converting drums to disk on an 850

[Estaban]

the 850s had drum brakes on the rear wheels and I have always wanted to convert mine to disks.

I have never ran into a kit and since the 850s are rear-engine with trans-axles their rear end does not match up to a 124 for me to use it's equipment (as I had hoped).

Anyone have any ideas how I could make that conversion?

[kmead]

The first question I would ask is, why?

Although rear disks may look better than the existing drum, they likely won't work any better. I can assure you the e-brake certainly won't work as well.

There are a few diagrams for a bracket to complete this job.

Go here to get them:

http://dl.dropbox.com/u/3359580/850%20R ... racket.zip

I would want to verify the info for the brackets to be sure they have the correct measurements. You will need to disassemble the rear brakes, hub and axle from the semi trailing arm.

This bracket from a 128 conversion will be nearly identical to the one you need to make (the brakes on a 128 are nearly the same as an 850):

You might contact Courtney Waters who made these brackets: http://www.mirafiori.com/~courtney/misc/portfolio/

Hope that helps some.

[Estaban]

thank-you, this is the kind of information I needed.

I was thinking it would be better brakes, I was always told disks are better then drum, and maybe a little jealous of you guys with 124s that came with disks in the back even in the early 70's

time to visit my machinist...

[kmead]

Glad it helped.

I would verify the drawings relative to your cars actual parts or if you have a rear arm with all of its components, I would fab everything up and verify it on that before tearing your car apart.

The honest answer is that drums on the rear are likely just as effective as discs, or I should say that drums are up to the job of the amount of braking needed at the rear wheels.

Rear brakes do at most 20% of the braking on a car, less than that on most lightly loaded cars. A rear engine car can get a bit more braking back there due to the weight bias but for the most part under normal driving conditions the drums are likely good enough.

On a racecar perhaps not.

I think it will be a fun project and one I might do on my coupe for the same reasons as you but I don't think its really necessary. Not that it will stop me either...

[Estaban]

building one on a bench first is not a problem for me. My dad bought/swapped/traded 850 spiders (and one coupe) as I grew up for parts.

I have the hardware for four 850 spiders, engines/transmissions for three, and a world of parts that aren't worth the space they take up in my garage. When my wife bought baby she bought the whole shooting match.

And one of my tenants happens to work in a machine shop. He could build me those plates without to much time or probably expense off that one diagram (if I had a good drill press and milling machine I could do it myself)



this won't be a priority job, but I can get it started without disabling the car.

I will measure the caliper holes and axle holes before commissioning the job. the 124 used the same caliper frame as the 850 front disks, I have half a dozen of them somewhere...

[kmead]

Please share what you learn and how you did it. Some pics and updated drawings would go a long way in helping others.

I have been collecting info for years on this subject, there hasn't been much avaialable as most of it came from the pre internet age.

Karl