4 wheel disc brake help

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I've converted my 1976 FJ40 to 4 wheel disc brakes. The front brakes are original discs, the rear are a JTO kit with '85 Monte Carlo calipers. I installed a master cylinder for a FzJ80 to control everything with a Wilwood 260-12627 proportioning valve so I could tune it in. My issue is that I have the proportioning valve at the max "less brake" setting and my rears still lock up first. Do I have the wrong proportioning valve? Do I have something connected improperly? Any input is greatly appreciated.
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pbgbottle

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I still have the 1978 fj40 master and my prop valve is at max and it will lock my rear still on heavy stops. I know not much help.
 
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The proportioning valve is published with these spec's: "Pressure adjustments range from 150-1200 PSI and provide for a maximum decrease of 57% in line pressure, the most of any available valve." It looks like the Monte Carlo calipers simply have more braking than what you need.
 

Skreddy

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I have a 1970 with front disc and rear drum. I use a master from a 92 FJ80, non ABS. My lines are hooked up different: front port to rear brakes, rear port to front brakes. My master looks slightly different than yours but basically the same. No prop valve on either.
 

1MAC

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The rear brakes are going to lock up as long as you have no weight in the back, right? Weight shifts mostly to the front when you brake and a front engine vehicle with no cargo or passengers in the back won’t have much downward force on the rear end.
 

77mustard40

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What condition are the front calipers and pads in, could it be a sign that you need to take a look at the front?
 

tornadoalleycruiser

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all new flex hoses? ALL of them, not just the front and rear drop hose.. Did you replace the front knuckle flex hose?
 
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I think this is the nature of the monte carlo setup. The rear brakes are just too strong compared to the front so they will lock when the rear unloads. I read at one time that an alternate is some 2005-14 mustang rear calipers. I have them on the shelf but have not got around to installing. Pretty sure the bracket has to be changed from the monte carlo setup. The pads are definitely smaller on the mustangs.
 
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FWIW , I have a 1970 FJ40, stock MC, no proportioning valve, front GM calipers, 3/4 ton bolt on ones, rear gm metric calipers ( almost same as Monte Carlo ) , stops good, rears will lock if you really try but with soft suspension the weight transfer will cause the rears to lock sooner.
 

tornadoalleycruiser

Erik TLCA #5303
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You are turning the valve counter clockwise? All the way out and it still has issues?
 
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Your brake pad material will also make a big difference. I’ve always used the fastest wearing organic pads on my 76 front 40 brakes. If they’re too hard they don’t wear fast enough and the pistons freeze because they don’t move much. They still lasted 95,000 miles. My view is they were $21 a set and the rotors were about $250-300 a pair at the time… which do you want to wear out first?

To go to the other extreme… ceramic last longer but require more force to work (or so I’ve been told). So they would be the worst on the front.

What are your front pads made of? Were the front rotors machined? Are they broken in?

Same questions for the rear brakes?

You’ll always be able to lock the rear brakes if the weight shifts forward enough from a hard brake application… but they shouldn’t lock with everything but the lightest brake application. I have read on mud of using a stock proportioning valve in series with an adjustable one.

I’ve got a heavier rear end because of an 1/8” steel tub and a lighter front because of a SBC swap. That combined with Chevy full size rear calipers has meant the Willwood valve has been enough (so long as all brakes are happy). I’ve generally run faster wearing pads in the rear (also) because they are 3/4 ton front brake pads and I don’t need maximum braking out of them.
 
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Yes, on a wet road, rears locked up and started to come around

That’s not fun… been there done that. I’ve had the rear wheels stop on the stop line with the truck facing the wrong way on the road… it was the most exciting the first time it happened.

Always be careful of wet roads after a long hot dry spell. I’ve come around a corner sideways when I let off the gas because I saw it was wet. The rears locked up because of engine braking. I was only doing about 30 mph at the start of the highway on ramp. I would have been fine on dry pavement, but not so on wet oily road.
 
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tornadoalleycruiser

Erik TLCA #5303
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which specific master cylinder? ABS or Non ABS etc..
which specific front calipers? Piston size etc. if you have the specific year maybe we can determine your piston size. you said 76 original. meaning same exact small piston caliper that came in 76? or did you get rebuilds of a later year and size?
Brake pedal feel? is it high? Tight? Mushy? any other details.
Front axle? Do you run a backing plate? or backing plate delete? Wheels?
i'm asking for future clearance issues if a larger front caliper might assist in bias balance.
 
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which specific master cylinder? ABS or Non ABS etc..
which specific front calipers? Piston size etc. if you have the specific year maybe we can determine your piston size. you said 76 original. meaning same exact small piston caliper that came in 76? or did you get rebuilds of a later year and size?
Brake pedal feel? is it high? Tight? Mushy? any other details.
Front axle? Do you run a backing plate? or backing plate delete? Wheels?
i'm asking for future clearance issues if a larger front caliper might assist in bias balance.

‘76 calipers will have two smaller and two larger pistons. They’ll clear a stock welded rim without modifications and an aftermarket white spoke with a 1/4” spacer. Newer calipers have four of the larger pistons. I’ve read (& it makes sense) that they increase front braking noticeably. The larger calipers do need minimal grinding to clear stock rims (but I’ve not installed them personally).
 
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FJ80 (non abs) master has the front circuit furthest from the firewall as I understand it, which is consistent with what you have plumbed. Is the FZJ80 master the same? The port orientation is different and the FJ ports both point to the side, but there are also multiple versions of each type.
 

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