marv h.

So my brakes dont work untll I start the engine. If I park on a slope and go to start it up, when I mash the clutch & the brake, it will roll until it fires up, the the pedal goes down some with a squeal, and the brakes work all of a sudden. Does anyone know what this might be?
Tanks Marv.

SMOKNISB

Thats normal. Thats why they make parking brakes. Brakes work off hydraulic pressure. Most brake systems work off engine vacuum. But my 99 has a hydroboost system. It uses the power steering pump and fluid to make pressure. Not exactly sure how that works, but you get my point. They should work a little, but not very well. You might try bleeding your brake system.

gmctd

Normally both the vacuum booster and the hydroboost units store enuff energy for two full stops after the engine shuts down -

- that large flat 90deg elbow in the vacuum booster cover is a one-way valve, which lets the vacuum pump draw down to ~26"HG, but won't allow Barometric pressure to seep back in - if your vacuum booster won't hold that vacuum, indicated by hard pedal with engine off, either the valve is leaking or the booster itself is leaking - time for replacement

- that long blue cylinder - some are gold - on your hydroboost is a hydrualic pressure accumulator, storing reserve pressure from the power steering pump - if your accumulator won't hold that pressure, indicated by hard pedal with engine off, then the accumulator is leaking internally, and time for replacement - can also be failing hydroboost unit, leaking back internally - accumulator may no longer be serviceable separately, requiring hydroboost unit replacement - which is probably best, as your truck is now getting fairly long in the tooth, eh?

marv h.

Thanks gmctd, thats a lot of info. I guess I need to study up on this system, because I dont know any of those parts you listed. And yes 205 K, she is needing some attention here and there.

John Faughn

Also making sure that the rear brakes are adjusted right can help .

gmctd

Correct, on the rear brakes adjustment - just pop the rubber plugs out, check the distance between the shoes and the drum - adjust the star wheel till the brake locks against the drum, then back off one full turn - or, with the wheels off the ground, trans in neutral, emer brake off, tighten till the wheel won't spin, then back off till you can rotate the wheel - as mentioned, too much shoe\drum clearance could also be the problem

Pop the hood, look for the brake master cylinder, above the steering column - directly behind it you will see either a large round black can with a large vacuum hose attached to the one-way valve in the cover, the vacuum booster, or a smaller, narrower device with power steering hoses connected to it, the hydroboost unit - over on the engine-side of the hydroboost unit will be a blue- or gold-anodized aluminum cylinder - that is the accumulator

The one-way valve, the vacuum booster and hydroboost unit are each replaceable

marv h.

OK I will check my rear break adjustment, and I saw a blue cylinder by the boost unit. There is some seepage around a seem on the booster, so it is probably leaking a little.

gmctd

Just pop the rubber plugs out of the backing plate, use a flashlight to check the space between the shoe and the drum - the two bottom-most plugs let you see the front and rear shoes, one of the two upper plugs is for the star-wheel adjustment, depending on which brake you're adjusting, left or rignt

Post if you have any further questions

marv h.

Perfect, I can do that. Thanks