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4 Wheel Disk Brake Woes...

Discussion in '40- & 55-Series Tech' started by sfrolich, Feb 25, 2003.

  1. sfrolich

    sfrolich

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    Hi,
    A few years back I had a 4 wheel disk brake conversion done on my 71 FJ40 at BTB Products in San Jose (now they are in Nevada). When I had it done, the rear brakes would lock up early and BTB told me to wait until the brakes were broken in. Well now they ARE broken in and I still have the same rear lockup problem.

    I thought an adjustable proprtioning valve would solve my problem so I put one in that a friend gave me and it did help a little but it still locks up.

    I have blead the front and the back brakes with no change.

    I believe the front axle is out of a later model FJ40 with disk brakes and the rear are a BTB conversion item http://store.btbprod.com/cgi-bin/bt...aff3b68273f0a0a0a0605d1+EN/products/30&2D3130

    I have a power boosted master cyl. that has two different size reserviors... Does that mean it is a Disk/Drum master cyl? I guess there wouldn't be a Disk/Disk master cyl. for an FJ40.

    Does anyone else have this setup on their rig and do you have any rear lockup problems?
    What master cyl. are you using?
    Does anyone have any other ideas on how to fix the problem?

    Thanks, Scott
     
  2. Design311

    Design311

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  3. sfrolich

    sfrolich

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    Thanks for the info. I'll have to check that but I have a feeling that this isn't the problem. If the residual valve was in my brake system I would think the back brakes would be sticking a little when not pushing the brakes. My rear wheels spin pretty freely.

    Any other ideas? Please help!?!

    Thanks, Scott
     
  4. beanz2

    beanz2 Moderator

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    I've heard of people using a second proportioning valve inline to reduce the hydraulic force to the rear. The brake piston area on a Chevy caliper is so much larger than in the Toyota front caliper so the force the Chevy caliper applies is higher for a given brake line pressure.

    Dave
     
  5. Erics75

    Erics75

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    Hi scott, are you using metallic pads in the rear? If you are, then changing to non-metallic may help. Also your M/C is for a disc/drum setup, the larger resevoir is needed because disc brakes do not "self " adjust to account for wear and the cylinder area is large. You could still have a check valve in the M/C and be able to turn the wheels freely, there may be only 5 lbs or so of pressure. Check the port of the smallest resevoir, insert a paper clip into the port hole and check for a rubber ck.vlv. or ck.ball. It upsets me to hear of a shop tell somebody such a bunch of BS. They should have fixed the problem, its obvious whoever you talked to was a lazy ass or totally ignorant.
     
  6. petescoffee

    petescoffee

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    A previous poster suggested the use of a master cylinder out of a 93 Landcruiser as they had 4 wheel disk brakes.
     
  7. sfrolich

    sfrolich

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    Thanks for all the info. I'm not sure what pads are on the rear but they are probably some cheepos...

    For now I think I'm going to put the old proportioning valve in-line with the adjustable one to see if I can get the rear to stop locking. I'm also going to check inside the master cyl. to see if there is a residual valve in there and take it out.

    I'm pretty sure I have a late 70's master cyl and disc brake booster. I'd like to know what the bore is on the master cyl. though.

    I'm afraid after I get the two valves in the system I'll get the rear to not lock up but I won't have any braking power!

    I'm sure when they did the conversion that they swapped my axle out for a later model one. Does anyone know if there are better front calipers I can get for mokre braking power???

    Thanks, Scott
     
  8. beanz2

    beanz2 Moderator

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    I've used 88-95 4Runner calipers. They require some trimming of the backing plates but they bolt up.
    [​IMG]
    The pic shows it next to a minitruck caliper, but the 40 caliper is the same size

    Dave
     
  9. beanz2

    beanz2 Moderator

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    The brake pads are also larger.
    [​IMG]

    One caveat though, not all disk brake compatible wheels can clear the 4Runner calipers. I lucked out with a set that did, but on the other cruiser I had to use a spacer :(

    Dave
     
  10. Cruzfj40

    Cruzfj40

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    This may have been covered but try an adjustable proportioning valve form Willdwood like they use on race cars for brakebias you can close the valve off compleaty if you want I run one on the front and rear the one in the front I use when running on icey roads to stop front brake lockup.