5 LUG CONVERSION - BRAKE BOOSTER QUESTION - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 9 Old 04-29-2009, 11:57 AM Thread Starter
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5 LUG CONVERSION - BRAKE BOOSTER QUESTION

So I'm going to start my process of switching to cobra brake setup on my 89 LX.

After reading many many articles on this I have a few questions / possible options:

Instead of removing my stock brake booster (which is brand new) for a much larger one like the 93 Cobra / sn95 (94/95 Cobra) can't i just hook up a vaccumm canister to the stock one I already have in place, to provide much more vaccumm for the breaks and it'll equate to the same as switching to a large volume brake booster???? Has anyone done this before and worked great??

I know it's recommended to switch to a cobra M/C (which I plan to) and gut the stock proportioning valve and use an adjustable one. Has anyone used the stock 89 (non-sn95) M/C and just gut the proportioning valve and used an adjustable valve from Wilwood on a 4 lug disc setup? Did this work correctly and efficiently??? If not why not?


Any suggestions as far as removing the lines to the stock proportioning valve for a 3-2 Conversion setup? I've tried line wrenches and it's not working? If I heat the proportioning valve to loosen the seal, will it destroy something internally voiding it's proper functionality??

Any experienced help would be very appreciated.

Thanks

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post #2 of 9 Old 04-29-2009, 01:54 PM
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Originally Posted by MUSTANG89LX View Post
Instead of removing my stock brake booster (which is brand new) for a much larger one like the 93 Cobra / sn95 (94/95 Cobra) can't i just hook up a vaccumm canister to the stock one I already have in place, to provide much more vaccumm for the breaks and it'll equate to the same as switching to a large volume brake booster???? Has anyone done this before and worked great??
No. Adding a vacuum bottle won't increase the amount of vacuum you have, but it'll give you more pumps of the pedal when vacuum is low (like if you have a REALLY radical cam that won't pull much vacuum at idle.)

If you want more vacuum boost to lower pedal effort, you have to go with a larger diameter.

IF you want to increase the vacuum assist. If not, stick with what you have. I did ('88 GT,) and I'm perfectly happy with the pedal effort.


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I know it's recommended to switch to a cobra M/C (which I plan to) and gut the stock proportioning valve and use an adjustable one. Has anyone used the stock 89 (non-sn95) M/C and just gut the proportioning valve and used an adjustable valve from Wilwood on a 4 lug disc setup? Did this work correctly and efficiently???
No. You need to match the MC bore with the front caliper's piston area. Ford used a 15/16" and 1" bore master cylinder in conjunction with the 94-98 PBRT Cobra Calipers (I don't know what was used for the later PBR Cobra calipers.)

If you use too small of a master cylinder bore, you'll end up with a long, soft pedal and the brakes will lock up much easier. If you go with too large a bore, you'll end up with a short, hard pedal, and the brakes will be very hard to lock up.

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Any suggestions as far as removing the lines to the stock proportioning valve for a 3-2 Conversion setup? I've tried line wrenches and it's not working?
Vice grips and replacement lines.


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post #3 of 9 Old 04-29-2009, 02:34 PM
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I am using the stock '86 brake booster and a 1" bore Lincoln Town car Master cylinder (as per mjbobbitt's website) with my 5 lug conversion (Mach 1 front calipers and Varga rears). The pedal feel is ok to me and for my car usage (bit of street driving and autox). I am using the pads that came with the calipers so the compound is fairly soft. That will change the feel of the brakes so take my opinion for what it's worth.

Now is the perfect time to buy some bulk double-walled and brazed brake line and a double flaring tool!
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post #4 of 9 Old 04-29-2009, 03:53 PM Thread Starter
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Thanks Guys
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post #5 of 9 Old 04-29-2009, 04:01 PM
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Now is the perfect time to buy some bulk double-walled and brazed brake line and a double flaring tool!
BundyWeld is good stuff, as is the stuff from Classic Tubing. Don't get stainless tubing. this is MUCH more difficult to flare and your garden-variety flaring tool probably won't work.

The tubing from Summit Racing is garbage and will easily split when being flared.

Classic tubing is also an excellent source for flare nuts.

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post #6 of 9 Old 04-29-2009, 08:09 PM
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Guys, great feedback. With respect to the booster, the '93 Cobra booster is the same size as the SN95 vacuum booster, which is larger than the FOX boosters. If you would like to try your stock FOX booster I suggest using a smaller master cylinder size. The '94/'95 Cobra used the 15/16" master cylinder which would be a good fit for the smaller FOX booster. Pedal travel will be longer with that setup than with the 1" master cylinder and the larger '93 Cobra booster, but that is the price you will have to pay. You can always try it and change boosters later if you feel the need.

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post #7 of 9 Old 04-29-2009, 09:23 PM
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Agree, try the 15/16 M/C first and if you don't like it then swap the booster. I ran a 15/16" M/C with stock 82GT booster and the Cobra calipers for years and liked the pedal feel and ability to modulate the brakes. I found the 1" bore to be too short and stiff for my taste, couldn't modulate the brakes as well and didn't feel I had control of the brake pressure.

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post #8 of 9 Old 04-30-2009, 07:58 AM Thread Starter
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Great info guys about the M/C and the booster.

Thanks a lot, this really helps
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post #9 of 9 Old 05-03-2009, 01:18 PM
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fwiw, i run the 93 cobra mc, the stock size 89 booster, 38mm fronts, and standard cobra rr calipers. pedal feel is real good to me, however lockup is near impossible with good tires.
im affraid a switch to the 94/95 booster may end up making the pedal too hard, but alot of guys run it, so i will try it out too.
and last, napa sells the 93 cobra mc for about $100 brand new (when i bought it three or four years ago)

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