Jump to content
  • 0

Brakes locking


doublenix55

Question

I have a 2010 Sierra. Last week I was told that I needed to replace my master cylinder because it was leaking. So I had it replace the next day while I was driving the brakes locked up on me. So once I made it back and told them what happened they checked it out and said they couldn't find anything wrong. So he put another master cylinder on thinking the first one he put on was bad. Same thing happened again. So I took it to someone else and he said the brake lines were not bled correctly and there was air in the system. So he bled them one at a time and said that I shouldn't have a problem. I drove it for 20 min and they didn't lock up while I was driving they locked up while the truck was idling for 10 min. So I took it back and he has now bled them two more times and the same thing keeps happening. Does anyone know what the problem might be?

Link to comment
Share on other sites

3 answers to this question

Recommended Posts

My breaks locked at 90 mph when I got on them cause of deer when they locked the ass started to get loose so I immediately stepped on the gas hammered down and smoked a big ass deerL Tahoe got lucky as shit though no mechanical damage minor cosmetic need new grill passenger DTRL bumper and pumper valance and that's it very fortunate anyhow I put the code reader on my truck couple weeks later cause my check engine lights been on for a little bit now and it comes and goes depending on weather and fuel I run anyhow the normal codes came back plus 4 new ones all electronic brake control module and I was like I thought I only had one break control mod any how the codes where for each tire that locked thus 4 codes and the BCM also passed the test when the obd2 reader was hooked up they were intermittent codes so my BCM works fine unless I'm hauling ass and get on the breaks well enough to cause a lock up none the less I'll eventually change it only problem is its 400 or 500 dollars for a new reman you can get a used one for about 100 but no telling when it will go bad and no warranty so it's kind of a gamble anyhow I'd check you BCM

Link to comment
Share on other sites

Sounds like an engineering problem to me. I've worked on vehicles 40 years old that never experienced such an issue. Been around cars my whole life and never heard of that happening. Nothing surprises me in the 21st century anymore.

 

The fact this is even possible on a 5 year old vehicle, by only replacing a master cylinder, just boggles my mind ... :nonod: Only possible way that could happen is by adjusting the pushrod way the heck out ... but anyone with blood flow to their right foot would immediately notice something wasn't right when they started bleeding the brakes. Shouldn't be touching the pushrod on a master swap anyway.

 

Don't even know if they're still adjustable anymore, since the last power booster / master swap I did was on my '72 El Camino 15 years ago.

 

Air won't lock brakes up. Don't know what to tell ya there. Probably need to find a few new mechanics ...

Link to comment
Share on other sites

It would take gross incompetence, but, if the mechanic somehow managed to swap the lines on the master cylinder that would add a residual check valve to the disk brake system, and would cause what you are seeing.

 

To diagnose this you need to open the bleeder on a front wheel as soon as it locks up and see if the fluid squirts out like it is under pressure. If it does, and the brakes are no longer locked up, then you have one of two things wrong, what Jsdirt said, or what I said. Those are the only reasons for this to happen.

 

To see which one it is, once the brakes are locked up again, loosen the mounting bolts for the master cylinder where it attaches to the booster. What you want to see is a large gap between the booster and the master cylinder. See if that releases the brakes right away. If it does, then something is making the piston in the master cylinder cover the compensating port. Usually caused by incorrect push rod adjustment or application.

 

Something else to consider is maybe they are installing the incorrect master cylinder. It may be a batch of boxed wrong parts. Since this started after the replacement, then it must be the master cylinder creating the issue, but may not be the master causing it.

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.



×
×
  • Create New...

Important Information

By using this site, you agree to our Terms of Use.