LocostUSA.com

Well, I ran my specs through the Brake Spreadsheet (very cool tool!), and came up with this: My ideal bore for the front is .947 (about 15/16"- 1.1" stroke), and the rear wants .815 (about 13/16"- 1.1" stroke).. I'm currently running a 7/8" bore (stroke unknown), so I'm coincidentally already splitting the needed bore difference..

Two flaws in my setup keep coming up.. I'm pretty certain I glazed the pads, which can't at all be helpful, and is a pretty easy and cheap fix.. The other thing is improper pad travel/pad alignment, particularly in the rear.. my donor car was big and heavy (1996 T-Bird), and I should easily be locking up these rear rotors.. something's wrong back there.. the rear calipers have an integrated e-brake, and there's a funky 'hidden turn screw' adjustment that can be made on the caliper..

More experimenting: As it is, I can cruise at 20-30 mph, shift out of gear, fully pull the e-brake, and it of course slows the car, but not as quickly as you'd think (I've been in cars where pulling the e-brake works really well to slow/stop/lock up the rears).. -my cables are all tight, and there's good tension on the pull handle, just not as much braking action as you'd think (could be a result of the glazing though)..

I haven't looked into it yet, but the caliper ebrake adjustment must be a means to get the piston adjusted out closer to the rotor-- being a 1996, I'd think this would be self-adjusting(?).. (maybe it's currently out of adjustment and the piston is having to travel too far as the brakes are applied?).. I'll get on it over the holiday and see what's to be learned..

--ccrunner

_________________
Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com

It would be a quick check with a feeler gage to see that the pads are parallel to the disks (and not pulled away).
The e-brake on the T-Bird calipers should indeed be self-adjusting. Not certain how that one works, but it should not affect pad distance to the disks when it releases. Pads stay in contact and only "retract" based on run-out and relaxation of the fluid pressure, not like drums that pull away.

_________________
Planning a Duratec powered, Miata suspended 442

Preloading[tm] the MC doesn't work (like you found),
It causes the MC piston to cover the relief port.

Perhaps the low pedal is being caused by pad knock-back?
Loose wheel bearing or axle endplay can cause this.

You should be able to lock both the front and rear wheels, then use the proportioning valve to stop early rear lockup.

_________________
Honey anyone?

I cannot find front brake specs for the 1800. Could you post your front caliper bore and rotor diameter?

Bill

Hey Bill- without crawling under the car, I went with memory for disc diameter at 10" (I can't find this info anywhere online, and I don't have time just now to verify it on the car, but it's close).. For front calipers/pistons, I found the 2 smalls to be 38mm each, and the big one is 54mm (as you know this is a funky 3 piston caliper)..

--ccrunner

_________________
Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com

A person can get a rough idea of the cars braking power by multiplying the area of the cylinder times the diameter of the rotor. I think of this as effective brake power, or EBP. Doing this for your car, I assumed the front and rear rotors are 10" diameter. The front cylinder area is 3.33 sq. in or 33.3 EBP. The rear bore area is 2.51 sq in or 25.1 EBP. The rear braking power is 75% of the front braking power.

Doing the math for my Alpine, front bore area is 4.9 sq. in. Times 11.5" rotor diam =56.42 EBP
Rear bore are is 2.15 sq. in. Times rotor 10" diam =21.15 EBP, which is 37% of the front EBP and it still needs a lot of proportioning.

Looking at an early Saturn rear brake setup, we find 1.25" bore or 1.96" sq in
Rotor diam 9.65", giving 18.9 EBP which is 56% of front EBP. Still probably too high.

All this has nothing to do with your inability to lock up the rear brakes. When you solve that problem, I think you'll find you can't keep them from locking up. It does mean you are going to have to rethink your basic brake setup.

Bill

**Wanted to check in with a result.. I thought awhile ago that I may have glazed the pads (I got things VERY!! hot at initial install/ testing), creating my own problems (hard to see in the pic, but the pads I took out were 'shiny' for lack of a better term).. that does in fact seem to be the case ... I swapped out the pads all-around, and what do you know? Now she stops just as she should, and the pedal 'feel' is just as it should be ....SO nice to have this figured out- I now have total confidence in the car's ability to panic stop..

Thank you for your thoughts and help on this one-- brakes are nothing to mess with..

--ccrunner

_________________
Dean

1972 Honda N600 Restomod "ccrunner's N600 VFR800 repower"

1963 Volvo P1800 Restomod
http://locostusa.com/forums/viewtopic.php?f=36&t=16309

1959 Berkeley SE492 Restomod...
viewtopic.php?f=36&t=19397

"ccrunner's 1960 MGA coupe Restomod" found on MGExp.com