About two months ago I replaced the vacuum booster on my 97 and there did not seem to be additional problems. It has had very little driving since. About a week ago I needed to drive it and found that the brakes were locked. To drive it I had to pull the brake pedal up with my foot. In addition the brakes were quite sensitive and would lock up with any application of the brakes.
Where should I start looking? Master cylinder, vacuum booster or other.
TIA

pbgsho2

 

Not sure but here's a bump

 

I would start at the master cylinder. And double check the installation of your booster just to be sure.

 

check master cylinder pushrod length. it is very critical. 1/8 inch will make the difference between releasing the brakes or keeping them applied.

 

i would also check the master cylinder corrosion can devlop around the base of it and cause it to aactually clamp down on the piston indise

 

If the vacuum booster was the only thing you changed and then the problem happened. I would be looking at it first. My 96 had an issue with the ABS valve to where it was getting trash in it and that caused rear brakes to lock up. However it wasnt a pedal issue. The pedal was acting normal other than the rear brakes were always applied.

 

Vacuum pump wouldn't cause that issue. It just makes the brakes really hard to apply (hard pedal) if there's low vacuum.

I don't suppose any warning lights came on?

 

correct, vacuum pump will not cause this problem. but when you remove the master cylinder to replace the power booster, they very rarely tell you to make sure the master cylinder pushrod is reset to properly release residual pressure.
if you do not reset it, the master will stay applied a bit, retaining pressure in the front lines.

 

tjc transport identified the problem. The pushrod in the boster was too long. I shortened it which reduced the problem. It still needs to be shortened more and I believe this will solve the problem permanently. I put the rod length in the middle of the range shown in my shop manual. Apparently there is something in the booster, which over the short time between installation and the problem has changed causing the issue.
Thanks for the solution.

pbgsho2

 

no problem. i like to set the push rod short. i would rather have a little less pedal travel than have the brakes slowly start sticking while driving.
i learned my lesson with this a long time ago when the booster went on my 79.
it took me almost 3 weeks to figure out the push rod was too long, allowing residual pressure to stay in the front brake circuit and after around 10 brake applications the fronts would be locked up and take about 6 hours to bleed off.
i actually figured it out only after replacing both front soft lines.
took it for a test drive and they started dragging again.
the only way to drive it was to stop after using the brakes 5-6 times and releasing pressure by loosening the lines at the master.

once i shortened the rod all problems disappeared.

 

Wow, I just realized my post didn't really apply. I translated booster and pump fro some reason. Sorry about that. I must have been looking at multiple tabs or something.