Carrier bearing cap question (when replacing with aftermarket)

Discussion in 'Got gears?' started by Tom Miller, Feb 12, 2017.

  1. Tom Miller

    Tom Miller Old car enthusiast

    OK guys,
    I picked up a 12 Bolt yesterday that is complete but disassembled.
    Complete other than the bearing caps are missing.
    I know Mark Williams and Moser make steel replacement caps, I have one in a box from an old project.
    My question is, yesterday I had some caps from another rear I put in this rear, and tightened them down to check how they lined up with the bearing race bore in the housing, which they looked pretty good. But, with a bearing race in place, the caps don't tighten onto the race. I would say I have a very nice slip fit when the cap is torqued down.
    Is that correct? Or, should material be removed from the cap bolt surface so the race is "clamped"?
    First time I've ever ran into this. Never had missing caps.
     
  2. monzaz

    monzaz Jim

    YaH, That might have been one to pass on... There is always a risk that stuff like that is not going to fit properly and cause a tragic mess down the road.

    Aftermarket caps should be machine by a professional machine shop I personally deem them NOT necessary as if you were actually going to use this 12 bolt Chevy for all out racing you should just buy a aftermarket piece Moser, Strange, etc.
    From the factory GM 12 bolt Chevy rear can handle quiet a bit and the reason it was designed for BIG BLOCK GM motors and torque. BUT now since you have a glitch in the works (NO CAPS...MIS MATCHED CAPS) you can not expect it to perform as good as it should.

    So for the street I am sure it will be fine for as many miles as most Muscle cars travel these days and stuff we do on the street. Racing- limit it to weekend fun runs, no bracket racing every weekend.


    HAve you tried the cap (s) on the other side to see if it fits better?

    Personal opinion.... I am sure you will be fine and doubt anything will just explode as long as your doing fairly stock stuff with the rear...Again I do not condone swapping mismatch caps...BUT am realistic to the fact that you want to try and make something work for you.

    You have to accept that it could fail somewhere down the road because of this...Customers call.

    Jim
    J D RAce
     
  3. Tom Miller

    Tom Miller Old car enthusiast

    Well, I'm a Tool and Die maker, so I'm confident in my machining capabilities, and pretty positive I can match or exceed production line tolerances. It's not like a main bearing cap that is registered into the block. This only centers with the bearing race.
    I just need to know if it should "clamp" onto the bearing race with a slight press, or if it should just be a very nice slip fit with no play? Case spread on the bearing shims hold it tight side to side, so My gut feel is that you don't want to clamp the race to avoid a possible out of round condition.
    Thanks for your input Jim.
     
  4. hugger

    hugger Well-Known Member

    Got a rear laying around to measure the bore and race that would tell you for sure, but I'm thinking it is actually a very light clamping load
     
  5. Bens99gtp

    Bens99gtp Well-Known Member

    I agreed with hugger, you don't want that outer race to spin in the cap. The side shims when I set a rear axle up are installed to provide about .007 or .008 preload to the bearings. I know the cap does clamp down slightly cause if after all the shims are in if you measure backlash there, then clamp the caps down it will change and so will the rotating torque when measured on the pinion nut.
     
  6. Jim Weise

    Jim Weise EFI/DIS 482

    Tom,

    Your Carrier bearing bore measurment is 3.0625 +/- .001

    Measure and machine the bottom of the cap as required to achieve this, and you should be fine.

    If you have an aftermarket cap, put it on the Driver side.

    Most of the rear end specialists still sell replacement HD caps.

    A TA Girdle is an excellent addition if your going racing. I pounded on a 12 bolt in a 10 second Regal with a Trans brake that let go at 5000 rpm for years, this was after I narrowed it and put it in that car.. I took it out of the 70 GS we raced with the same drivetrain into the low 11's at 4100 lbs..

    HD Axles with C clip eliminators, a spool and the soft gears, and a TA cover is all we ever had, and it held up well to the abuse.

    JW
     
  7. Tom Miller

    Tom Miller Old car enthusiast

    Thanks guys.
    J.W., yes, I have an aftermarket steel cap I was going to I stall on the driver side. I have to machine the mount surface to achieve the 3.062 dimension that you pointed out.
    Monzaz- Yes, I swapped the factory caps around to get them to mate up better. One cap fit good on both sides, the other would walk, or shift over once the body of the bolt entered the cap under the bolt head. I will use the one that fits best on the passenger side, and use the aftermarket Mark Williams cap on the ring gear side after machining it to spec.
    Thanks again for your input everyone.
     
  8. BrianTrick

    BrianTrick Brian Trick

    Make sure it fits square on there too. If you look on the inner side,it might have a true circle,but the outer side might not,depending on how that cap was machined to its original housing. Sounds like you'll get it right though.
     

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