Good day all! I need to swap out my master cylinder tomorrow or Tues at latest. Have done this job on many other vehicles,but never an S series-I have the correct line wrenches etc and know how to bench bleed a master. My question is regarding the plastic clips attaching the thrust rod to the brake pedal. I can see that I only need to drop the lowest panel of the dash to access these;BUT as with most old plastic parts,they break! Should I have a set on hand at home before I do this swap? I'm sure they are a dealer only item. Or are they durable enough to go ahead and do this job in the morning confidently without a set on hand? I highly doubt a local GM dealer will have these on the shelf,but I may be wrong- Thanks for any input! 97 Jimmy 190K 4.3W 4x4 rear drums- only $2500 in it and owned for 2.5 years! Gotta love it!

 

Your 1997 Jimmy should have power brakes, in which case, the master cylinder attaches to the booster and there's no need to go under the dash. What you will need to be concerned with, is if it has ABS, which it most likely does, you'll need to do the automated bleed with a capable scan tool after you replace the master cylinder. During the replacement, air will be introduced into the ABS unit, (unavoidable, even after the bench bleed). The automated bleed will expell the air into the lines, then you bleed it out of the lines at each wheel.

 

Hmmm-I did not want to hear this! Please descibe an "automated bleed" procedure and as to why a scan tool will be required.I know very little about ABS other than wheel sensor replacement. I am also concerned about the bleeder screws at the rear cylinders as I believe they are original and can already picture breakage...Thanks

 

Hate to give you bad news but, it's not all that bad. It's more like, "the nature of the beast". During master cylinder replacement, there will be an air bubble trapped between each line and the master cylinder, ain't no two ways about it. When you apply the brakes, the bubbles will be forced into the ABS unit. The air will not travel through the ABS unit on its own, it will get trapped. During the automated bleed, the operator keeps steady pressure on the brake pedal while the EBCM operates the solenoids, (inside the ABS unit) in a sequence that forces the air bubbles into the brake lines. The only way to initiate the automated bleed is with a capable scan tool. Once the air is in the lines, each wheel needs to be bled to allow the bubbles to exit.