Let's talk brake boosters!

Markos

Markos

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Every time I walk by my CSI (with no hood), I say to myself "my god that brake booster is huge!".

So I looked around the site, and I see Gransin has what appears to be a normal booster on his 3.0CSI. Luis A. has one on his 3.0S very similar to mine. Then we have the 2002tii conversaions, and the 2000CS boosters which look a lot like the one on my CSI. From what I read, the very late model CSI's got a very large booster. As you can see, the front of the booster is a good 15" from the firewall. The master cylinder is about 2" away from the battery tray. I also read that the big boosters get in the way for certain repairs (steering?).

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Moving to my 2800CS, it has a comparitively tiny booster. I read that the 2800CS has a very slim model, and they are hard to come by. Is this it? If so, I think I know someone who has a few NOS units.

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the booster, tiny or big is always in the way for repairs,...
but big boosters are doublé effect , so much more efficient,
in this case the bigger the better

but my old 1971 CS has the small one, and i do not want to modify the routing of the brake lines, so yes i am interested in a NOS

do you need a big one ? i know a source...
 
I am going to be rid of mine altogether soon and go to a hydraulic booster system like that used on the e24
The RHD system is just hopeless and a real compromise, it works (just) but has no feel or feed back through the pedal to speak of
 
I was under the impression that replacing the big booster with a smaller tii one had no effect on braking... Not true?
Click to expand...

With the Tii booster you need to press harder than the larger/later CS boosters. The only reason you need a Tii booster is with some of the side draft carb setups or if you use the b35 intake manifold.
 
The booster all but precludes any attempt at adjustment of the steering box. Seems almost intentional.
 
Probably got big to hold more vacuum for easier pressure on the pedal.

If one swaps to hydraulic, one should write a how-to post!
 
Ill tell ya

Well im have the tii booster so i can tell you the diff as soon as i finish in a month or so
 
while I was racing my e12 and it still had the M30 in it , I went on a quest to remove as much weight from the driver front corner as possible. The e12's also came with a large booster similar to the one in the E9's , I found that a smaller booster from an e28 528e bolted on and had zero noticeable difference in pedal feel . The diameter is similar but its not as thick . I don't know if this would bolt on to an E9 but maybe someone is willing to try ??

BD
 
I´m not an expert but i think it´s the diameter that counts! Larger diameter gives you more breaking power unless you install a dual diaphragm brake booster. The extended length can be the result of a need for a vacuum reservoir due to the increasing numbers of vacuum consumers on newer cars. Or a compensation for the lost volume in a booster with smaller diameter.
 
Bmachine said:
I was under the impression that replacing the big booster with a smaller tii one had no effect on braking... Not true?
Click to expand...

Not true. You might not notice the effect, but to the discerning driver, there is a difference. Here's a chart providing rough differences of "free pressure" or boost with different size boosters: http://www.classicperform.com/PDFs/BoosterBrakePressureChart.pdf The same argument about feeling the difference might apply to different friction compounds. Setting aside resistance to heat, some pads have more of a bite than others, yet in the staging area or a parking lot, all “arguably” feel "somewhat" compliant when slowing the car, and unless you are using a pad that works best when hot, you might not notice the difference with "light" driving.

Forgetting about the size of boosters, race cars routinely run without power assist. http://e9coupe.com/forum/showthread.php?t=15489 Boosters would likely reduce driver fatigue, but weight reduction is likely more important on the track. Adequate braking without a booster is provided by different brake pedal leverage, master cylinder sizing, greater braking surface area, and aggressive friction materials. Besides, some drivers contend, rightly or wrongly, that they have more control without the power assist.

There are several reasons why the 02 and 2800cs were probably equipped with a smaller sized booster, not the least of which is the fact that both had rear drum brakes and drums tend to be "self-actuating." Disks do not have the same property. Another obvious reason is the practicality of the extra size and weight of the jumbo booster found on later E9 and E3s. If weight and space were significant concerns, the smaller booster is a fair compromise, but all things being equal, pedal effort is going to be slightly greater with a smaller booster. It is not hard to see where the average driver would much prefer driving with the least amount of effort. One supposes that a parallel notion is that stopping with less physical effort is probably safer too.

Again, depending upon diving style, other modifications and lower body strength, you might not notice any difference between the brake booster choices mentioned in this thread. Consider that “a few” 02, E9 and E3 drivers claim to prefer driving their cars without power assisted steering, and some might claim that with the biggest bus sized steering wheel, skinny tires of yore kept at maximum pressure, the advantage of power steering over manual is minimal. Of course others may disagree and I can think of someone who refused to drive my 02 because it did not have power assisted steering.:p

E30 with booster deleted.
imQVUa.JPG
 
teahead said:
Probably got big to hold more vacuum for easier pressure on the pedal.

If one swaps to hydraulic, one should write a how-to post!
Click to expand...

This thread has some legs! Thank you all for the knowledge sharing. I'm definitely interested in the hydroboost conversion, more as a curiosity at the moment. I emailed the guy with the NOS slim boosters. Also, it looks like Alex (George Briggs) is selling a used one. See the parts section.

The CSI booster and arm has to weigh at least 20lbs! I'll be sure to weigh when I remove mine. I'm pretty certain that I'm going to swap disks onto my 2800. I don't think I'll swap boosters.
 
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