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Old 01-01-2003, 03:43 PM
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In my street rod I have front disc, 11 inch on Mustang II. Rear is GM drum. I wanted to get stronger pedal so I put in 2LB residual valves in front lines and 10 LB in rear. Test drove today and front disc will lockup and smoke tires. Rear are still slugish and don't appear to operate much better?? Is this normal performance for this type of setup? I thought maybe rear might need adjusting?? Any suggestions. TX DAVE SHANK

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Old 01-01-2003, 04:23 PM
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sounds like the wrong proportioning valve setting.are you using a multivalve or an adjustable prop valve in the rear line?
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Old 01-02-2003, 09:31 AM
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BOB: I am using the proportional valve that came with OE master cylinder. I am not sure of what spec's are for that unit. I have put the 10 Lb residual valve between master cylinder and proportional valve. It is not a adjustable type proportional valve. I noticed big difference with front disc action, it will now look up front wheels but not rear drums?? Is that normal action for a hard slam on brake test?? TX Dave Shank
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Old 01-02-2003, 08:14 PM
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the way the brakes are originally designed they are supposed to activate the rears as you depress the pedal untill you get to a predetermined pressure then bias to the front, this keeps the rears from locking up in a hard stop, but it sounds like yours isn't getting correct pressure to the rear at all, try a tech at Master Power brakes or one of the online specialists they can lead you to the proper valve. They will want front and rear weights, wheel cyl sizes, master size, caliper and rotor size and tire size.
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Old 01-04-2003, 11:45 AM
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No, you don't have it right yet. You should be able to lock up both simultaneously and then bias the front a little more than the rear. Otherwise, you will lock the rear up first which is dangerous in a corner braking situation or on wet pavement, it will cause induced oversteer and you will be doing a 180 when it would be least helpful.

I'm not suggesting you are as stupid as I was in sorting out my braking situation, but here is what happened to me. I had a similar problem, good brakes up front, poor in the rear and I thought I had done everything just right. I had new everything except for the rear drums which were from the junk yard. It finally turned out that the rear drums were so worn that even with full turn out of the adjustment screw, the rear brakes shoes were not making a good contact patch with the rear drums. You have to visualize that the radius of the new shoes was a much smaller radius than the larger drums and even though the pedal was firm, there was not good contact with the drum. I bought new drums and put them on, problem solved.

You only need the residual valves when your wheel cylinders are mounted higher than the master cylinder....they keep the fluid from running out of the wheel cylinders and into the master.

If you can use a proportioning valve with the same size front and rear pistons and master cylinder as was stock with some application you can be assured you have an appropriate valve, otherwise I would go with an adjustable valve.

[ January 04, 2003: Message edited by: F-1Rodder ]</p>
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