Vacuum Or Hyraulic Brake System?

[darisb]

The brakes are a little spungy and the brake warning light comes on after driving on the the '92 5.7l K1500 Extended Cab I recently purchased. I'm looking at rebuilt master cylinders, and there are two listed. One is described as being for a "hydraulic brake system" and the other is for a "vacuum brake system". I'm not sure how to determine which one I have. Is the hydraulic system non-power brakes and the vacuum power brakes. I'll have to take another look, but I'm pretty sure the master cylinder was bolted to a power brake drum mounted on the firewall.

 

Thanks,

Daris

[hubbycap]

Sounds like vacuum assisted brakes to me. It would have a large vacuum hose connected to it. The hydraulic assisted, or hydroboost, would have a small high presure hydraulic line connecting to the power steering pump.

 

And hey, in the early to mid nineties they all seem spongy. You're probably wasting your money.

[redvett]

He says the brake warning light comes on so he has a imbalance it the two systems. Could be a leak at the M/C or wheel cylinders. All #1500 trucks had vacuum boosters with exception of L/D Diesels that had Hydravac systems

[HawkScot]

When we bought our 92 Suburban used, it had spongy brakes and you could push the peddle to the floor in a panic stop. Had the dealer replace the master cylinder as part of the purchase, brakes were great after that (and still are). Look for leaks at the wheel cylinders and brakes lines (especially on the fronts, as many leave the caliper hanging from the brake line when replacing pads).

[darisb]

Thanks guys. I'm pretty sure the seals on the master cylinder are going. There is a little grim around the bottom of the MC, but I don't see any evidence of an actual leak. The pedal will firm up if I pump it a couple times. The fluid is about 3/4 full and doesn't seem to be going down. I have only driven it home and around the block a couple times. I need to take a look at the discs and backing plates for signs of leaks, however I don't see any leaks on my driveway and the cast rims are clean.

[hubbycap]

Sorry, I overlooked the brake warning light, of course that would change the situation entirely. I replaced the vacuum diaphram in my '95 about a year ago and it didn't change a thing in regards to pedal firmness. I also installed loaded calipers, replaced the flexible brake lines at the front wheels and renewed the brake fluid at the same time. Never had a firm pedal in that thing.

 

Brake fluid level will drop slightly with pad/shoe wear.

[AirForceAngler]

A while back I did a flush and refill on my brake fluid in my 2000. It seemed to firm the pedal up a little bit. As with most later model Chevy brakes they have always felt spongy.

[98 Z71 SLT]

Check one more thing before you go buying any parts.

 

MAKE SURE that your steel REAR brake line has not rotted out. Around WI, we are always replacing the rear brake line that runs down the frame rail, and feeds the rear drum brakes. These lines always rot out, and leak brake fluid. Follow the line where it goes between the fuel tank and the frame...that's where they rupture.