Hey guys- I need help diagnosing and fixing my brake system.. the car is in the non-traditional builds area:
viewtopic.php?f=36&t=16309 , and I've been chasing brake demons for awhile; I seem to be out of my depth.. Here's what I have-
-Master cylinder is part # MC M39451 (aka) Wagner MC 108134 (most agree it's a 7/8" bore MC, but it's been listed as both 21.0 and 53/64")
-Front brakes are 'stock' 1966 Volvo 1800S discs/rotors/calipers
-Rear brakes are 'stock' Ford T-bird (1989-1997) discs/rotors/calipers
-System is now using DOT4 'plus' fluid
-All 4 brake hoses are now stainless steel
-The Volvo 1800S pedal ratio has been modified to (now) be approximately 6:1
-This is a manual setup; non vacuum-assist
-The car is about 2400lbs (and about 300hp- goes fast, stops slow)
-An adjustable proportioning valve (dial type) is plumbed into the rear circuit
-I'm 100% certain there is no air in the lines (also bench bled the MC prior to install)
The problem is the brakes are not as effective as they should be- put another way, they don't grab hard enough... it almost feels like the pads are coated with WD40, and they'll take their own sweet time to slow the car.. More pedal pressure is of course helpful, but it never seems enough... I can sort of get the rear wheels to almost lock up, but I have to really, really push hard on the already soft-ish pedal, which feels like it's near the bottom of it's travel..
So here's where I did some experimenting, which may be helpful.. I know you're not supposed to 'preload' the master cylinder, but I did just that, and I learned a few things.. I adjusted the brake rod to where the MC plunger was about 1/8" into it's travel, and I went around the block once.. I knew the pedal would lose it's travel and get harder and harder with each push of the pedal, but I wondered what, if anything would the brakes do with this preload on them? in short, they worked really well!.. The pedal of course firmed up, and the "WD40 on the pads" feeling went away- the brakes actually had good clamping force! After a short time, the MC loaded up and I lost pedal travel..
It was nice to learn that when there's enough hydraulic pressure in the system, the calipers/rotors seem to work really well.. now it seems a matter of getting the right pressure and pedal feel.. So what do I do now? What component is to blame for the poor performance? I'm here to see what you guys think.. My gut tells be it's a master cylinder size/stroke issue?.. My MC donor car was a little 1990's econobox with tiny four wheel disc brakes/calipers.. maybe this master cylinder isn't moving enough fluid for these four larger calipers? (I can't seem to find info on the stroke on this MC).. Maybe go up to a 15/16" bore MC to firm up the pedal (but then I need more pedal pressure, which I can't seem to generate enough of as it is?).. I can go to a remote reservoir power brake setup, but really, if I design what I have correctly, shouldn't I be able to get really capable non-power brakes dialed in? Frustrating..
I'm stumped. The car is fast, but I no confidence in the brake's ability to get me stopped in a panic.. any thoughts?
As always- thanks for your input
-ccrunner
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Dean
1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"
1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=163091959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com