Rear trailing arm question

teahead

teahead

aka "Rob"
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Obviously they are easy to tell the diff between 2800CS and 3.0CS w/the brakes still on, but how does one tell with everything removed?

e.g.:

trailing-arm comparo.jpg



For example, the ad says 2800CS, but how can one tell?

s-l1600.jpg


www.ebay.de

BMW E9 2800CS HA Querlenker hinten rechts - top Zustand BMW-Nr 33321102427 | eBay

Entdecken Sie BMW E9 2800CS HA Querlenker hinten rechts - top Zustand BMW-Nr 33321102427 in der großen Auswahl bei eBay. Kostenlose Lieferung für viele Artikel!
www.ebay.de
 
teahead said:
Obviously they are easy to tell the diff between 2800CS and 3.0CS w/the brakes still on, but how does one tell with everything removed?

e.g.:

View attachment 136346


For example, the ad says 2800CS, but how can one tell?

s-l1600.jpg


www.ebay.de

BMW E9 2800CS HA Querlenker hinten rechts - top Zustand BMW-Nr 33321102427 | eBay

Entdecken Sie BMW E9 2800CS HA Querlenker hinten rechts - top Zustand BMW-Nr 33321102427 in der großen Auswahl bei eBay. Kostenlose Lieferung für viele Artikel!
www.ebay.de
Click to expand...
Directly below the shock mount stud you can see two bolt holes that mount the calipers
 

Attachments

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    20220216_182503.jpg
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Just from the picture I am seeing a machined face for the caliper mount, also the thickness of the mounting plate seems beefier. So I would say no
 
Picture is 3.0cs(i) in my opinion. But the description says „Archivbild“ which means translated to english something like „example picture“. So it’s not the actual selling item.
 
teahead said:
Is that the only diff? Can one just drill the holes?
Click to expand...
I've done a lot of modifications to my car, and even made some stuff that is in my car, but I wouldn't drill and tap the holes for the carriers. How brakes are attached to the car is rather important. I want factory quality work on that.
 
teahead said:
Obviously they are easy to tell the diff between 2800CS and 3.0CS w/the brakes still on, but how does one tell with everything removed?

e.g.:

View attachment 136346


For example, the ad says 2800CS, but how can one tell?

s-l1600.jpg


www.ebay.de

BMW E9 2800CS HA Querlenker hinten rechts - top Zustand BMW-Nr 33321102427 | eBay

Entdecken Sie BMW E9 2800CS HA Querlenker hinten rechts - top Zustand BMW-Nr 33321102427 in der großen Auswahl bei eBay. Kostenlose Lieferung für viele Artikel!
www.ebay.de
Click to expand...
after all the home work I did 2800 dos not have the place or the 2 hole to install the break caliper
 
the short answer is not really. the rear springs are very different mounting on the e3 and e9.

you can do anything if you are willing to spend the money to sort it out ... for example, the e3 trailing arm might be less costly than the e9 ... but what you have to replace and re-engineer to make it happen can be quite significant. then you will find out if the cost was worth it. for example, can you put an e12 or an e28 rear subframe and trailing arms on a coupe. i can tell you it has been done, but it was a ton of work.

i know the rear subframe is also different on the e3 + e9 ... that may create some suspension alignment issues ... but i'm positive about that ... or if that would position the wheel to NOT be in the center of the wheel well. i do not know this for sure.
 
rsporsche said:
the short answer is not really. the rear springs are very different mounting on the e3 and e9.

you can do anything if you are willing to spend the money to sort it out ... for example, the e3 trailing arm might be less costly than the e9 ... but what you have to replace and re-engineer to make it happen can be quite significant. then you will find out if the cost was worth it. for example, can you put an e12 or an e28 rear subframe and trailing arms on a coupe. i can tell you it has been done, but it was a ton of work.

i know the rear subframe is also different on the e3 + e9 ... that may create some suspension alignment issues ... but i'm positive about that ... or if that would position the wheel to NOT be in the center of the wheel well. i do not know this for sure.
Click to expand...
thank you very much, that was good enough, I fined a good trailing arm for my 2800 now I can change and have a rear disk break but now I order a barring and seal but the ting is I don't know how I pull off the old barring and seal or what kind of tools I should use I took it to local mechanic they didn't want to do it now I am back to square one if you know what kind of tools I have to use please explain me
 
its a PITA job to break everything loose from the subframe and put all the new things on ... it is also time consuming. i would look for another mechanic ...
 
rsporsche said:
its a PITA job to break everything loose from the subframe and put all the new things on ... it is also time consuming. i would look for another mechanic ...
Click to expand...
it is on the floor I am kip looking how do I hammer the barring's to pop out not to damage the arm or I have to spend time driving around to fined a good mechanic and always good mechanic are busy
 
If you are trying to modify a 2800 rear trailing arm to accommodate disk brakes, I don't think that is possible. The 3.0 trailing arms have a machined surface and a set of holes for the installation of the carrier that holds the calipers. That machined surface needs to hold the carrier, and thus the caliper, at precisely the correct orientation relative to the two friction surfaces on the front and rear of the rotor. And the holes need to hold the caliper at the proper angle relative to the outside diameter of the rotor.

You either need 3.0 e9 trailing arms, or go back to drum brakes if you want to keep the 2800 trailing arms.
 
Ohmess said:
If you are trying to modify a 2800 rear trailing arm to accommodate disk brakes, I don't think that is possible. The 3.0 trailing arms have a machined surface and a set of holes for the installation of the carrier that holds the calipers. That machined surface needs to hold the carrier, and thus the caliper, at precisely the correct orientation relative to the two friction surfaces on the front and rear of the rotor. And the holes need to hold the caliper at the proper angle relative to the outside diameter of the rotor.

You either need 3.0 e9 trailing arms, or go back to drum brakes if you want to keep the 2800 trailing arms.
Click to expand...
Well, as has been said before in this thread, anything is possible with enough money, but it would undoubtedly cost more to do it properly (find some disc brake arms to accurately measure the differences, weld on new steel of the right type to your 2800cs arms to make the caliper mount, heat treat the welds to make sure the steel is the proper strength with no built up stresses, machine the new steel to match specs, drill the mounting holes in the right place at the right angle and tap them, repaint or powder coat the arms and install new bearings, install the new calipers and rotors you bought and install arms) than to buy good used 3.0 e9 trailing arms and bolt them on. It's not easy to find disc brake arms, but they do come up from time to time.
 
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