Silverado 2500HD hard pedal and brakes locking up

Realism

Original poster
Member
Nov 25, 2015
179
Idaho
Having some issues with my friend’s 2005 Chevy Silverado 2500HD hydroboost. The issue that is presenting is with the brakes. Currently the brake pedal is hard and feels way over sensitive, giving about ¼” of travel before the brakes really grab hard. It has locked up a few times. Bear with me explaining what happened and what’s been done. You might even get a good laugh out of it.


My buddy called me up and said his truck was making a whining sound and the brake felt funny, the whining was worse when he was turning. He brought it to me and I’m thinking power steering fluid is low. He tells me it looked full and he only added a small amount to top it off, but the guy he bought it from mentioned it has a leak. When I point out to him that his power steering reservoir is empty, he says “oh, I didn’t know that was where the power steering fluid goes.” I look at him, cringing at the oncoming response, “Where did you put the power steering fluid?” He points to the Master Cylinder. I guess somehow he forgot to read and missed the label on the cap that said DOT 3 BRAKE FLUID ONLY. He hadn’t driven it very far since he mixed it, so I sucked out about half the fluid in the MC trying to get the PS fluid on top. At this point we parked it and I told him to go get a couple of bottles of brake fluid and a bottle of stop leak for the power steering. While he is out doing that I’m mentally berating him for his mistake and hoping that he didn’t get any PS fluid into the MC and lines. The MC cap was a little swollen, but I couldn’t tell for sure if it was his oops or just age, at this point I’m thinking there might have been some swelling that went on.


He gets back and we proceed to bleed the hell out of the lines with 3 bottles of brake fluid and fill the Power steering pump with PS fluid and the stop leak. I do the procedure turning the wheels and working it into the lines. I’ve never dealt with a hydroboost system before this. We get this all done and everything seems okay. I tell him to keep an eye on it and at the first sign of trouble or swelling, get it to the nearest shop or park it. 19 years old, do you think he listened? So about two months go by without any issues, then his gf who is driving it now starts having problems. She told me that the brake pedal was soft and would travel pretty far down and was having difficulty stopping. Then after this the brake pedal became firmer, but the wheels went and locked up on her. She had it towed to her place and gave me a call to come look at it. I’m thinking at this point that everything is probably swollen and the entire brake system is toast.


I check the power steering reservoir and its low, so I add some PS fluid to it. Did a booster check and it checks out fine. I’m not feeling anything wrong with the brake pedal so I take it out for a drive. The pedal does feel a bit hard to press on with maybe ¼” of travel before the brakes kick in. I give it a few hard brake applications while Im driving it and don’t notice anything out of the ordinary, so I pick up speed and slam on them a few times to activate the ABS, seeing if I can replicate the brakes locking up. Nothing, but as I near her house I start to feel it slowing down and the brakes grabbing until they lock up. In drive without pedal application it wont move, so I give it gas and get it the last 100 feet or so to her place and park it. Jack it up and try to spin the front tires. Could not get either one to budge. Take the driver’s side tire off and try to move the caliper, but its on there tight. Crack the bleeder and didn’t get a gushing stream, at least not until I compressed the caliper piston a little using a screw driver as leverage. Got the caliper off and checked the piston boots for swelling. No swelling and the boots like perfectly healthy. I think my friend put more brake fluid in, because I noticed that it was at or maybe a little above the max line. I bled it through that drivers front caliper until it was between max and min. Put the tire back on and checked the other side, which the wheel spun freely and was no longer locked up. I pulled the inlet hose to the hydroboost to see if maybe there was a blockage between it and the PS pump. No blockage. Took it for another drive around with some hard braking and made the ABS fire as well. Didn’t get them to lock up and it didn’t feel like they were grabbing, but the pedal was still pretty hard with that same sensitive ¼” travel before you could feel the brakes applying. Told her to just test drive it around the neighborhood a few times over the next few days and see if everything remains good to go.


