Question: Brake Problems, 94 6-speed with Z07 and RFTs options (among other options)

[Todbo]

Hi All,

In getting my 94 ready to visit Gordon Killebrew last Thursday (that's Atoka, TN - Cross Plains, TN and return) at about 1 mile after starting I noticed I had a slight drag from my brakes and slightly higher RPMs. Thinking that the hand brake was slightly engaged, I stopped and made several attempts to release the hand brake, however, such attempts only served to increase the brake drag. Being stopped on the side of a busy highway l drove another mile to a place where it was safe to get off the highway. At that time both of my rear brakes were smoking slightly. After attempting to release the brakes for about 20 minutes all of a sudden, I found that I had no-brake drag and normal RPMs, but with a slight reduction in brake pedal height. After driving about 5 miles the pedal returned to normal height and I decided to go on to Gordon's, and I completed the trip without any additional problems.

The 94 had been in storage since the 2017 Birthday Bash and after airing up the tires and spare I had raised the brake handle slightly the day before when cleaning the interior, and although I had not gotten a brake warning light that morning, I continued to assume the brake drag was hand brake related, and thus Gordon and I did not focus on the brake matter. However, coming back into Nashville on I-65 I again found I was getting a slight brake drag, and that my RPMs were higher than normal. Stopping in Nashville, I removed the cover on the brake handle and again went though several attempts to free the brakes. After about 20 minutes I again found that I had no brake drag. Getting back on I-40 at about 1 mile East of Centerville TN I suddenly found I had a significant brake drag and high RPMs. Limping into the LOVE'S station off the interstate the motor would barely pull the car in second and both of the front brakes were smoking. At that point it was obvious there was more than hand brake drag. At this point I still had a full break pedal, however, after letting the Vette set about 30 minutes without any attempts to disengage the hand brake, I found the foot brake pedal going to the floor, and zero brake drag, and normal hand brake function. Hand brake function remained normal the next day when I loaded the car on my trailer to tow it back to Atoka, thus is this a master/wheel cylinder, or ABS, or other problem?

FYI, I checked the ABS fault code after the drag disappeared and found all dashes, so unless the fault disappears when the drag disappears, perhaps the ABS can be ruled
out, eh. In the last brake drag(at Centerville), both front wheels apparently got hot enough to lose the center caps. Caps in the rear wheels and all vinyl lug nut caps are OK. Any ideas as to how much heat the tire sensors can endure?

Thanks for your consideration.

 

[Toms007]

Well, first off a welcome is in order. Now for the problem at hand...That’s a puzzler. What’s happening doesn’t make much sense to me....my first thoughts were possibly just a stuck hand brake shoes....but I think you have eliminated that possibility. So my next thought was caliper pistons not releasing...I’ve had that happen on a pickup I had, but those just grabbed and didn’t release at all. Which
leads me to think the problem lies in the ABS, but no codes kind of rules that out. I’m hoping one of our resident techs will check in here pretty soon and give you a better idea than I was able to do.

 

[Hib Halverson]

So you have a rare C4 with runflats...interesting.

If you are driving the car until the front brake are smoking, clearly there's a problem you need to repair.

As for the survivability of the LTPWS sensors doing an incident of high brake temp...information about their durability would be hard to find, but I wouldn't drive the car much until you fix the brakes. Those sensors are impossible to find and you really need that system with RFTs.

Brakes locking up can be the master cylinder, perhaps the brake booster or the ABS modulator but, I would think, if you have an ABS issue the Service ABS light would be on. Check the 94 FSM. There could be ABS codes not readable from the IP.

 

[Robertwav1]

Just thought I'd mention I had a car once the brakes would stay locked the more they were used. I did manage to bypass a valve externally mounted on the brake booster which was the problem, it was faulty. In doing research at the time I also looked at the cross section of a brake booster which also has an internal check valve. I believe I removed the vacuum from the brake booster and the brakes didn't lock up anymore and it's how I found the problem. Of course the car was hard to stop but the brakes were working fine. Possibly isolating the booster might give you a little insight. I too thought it was the ABS on the vehicle since it had all kinds of codes however, it wasn't the case. Hope it helps some.

 

[Todbo]

Todbo

Robertway, Hib Halverson, and Toms007,

Many thanks for your comments. I'm in the process of getting a FSM before I start the repair. Robert, if you have any photos of the booster valve repairs on your car, I'd appreciate copies. One of Sonny Kilgo's friends advises that the suppy hoses to the calipers on his car, were deteriorated, and not letting the fluid pressure off.

