Master Cylinder Rebuild or New

Schrup · Schrup's Garage

I recently changed my brake fluid & the old fluid looked really bad. I have decided to rebuild all my calipers, install new flex lines, & change my master cylinder. My pads & rotors look new. After I changed the fluid I used speed bleeders, but didn't care for the results, so I bought a power bleeder. My pedal was ok for a couple of weeks, but now has a couple of inches of travel unless I pump it. I tried not to push the pedal too far when I bled them the first time but think the seals are bad. With the way I drive I don't ever want to wander about my brakes. I researched this a bit & saw mention of a rebuild kit for the M/C. Is this worth the time or am I just better off buying a new one ($96).

jphillips-998 · jphillips-998's Garage

I would say for a hundred bucks by the new M/C. I replaced mine a few months ago and it was a pretty easy job. If you rebuild, you have the confidence that everything is new and in working order so the M/C can be ruled out if you have brake issues in the future.

Chuck Moreland · 10-07-2003, 01:15 PM

Rebuilding the MC is an easy job, easier than the calipers.

sammyg2 · 10-07-2003, 01:30 PM

If the problem in the master cylinder is ONLY the rubber seal you can rebuild it. BUT, based on the decription you gave on the fluid I would suspect it was contaminated and probably caused at least some corrosion in the M/C. If that is the case you should replace it. Rebuilding a master cylinder that has some pitting in the bore is not a reliable fix IMO. You could pull it apart and inspect it and then decide.

Early_S_Man · 10-07-2003, 02:13 PM

This is not a decision you can make without disassembling the master cylinder and inspecting the bore ... generally pitting will be visible on the lower crescent of the bore if absorbed water has damaged the master cylinder!

If there isn't any pitting on the lower arc of the bore that you can feel with your fingertip after running a brake cylinder hone in the bore ... then you can be confident that a rebuild will be successful, assuming that you assemble the new parts correctly! All new parts ... pistons, cups, and seals are provided in the ATe rebuild kits. I have never had a failure within five years on any master cylinder I rebuilt in the past 30 years+ ... and I have been using Dow Corning 4 Silicone Grease to lubricate the bore, cups, and seals all that time! Ate used to provide a tiny tube of identical silicone grease with all of their 911 master cylinder kits, though not in VW kits!

1. Use isopropyl or methyl alcohol to clean the master cylinder body and bore ... especially after using a brake cylinder hone!

2. Use a genuine ATE rebuild kit.

3. Use silicone grease to coat the bore of the used master cylinder after thoroughly drying the bore after cleaning with alcohol. Use silicone grease on all of the cups and seals prior to installation onto the pistons.

CarreraS2 · 10-07-2003, 02:14 PM

I tend to rebuild calipers because there are 4 of them, and replacements are usually pretty expensive.

I tend to just replace the MC with new, because there is only one of them and replacements are cheap and tend to last a long, long time. Plus, I hate the labor involved with taking out and putting the MC back in, dealing with the brake fluid, etc. For the $100 or so that a MC costs, I just replace.

Schrup · Schrup's Garage

Thanks guys, I have just ordered all my stuff ($300), but that also includes new lug nuts ($85). I'm just going to install a new one & if the old one looks rebuildable I'll buy the kit & keep it as a spare. Thanks for the advice. Looks like it's time to put her away for the season.