Now I’m a little unsure what caused the hard brake pedal and the wheels to lock up. My initial thought was the inability to read creates a $3,000 problem to fix, but since I found no evidence of other rubber parts swelling . . . I considered the possibility that the seals in the MC are swollen and not allowing pressure to release, but the gf’s statement of the brakes being squishy and excessive pedal travel contradicts this assumption. However, what throws me is that the pedal did get harder and the wheels locked up later. Hard pedal is a sign of the brake booster/ hydrobooster going bad, but it checked out fine when I tested it. Could the MC being filled to the max be the cause of the brakes locking up? I don’t think this explains the hard sensitive brake pedal though. I know hydroboost brake pedals do feel stiffer and have a different feel to them compared to a standard vacuum assist. Could the stop leak have gummed something up in the hydroboost? If so, why did it check out fine. Im at a loss for explanations here, but Im keeping my bases covered and working on assumption that the problem may repeat itself. What do you guys think?
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
A monumental screw up for sure that confirms that those who have no business being under the hood should keep it closed.

Although I have no knowledge of the hydroboost system, the fact that a petroleum product was added to the brake fluid certainly destroyed certain parts of that system. I'd start by the first affected part and go from there. The master cylinder is certainly done so I'd replace that first along with the flexible lines from it. If the brakes are still acting up, especially at an individual wheel, replace both caliper's and flexible lines on that same axle or I'd replace the fronts first, then the rears. If still screwed up, only thing left is the ABS valve. So basically going from least to most expensive but I might be inclined to go from first to last in the branch (MC>ABS>calipers).

If I were a betting man, I'd put my money on the master and the ABS according to the symptoms.
 
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Realism

Original poster
Member
Nov 25, 2015
179
Idaho
It is both front locking, I didnt check the rears. Even though my fear is that the brake system is compromised, I'm also being led to understand that the problem (if it crops up again) is either the MC or the hydroboost. I'm finding that hydroboosts have a habit of leaking at the two inlet/outlet sections and a leaking hydroboost can cause issues where the piston pressing into the MC does not fully retract. This could be the source of the leaking PS fluid. It sounds like it is a somewhat common issue. I should know more on it if the problem presents itself again in the next few days. If it does I can loosen the mounting bolts on the hydroboost and if that releases the pressure on the wheels/brakes then the hydroboost is faulty, if not then the MC is to blame. My thoughts anyways.

I did test for the ABS and it appears to be functioning correctly. I checked the code history and the only thing that I could see was the Drivers front wheel had a code a while back over a speed sensor not working properly.

And totally agree with you. Stay out from under the hood or elsewhere if you don't know what you're doing. I had to show this guy how to put brake pads on a car. Kept urging him to at the very least pick up a Haynes manual to read and understand at least the basics of car maintenance.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
Although I can understand bonehead moves, like trying to boost a vehicle and reversing the polarity (and getting magic smoke!), putting the wrong fluid somewhere it clearly states what goes in there is beyond bonehead. :hopeless:

Hope it's something simple.
 

Realism

Original poster
Member
Nov 25, 2015
179
Idaho
No kidding. This is the same person who changed his own oil, but forgot to put the drain plug back in until he put the full 10 quarts in and noticed it was just pouring out the bottom. I about died laughing when I saw it.

Sounds like the Silverado is still being temperamental, so time to pull the bolts and see if its the booster or MC. Hoping its just the hydroboost, cuz I hate replacing master cylinders and going through the whole bench bleed and installation bleeding process.
 

Mooseman

Moderator
Dec 4, 2011
25,262
Ottawa, ON
No kidding. This is the same person who changed his own oil, but forgot to put the drain plug back in until he put the full 10 quarts in and noticed it was just pouring out the bottom. I about died laughing when I saw it.

Been there after an oil pan swap. Earned me the nickname "Slick" for a while. But at least I didn't put brake fluid in the oil.

Hope it works out. I did the bench bleed on the car last time using an assistant to push the pedal and I hold the hoses. Hook the lines up right after, minimal spillage.
 
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