Is it the master cylinder?

Hi all,

Here's hoping my story will help one of you guys from banging his head too hard at his brakes.

A couple weeks ago, I decided to check my rear drums because the car was pulling left when I hit the brakes, but it wasn't pulling the wheel. No biggie I thought. I pulled the right side drum and it was caked in grease! The axle seal had failed. The seal failed because the axle bearing had started eating the axle. Fun.

Ok, so now ordered new seals, bearings, full rear brake kits(springs,shoes,cylinders,drums), and a new axle. Spent a weekend putting it all together, marveling at how easy pulling the axles was, and thanking the GM engineers that made knocking the differential pin too far through didn't require drilling out the pin. Put it all together, and all seemed well. Brakes seemed a little shuddery (Current manufacture drums seem to all be terrible), so I pulled the Napa set, and ordered the ACDelco drums. Much better! Odd though, they get shuddery after a drive. They would shudder while braking, and keep going while rolling. Felt like a wheel/driveshaft imbalance that would get better if you accelerated briskly.

I started taking an IR thermometer with me to check temperatures. After driving to work a couple times (30miles each way @ 60-70mph) the rears would get to around 205F-210F while the fronts were only showing 135F-145F. Weird. I chalked it up to the shoes were still bedding in and would be hot and odd until they would bed properly.

A week later, they're still doing it, only a little better. I finally decided to check my master cylinder to see if it was leaking into the brake booster.

Sure enough, it was, but it was a very slow leak, pedal was always firm, level dropped very slowly (months between top ups of the rear(front brake) section, thought it was the calipers moving). I got a new master Dorman brand box that was labeled Wagner MC. Bled it with Dot3, and mounted it up.

What a difference! Car has a bit of nose-dive on hard braking, and the temperatures are now after hard use 201F on the front calipers and 150F on the rear drums! This car has had poor/ok-ish brakes since I'd gotten it around 3 years ago. It got new calipers,rotors,drums etc but never checked the master. Wish I would have started there!

TLDR: If the brakes are overheating in the rear, or if it seems to take too much pressure to stop, or stay stopped at a light, check the master cylinder.

I really wasn't looking forward to the very shaky run to Wagonfest!

Glad you found the issue. Another problem item can be the proportioning valve. I had one fail. The reservoir in the front would fill the rear reservoir, and the braking was weak. The proportioning valve is not available new, or rebuilt.

I had issues with my '92 Custom Cruiser was pulling hard to the right on braking. The slower you braked the less violent the pull was. I ended up changing calipers,pads,rear shoes, rear wheel cylinders, hoses and the master with no effect. It got increasingly worse to the point that the car was borderline safe for driving. Finally one night I removed the output lines for the front calipers from the anti lock valve unit on the left frame rail next to the power steering pump. I had my wife apply the brakes while I observed the flow from the open ports. I was almost giddy happy when the left output shot a hard strong stream of dot 3 out while the right side slowly drizzled out. This was the problem! The next day I procured a replacement from my local pick and pull, changed it, bled it and had no more issues. If you experience hard pulling with no obvious explanation, bare this in mind.

Funkwagon455 wrote:

I had issues with my '92 Custom Cruiser was pulling hard to the right on braking.  The slower you braked the less violent the pull was.  I ended up changing calipers,pads,rear shoes, rear wheel cylinders, hoses and the master with no effect.  It got increasingly worse to the point that the car was borderline safe for driving.  Finally one night I removed the output lines for the front calipers from the anti lock valve unit on the left frame rail next to the power steering pump.  I had my wife apply the brakes while I observed the flow from the open ports.  I was almost giddy happy when the left output shot a hard strong stream of dot 3 out while the right side slowly drizzled out.  This was the problem!  The next day I procured a replacement from my local pick and pull, changed it, bled it and had no more issues.  If you experience hard pulling with no obvious explanation, bare this in mind.

I was hoping it wasn't the ABS unit, but you're probably right. It still pulls left a little. The pick and pull near me has an OCC wagon. Hopefully it's still got the ABS pump!

Thanks!

What color is the interior of the OCC? What OCC only parts are still on the car?

Interior is red cloth, outside white. I think the right rear taillight was there. Don't remember if I saw the grill (it's been a couple weeks)

What condition are the front seat covers/cloths in? I might be interested in the front seats. Grab any complete tail lights you find. An extra grille is always nice to have. How about cladding with the bottom mount.

The seats looked alright. I'll pull them off they're in good shape. Not sure you mean by cladding.

The plastic around the bottom of the exterior.

I think it was pretty rough but I'll take a better look tomorrow

Fred Kiehl wrote:

What condition are the front seat covers/cloths in? I might be interested in the front seats. Grab any complete tail lights you find. An extra grille is always nice to have. How about cladding with the bottom mount.

The OCC tails are the short ones correct? Got a set today that are much shorter than the ones on my Caprice.

The OCC has the longest tails. About an inch and a half.

Fred Kiehl wrote:

The OCC has the longest tails. About an inch and a half.

Thanks. I have RMW tails then.

The ABS modules are typical with Caprice,Roadmaster sedans and of course B body wagons.... Cheap/plentiful

The 94-96 modules may be a little different than the 91-93. Check the fittings to make sure it fits if it is not in the year brackets.

Great information, thanks for posting the saga.