Rear disc brake conversion with parking brake

Re: GM Seville 79-85 rear calipers

I wish I had known all this stuff before I purchased my disc brake conversion, so I thought I would offer up what I found.

Gm and all the suppliers state the the parking brake must be applied every time the car is parked. This isn't for safety, it is to keep the calipers adjusted. If the parking brake is not used regularly the calipers get out of adjustment and there are no brakes!

Getting the parking brake adjusted properly when they are installed is critical. Some instructions say you may have to repeat the process up to 25 times to get the proper adjustment. Some people can never get them adjusted; give up and buy the non-parking brake version. Others say they have no problem. If you Google the calipers you'll see both opinions.

Those that got the calipers from a salvage yard report that the parking brake is usually frozen. That's because once they get moisture in them, they corrode and seize. Almost all suppliers say you need to change the brake fluid once per year. It seems that time is the factor for the corrosion not usage.

I got mine from Speedway, p.n. 901-31046, but CPP, MP, TMS and most other suppliers offer the same calipers for their rear disc conversions. It is interesting that the suppliers have different instructions for adjusting them. Speedway instructions also indicate they are difficult to bleed; they have a specific method for bleeding them.

Here's a link to a thread that shows how they work:
http://classicbroncos.com/reardiscs.shtml

I found that CPP had a really good brake troubleshooting chart and good instructions on these calipers. Here's a link:
http://www.classicperform.com/TechBook/BrakeTroubleshoot.htm

MP also has good instructions:
http://www.mpbrakes.com/docs/orig-guides/DB1791BR-INSTALLATION%20INSTRUCTIONS.pdf

Many people say they are happy with these calipers. I'm not badmouthing them, just pointing out that they can be difficult to install, require regular PB application, and frequent fluid changes.

The photo shows the ones this post is about.

I bought a Speed disc brake conversion kit, using the pressed steel disc adaptors. Also had the parking brake callipers. You're not wrong, the calipers can be a bitch to adjust, but the disc adaptor run out of true too. The discs 'wobble about a 1/16" a they turn. I tried adjusting, rotating, indexing them etc, no different.

For a few bucks more you can get the solid cast adaptor, I think they are a standard disc brake unit assembly from some GM car or other.

I don't think you really need to use the parking brakes every time you stop, just once in a while to take up the slack.

If I did it again I'd use non-parking brake calipers, and fit a drive shaft disc brake system or similar.

I also learned that a GM 1" disc/drum master cylinder will not operate four disc brakes, simply does not supply enough fluid to the 'drum' output. I've ordered a 'vette 1" disc/disc MC now.

yep

GM Seville 79-85 rear calipers is the system on my 3Oish, works great. they are attached to a ford 9 inch rear-end.

Later

skull said:

GM Seville 79-85 rear calipers is the system on my 3Oish, works great. they are attached to a ford 9 inch rear-end.

Later

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I think all the parts are available over the counter, to make your own conversion, as long as you can cut and weld the caliper mounting brackets yourself.

King Herald said:

I bought a Speed disc brake conversion kit, using the pressed steel disc adaptors. Also had the parking brake callipers. You're not wrong, the calipers can be a bitch to adjust, but the disc adaptor run out of true too. The discs 'wobble about a 1/16" a they turn. I tried adjusting, rotating, indexing them etc, no different.

For a few bucks more you can get the solid cast adaptor, I think they are a standard disc brake unit assembly from some GM car or other.

I don't think you really need to use the parking brakes every time you stop, just once in a while to take up the slack.

If I did it again I'd use non-parking brake calipers, and fit a drive shaft disc brake system or similar.

I also learned that a GM 1" disc/drum master cylinder will not operate four disc brakes, simply does not supply enough fluid to the 'drum' output. I've ordered a 'vette 1" disc/disc MC now.

Click to expand...

I am still thinking about using the non-parking discs and a pinion mounted disc brake.

I am sure you're correct you don't need to apply them every time you stop. Here in Flatland we never use parking brakes, so it will be a challenge to remember to apply them even occasionally.

Didn't know that the 1" master wouldn't put out enough volume for 4 wheel discs. That would explain why the pedal needs more stroke than I'm used to.

skull said:

GM Seville 79-85 rear calipers is the system on my 3Oish, works great. they are attached to a ford 9 inch rear-end.

Later

Click to expand...

Skull, that's good to know. A lot of folks have the same result as you.

I know a guy who gave up on those calipers after 6 months of not being able too get them to work. He gave the calipers to a friend who had no issue with them. Put them on his car and they work great.

DJ3100 said:

Skull, that's good to know. A lot of folks have the same result as you.

I know a guy who gave up on those calipers after 6 months of not being able too get them to work. He gave the calipers to a friend who had no issue with them. Put them on his car and they work great.

Click to expand...

I used those exact same calipers on my disc conversion on my last golf cart but I'm only using the parking brake, connected to the stock cart mechanical brake cables. I can see how using the park brake will keep them adjusted, it was a bugger getting them set right for this app, no doubt moisture and disuse could cause them to seize up.

zzrodder said:

I used those exact same calipers on my disc conversion on my last golf cart but I'm only using the parking brake, connected to the stock cart mechanical brake cables. I can see how using the park brake will keep them adjusted, it was a bugger getting them set right for this app, no doubt moisture and disuse could cause them to seize up.

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That's thinking outside the box, I would have never thought of just using the mechanical part. The parking brakes do seem to hold pretty well.

Even though they were a bugger to set up, at least you didn't have brake fluid running down your arm.

zzrodder said:

I used those exact same calipers on my disc conversion on my last golf cart but I'm only using the parking brake, connected to the stock cart mechanical brake cables. I can see how using the park brake will keep them adjusted, it was a bugger getting them set right for this app, no doubt moisture and disuse could cause them to seize up.

Click to expand...

There is a very fine threaded adjuster inside, with some sort of ratchet mechanism, that takes up the slack as the pads wear. The hydraulic piston part can only move so far before it runs out of travel, so the handbrake mechanism needs cranking occasionally to screw in the device that takes up the slack.

I have a short Speedway handbrake connected to mine, connected with the correct cables, but it is worse than useless. You'd never stop the car in the event of hydraulic failure.