3.0cs brake booster

[rsporsche]

hey guys - i was looking up a little information on RealOEM on the brake booster for the coupe. i am aware that it is different between the 2800cs and the 3.0cs ... at least in size - they are both listed as the ATE T51. my understanding is that the 3.0cs uses the 7" thick model and the 2800cs uses the 3.5" thick model. according to realoem, the early e24, the e12, the e3 and the e9 all use the t51 booster. when searching for other uses i found that several mercedes also used the t51 - w108, w109, w111, w112 and w113.

i know that some people use the tii booster with weber triples ... realoem shows that as a t51 also. my guess is that there must be some sub-model number.

so what do you know about this?

 

[HB Chris]

The only difference is the part number and only 2800CS and early 3.0CS uses the thin one. Mercedes used the later large booster.

From our FAQ:

• Brake booster changes from pancake style to thicker style at 2240222 and 2250146, Master Cylinder diameter changes from 23.8mm to 22.2mm

 

[halboyles]

I had to do a great deal of research when trying to produce a version of the ATE T51 booster for use with side drafts on the M30 powered BMWs. Dozens of ATE T51 booster models were used in the sixties and seventies mostly on European cars but also on a few US cars. There are four major differences between the models: cannister diameter/length, push rod connection, vacuum port connection and single or dual diaphragm. The master cylinder attachment configuration seems to be one common feature. I think that the T51 designation covers so many different models that it is almost generic.
The booster we all refer to as a "tii" booster actually appeared on the 2000CS, 1600GT (?), and 2002ti/tii/turbo.
And, to further add to the discussion/confusion, here is an original ATE booster brochure of the period and an image trying to explain the numbers on an ATE T51 booster.

 

[rsporsche]

MANY thanks Chris + Hal. my 2800cs booster has gone missing in action while the engine was out for painting. so its time to get a new one and was wondering if there was more boost with the 7" model

 

[Honolulu]

my '69 2500 sedan had the greatest, lightest, smoothest brakes of any of the couple dozen older bimmers I've owned. It beat my wife's '73 Bavaria booster hands down, all my 2002s including '72 and '74 tii, 635CSi, 3.0CS, 2800Cs, all of them.

All I can remember, nearly 40 year later, was that it was not the "thick" booster, was not the tii (7"? diameter) booster, and that the brakes had been gone over by a local indie shop (owner now passed on) for the previous owner. Maybe some of the wonderful lightness was attributable to overhauled calipers, I dunno.

Not that I'd change the present booster on my 3.0CS, but I've wondered from time to time, what the "secret" might have been.

 

[halboyles]

was wondering if there was more boost with the 7" model

The big difference between the original e9 boosters and the "tii" booster is that the tii booster uses tandem/dual diaphragms. Assisted boost is determined by atmospheric pressure and the total surface area of the diaphragm/s. The 7" dual diaphragm booster should provide the same or more boost than any original booster. Attached is an interesting article about the calculation of assisted boost.
We currently have the ATE T51 tii brake booster modified specifically for use on the carbureted e9s. It is a bolt-on kit. Please visit: https://www.2002sonly.com/2002ti-tii-turbo-e9-brake-booster

my '69 2500 sedan had the greatest, lightest, smoothest brakes of any of the couple dozen older bimmers I've owned.

In my experience, the braking performance of vintage BMWs with rear drums can be dramatically improved by properly adjusting the rear shoes using the eccentrics. I imagine that might have been part of the reason for your '69s braking performance.
Since I am in promotional mode for our 2002s Only products, we also have an improved reproduction of the original eccentric adjusting tool. Please visit: https://www.2002sonly.com/tools

 

[teahead]

I never driven a 2800CS and a later 3.0 to compare braking power of the two diff boosters, but I would imagine the latter would have less pedal effort; otherwise, why would they change it?

