My 92 brakes seem to get tighter after I drive for several miles. It will pick up speed coating down hill and roll back on an incline but after 30 or so miles of stop and go around town it will loose speed coasting down the same hill as above and will not roll back on a slight incline. it's almost like the emergecy brake is slightly on. Any ideas?

 

First thing I would do is pull a wheel and check the relationship of the pad to the rotor. The pad should be close to the rotor, but not touching. The rotor should be able to spin freely. The distance between the pad and rotor can be adjusted by removing the master cylinder from the booster and shortening the length of the pushrod coming out of the booster. You don't have to open the hydraulic system, and small adjustments of the pushrod are multiplied and become large adjustments at the brake pedal and also at the pad. I would start out by turning the adjusting nut 1/4 into the pushrod and see where that leads you.

Next thing I would do is flush the brake fluid. Run enough through each caliper so you can be reasonably sure that the old fluid has been evacuated. You may have a high concentration of water in the fluid and it could be heating up and expanding.


If none of those fixes remedy the problem, I'd start looking hard at the brake caliper hoses. If they are the stock hoses, they could be due for replacement.

 

Good advice ... had a similar problem with my 92. The brake system flush fixed it.

 

I finally got time to mess with the car. Idling and pumping the brakes caused rpm to go up and hard sustained pressure nearly kills the motor. Fluid is black so it will all get replaced. What is the hose from the fluid bowl with the hose clamp for?

 

The hose goes feeds fluid to the ABS unit in the well behind the driver’s seat. After you have purged all of the old brake fluid and filled the reservoir with fresh fluid you should bleed the ABS unit first. If you don't bleed this you may not be able to get a solid pedal and you want to start with fresh fluid in the unit anyway.

I would suggest using something to catch the fluid when bleeding the ABS since there is no place for the fluid to drain.

If your fluid is black it's definitely time to replace it. Once you go through this procedure you may want to keep an eye on the color change in the fluid over the next couple of months, because it's going to get dark again. At which point you may want to do a flush and fill again.


Also, I'm a little troubled by the way the engine behaves when you described applying the break. Sounds like a vacuum leak to me, which would also give you a hard brake pedal.

Other forum members opinions/suggestions please.

Brian

 

I agree. The increase in idle speed when depressing the brake pedal is the classic symptom of a power booster leak. Either the case on the booster has cracked, or the diaphragm inside the plastic housing has a hole somewhere.

I would start by removing the master cylider from the booster. It's only two nuts that have to come off. You will not need to open the hydraulic system to have a look behind the master. Once the nuts are removed, gently pull the master cylinder away from the booster while being careful to not crimp or kink the hard lines attached to it. Once you have it removed from the booster, have a look at the back of the master cylinder and the area around the pushrod on the booster. If there is brake fluid present there, the seal in the master is compromised and will have to be replaced. Might as well rebuild the master, or replace it with a rebuilt unit.

If brake fluid is present on the booster, it has likely migrated to the diaphragm and has eaten it away. You will need to replace the booster if this is the case. There used to be booster rebuild kits available, but I haven't seen them in awhile. If you do a forum search, you should find the link to the company that sells metal cased power boosters. I personally replaced my booster with one from Oreilly 3 years ago and it's been fine since. Usually they fail when the case becomes brittle due to the engine compartment heat.

 

Thanks, guys. I am going to replace the both parts and start new. I to was baffled by the hard pedal and drop in idle speed. I have not looked at the ABS. Does it bleed by the same method as the calipers? Do I need to change the fluid in the resevoir behind the seat? How?

 

I'm out of town so I can't look at my 92 to be 100% sure about bleeding the ABS. I did a quick search and found this post from "Tom Piper" another forum member.
________________________________________ ______________________________
"The one thing the '92 has is a ABS "Prime Pipe" from the left hand side of the master cylinder reservoir that runs directly to the ABS unit behind the seat.
There is a bleeder valve on the side of the ABS unit to bleed this Prime Pipe. You can simply vacuum bleed it, making sure the reservoir does not run dry.
I'm not sure, but I don't think later LT1s have that.

Tom Piper"

There is no reservoir at the ABS unit behind the seat. The hose you questioned is just a brake fluid path between the master cylinder and the ABS. The vacuum bleeder referenced by Top Piper is a handy tool for bleeding and other things. I don’t think they’re too expensive and you may be able to Rent/Borrow one at Auto Zone.

Brian

 

Thanks. I think I'll be fine now. As we say down here "preciate ya"!

 

You're welcome!!


P.S. Nice collection of cars!

 

That is caused by a failing booster, a very dangerous situation in a panic stop. How'd you like to kill it and loose power steering too!?

 

Finally finished the brake project. Works great and the flush was not too bad either. Fixed the parking brake with some spray lube whilw I had the seat out. The idle is now steady at 600 and it's never done that. Idle drops right down when I dtop which was not the case before. This thing was bad when I bought the car two years ago. Amazing!

 

I have developed half of your problem. After a spirited run using the brakes hard they tighten up and drag just a little. The pedal goes down very little before it starts to stop you. I think that I need to replace the brake fluid, that it's old, I've had the car for 6 months, and probably there's air or water in it causing this to happen. The only question is the ABS, you say to bleed it first, I haven't looked at it, is there a nipple like on the slave cylinders?

Thanks

 

Evan, it sounds like your booster pushrod is adjusted too far out. It may be blocking the ports to the master cylinder reservoirs. Screw it in until you have a tiny bit of play in the brake pedal before it hits the master cylinder piston.

Thermal expansion of the brake fluid should not cause the brakes to drag.