Rear Brakes (or lack thereof)

The next day I went outside somewhat excited to start tweaking things, kicking tires, and truly looking at what I had bought. I knew I had lots of work to do on the truck overall, so to get it as close to tools and stuff I opted to pull the motorhome out and park the GMC sideways behind it, in front of the shop door. I squeezed the motorhome back in so they were both behind the gate. Putting the truck there was the obvious choice anyway because having no idea idea how long it would be laid up for, it would keep it from blocking any other vehicles.

 

When I start to work on vehicles I buy, I almost always start with the brakes, and this truck was no exception. After all. stopping is much more important than starting! As I mentioned previously, the brake warning light lit up like a Christmas tree while we were on the road headed home after buying it, so inspection was definitely required.

 

During my half-assed initial inspection I saw the true cause of the brake warning light, and it wasn't the emergency brake. There was brake fluid all over the left rear backing plate and tire. I popped the top off the master cylinder and the rear half of the system was dry. It had flown the coop through the left rear wheel cylinder. There was brake fluid 'spin art' everywhere. The brake shoes were in real good shape wear-wise, but there was no way they were going to remain--cleaned well or not. Because of the C6P Heavy Duty Chassis package, the truck is equipped with, among other things, 13" x 2 1/2" brakes! I like that. The stamped code on the differential housing is BJB, and according to my manuals, translates to 4:10 gears. Figures. I was hoping for 3:73.

After checking what all I needed, I went inside and ordered rear brake shoes, wheel cylinders, and a master cylinder from Rock Auto. I opted for 'fleet quality' Centric riveted shoes--top of the line--so they would wear well, stop well, and do both quietly. The drums were great and showed very little wear, luckily.

When the brake parts came I was excited to get them installed and finished up. The install went well, with no rust issues or anything. When I put it back together, I couldn't get anything more than a trickle out of the left rear bleeder. I tried to access the proportioning valve to reset it, but it was mounted down low, on the engine crossmember. I took the radiator out, and the fan off, making plenty of room. Try as I might, I couldn't get the proportioning valve piston to move freely back and forth. I got it released once, but as soon as we tried to bleed the brakes it stuck to one side again, shutting off the rear brakes. Sigh. Oh well, it's not like I didn't have anything else to do, haha. I did some research and found a good proportioning valve and ordered one up. I think it was about $50. At the same time, I also ordered a new brake line for the left rear--mainly because I wanted a new fitting on the brake drum end.

Another item in the braking system had me a little concerned. It's a 'load-sensing' valve that's mechanically attached to the frame and rear end. What it does is, it restricts full braking to the rear brakes if the truck is riding at normal height. When you put a load in it, the truck 'squatting down' would allow full brakes to the rear wheels as well as the front. It was designed to keep empty trucks from having their rear brakes lock up unexpectedly. It turns out that GM sent out a bulletin some time later, instructing dealers to bypass the valve and remove the linkage. It was GM bulletin 88-T-151 (shown on the reference materials line at the very top of the blog page). Here's what the whole setup looks like in the GM parts catalog:

Most of it was removable without cutting, but there are still couple residual brackets remaining that I'll remove more cleanly sometime in the future, along with cleaning up the altered brake line routing.

When all the new brake goodies showed up I got them all installed without a hiccup. I love working with new parts! Brenda hopped in and lent her brake-bleeding leg once again, this time with instant results. That's what I like.

After driving the truck I noticed no sign of early lockup or anything else. Nice braking!

During the two weeks or so that I had the truck up in the proctologist's saddle I was able to work on a lot more items that needed attention, and there was no shortage of those!