy and interesting but I wish there was a better how to manual, that being said it has already saved me money. Good luck.

 

[xlrlist01]

Anybody have experience with this unit, using the GM pcmcia card? US$213.00 - GM Tech2 Tech 2 Scanner with CANdi TIS Works for GM/SAAB/OPEL/SUZUKI/ ISUZU/ Holden

I can't speak for this unit. You need the pcmcia card which covers Cadillac (which IIRC is included in the N. American GM pcmcia card). GM made a series of different pcmcia cards for different regions. Just check with the seller. They have been known to throw in the correct card FOC just by asking.

 

[luxuryrules]

Awesome, thank you both!

Edit - found one, seller including card for me, ordered immediately. Once again thanks everyone for their input!

 

[luxuryrules]

Followup. Shims are removed and will stay removed. Current plan is to see what the Tech2 finds when it shows up; and if nothing else I'll at least do the ABS bleed since I couldn't do that before, on the chance that some of the contaminated fluid is gumming something up in there.

General question is, with a tech2 in my hands, is there anything a shop can do that I can't? I'm still betting there's better expertise among you all than a shop, I'd prefer to learn from you all if I can.

 

[mickeytee]

A tech two is is a very useul tool. It has to be used in conjuction with the factory shop manuals. they tell you what procedures and in what order to do things. Ylu will need to kearn a little about the xlr bracking system. The reference you read on trucks use hydro brakes master cylinders. They are a heavy duty system that uses a power steering pump to activate the brakes which allows less pressure on tbe pedal to activate huge calpoers that hold 3-4 times the fluid that the xlr uses.those systems use retiurn lines from clipers which the xl does not. The xlr abs traction control system is very complicated but rarely fails. And by the way master cylinders and vac boosters are both readily available new for our cars but i highly doubt that is your problem as the booster is really not needed . just makes the pedal a !ittle harder to press if bad. The master will fail when worn out causing the pedal to go to the floor when you sit at a red light holding the brake. A quick release and press will work it but tells you its time for a replcement. I woukd suggest you limit your google searches to only systems like the corvette and xlr have.

 

[luxuryrules]

I have factory shop manuals, yes. Thank you for the suggestion!