No really, I want to skid.
September 12, 2008 4:17 PM Subscribe
RaceCarFilter: I'm speccing out my rally car. What do I do about brakes?
I'm building a rally car from a turn of the century Toyota Celica, one of the cheap trims--not the turbo version. I've tracked down the perfect adjustable coilover suspension. Now, I need adjustable brakes. And to disable ABS.
I have literally no idea what part I'm looking for to accomplish this. A race-specific master cylinder? A complete new brake system? A widget that I must fabricate?
Ideally, I want to be able to adjust the brake bias (fore/rear) without tools, from somewhere under the hood (it must not be adjustable from the cockpit). Failing that, or if such a thing is more than a couple grand, I'd be content with being able to adjust it in the garage--even by swapping out parts, I guess.
Also, how do I disable ABS in the cheapest, most reversible way? Do I just pull the leads to the ABS computer or to the hydraulic actuators? Will it squawk when I plug it back in? If the ABS is on, will it play nice with my adjustable bias? (As a bonus to the Celica application, how would I kill ABS on a Subaru?)
I'm building a rally car from a turn of the century Toyota Celica, one of the cheap trims--not the turbo version. I've tracked down the perfect adjustable coilover suspension. Now, I need adjustable brakes. And to disable ABS.
I have literally no idea what part I'm looking for to accomplish this. A race-specific master cylinder? A complete new brake system? A widget that I must fabricate?
Ideally, I want to be able to adjust the brake bias (fore/rear) without tools, from somewhere under the hood (it must not be adjustable from the cockpit). Failing that, or if such a thing is more than a couple grand, I'd be content with being able to adjust it in the garage--even by swapping out parts, I guess.
Also, how do I disable ABS in the cheapest, most reversible way? Do I just pull the leads to the ABS computer or to the hydraulic actuators? Will it squawk when I plug it back in? If the ABS is on, will it play nice with my adjustable bias? (As a bonus to the Celica application, how would I kill ABS on a Subaru?)
Best answer: Getting the ABS to work with the adjustable bias is possible and relatively easy. Stopping the ABS to work is simply a matter of either pulling the fuse, or unplugging all the wheel speed sensors if the fuse is shared with something you still want. They are designed to be a 'fail safe' system, so they fail to perfectly normal, old fashioned brakes if the electrics fail. If you use the right bias adjuster, your ABS simply won't know its there. The easiest way I can think of (especially for cockpit-only adjustable) would be any of the lever or screw proportioning valves on this page. Basically, you plumb a restricting valve into the feed for the rear brakes (in the main line running front to rear before it splits) and restrict the flow relative to the front (constant) brake pressure. Normally, you'd plumb the brake lines inside (I strongly recommend this) and site the valve on the transmission tunnel within hands reach. However, for your (presumably regulations/class dictated) desire to put it outside somewhere (if it isn't regulations it makes no sense to have it out of reach, incidentally) just means that you need to route your rear brake line so that you can mount the restrictor somewhere in the bonnet area. The extra length of brake line to facilitate this will be irrelevant to the function of the brakes, but it will need to be after the ABS valve block to prevent any oddness from the ABS. Pay attention to your line routing to make sure there are no air blockages, though. Ideally, no 'up and over' complicated plumbing if it can be avoided. It'll save you money on fluid come brake bleeding time.
The ABS won't know that there is anything restricting the line, if you plumb it back up. You may need to have the ABS connected (check your manual) when you bleed the brakes after installation, mind you, as air in the valve block may give you an odd pedal feel until it works its way back out.
That should give you all you need for very little expense. One thing to make note of is that while you want front bias for handling and the extra stopping, you may need to beef up your handbrake for the tighter stuff. A hydraulic handbrake kit is excellent, but pricy. Just adjusting the standard one may well work, but rear discs (I'm not sure if you have them) generally suck for stoppy-turny-stick moves and the hydraulic version may be your only hope.
posted by Brockles at 5:45 PM on September 12, 2008
The ABS won't know that there is anything restricting the line, if you plumb it back up. You may need to have the ABS connected (check your manual) when you bleed the brakes after installation, mind you, as air in the valve block may give you an odd pedal feel until it works its way back out.
That should give you all you need for very little expense. One thing to make note of is that while you want front bias for handling and the extra stopping, you may need to beef up your handbrake for the tighter stuff. A hydraulic handbrake kit is excellent, but pricy. Just adjusting the standard one may well work, but rear discs (I'm not sure if you have them) generally suck for stoppy-turny-stick moves and the hydraulic version may be your only hope.
posted by Brockles at 5:45 PM on September 12, 2008
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The brakes sub-forum on the NASIOC board would help with the subaru. There are several people who run rallies, and rally-cross on there. Also you could spend some time perusing this board for rally-prep ideas. Again it's subaru based, but there would be a lot of commonality in prepping for rally stages.
Good luck! And do you have a website detailing your build? I'd love to check it out.
posted by gofargogo at 4:50 PM on September 12, 2008