OK.....Just got through doing a disc brake conversion on the front axle(67 FJ40 w/SBC, ball and claw axle, JTO front disc conversion, Geo Metro booster, wilwood proportioning valve). One problem, I have to pump several times to get a firm pedal. I know this has been discussed ad nauseum but I have done everything I can think of and read on this forum. 1)bled, bled, bled, and rebled the system 2) adjusted the rear drum brakes (till tight and then backed off three clicks), 3) checked for leaks (there are none) 4) checked pushrod length. The set up is this Geo Metro booster and M/C, front lines run to the calipers which are GM, rear line runs to the Wilwood proportioning valve and then to the back drums. Now, if I clamp off the rubber line at the rear of the rig (using a wood c-clamp) it brakes fantastic, better than I could ever get it to with the drums. It really hauls it down, with a really light pedal feel. I couldn't be happier with that part of it but when I release the clamp and put the rear drums back in to play I have to pump the brake pedal 4 or 5 times to get a firm pedal. I am POSITIVE that I have gotten all of the air out of the system, and yes I know all about the air trapped in the wheel cylinders problem. I am POSITIVE that I have adjusted the drums correctly. The only thing I can think of is maybe I need a residual valve in the rear drum circuit? If so, 10#s or 2#s? Anything else I might be missing here? Thanks in advance?
Disc front/ Drum rear- Residual valve needed? (1 Viewer)
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Bleed the rear brakes, you might have to do it by pulling the drums and top plungers and filling the cylinders with brake fluid and putting the plungers back in. There are several posts about people having to do this in order to get the rear brakes properly bled.
It sounds like AIR in the system and since you clamped the brake lines in the rear and it solved it I think you know where the air is. Not sure I would want to keep using the soft brake lines that were clamped so tight it sealed them.
It sounds like AIR in the system and since you clamped the brake lines in the rear and it solved it I think you know where the air is. Not sure I would want to keep using the soft brake lines that were clamped so tight it sealed them.
shipmag
Hagler Technology LLC. Aka Shipmag
Fast Eddy Im dumb what is a residual valve look like and what does it do and where does it go. I may have this same problem on my 74 FJ40 stock front disc conversion with stock rear drums. Havent got the proportional valve installed yet. I know that needs to be done. This is the first I have heard of a residual valve.
my experience is with the Man-a-fre disk brake conversions (no idea about the Geo Metro stuff)
typically, upon conversion with any of the aftermarket bolt-on kits, the residual valve is removed from the OEM drum brake master cylinder for that circuit where the disk brakes have been installed - so, if you installed disks in the front, you remove the residual valves from that front circuit outlet of the brake master cylinder
when you install disks in the rear, you also remove the residual valve from the master cylinder that was still in the circuit for the rear brakes - then you also install a proportioning valve to dial in the relative brake pressures between front and rear circuits (if you wouldn't use the prop valve, the rear would lock up before the front, which you don't want) - (some people leave the residual valve in the rear circuit regardless - I found it didn't work for my Man-a-Fre/GM caliper rear disk conversion kit, as it would have the brakes dragging all the time, so I removed the residual valve)
typically, upon conversion with any of the aftermarket bolt-on kits, the residual valve is removed from the OEM drum brake master cylinder for that circuit where the disk brakes have been installed - so, if you installed disks in the front, you remove the residual valves from that front circuit outlet of the brake master cylinder
when you install disks in the rear, you also remove the residual valve from the master cylinder that was still in the circuit for the rear brakes - then you also install a proportioning valve to dial in the relative brake pressures between front and rear circuits (if you wouldn't use the prop valve, the rear would lock up before the front, which you don't want) - (some people leave the residual valve in the rear circuit regardless - I found it didn't work for my Man-a-Fre/GM caliper rear disk conversion kit, as it would have the brakes dragging all the time, so I removed the residual valve)
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the residual valve is a little black plastic disk-looking thingie behind the big hex nut on the master brake cylinder - you need to remove it from the circuit for the front brakes that you just installed a front disk conversion
[if you were to leave the residual valve in the circuit, you'd have perpetually dragging brake calipers]
Downey
SILVER Star
Pressure problems
Essentially, disc need 2 lbs residual pressure and drums need 10 lbs. I have no idea what pressures are built into your Geo stuff (don't even know what ft. & rr. brakes were on a Geo). Sounds 1,000 percent like you put a 2 lb. residual valve into the line going to rear drum brakes. That would mean you are not holding enough oil pressure at the rear brakes to keep the brake shoes up to the drum, have to pump them up to the drum. A Toyota T-100 master cylinder would have been an excellent choice because (a) It already has the right bolt pattern (same as your FJ40), (b) it would give you the right pressures, and (c) it has a 1 1/16" macho piston to move serious oil---zero pumping required!!!!
Essentially, disc need 2 lbs residual pressure and drums need 10 lbs. I have no idea what pressures are built into your Geo stuff (don't even know what ft. & rr. brakes were on a Geo). Sounds 1,000 percent like you put a 2 lb. residual valve into the line going to rear drum brakes. That would mean you are not holding enough oil pressure at the rear brakes to keep the brake shoes up to the drum, have to pump them up to the drum. A Toyota T-100 master cylinder would have been an excellent choice because (a) It already has the right bolt pattern (same as your FJ40), (b) it would give you the right pressures, and (c) it has a 1 1/16" macho piston to move serious oil---zero pumping required!!!!
