Brake Boost Delete

SimonWright · **Posted:** Mon Nov 21, 2011 12:45 pm

I want to delete the brake boost from my rally car - drop it down to manual only. Has anyone here ever down such a modification?

Thanks.

Simon

Vincent Keene · **Posted:** Mon Nov 21, 2011 1:42 pm

SimonWright wrote:

I want to delete the brake boost from my rally car - drop it down to manual only. Has anyone here ever down such a modification?

Thanks.

Simon

Why do you want to do this?

Kevin Allen · **Joined:** Thu Aug 28, 2003 6:42 pm **Posts:** 3479

So he can install anti-lag, duh.

SimonWright · **Posted:** Mon Nov 21, 2011 4:54 pm

If anti-lag means I won't be so slow I'm all for it. :lol:

I've been LFB'ing for a couple of years now and after my recent course at the Team O'Neil rally school I improved those techniques in rally car weight transfer and should be able to take turns even faster than before. However, in some sections I know that I'm going to run out of vacuum boost with the nearly constant LFB. In the course I started with moderately modified Ford Fiestas (that had retained the boost) but the last two days I was driving Fiestas that were rally ready. These cars had the boost removed and were a bitch to drive at first especially since they hadn't yet replaced the master cylinder to compensate for the loss of assistance. It probably took 80lbs of leg force to brake at times! However, I soon adapted and was able to handle these cars much better. Knowing that the brakes will always be consistent is a big plus - I discovered what is what like to use up all the vacuum earlier in the week. Plus there's one less system to fail in the car.

So, after discussion with one of the mechanics at the school, I think I want to move to manual brakes on my Focus. He said that replacing the master cylinder with one from a Fiesta will return the brake pedal feel and allow a good range of modulation.

Anyone want to help or advise?

Thanks.

Simon

Vincent Keene · **Posted:** Mon Nov 21, 2011 5:20 pm

SimonWright wrote:

These cars had the boost removed and were a bitch to drive at first especially since they hadn't yet replaced the master cylinder to compensate for the loss of assistance. It probably took 80lbs of leg force to brake at times!

Ryan and I experienced this when we switched to larger M/C on his old CRX. It took way too much leg effort to stop, so we switched it back.

SimonWright · **Posted:** Mon Nov 21, 2011 5:38 pm

Yes, I'm expecting it to become harder, especially if I don't adjust the m/c as well. I've never been inside a brake boost so don't know what's involved.

Simon

DickRasmussen · **Posted:** Mon Nov 21, 2011 7:44 pm

Simon,

In addition to the relative sizing of master cylinder and caliper cylinders there may be appropriate higher coefficient pad materials available. Keep in mind that more mechanical advantage in the hydraulics means longer travel at the pedal which you may not like.

The guys at places like Essex Parts might be able to give good advice. They sell different brands of brake pads.

http://www.essexparts.com/

George Bright · **Posted:** Mon Nov 21, 2011 8:37 pm

When I Auto-Xed my 510 Datsun I ran Ferrodo DS 11 pads and Datsun Comp shoes on the rear. IT took 300 lbs of pedal force to lock the fronts. This was with the stock master cylinder that did not run boost. I did not left foot brake much.

The other issues for you will be that the booster probably mounts to the firewall with a different pattern than the master cylinder and maybe having a rod the right length betwwen the pedal assymbly and the master cylinder.

Charlie Guthrie · **Joined:** Thu Aug 28, 2003 8:14 pm **Posts:** 832

Speaking strictly from ignorance, it would seem that you are swapping one problem for another. It would seem that your main problem is that the vacuum storage in the diaphragm unit of the power brakes is insufficient for continuous use. Rather than eliminating the vacuum boost would you consider adding an additional vacuum reservoir (as in larger vehicles) or adding a vacuum pump such as may be found on older diesel vehicles? It would seem that you could add an axillary vacuum tank with a check valve to store sufficient vacuum to allow for many uses in a set of turns and then recharge on the next straight. Since vacuum is low pressure, the vacuum chamber could be thin walled or lightweight. Heck, you could seal up your roll bar and make a huge vacuum chamber. (My apologies to Remchak for drinking before logging on) :lol:

Charlie G

Don Ingerslew · **Posted:** Wed Nov 23, 2011 12:23 am

This is done frequently in kit cars. Matching the new MC and/or changing the pivot point for the pedal might take a few attempts. I settled on my third version on the Yellow 64 FFR. You might want to look at the FFR forums to get some ideas. Check the roadster section and search on brakes. http://www.thefactoryfiveforum.com/

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Brake Boost Delete

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