master cylinder for 90 ZR1

[carnold]

Is the AC Delco #174-820 (Chev. #10157996) master cylinder replacement for a 90 ZR1 a PBR? Has anyone rebuilt a PBR with the AC 175-619 rebuild kit and did it work out OK? If I choose to rebuild do I need anyother parts beside the rebuild kit.

[tomtom72]

Okay this may not be something you want to read but I just bought a master cylinder for my 90 in Mar 06. AC Delco p/n on box is 18M399. There is another # on the box, 18030641, I guess that's a good GM # as it comes back as a master cyl on two GM dealer sites' search engines.

The master cyl is a PBR/ made in Australia in an AC Delco box. I bought the rebuilding kit from RockAuto.com and it is an AC Delco kit in an AC Delco box listed as a wagner or raybestos kit(?) on the site, I forgot which.....I haven't yet done the work but it looks like everything the FSM lists is in the kit....I may send it off to a rebuilder locally to have mine sleeved first & have them put it together along with a DRM bias spring.

I can't explain why your #'s and the #'s on the master I just bought (bought it from the last detail in Atlanta) don't match. Did you get those #'s from the parts CD that whiteracing.com sells? If so those are original 90's #'s and alot have been changed over time by GM.

:cheers:
Tom

[carnold]

Actually GM and AC Delco have 2 different part numbers and know one knows why. They are both good numbers and the number I used cost about $80 more. I found a NOS PBR on ebay for $99 so I jumped on it.

[tomtom72]

They proly do that to confuse us!

Oh, I made a mis-type/brain fart on the rebuilding kit. The box has a Raybestos label on it and the contents are in a sealed plastic bag with a PBR instruction sheet in the sealed bag....I guess it's a good thing that this stuff is made by some one reputable....better than the clutch hydraulics!

:cheers:
Tom

[Jeffvette]

Actually GM and AC Delco have 2 different part numbers and know one knows why. They are both good numbers and the number I used cost about $80 more. I found a NOS PBR on ebay for $99 so I jumped on it.

You have two part numbers as there are two models to choose from. You have the original dual resevoir model, and the updated single resevoir model.

Either fits and no issues.

As far as rebuild kits, don't like them. Never have, never will.

[petefias]

As far as rebuild kits, don't like them. Never have, never will.

I took apart my leaking MC to see which seal was broken/cracked and could not see any whatsoever, no tear, hairline crack, wear of any sort. And I looked under a magnifying glass. There was no scoreing, or any wear in the cylinder. I decided not to even try the rebuild kit and got the new MC. Given, the leak was very small (about a half dollar size puddle overnight), pedal stayed semi-firm. I had to reuse the reservoir from the old unit (didn't have the nipple for the ABS pump feed). New MC works fine.

[Tom]

Did you take apart and inspect the parts for the valve that is built into the cylinder? I had one master cylinder where this valve was leaking. Brake fluid would go from one reservoir to the other as well as leak out around the switch that screws into the valve.

[petefias]

Did you take apart and inspect the parts for the valve that is built into the cylinder? I had one master cylinder where this valve was leaking. Brake fluid would go from one reservoir to the other as well as leak out around the switch that screws into the valve.
The leak was at the back where it attaches to the booster. What I couldn't find was the cause of the leak. The seal that was suppose to seal at the end looked brand new. That is why I didn't even want to try a rebuild kit.

It was a major pain to originally locate the leak because it seeped out in the back and along the booster housing onto the SS lines going to the rear. At the bottom where the SS lines have a connector is where the fluid accumulated and dripped to the floor. I ended up removing the SS lines and check them with a vacuum pump (they were fine) so I worked my way back until I found the source.

Not sure why the seal went since I never used Dot 5 or Silicone fluid (own the car since new). The car only has 25K miles. I use mostly Valvoline synthetic and it seems to work.

[Tom]

The first one that I had leak, leaked at the booster but on mine the fluid ran down the front of the booster and I could see the fluid level dropping in the reservoir and the trail of brake fluid down. The second one that I had leak had the fluid coming out around the switch on the valve as well as the fluid level dropping in one reservoir and increasing in the other. I didn't bother rebuilding the first one, just replaced it, the second one failed shortly after I installed it so it was still under warrany so it was just replaced as well.

I work with hydraulic components in my current job and sometimes it takes a lot of work to find why a part is leaking. Small, tiny flaws on the seal surfaces that can cause leaks are sometimes very difficult to find. Putting the surface you are inspecting under tension while inspecting the seal usually helps. On some seals I have had to use a microscope at 10 to sometimes 30 magnification to find the flaws in a seal.

Flaws in the bores of small diameter cylinders can be even worse since you don't have very good access to look at the surface. If you have no plans to ever do anything with the leaking cylinder you can cut it in half lengthwise so you can find the problem. I have done this with cylinders where I couldn't find the problem any other way.

[Tom]

....I guess it's a good thing that this stuff is made by some one reputable....better than the clutch hydraulics!


The original clutch master cylinder in my '90 was made by Lucas Girling as well as the replacement clutch master cylinder I bought at a Chevy dealership. They are a very large and reputable supplier of hydraulic components, both clutch cylinders and brake components. They started making the clutch cylinders for the '84 model year Corvette and made them for many GM applications using hydraulic clutch actuation.

The dust boot on the end of the cylinder will have Girling molded into the surface if it is a Lucas Girling cylinder and also if you take the cap off the clutch master cylinder and look down at the bottom flat of the moisture barrier it will have Girling molded into it if the master cylinder was made by Lucas Girling.