Another point not included in my help question, is the inside of the right rear tire (only) reveals wear down to the threads of a two & 1/2 inch width (for a tire with 30% remaining tread), which occurred during the trip. As you probably know, one gets close up and personal with the rear tires in the air-up of the C4 spare, eh. And the right tire was fine when I departed on the trip. And, I did not hit anything. Anyway ideas appreciated!

 

[Toms007]

The treadwear would tend to make me think that you need have a four wheel alignment done. And while you are at it, it might be time to disassemble the brakes to check for any problems in that area.

Keep us posted on what you find.

 

[Todbo]

94 6-speed/Z07

The treadwear would tend to make me think that you need have a four wheel alignment done. And while you are at it, it might be time to disassemble the brakes to check for any problems in that area.

Keep us posted on what you find.

Thanks.

Just got the FSMs (1&2) and am studying those.

FYI after sitting on trailer for two weeks, still had zero bake pedal when I unloaded it Friday- with handbrake. But, when I drove it across my lake levee to mail box (1/4 mile), while testing brakes, all of a sudden, found I had full pedal brakes. Just like the outbound initial lock-up at mile 2, and the 2nd and 3rd inbound lock-ups in Nashville and Centerville, respectively, the brakes have returned to normal after some period of time, and repeated applications of both foot and hand brakes. For the 1st and 2nd lock-ups the rear brakes appeared to be locking-up, but 3rd lock-up had smoking front brakes (which rule out the hand brake, eh). At 3rd lock-up, the 94 went from 95% lock-up for both or one end, to zero foot brakes after sitting for about 30 minutes, and/or with repeated foot and handbrake application. I think I tried the foot brake once before loading it the following day and once when unloading it on Friday, with zero pedal, so the 94 goes from normal,- to lock-up, - to zero foot pedal - to normal brakes (normal? with all this going on, well the handbrake seems normal?!!!).

If anyone has ever had anything like this "normal-lockup-zero-normal" challenge, l would appreciate your response. Vacuum booster? Clogged Caliper hoses? MC proportioning valve has different functions, eh?.

Will jack up the rear end this week and see if I can get the bakes to lock-up again, as well as look at the ABS tests again.

Yep, this baby is going to get a complete alignment and new rear tires as soon as the brake problem is solved/repaired.

 

[LLC5]

Thanks.

Just got the FSMs (1&2) and am studying those.

FYI after sitting on trailer for two weeks, still had zero bake pedal when I unloaded it Friday- with handbrake. But, when I drove it across my lake levee to mail box (1/4 mile), while testing brakes, all of a sudden, found I had full pedal brakes. Just like the outbound initial lock-up at mile 2, and the 2nd and 3rd inbound lock-ups in Nashville and Centerville, respectively, the brakes have returned to normal after some period of time, and repeated applications of both foot and hand brakes. For the 1st and 2nd lock-ups the rear brakes appeared to be locking-up, but 3rd lock-up had smoking front brakes (which rule out the hand brake, eh). At 3rd lock-up, the 94 went from 95% lock-up for both or one end, to zero foot brakes after sitting for about 30 minutes, and/or with repeated foot and handbrake application. I think I tried the foot brake once before loading it the following day and once when unloading it on Friday, with zero pedal, so the 94 goes from normal,- to lock-up, - to zero foot pedal - to normal brakes (normal? with all this going on, well the handbrake seems normal?!!!).

If anyone has ever had anything like this "normal-lockup-zero-normal" challenge, l would appreciate your response. Vacuum booster? Clogged Caliper hoses? MC proportioning valve has different functions, eh?.

Will jack up the rear end this week and see if I can get the bakes to lock-up again, as well as look at the ABS tests again.

Yep, this baby is going to get a complete alignment and new rear tires as soon as the brake problem is solved/repaired.

Your description of this problem is pretty abstract, but if I am reading both posts correctly you have a brake pedal going to the floor issue, brakes locking up problem (does the car not move?), hand brake problem, and originally something about your idle?

As for the pedal issue I would be looking at the master cylinder and rubber brake lines and complete fluid flush. For the hand brake just make sure it is adjusted properly. Idle issues could be a lot of things from vacuum leaks to idle controller, to ignition problems. Tackle one problem at a time.