Rear brake conversion?

[Dave L]

My 70 2800 cs had a bizarre rear brake incident yesterday that I don't even know how to explain... Moving on to the repairs, I can either rebuild the rear drum system (needing new parts since now most are missing on one side) or I can do the conversion to rear disc's. Does anyone know of a write-up on the rear drum to disc conversion procedure and a list of parts needed? Has anyone else personally done this job? It seems like the smart move, is it?

 

[lloyd]

My 70 2800 cs had a bizarre rear brake incident yesterday that I don't even know how to explain... Moving on to the repairs, I can either rebuild the rear drum system (needing new parts since now most are missing on one side) or I can do the conversion to rear disc's. Does anyone know of a write-up on the rear drum to disc conversion procedure and a list of parts needed? Has anyone else personally done this job? It seems like the smart move, is it?

http://www.e9coupe.com/forum/threads/rear-disc-brake-conversion-on-1970-2800-cs.383/


Answers to your questions are very subjective. I have never given the upgrade much thought for an E9, so my thoughts are as a civilian observer. I am mildly familiar with the 2800 drums and have dealt with similar versions on 02s and other drums systems. Do you have all of the parts to perform the conversion?

Without fully knowing what you have to salvage versus what you will need to obtain from a donor vehicle, only you can answer your question.

Subjectively, there is nothing particularly wrong or bad about the 2800 drum brakes. Comparison with the disk setup is somewhat unfair. The disks tends to be superior because of greater swept braking area, they are less susceptible to over heating and there are probably more friction material choices. However, the drums may actually be lighter (I do not know this as a fact), and for the most part, your car's front brakes do most of the work. (They do tend to require slightly more maintenance and adjustment - than the disks. But the maintenance tends to be relatively minor unless you put a lot of miles on the car.) (A tiny advantage for the drums is that they can be adjusted to provide less drag. Less drag = greater fuel economy. They may be "less modern" but until recently, they were still used by a few high fuel mileage vehicles, e.g., Prius.)

Unless you are a hard driver, and do a lot of downhill driving the drums are adequate for average driving situations. Another consideration might be the originality of the car. Some upgrades are not welcome by hard core purists. Others could care less.

 

[teahead]

Not cheap, but brings the 2800 up to more modern technology.

- rear control arms from a 3.0CS. Used-only. $$$. Just sold a set for $550. Plus the cost of new bearings/seals (you'll want to do that).
- rear calipers from a 3.0CS or E24 (E12-based E24). E12s had solid, not vented rotors. You can use E12 calipers but you'll need spacers for the extra width vented rotors.
- rear parking brake parts from a 3.0CS or E12/E24 (except the cables). Cables can be bought new.
- rear vented rotors from a 3.0 CS or E24. Can buy new.
- rear protection plates from a 3.0CS (hard to find). You can use early E24 (brand new, $45 each), but will require some trimming.
- not sure about brake hoses; might as well get new ones if needed for the swap.

 

[mulberryworks]

The reduced maintenance for disks is attractive. But, a friend put disks on his VW in Seattle, but changed back to drums because he didn't drive it often enough to keep the rotors from rusting up and drums didn't have that problem.
The trailing arms are a bit scarce though they do come up from time to time. Scarcity drives up cost as well.
I'm not going to drive my 2800cs very hard, so I'm keeping it stock.

 

[teahead]

You can get zinc-washed rotors to prevent rust

 

[Vern]

http://www.e9coupe.com/forum/threads/rear-disc-brake-conversion-on-1970-2800-cs.383/


Answers to your questions are very subjective. I have never given the upgrade much thought for an E9, so my thoughts are as a civilian observer. I am mildly familiar with the 2800 drums and have dealt with similar versions on 02s and other drums systems. Do you have all of the parts to perform the conversion?

Without fully knowing what you have to salvage versus what you will need to obtain from a donor vehicle, only you can answer your question.

Subjectively, there is nothing particularly wrong or bad about the 2800 drum brakes. Comparison with the disk setup is somewhat unfair. The disks tends to be superior because of greater swept braking area, they are less susceptible to over heating and there are probably more friction material choices. However, the drums may actually be lighter (I do not know this as a fact), and for the most part, your car's front brakes do most of the work. (They do tend to require slightly more maintenance and adjustment - than the disks. But the maintenance tends to be relatively minor unless you put a lot of miles on the car.) (A tiny advantage for the drums is that they can be adjusted to provide less drag. Less drag = greater fuel economy. They may be "less modern" but until recently, they were still used by a few high fuel mileage vehicles, e.g., Prius.)

Unless you are a hard driver, and do a lot of downhill driving the drums are adequate for average driving situations. Another consideration might be the originality of the car. Some upgrades are not welcome by hard core purists. Others could care less.

Some purists want the Fred Flintstone version...good for them. I, for one, am not driving Miss Daisy... If I did, even she would want the 3.0 disc brake upgrade.

 

[Bmwphatpat]

I have a complete ventilated disk rear subframe with trailing arms, brakes, axles, hubs etc. from a salvaged 3.0cs. Should be plug and play for your 2800?

I have the rear diff too, not sure you'd need that though.

Pm me if you're interested.