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Old 12-14-2018, 05:13 AM   #1
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1998 GMC 454 hydroboost issue!

Ok ladies and gentlemen, I have a 1998 GMC 3500 dually with the 454. I just replaced the hydroboost due to it leaking power steering fluid. After replacing and bleeding as instructions from another forum suggested, the steering and brakes felt fine. After driving about 15 miles and coming to a stop, the brakes would not release. I sat and let the fluid cool and brakes freed up enough to get it back home. What could be causing them to stick after warming up? I'm new to hydroboost systems so any help is much appreciated!
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Old 12-14-2018, 07:37 AM   #2
95 S_Trucker
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Re: 1998 GMC 454 hydroboost issue!

Sounds like the pushrod between the booster and the master cylinder is too long, or the new booster is bad. Quality control on reman units aren't the best. You don't know how good they were rebuilt and if they were rebuilt with the correct parts. 1/8" can make a huge difference.

If it were mine, I would try another booster. I am assuming you used the pushrod that was original to the truck?
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Old 12-15-2018, 05:35 PM   #3
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Yes it is a reman and I used the pin and spring from the orginal booster. Could the pin being too long cause it to only get stuck after warming up? It does fine until you drive it down the road and get it warmed up.
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Sounds like the pushrod between the booster and the master cylinder is too long, or the new booster is bad. Quality control on reman units aren't the best. You don't know how good they were rebuilt and if they were rebuilt with the correct parts. 1/8" can make a huge difference.

If it were mine, I would try another booster. I am assuming you used the pushrod that was original to the truck?
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Old 12-16-2018, 10:11 AM   #4
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You should be able to tell if that's the case

Correct me if I'm wrong, (like I have to ask) but if the assumption is the booster and the push rod are involved. Wouldn't the rod have to be sticking in the depressed position to cause the problem?

So if that was the assumption, then wouldn't it follow that the pedal at that point would have no resistance for the first part of it's travel until it met up with the push rod on it's subsequent depressing? In other words it should have no resistance on the next push of the pedal while the problem is occurring.

Would be interesting to know. The answer to this question will tell you if your assumption is correct.

I would also think that if the push rod were stuck, you won't build up pressure in the system and pedal get harder and harder like a normal system as you pump it up.

If there is resistance to the pedal when you depress it again, I would look into the front brake hoses.

In case you aren't familiar with hose problems causing the calipers to stick. What can and often does happen is the inner liner of the hose collapses when your foot is taken off the brake. It is created by suction of the fluid backward. This causes the caliper(s) to lock up. This however is not a perfect seal (liner collapsing) so over time it leaks enough fluid to finally release.

Seems more logical than a mechanical binding that eventually releases.
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Old 12-16-2018, 04:28 PM   #5
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Re: 1998 GMC 454 hydroboost issue!

This is a pretty common occurance with bad quality control in the remanufacturing process. I’ve had it happen twice in my shop.

Google brakes not releasing after hydro boost replacement. You will find hundred of people saying the exact same thing. After driving the brakes drag. Then they get a replacement for the replacement and all is good.
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Old 12-16-2018, 09:31 PM   #6
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Re: 1998 GMC 454 hydroboost issue!

Quote:
Originally Posted by 95 S_Trucker View Post
This is a pretty common occurance with bad quality control in the remanufacturing process. I’ve had it happen twice in my shop.

Google brakes not releasing after hydro boost replacement. You will find hundred of people saying the exact same thing. After driving the brakes drag. Then they get a replacement for the replacement and all is good.
The reman stuff is hit and miss anymore. I resealed mine with a $20 kit off the internet. There really isn't much to them.

Last edited by 82C10step; 12-16-2018 at 09:32 PM. Reason: Forgot a word
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Old 01-08-2019, 12:27 AM   #7
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Re: 1998 GMC 454 hydroboost issue!

Ok, just for future reference if anyone ever needs it, I sent the reman hydroboost back and they sent me another reman part, (parts were bought through RockAuto and they replaced it with no hassle so hats off to them). I installed the new part and had the same issue. I remember reading on another thread that the master cylinder had to be shimmed out from the hydroboost. With the brakes still locked down, I loosened the bolts that hold the master cylinder to the front of the hydroboost. I was able to hear and feel the brakes release instantly. I then added washers to shim the master cylinder out from the hydroboost. I made another test run and had the same issue. After adding another washer, which was a total of around 1/2" to 3/4" worth of shimming, the brakes worked perfect. So if it were me and you replace one of these, take a 15mm socket and ratchet with you on the first test drive just in case they get stuck you can simply loosen those 2 bolts and get the pressure off the brakes to get it home. Then shim accordingly and test again. If you're stranded on the side of the road with locked up brakes without a ratchet, wait patiently for the brake fluid to cool and brakes will release and you can get it home. Just stay off of brake as much as possible to prevent brakes from locking up again.
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Old 01-08-2019, 09:04 AM   #8
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Re: 1998 GMC 454 hydroboost issue!

So you are driving around all of the time with washers in between you booster and master cylinder?

You need to get the correct booster(might have to try another brand) or check to see if your push rod is the right length.
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Old 01-08-2019, 09:52 AM   #9
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Re: 1998 GMC 454 hydroboost issue!

If you're running 3/4 inch of shims, somethings not right. You got the wrong parts combo somewhere.
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Old 01-08-2019, 10:42 AM   #10
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Uh shims?

http://my.cardone.com/techdocs/930394-52.pdf

Did you happen to leave out the spacer?
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