Brake Problem (Comedy of Errors)

[chuckf]

I lost my brakes. So I investigated the problem and I noticed that there was no fluid in the master cylinder. I noticed fluid by the hydraulic booster. 1st error - I assumed that the fluid was from the master cylinder (not knowing that the MCyl and the HyBooster are independent fluid units- don't laugh too loud). So I removed the hyd booster and disassembled it to replace the seals (2nd Error) GM dealer does not sell seal kits. So I ressembled the hyd booster. It dawned on me when I was removing the master cyl that the brake fluid loss was not at the hyd booster. Further inspection I found that the bake brake cyl let go. I replaced both rear brake cylinders, cleaned out the master cyl and re-assembled everything. Bled the brake lines and bled the hydraulic booster according the service manual.
Here's the problem: With the truck running the brake pedal will not return quickly and there is very little braking. I bled the brakes (right rear, left rear, left front, right front in that order) 4 different times. I got air to come out of the bleed valves and had good fluid flow. Still no brakes, and pedal very slow to return. Check for hydraulic fluid on the return line of the booster - ok booster fully purged. The service book diagnostics says that if the pedal does not return replace the booster. Since I dis-assembled the booster I assume I damaged something (oring, or check valve or accumulator). So I got a used booster and replaced the booster. I also installed a new master cyl ($25). Re bled the lines again and again and again. Still can not get the brakes to work properly or the brake pedal to return quickly. I know this is a lot of information, but I must be doing something wrong. Any help would be appreciated. If anyone knows where I can buy a seal kit for the booster, I can rebuild the first one have it as a spare.

[rjschoolcraft]

Did you make sure to bleed all of the air out of the booster/power steering system?

This can be done by raising the front of the truck (to allow the wheels to turn easily) and turning the steering wheel back and forth (lock to lock) repeatedly with the cap off the pump reservoir. When you no longer see air bubbles, you're done.

[chuckf]

ronniejoe.
Yes, I followed the procedure as outlined in the service manual.
1. Raise the front wheels.
2. (engine off) turn the wheel lock to lock 20 times (40 if there is cooler, which there is).
3. Lower front end.
4. Start engine let warm up for 2 minutes.
5. Check for smooth operation of power steering.

I followed the procedure of getting the air out of the booster when I re-installed the original booster. After I installed the used booster I did not. I will go back and do it again. Thanks.

[Govt issue]

I had a truck once that had a failing abs control board. The rear breaks wouldn't completely bleed unless the key was on. Some fluid would come out but not enough psi.

[JohnC]

I'm no expert here, but I thought I heard that if a lot of air gets introduced into the brake system the ABS needs to be bled using a Tech 2.

[damork]

Chuckf,

With respect to your hydroboost, I have been trying to find the seal kits as well.

I finally made the connection by talking with Bendix who is now owned by Bosch. Apparently they discontinued the seal kits and made the units difficult to rebuild or even disassemble. Theory is if they need seals, they probably need more.

I disagree with that theory and have rebuilt them before resulting in a lot more miles from them. Seems like a good design they were not getting enough revenue out of, but who knows.

There is a company called Precision Rebuilders at 1-800-325-2690 where you can get rebuilds (http://www.precisionrebuilders.com). They told me the best way to find the exact replacement is to give them a number stamped in the actuator rod of your boost unit. Tim Henderson was the person I talked to. Prices beat anything I've seen so far and they were selling direct.

[chuckf]

damork,
Thanks for the info on the seals for the booster. I appreciate the follow up.

Comedy of Errors resolved:
If the brake lines have any air (even the smallest amount) the booster can act like it is not operating properly. I did have some air in one of the front brake lines. The bleeder valve on the driver side was rusted and I was trying to bleed from the flex hose (attached at the calipher, about an inch away from the bleeder valve - add to the list of errors). I had to drill out the old valve and retap the hole for a new one. Once ALL the air was out of the line, the booster responded properly and of course the brakes did as well. Problem solved. Thanks for everyone tongue.gif s help.

[chuckf]

ronniejoe,
Eventhough I followed the procedure in the book I didn't. You were right on with your comment on bleeding the system correctly.