maybe368

Ok, I know that this isn't directly related to first gen Cummins, but there are some of us that have done a rear disk brake conversion using the '76-'78 Cadillac Eldorado rear calipers with P-Brake. I have found that half of the people with these calipers hate them, these are the ones that don't know how to adjust them and the other half love them, because they do. Well now, we will all be able to properly adjust them. It is very important to use the P-Brake because that is how these calipers adjust. They do not self adjust like "normal" calipers. I did many searches for information on this and there is a lot of it, but no real clear explanation of how to adjust the P-Brake. Here is a pretty good video on how to disassemble the caliper, but a warning, he uses a few bad words, not too many, but some: It is kind of long, but pretty good.

I had a real hard time figuring out how these things work, it is not intuitive. He takes them apart in the video, but I included a few pics. There is a ratcheting mechanism inside the piston, that he also shows in the video. Here are a few pics:

maybe368

I got ahead of myself with this part, so, make sure and do the next post before this one. Even after watching the video and reading countless threads on it, I still needed an epiphany to finally know how to do it. In order to adjust the p-brake, you need to do it before you bleed the caliper and put hydraulic pressure on the system. I bought reman calipers and 1 of them was identical to what I had, but the other was missing a threaded hole, which I put in myself. The other thing is that they do not come with the P-brake levers, unless you buy them from the conversion kit suppliers. Look closely at the pics, because the P-brake spring is a bit tricky. but if you use a screw driver to stabilize it, it is pretty easy. there is a tab on the caliper that you can catch by hand, then you insert the screw driver to then put the spring over the tab and into position:

maybe368

In order to adjust the P-brake, the caliper needs to be completely installed on the rotor, but with none of the above P-Brake parts installed. Also, do not bleed the caliper or apply the brakes until the P-Brake is adjusted. With the caliper installed in the rotor, turn the nut in the direction of cable pull (it's CW on one side and CCW on the other) to put the piston against the rotor. Then turn the nut the opposite direction in order to index the lever against the stop on the caliper. When you do this, the nut goes kind of into the hole in the caliper, so I found that the easiest tool to do this is the P-Brake lever.This is the part that I kept leaving out, the lever must be indexed against the stop WHEN THE NUT IS TURNED IN THE DIRECTION OF CABLE PULL ALL THE WAY (nut is protruded away from the caliper). IF THE LEVER IS NOT AGAINST THE STOP WHEN THE NUT IS TURNED ALL THE WAY IN THE DIRECTION OF CABLE PULL, TURN IT ALL THE WAY THE OTHER DIRECTION (nut closest to caliper) AND THE NUT WILL SLIP ALLOWING YOU TO CHANGE THE INDEXING. Keep doing this until the lever sits on the stop when the nut is turned out all the way(direction of cable pull)., Do this carefully so that there is no more than a 1/2" gap when the P-Brake is applied. See Pics:

maybe368

Once you have the P-Brake adjusted, you can then bleed the calipers. Unfortunately, the only way to correctly bleed these is remove the cover from the MC, remove the caliper, hold the bleeder valve at 12 o'clock, open the bleeder and wait for the fluid to appear. Move the caliper around and shake it until there is no more air. Tighten the bleeder and reinstall the caliper. That is all of the bleeding that was necessary, they should all be that easy. I tested the P-Brake and it killed the Cummins. I am now in the 50% that loves these calipers. I hope this helps and please correct anything that I may have messed up...Mark

thrashingcows

I have the same basic caliper...though a bit smaller...on the rear disc set-up on my 68 Chrysler wagon and it's 8 3/4 rear end. Took me days of reading and fiddling to finally get the park brakes set-up correctly and working right.

I would never do a rear disc conversion on Patches, or any other vehicle again....actually planning on pulling the rear discs off the wagon and putting the 11x2.5 drums back on.

maybe368

Yeah. you have the smaller post '78 version. They are 5 1/2" bolt hole center to bolt hole center, while the '76-'78's are 7 1/2". There are quite a few descriptions on how to adjust these. but they are about as clear as mud. It took me 3 edits before I was somewhat satisfied with my version. Now that they are adjusted right. they are working beautifully...Mark

sooty

update to rear disc brake mod, with caddie caliper, egr is offering a hd independent mechanical caliper, im looking to use with a regular 7" pin front caliper on the rear, to increase rear holding capacity, the egr model is sold as a tow truck upgrade, egr model #EGRMANBR, on their site is a 2 caliper bracket made only for the ford sterling, and gm 14 bolt diffs, and why dana wasent included??? it would be real easy to attach a supplement welded bracket to the existing install to provision the 2nd caliper up top on the rotor. im also working on a 2004 d80 rear disc/drum ebrake conversion to d70 axle for our trucks, utilizing a 1-1/4" thick bolt-on adapter plate, coming soon.....

maybe368

Sweet, so the extra caliper is for p-brake only? Or does it brake also with the normal braking? Egr makes good stuff, but it is pricey...Mark

sooty

just e brake only, allowing much simpler pad changes on driving caliper, might add pricey too, 350. the disc kit was 700. 10 years ago,

Scott Snow

Mark (Maybe368), thanks so much for this write-up. Definitely the most informative and logical instructions on how to bleed and adjust these GM 7" rear calipers. I'm using these calipers on my 75 Olds Delta and for the first time, I'm now part of the 50% that loves (really likes) these calipers. When I converted in the mid-2000s, there was no adapter bracket for the GM 8.5 rearend (no longer using Type O rearend) so the differential shop welded on some 7" brackets. First problem were brackets not square to the rotors which created crooked pad contact... Second issue was my too much caliper travel caused by improper e-brake adjustment and poor bracket alignment. My bled valves are located high so don't think air in the lines was an issue but I followed your instructions anyway.

My solution was to remove the slightly skewed weld-on brackets, remove c-clip axles (new seals), modify/install the original cadillac brake brackets and adjust per your instructions. Braking is night and day improvement though e-brake isn't comparable the drum e-brake. Thanks again! Scott