post brake job wierdness

[Clinton]

Hello all,

Finished my first brake work on this vehicle and have some wierd symptoms. First what I did: new 'Performance Friction' disk pads, cleaned up and greased slide pins and surfaces with 'Sil-Glide' silicone grease, broke free and examined drums, confirmed that my front disks were doing all the work, adjusted shoes to slight drag, checked park brake cable, completely bled system to replace 6 year old fluid with 'Valvoline SynPower' DOT 3/4 fluid. Now to break those rear drums free I had to use some stategy learned here, the mini sledge and pry bar wasn't cutting it. I ran it in gear while on jack stands in Drive and Reverse and stopped hard. This works well and I had to seat the pads to the rotors up front so it accomplished this too.



Okay, so I go to test. Pulling out of the drive I noticed the 'hard pedal ' symtom. This went away on the test and stopping power was improved, no squeals, no pulling, just good results. Until I get almost back and the 'hard pedal' returns. I read the diagnostic section in the service manual and learn about some stuff I didn't know before, then do a little research on the TDR, have a bite of lunch and then go for another drive. Same exact result. 'Hard pedal' leaving the house, goes away during the drive, then back as I return. The brake and ABS lights come on when this happens, so it makes me think I've got a vacuum line problem. My vacuum lines look okay. I didn't want to get into that without checking here first.



Is there anything I can do to check the booster or it's check valve without a vacuum guage? I'm guessing I'll need to get one. The 'hard pedal' symptom is like taking the power out of your power brakes, like stopping with engine turned off. At least I know my warning lights are working okay. Now what did I do to create this problem? The job went a-okay, no surprises, no left over parts, nothing out of the ordinary. The breaking free of the drums on jack stands was new to me, but I think that's a pretty good physics lesson, or is it? Sorry for the long post, but everytime I post folks say they need more info, I think that about covers it. Thanks.

 

[illflem]

Your diagnosis is the same as mine, loss of the brake booster due to a vacuum leak. It could be coincidence but I'll bet something was knocked lose in the master cylinder area while you were bleeding. Sometimes if you have someone rev the truck up to full vacuum then shut it down while you have your head under the hood you can hear the last hiss of air from the leak once the engine noise is gone. A hand operated brake bleeding vacuum tool is also handy for finding leaks.

 

[Clinton]

update

Took truck on longer test drive and confirmed some type of vacuum problem at the booster. Lines and connections all look okay, but get the warning light at stops where brakes stay on. Looks like I'm depleting the vacuum at extended stops. When I was trying to break the drums free (on the jacks) it took quite awhile and many stops to accomplish, I'm wondering if I toasted the booster's check valve. Rear axle was on stands, front axle was on the ground with front tires not rotating and brand new pads. Drums were way out of adjustment and siezed up pretty good so I really had to push the pedal. The leak is small as it doesn't trigger the warning light if running over idle, if light comes on at an extended stop and I put it in Park (and release pedal) light goes off quickly as vacuum builds. Gotta check the check valve I guess.

 

[jrobinson1]

I thought I had a vacuum leak. Easy check w engine off... Pulled hose of the vacuum pump and put compressed air to it. Found my leak real quick w/ someone on the airtank and me lookin.



I was afraid that it would blow connections of so I kept the pressure low. 20 - 30#. (Maybe someone will chime in if that could cause damage to components, my system still seems fine) Just keep in mind your puttn press on vac sys. Could show you some that only leak w pressure but gets you closer. I had some lines worn through and connector on t-case was leaking.





james