 

[rsporsche]

its curious as the master cylinder decreased in diameter ... which should mean more pressure from the smaller diameter cylinder ... i don't know what the pressure difference is between the 2 boosters ... but one would imagine there is more in the 3.0cs booster ... but not necessarily. my guess was the change from drums to discs had more to do with the changes.

my 2800cs had a newer style master cylinder put in by the PO. not sure what it came from, but presumably it was from an e23 / e24. my take was the brakes took some effort to stop the car. but as we all know it could be a number of things ... that is why i want to go back in with all new everything.

 

[BluE9]

The big difference between the original e9 boosters and the "tii" booster is that the tii booster uses tandem/dual diaphragms. Assisted boost is determined by atmospheric pressure and the total surface area of the diaphragm/s. The 7" dual diaphragm booster should provide the same or more boost than any original booster. Attached is an interesting article about the calculation of assisted boost.
We currently have the ATE T51 tii brake booster modified specifically for use on the carbureted e9s. It is a bolt-on kit. Please visit: https://www.2002sonly.com/2002ti-tii-turbo-e9-brake-booster

In my experience, the braking performance of vintage BMWs with rear drums can be dramatically improved by properly adjusting the rear shoes using the eccentrics. I imagine that might have been part of the reason for your '69s braking performance.
Since I am in promotional mode for our 2002s Only products, we also have an improved reproduction of the original eccentric adjusting tool. Please visit: https://www.2002sonly.com/tools

Hi, this is great. If I am understanding this correctly you are saying this kit will fit by 1971 2800CS as a bolt on replacement booster and offer equivalent functionality? And I can send in my current booster for a core refund or potentially a rebuild?
Thanks,
Greg

 

[halboyles]

you are saying this kit will fit by 1971 2800CS as a bolt on replacement booster and offer equivalent functionality? And I can send in my current booster for a core refund or potentially a rebuild?

Yes, it should bolt on to your '71 and allow adjustment to the pedal height just like the original pedal rod. As far as cores go, we only accept the same kind of booster (ti/tii/turbo) as a core. Save your original as someone, someday will need it.
Here is a link to our website where you can buy this booster: https://www.2002sonly.com/product-page/m30-booster

 

[BluE9]

Kindly, do I need any other linkages, connectors or seals to accomplish the install? Many thanks!

 

[BluE9]

Sorry for all of the questions, is the brake assist equivalent?

 

[halboyles]

No, we provide new nuts/bolts, OEM master cylinder seal ring, ATE T51 label, installation tips sheet and our world famous Wedgie Tool for free!

 

[halboyles]

Because the ATE T51 booster uses dual diaphragms, it probably provides more boost than the original booster.

 

[BluE9]

Because the ATE T51 booster uses dual diaphragms, it probably provides more boost than the original booster.

Many thanks for the quick reply and the keen information! I will give it a go!

 

[Krzysztof]

Very interesting information! Thanks Hal!

It reminds me the differences between the booster in E30s.

Most of models (including M3) were using single diaphragms:

but iX where dual diaphragm was used .... and popular for further swaps to e.g. S50B32 due to smaller diameter


So quite popular solution over years.

 

[BluE9]

Many thanks for the quick reply and the keen information! I will give it a go!

Thanks again, I ordered one today for my 2800CS.

 

[sfdon]

“installation tips sheet and our world famous Wedgie Tool for free!”


I want these Hal!!

​

 

[halboyles]

“installation tips sheet and our world famous Wedgie Tool for free!”

Some of them are headed your way.

"Don't get your panties in a bunch, just use our Wedgie!"

 

[BluE9]

Yes, it should bolt on to your '71 and allow adjustment to the pedal height just like the original pedal rod. As far as cores go, we only accept the same kind of booster (ti/tii/turbo) as a core. Save your original as someone, someday will need it.
Here is a link to our website where you can buy this booster: https://www.2002sonly.com/product-page/m30-booster

Hi Hal,

I recently purchased one of your double diaphragm boosters for my 2800CS and realized that my car seems to have the "thin" type booster. Will your booster still work? Rather than returning your booster, I would prefer to use the one you sold me. I just need to know how to instruct others how to adapt it. I left you a voice mail as well. Please help

Thanks,

Greg