hydroboost question

[magnethead]

ok, i'll say off the bat that my rear drums are 20 years old. Front discs are about 5 years old.

on my truck, whenever i press the brake pedal, it tends to change in firmness. I've gone through 2 MC's in as many years, and they really only last about 6 months before the pedal goes back soft. but now i've discovere that if i left foot brake and pop the throttle while braking, the pedal becomes hard as a rock briefly (only about 2 seconds). A few times i've done it i've had the pedal halfway down, and the second i pop the throttle (without pushing my left foot any more than it was) the right front will lock up.

Does anybody know what might be going on? I'm wondering if the pump isn't making enough pressure to run the brakes, or if the hydroboost unit between the wall and MC might be going bad? I've also replaced 2 hydraulic lines, one was punctured and the other was worn. Also, if i turn rather sharp, the pump starts squaking pretty bad. It's unavoidable, it mostly happens when i go to school, i have to be on the other (read: wrong side for right handers) side of the road from the turn to be able to turn without it squaking. Fluid canister is full.

[bigblock79]

whe the hydroboost goes bad it will lose all the pedal at least that what my duelly did and pay the extra fo a gm one

[old Rusty C10]

check the vacuum line to the booster and the little check valve first and the rubber grommet like the other poster said usually when they go the pedal is gone or pulls to the floor

[magnethead]

where would these be on the booster unit (being I haven't really dealt much with the hydroboost unit itself). Being i get a firm pedal for only 2 seconds or so directly related to engine speed i wouldn't imagine the old rear brakes would be causing it? I'm using second gear to stop for now just to keep the engine spinning fast enough to have a pedal. And like i aid on right hand turns i have to go to the wrong lane to make the turn without the pump squaking (that migt just be the belts).

What else would make it lose pedal pressure until engine speed was increased?

[sick69]

Well if the power steering pump is going bad that could cause problems with the hydroboost unit considering that provides power to it. Or if the pump is low on fluid, or if the belts are loose enought to sqeel when turning there may not be enough fluid flowing to provide power to the brake system.


just my thoughts


Frank

[old Rusty C10]

the power booster is right behind the master cylinder on the firewall of the truck its the big round thing about six inches wide ya know on edit here im not sure we are talking about the same thing i was thinking power booster not hydrobooster thats a system im not familiar with i apologize if i confused you ive seen power boosters lose vacuum and therefore braking was soft or non existant

[Ivan D.]

Old Rusty, you're getting confused - hydroboost is a system that replaces the vacuum booster you speak of with a weird looking thing that runs off the power steering pump. It is a brake booster too, just instead of vacuum pulled by the engine it is hydraulic pressure from the pump that amplifies the pedal force. It's actually a pretty sweet system in that it's much smaller than the typical vacuum booster, is actually a little stronger than it, and on top of that when working correctly has the pedal feel of manual brakes.

[Ivan D.]

magnethead, yer I think it's the belt squealing, having both the brakes and the steering draw pressure at the same time is a little hard on the pump. I have the problem of losing a little steering assist when turning at low speed while braking at the same time, I've never had a problem with my brakes under same conditions. One thing you can do to keep pump rpms up is swap to a car pulley, those are 5.5" in diameter while truck ones are 7" IIRC, and if yer truck spends most of its life in low rpms that should help a lot - did that trick with the alternators in my car cause I'm hardly ever turning over 3k, worked like a charm, so now I'm planing on doing it with the truck's steering pump.

[magnethead]

If that works on the pump without creating excessive pressure, let it be known. Being that idle is 600 and highway speed is 2800, my truck has a real wide RPM range.

[Ivan D.]

Originally Posted by magnethead

Being that idle is 600 and highway speed is 2800, my truck has a real wide RPM range.

Wow, and you have a 1-ton dually crew-cab with a big-block - what kind of gas mileage do you get at freeway speeds? I only drive my truck up to 55mph cause that's like 2000rpms and and the engine sucks gas like there ain't no tomorrow, I can only imagine how bad yers can be...

[magnethead]

454 and 4.10's- about 8 MPG or so. Or about 23 cents or so a mile

[Pyrotechnic]

When I rebuilt the entire brake system on my 78, the first master cylinder that I got was defective acted like you describe. Sometimes it would be extremely firm where I would barely touch it the truck was braking hard, and sometimes the pedal would just go down to the floor and I had to pump it to get brakes.

It was a rebuilt master cylinder. I took it back and got a brand new one for basically the same price. I would have bought the brand new one first but I didn't know it was available until I showed up back at the store all pissed off.

[magnethead]

well on a unrelated reasoning, i no-longer have a mode of transportation.

new topic to ensue.