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Stock FC brake bias?

Old 07-06-05, 08:03 PM
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Stock FC brake bias?

I'm setting up my brake system going to dual masters and I'm wondering how much bias(or restriction) is built into that little thing hanging next to the stock MC? I know there is some hyd. bias built in with the difference in pistons in the calipers(fr/rr) but has anybody had a dual pressure guage set-up on one of these cars. I have one guage but its kinda hard to push the same each time to check front and rear line pressure.
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Old 07-06-05, 08:44 PM
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Hmm..
Cant answer that one.. but I do know that the people I know with dual Tiltons just scrapped the lot, and ran the lines directly to the appropriate side of the car.. using the balance bar for the adjustment..

(The set I got has been modified a bit with relation to the moment arm on the pedals.. but as far as the cylinders.. they are the same.)

But again... as a certain wacky dry-sump/wet sump "it ill nevor wurk maing" proved... some things that donít necessarily look correct.. may very well be perfectly functional.
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Old 07-06-05, 09:01 PM
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Hey don't be lettin out our oilin secrets! I'm using the stock pedal assembly with a bias bar added and dual tiltons on the firewall. This gets rid of the booster etc (-5 lbs!). A couple pieces of angle iron, a cutting wheel, angle grinder and some parts that were laying around the shop = brake system!
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Old 07-06-05, 09:45 PM
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WHO ME? NEVAH!

Not saying ****!

(Plus it is still a tad foggy in my memory as to what you actually did)
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Old 07-06-05, 10:02 PM
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Whatever it is, it's a LOT!
I vaguely remember someone had hard evidence that showed that the pressures were dropped so the rears only did 10% to 15% of the braking force!
Now, I forget the hard numbers in terms of line pressures, but there were brake performance gains from adjust more brake bias towards the rear versus the stock set-up.


-Ted
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Old 07-07-05, 12:31 AM
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If I go even one compound softer my rears lock up under braking, so I'd say the amount of additional rear bias possible is very little as compared to stock.
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Old 07-07-05, 01:12 AM
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I thought the brake hydraulics were split diagonally so you had to do major replumbing when going to dual cylinders. Am I on crack or what?
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Old 07-07-05, 01:29 AM
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Umm

I may be on crack... yeah.. I may be having a case of CRS..

On the 1st gen I started installing a Bias adjuster on Monday... no wait... I converted it from a Drum brake rearend.. and re-ran the rear lines...
OK that doesnt count.

On the 2nd gens.. there is a single line that runs to the rear and is split from there to the two sides.

The 1st gen has a dist block as well... and mine now has the hard line run DIRECTLY to the block... now via the prop valve.. But I cant remember if there was a valve of some sort up front originally. Cause that was a couple years ago that I did the rear disk conversion... and the car was owned by the person I sold it to.... before he sold it to another person and I bought it back.... and finished up making it a ITA car... that I had been doing for the two previous aformentioned owners..
OK if you followed that you are really awake.

No dont remember ever seeing any sort of diagonal braking thing on the 1st and 2nd gens.
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Old 07-07-05, 02:29 AM
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Originally Posted by RoadRaceJosh
I thought the brake hydraulics were split diagonally so you had to do major replumbing when going to dual cylinders. Am I on crack or what?
Yep, you're on crack!

The non-ABS FC's run a three channel brake master.
Two are for the fronts.
One is for the rear.
The rear channel goes from the brake master to the bias valve and then all the way back.
The split for the rears are right before the rear wells.



-Ted
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Old 07-07-05, 02:30 AM
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Originally Posted by Carl Byck
If I go even one compound softer my rears lock up under braking, so I'd say the amount of additional rear bias possible is very little as compared to stock.
Hey Carl, did you get the backwards?
Is "softer" supposed to be "harder"?


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Old 07-07-05, 10:31 AM
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Softer pads grip harder, they just don't last as long.
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Old 07-07-05, 12:41 PM
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According to the 87 FSM I'm looking at master cylinder to rear brake pressure rise at about a 1:1 rate until the prop valve sees around 425psi. At that point it bleeds down pressure. Max pressure at the master per the diagram is 1140psi at which point you should see 730-830psi at the rear calipers.
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Old 07-07-05, 01:59 PM
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A guy a share the shop with said,"Why don't you just check the shop manual, it will probably say in there" So I did and found exactly what C. Ludwig told us! I was logging on to post it. So between the line pressure cut and the difference in piston dia. the rears seem to be for show, OK not that bad. So the rear pistons are 47% as big as the fronts and they only get about 60-70% of the pressure.
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Old 07-07-05, 03:13 PM
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Originally Posted by RETed
Yep, you're on crack!

The non-ABS FC's run a three channel brake master.
Two are for the fronts.
One is for the rear.
The rear channel goes from the brake master to the bias valve and then all the way back.
The split for the rears are right before the rear wells.


-Ted
Ok, I must have been thinking of some brand X vehicle. Having a front/rear split makes things much easier.
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Old 07-07-05, 04:42 PM
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I know Saabs have that funky split you're thinking of Josh. Could be others too, so don't give up on the crack! Remember, rehab is for quiters!
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