1988 1500 Brake Nightmare

[stuffs2936]

I have been battling this issue now for days with advice from several active mechanics and still it is not resolved. After replacing a master cylinder on a 88 1500 with standard suspension with rear only antil-lock brakes. I am having an almost impossible time trying to get a good pedal and a good quick stop. The stop seems to be delayed and the pedal seems to just hit a rock hard stop. In chasing down this problem I have new rotors,new pads, rebuilt calipers, new front brake hoses, the new master cylinder and a rebuilt power booster. The pedal has a lot of travel before I get a bite and in a real panic stop just hits a hard spot about an inch from the floor board.

 

I am wondering whether the push rod on the booster can be screwed in and out to lengthen?

 

Also there is a lot of confusion on the rear abs. It has a hydraulic unit mounted near the master, and also the proportioning valve is there as well. After bleeding the brakes I get a hard and high pedal but when the engine is on the pedal travel increase significantly.

 

This has everybody stumped so far, Any ideas will be greatly appreciated,

 

Thank you in advance, John

[alwcurlz]

I have been battling this issue now for days with advice from several active mechanics and still it is not resolved. After replacing a master cylinder on a 88 1500 with standard suspension with rear only antil-lock brakes. I am having an almost impossible time trying to get a good pedal and a good quick stop. The stop seems to be delayed and the pedal seems to just hit a rock hard stop. In chasing down this problem I have new rotors,new pads, rebuilt calipers, new front brake hoses, the new master cylinder and a rebuilt power booster. The pedal has a lot of travel before I get a bite and in a real panic stop just hits a hard spot about an inch from the floor board.

 

I am wondering whether the push rod on the booster can be screwed in and out to lengthen?

 

Also there is a lot of confusion on the rear abs. It has a hydraulic unit mounted near the master, and also the proportioning valve is there as well. After bleeding the brakes I get a hard and high pedal but when the engine is on the pedal travel increase significantly.

 

This has everybody stumped so far, Any ideas will be greatly appreciated,

 

Thank you in advance, John

 

Sounds like a vacuum leak to the brake booster. I'd check the grommets/fittings and hose to the booster and replace them. I've had where the grommet into the booster looked fine, however, the grommet was leaking due to it shrinking, allowing air to slip past.

[grose67]

I dont know if it will help, but my mechanic suggests running the vehicle while you blead the brakes.

[Nytemare]

You could just have a bad master. I have had new and rebuilt ones that were bad out of the box. The seals dry up on the shelf...I would return it and tell the parts store its defective.

[stuffs2936]

You could just have a bad master. I have had new and rebuilt ones that were bad out of the box. The seals dry up on the shelf...I would return it and tell the parts store its defective.

 

 

Good Point, sadly it is a crap shoot to depend on new and rebuilt parts. In fact I was fighting this originally chasing a ghost because the parts guy gave me the wrong bore size on the master. Now I agree I might have a bad master. I have ordered a pressure gauge set and I will be able to see really what I have going on. I can get a solid pedal until I start the motor and then the master bottoms out in 30mph panic stops.

Thanks for your reply

[stuffs2936]

I dont know if it will help, but my mechanic suggests running the vehicle while you blead the brakes.

 

 

Thanks for that comment, a friend suggested that also. I have never had the motor running when bleeding but maybe there is something to that.

[stuffs2936]

I have been battling this issue now for days with advice from several active mechanics and still it is not resolved. After replacing a master cylinder on a 88 1500 with standard suspension with rear only antil-lock brakes. I am having an almost impossible time trying to get a good pedal and a good quick stop. The stop seems to be delayed and the pedal seems to just hit a rock hard stop. In chasing down this problem I have new rotors,new pads, rebuilt calipers, new front brake hoses, the new master cylinder and a rebuilt power booster. The pedal has a lot of travel before I get a bite and in a real panic stop just hits a hard spot about an inch from the floor board.

 

I am wondering whether the push rod on the booster can be screwed in and out to lengthen?

 

Also there is a lot of confusion on the rear abs. It has a hydraulic unit mounted near the master, and also the proportioning valve is there as well. After bleeding the brakes I get a hard and high pedal but when the engine is on the pedal travel increase significantly.

 

This has everybody stumped so far, Any ideas will be greatly appreciated,

 

Thank you in advance, John

 

Sounds like a vacuum leak to the brake booster. I'd check the grommets/fittings and hose to the booster and replace them. I've had where the grommet into the booster looked fine, however, the grommet was leaking due to it shrinking, allowing air to slip past.

 

 

Thanks, I did check the vacuum. In fact the brakes seem solid until i start the motor and when the booster kicks in the pedal really drops and the master bottoms out during 30 mph panic stops

[Dal2HS]

I am having a similar problem with a 94 2500 HD. My mechanic friend told me to set it with the back end elevated and bleed...bleed...and bleed the brakes. He said he has spent as much as a day and a half on one before all the bubbles were out.