Hey guys, I had a problem the other day on the highway. I took the vette out to run to the pep boys to pick up a cabin filter and air filter for the wife's car...but never made it. I was running about 75 or 80 mph on the highway and all of a sudden I felt a strange vibration...turned off the radio...no associated noise. Not a vibration like wheels out of balance...more like when you drive on a road with a coarse surface. They had just finished paving the highway (and have done a crappy job as I feel most of my vehicles can feel strange on that road at times) so I wrote it off for a few miles...until I started to smell burning brakes. So I'm wondering if someone ahead of me is having a problem or if it is related to my weird vibration...so I pull over, pop the hood, and start sticking my nose by each wheel trying to find where it's coming from. Turns out nothing seems out of order...no smoke or smell directly by any of the wheels...nothing is locked up...no warping of rotors...car did not pull at all. So, I get back in and start off...this time, acceleration seems a bit less than usual and vibration is still there. I let off the gas and car decelerates slightly more than usual...but not a lot. I pull over again and call a flatbed just to be safe and not screw things up...if brakes were dragging I didn't want to kill my rotors. While waiting for the tow...I got in and out of the car a few times and noticed the pedal felt hard...like if the car was off and you pumped them up...except the car was running. Tow truck came, and she rolled up and down nicely...backed her back into my shop with no problem. Put her up on the lift to check it out...all wheels spin freely...pedal feels normal...all rotors are same color and no signs of overheating. It's like there is nothing wrong...but there sure is something...and it shows up at highway speeds. My thought is maybe the master cylinder is hanging up a bit...just ever so slightly...enough to slightly drag the brakes evenly? Have any of you experienced this or heard of someone who has? I've owned many cars and trucks through my lifetime and drive about 40k miles per year...never had this...any suggestions are appreciated!

 

Just spit-balling here, but any chance it could be a bad wheel bearing allowing the rotor to oscillate and rub the brake pads?
Cheers-

 

Your brakes are probably sticking but the piston can eventually retract on it's own. I would use engage and dis-engage the parking brake, as this can cause the rear caliper to stick. Use the normal brake pedal in the driveway and drive it around the block. Then you can walk around the car and put your hand near the wheels. You will know which one is sticking based on heat. This is what I did to figure out which side on mine was sticking.

 

Since you have it on a lift, I would have a helper pump the brakes and turn each rotor (with the wheels off) individually. If one is sticking you should be able to find it this way. Sometimes the extra weight of the tire/wheel masks a slightly sticking caliper. You could also check each caliper by using a disc brake tool to compress the pistons.
Good luck, keep us posted on what you find.

 

A hard pedal usually means a booster issue with a lack or loss of vacuum. I'm not sure if its true with all years, but the earlier cars you can adjust the push-rod travel between the booster and master cylinder.

I had my brakes hanging up as well... I replaced the master cylinder and brake hoses as well as adjusted the push-rod travel. My booster was ok.

Another place to check while you're diagnosing is the moving slides at the calipers to see if they are gummed up like mine were...

 

Can be a brake flex line. When they get old they can collapse under pressure and not release the brakes. Will release over time masking the problem.

 

Thanks to all...hopefully more will chime in too!

 

My first thought when this was happening was a hanging up caliper as well...but remember...no pulling...the drag seems very equalized...which seems to point to master cylinder/booster. I also don't use the parking brake as it is an auto...doesn't mean it couldn't contribute to the problem. I did check the cables and return springs and all looks good there.

 

Did not know this was adjustable on a C4, Please elaborate.

 

If you remove the master cylinder you can see a small jamb nut at the end of the rod inside the booster. You can loosen it up and turn the rod to lengthen or shorten the travel into the master cylinder. Lemmy find a pic... hold on

 

Do you think that a booster issue could cause the brakes to hang up a bit? I'm thinking that if I pull the system apart to change the master cylinder I might as well do hoses as I'm sure they are 25 years old...but maybe booster too?

I'm not one to "throw parts" at a problem...but with a 25 year old car, I don't feel it's a waste of money. Especially on a braking system...

 

@81c3...when your brakes hung up...where the symptoms like mine or different?

 

Heres a pic and theres a lot of threads on it in C4 Tech Its just the very end that you can turn..

 

91 Having this same issue with both front brakes dragging, I first looked for this adjustment the rod on mine is solid. I read an articular M. Hiabeck wrote about this and he stated every time he found this it was the master cylinder at fault.

 

My problem was very similar to yours... If I was on a small incline/decline the car wouldnt roll freely. I could feel the car drag from a stop and stopping would also feel "wrong"... Didnt always do it... Here, let me give you a link to the thread I posted up when I needed help....

https://www.corvetteforum.com/forums...n-my-86-a.html

 

I would agree... I think for me anyway, it was between the master cylinder, first because it had a dual reservoir unit and the 86 should be a single.... not that, that would make the difference, but the part numbers are different for the dual and single reservoir units. I purchased the correct one.

Second, my slide bolts on the calipers had something resembling tree sap where the grease once resided... Im sure that wasnt helping fully release the pads.

I did many things at one time, so Im never going to be 100% sure on what actually fixed the issue, but it indeed is fixed.

 

If the master isn't protruding to far, I would do a caliper pin greasing. Mine seems dry every time I look. And my boots are fine!

 

Thank you, I am replacing the MC and soft lines with SS. Maybe they changed the rod on later models.

Soft lines are fine and caliper slides clean and greased. Hoping its a MC issue.

 

Interesting... I wasnt sure if all years were adjustable... now I know!

 

Seen this happen. Old lines fail internally and act like a check valve. They can cause a brake to drag and be pretty difficult to detect.

A hard pedal is usually the plastic booster. I had a vacuum check valve/boot act up once too.