Rear disc brake conversion on 1970 2800 CS

larkinca

larkinca

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I wish to upgrade my 2800 CS to have rear disc brakes, and understand that this is a fairly simple process using 3.0 CS trailing arms, and related parts. My questions are: (1) Is it correct that the 3.0 CS trailing arms with disc brakes can be transplanted to the 2800 CS without major modifications (cutting, welding, etc)? (2) When I do this will I also gain some rear track width (how much)? (3) I imagine there is some alteration of the hydraulic system needed (proportioning valve), if so what does it involve? (4) Does anyone have an existing write-up on the modification they could direct me to?

Many thanks in advance!

Alex Larkin
Mission Viejo, CA
1970 2800 CS - Nevada
1975 2002 - Mintgrun
 
hi alex, you already seem to have enough "gut" sense to do the swap just fine without a step-by-step checklist or "faq."

Proportioning valve shouldn't need changing but hard to say for your car, after 35 years every used car has its own peculiarities. Carl Nelson sells an adjustable proportioning valve that I hear is good!

Many people say you don't need to replace the master cylinder, I've done rear discs on 2800s and kept the original master as well as changed to the 3.0 master (larger bore) Again, there are so many individual differences in the cars you probably need to decide for yourself if you want to change or not, but in theory the larger bore brake master pushes a higher volume of fluid and since the capacity of the rear claipers is bigger than the old mini brake cylinders, you "need" the extra volume moving.

Be sure to replace the rear brake hoses with teflon-lined, braided jacket, D.O.T.-legal hoses, while you're at it replace the front hoses as well.

hope this helps!

dp
 
while your at it....... :wink:

put in stainless steel brake lines and M/Cyl. from a early 5 series.
may even want to consider a Adjustable Bias Valve popped in for 'fine tuning'.........very easy items to acquire that improve system & pedal feel.

-shanon
'70 2800cs
 
Thanks for the help! Will all years 3.0 CS trailing arms fit the 2800 CS? Also, and modifications needed to make them fit? Will my trach increase?

Thanks,

Alex
 
2800CS Rear disk conversion

The rear disk brake parts are the same for all years. There is no change in track. The swing arms bolt on without modification. I think you will need new brake hard lines to the rear calipers.
 
Rear brake conversion

I am looking for tips on rear brakes conversion and found this old thread... However, the initial questions have not quite been answered at that time, so I'm reviving the thread :)

Does anyone know if the swing arm swap is a simple bolt on or if it involves additional work?

Does the cross member also need to be changed or can the stock one (2800CS) be kept?

Thanks for your input!
 
All your questions can be answered--

if a dues paying member of the BMWCCA--Carl Nelson is a tech advisor for answering all of the preceding. He has also had the experience of performing numerous 2800 CS conversions at his shop over the past 20 years--including the BLUMAX in September 1995.

The conversion is a nice improvement--remember the front calipers must also be changed to accomodate vented discs all round. I must comment that I had driven about 340,000 miles with the original setup including every mountain road and the highest passes i could find in the Western US and not always traveling at posted speeds--oftentimes at a little over--sometimes a lot over--and all without an incident. I admit being very easy on brakes as front pads typically last me about 80,000 miles.
 
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Simple bolt-on and you can use the 2800CS rear crossmember.

As in my previous post from 2006, I think you need to replace the rear brake hard lines. Get all the rear brake hard lines from the donor car so you can see what you need.
 
Getting reading to do this myself but I have (had) a '73 3.0CS parts car for a donor and will be swapping the entire subframe with arms, rearend, etc. The rearend in my 2800CS is bad, so I figured I might as well change the whole thing while I'm at it.

Dan
 
i also have this on my list of things to do. might not happen til this winter though. i have the swing arms, i have new bearings + reconditioned hubs, ebrake cables + shoes ... just need the calipers + disks. my car already has the upgraded master + vented fronts + stainless hoses.

maybe by the time i get around to it, somebody will have published a great how to thread.
 
I'm buying parts from a parts car man, and I'm wondering if someone wouldn't mind condensing the knowledge in this thread to a simple bullet point list of what parts I should take of a 3.0CS for the rear disc brake conversion and which parts I should buy 'new' for the conversion. I really appreciate it!
 
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