6:1 pedal ratio on a booster? - Team Camaro Tech
Brakes, Suspension & Steering Conversion questions, Steering & Handling

 
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post #1 of 6 (permalink) Old Jun 19th, 03, 05:09 PM Thread Starter
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Seems like my other thread lost an audience so I'll start a new one.

From what I've learned, boosted brakes generally attach to the brake pedal in the lowest position. For a 68 camaro, that is a pedal ratio of 3.5:1. The attachment point for manual brakes gives a 6:1 pedal ratio. Is there any reason why a boosted brake system couldn't be ran at 6:1? If so, then it seems like a measly 10"Hg of vacuum would be enough to provide decent boost with a 1 1/8" master cylinder and 2.5 (or there abouts) caliper pistons.

-dnult

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post #2 of 6 (permalink) Old Jun 19th, 03, 06:40 PM
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Yes I think it would work.
I have seen boosters bolted flat against the firewall so they must be using the top hole.
This was on muscle cars that were modified. It makes sense to do that on cars with lower vaccum. I think the downside is longer pedal travel of the upper hole, it is twice the power brake travel.
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post #3 of 6 (permalink) Old Jun 19th, 03, 07:10 PM Thread Starter
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When you mention booster bolted flat, are you referring to the fact that the angle the booster makes with the firewall is more perpendicular making the top hole line up better? Do you think I'll have to worry about the pedal rod geometry if I use the booster mounted normally?

As far as pedal travel. I figure I was going to have more travel in the manual config since the MS bore was 1" instead of 1 and 1/8". So the boosted 6:1 should give me a travel somewhere in between.

I'm actually considering drilling a third hole at 5:1 so I can change to it if the pedal is too soft.

-dnult

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post #4 of 6 (permalink) Old Jun 19th, 03, 08:07 PM
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The booster is angled so there will be a straight push from the lower hole. If the upper hole were to be used, the booster would have to mount flush against the firewall, - in other words straight up and down so there is a straight push from the upper hole.
You can't angle the pushrod to just any hole position. There are plastic valve parts inside the booster that would probably break.

I have recomended to several people to use the S-10 "quick take up" manual brake master cyl, it has a 24mm bore with larger third piston at the rear to pump more volume.
With stock front piston area, you would be using one size smaller MC piston for easier pedal effort, but still have a high, short travel pedal.

It is not as good for use with the small bore calipers, you would need a smaller bore quick take up master cyl, which I haven't found - yet.
David

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post #5 of 6 (permalink) Old Jun 20th, 03, 12:57 PM Thread Starter
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ARGH! You're right about the angle on the booster. It's pointed right at the 3.5:1 position and 6:1 is a bit tight. I'm thinking seriously about modifying the flange to line up with the peddal at about the 5.5:1 position. I'll drill the 5:1 hole and hopefully have enough free-play to set it in either the 5:1 or 6:1 hole

I'm hoping I can cut a Vee in the flange from the bottom up to about 1" from the top. Then bend the V back together and MIG it. By modifying the bracket, I hope to keep heat off of the booster. Of course, I may screwing up a perfectly good booster. But it was free so to speak. The previous owner threw it in with the car.

I've been eyeballing that S10 setup as well and following the threads here. I guess I know what my project will be this weekend. Thanks for the heads up on the booster alignment.

-dnult

[ 06-20-2003, 05:20 PM: Message edited by: dnult ]

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post #6 of 6 (permalink) Old Jun 21st, 03, 06:11 PM Thread Starter
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Well here is an update on progress of running a booster with a 6:1 pedal ratio.

Today I cut the bracket holding the booster to the firewall and pedal assembly. I rewelded the bracket so the booster is paralell with the firewall. The push-rod lines up with the 6:1 hole. All in all, it turned out pretty well so far. The 'but' is that the pushrod is short by about 3/8" of making all the threads in the pedal clevis. Also, the booster valve is about 1/10" inside the firewall, which I think will give me problems with the boot. Looks like I'm going to have to shim out the booster, and purchase a bolt streacher for the push rod or fabricate a new clevis.

I'd say progress, so far is good, but there are those issues to resolve.

-dnult

Dave
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