Front Brakes Locking Up

[lance.brown]

A few weeks ago, I replaced the vacuum brake booster on my 1999 Tahoe with a Bosch Hydroboost and new MC.

Now (very intermittently) the pedal will get very hard and the front brakes will lock up. This has happened twice to me in the last two weeks on my way to work.

I pulled over, shut it down and let it cool off for 5-10 min. I opened the MC lid to see if there was anything unusual in the fluid, nothing seen. I cranked it back up and it drove fine.

Any ideas of what might be causing this issue?

 

[SunlitComet]

is the hb the proper application? does the brake pedal extend back when foot is removed? is the ps pump the proper application as well. if the pedal gets hard it sounds like the ps fluid pressure is dropping and the is not enough power in the accumulator either. possibly internal leak of booster as well. any fluid dripping in between booster and mc. did you reinstall the pushrod and return spring parts properly when they were mated together? sure the fluid is not overheating?

 

[lance.brown]

is the hb the proper application? does the brake pedal extend back when foot is removed? is the ps pump the proper application as well. if the pedal gets hard it sounds like the ps fluid pressure is dropping and the is not enough power in the accumulator either. possibly internal leak of booster as well. any fluid dripping in between booster and mc. did you reinstall the pushrod and return spring parts properly when they were mated together? sure the fluid is not overheating?

The HB is made for this particular model truck.
Yes the brake pedal does return to its normal position when you remove your foot.
I did not change the ps pump. Does a HB upgrade typically need an upgraded ps pump too? I was originally told that the ps pump would be sufficient.
I have not seen any fluid leaks. As far as I know, everything has been reinstalled correctly.

I'm not sure about the fluid overheating - how would I be able to tell if the fluid is overheating?

 

[SunlitComet]

fluid would smell burnt and lose it original color. if ps pump is still original how did you route your ps lines for the whole system?

 

[lance.brown]

Bosch/Bendix HB came with two steel braided lines. One comes off the ps pump to the HB, and then the other goes from HB to steering box. A return line comes off of the HB and splices into the return from the steering box back to the ps pump.

Fluid doesn't smell burnt, but it does look a bit darker then it did originally.

 

[SunlitComet]

so it sounds like you are missing a really needed cooler then. get the dirty fluid out and refill. test over time to see if it happens again and if so state fluid condition. i would recommend getting a cooler before pump first tho. here is an example of the factory coolers used. and these parts are mostly still available to make it like the original. I am concerned that your booster came with lines already. when we convert we buy the lines separately as they never come with the booster.