8 3/4 woes

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gumper

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After many, many years my 8 3/4 finally gave up. Not sure if I lost a carrier (Detroit locker), or the gear set. Now the decision is to fix the 8 3/4, or go to a 9”. 1.50 60’ car with 4.30s. Happened in the 1/4 finals of Pro class at our local track. The poor guy in the other lane red lit, so at least it got the round win.
 
Stick or trans brake car? If you go with Dana you will be able to reuse your axles and brake assemblies. I don't think 4.30s are available, but a one inch taller tire will compensate the difference. Depending on your trap rpm, 4.56 may work better, and a Dana will use less power to run than either an 8-3/4 and especially a 9 inch Ford.
 
I'm surprised the rubber insulated shaft held up?
Thats what i was thinking too!

Manage by fact. Take the rear apart and then decide. IMHO Rebuilding the 8 3/4 would be cheapest option, no narrowing - spring mounts etc
 
and if you broke it in 1st gear with a 727....check the sprag in the trans....otherwise the trans could explode....

yes..rebuild the 8 3/4...and in a few years replace the ring gear as sooner or later they break...check the sprag again...rebuild 8 3/4 ....OR

Buy a Dana S60......and be done with it....JMO
 
To the OP, I'm curious to know if the driveshaft ends are in phase with each other or did the rubber insulator allow the two pieces to turn? That may have contributed to the failure?
 
sounds like you chucked some teeth -- why build another 8-3/4 -- sounds like you actually drive your car the way it was meant to be driven -
go with the 9 inch Ford --strong differential ,, gear selection is extensive , parts readily available -- call Moser or Strange Engineering with the housing measurements you need to fit your car --you can have 8-3/4 flanges installed on the 9 inch housing to reuse your stock brakes - go with 35 spline axles ( Detroit lockers are available for this axle spline if you spend more time on the street ) -- 1350 u-joint yoke -- with a similar size driveshaft ,,,, yes it will cost $$$$ but do it right and you will never look back.

as far as horsepower loss it's nothing you will notice .
 
Transbrake car, and it happened as soon as the button was released. I heard a noise after the previous run, and had a feeling it was going to let go. The trans has low band apply in first, so hopefully it didn’t destroy anything internally. If it did then my season is over with a 11 round lead over second in Pro class points. I’m surprised really how the driveshaft has held up considering the abuse. The u-joints, and strap yoke only broke due to the gear failure. I’ll take the opportunity to upgrade both yokes with bigger joints, and build a new shaft. Also hoping the Detroit locker is ok. Will have to tear it down to check it out.
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Ouch! 489 Case? A Ratech solid spacer crush sleeve eliminator may help reduce pinion gear deflection some, but definitely time to consider an upgrade in the future.
 
Ouch! 489 Case? A Ratech solid spacer crush sleeve eliminator may help reduce pinion gear deflection some, but definitely time to consider an upgrade in the future.
It’s an aftermarket 489 case. I’m going to eliminate the crush sleeve which I thought I did when it was put together several years ago. Going to fix this one, and start saving for an S60 or 9”. Also going to build a new driveshaft with 1350 joints.
 
Good news is the locker is perfectly fine other than some stray particles from the gears making their way inside.
 
I have a setup question. I have never correctly set up a rear end (have used the old “feels good there” method), and wanted to make sure I’m doing it right on this one. On the pinion I used the same thickness of shims that were on the old pinion, and then used a crush sleeve eliminator. Followed those instructions, and wound up with one .016” shim to get about 16 in lbs of preload on the pinion. With the shim on the solid sleeve it’s within a few thousandth of the old crush sleeve. I don’t have a dial torque wrench, so I used a regular click type. When set at 16 in lbs, and a gentle pull it will click right before the yoke begins to turn. 17 in lbs it turns without a click unless I put a little more pressure on the wrench. Is this close enough to where I need to be, or will I need to go get a beam/dial torque wrench?
 
Well on the new pinion head it should have the pinion depth measurement. compare it to your old number on broke pinion head.
 
I spun a 7.25 that looked just like that opened up. Bummer. I got a new US gear 4.56 fine spline set for a 489 if your interested.
 
I spun a 7.25 that looked just like that opened up. Bummer. I got a new US gear 4.56 fine spline set for a 489 if your interested.
Had I not just bought these new 4.30s I would have considered it.
 
what is the range of the scale for that clicker torque wrench that you are using?
I doubt that a click wrench will have the sensitivity to be accurate to set bearing preload.
And the more I think about this the more I believe you really need a torque arm with a dial on it so you see the torque to turn in a complete 360 degree sweep of the bearing.
Until the bearing is properly loaded the torque to turn will be erratic. Once the proper load is on it it will level out. You need a dial torque read out to see that.
 
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As My68barracuda said, you need a dial type torque wrench, and measure actual turning torque. A clicker (if accurate at that low of a setting) is only measuring "breakaway" torque, which is always higher than turning torque. IMO 16 in/lb is too low for new bearings even for turning torque. Most preload specs for new bearings are in the 20~30 in/lb range.


Followed those instructions, and wound up with one .016” shim to get about 16 in lbs of preload on the pinion. With the shim on the solid sleeve it’s within a few thousandth of the old crush sleeve. I don’t have a dial torque wrench, so I used a regular click type. When set at 16 in lbs, and a gentle pull it will click right before the yoke begins to turn. 17 in lbs it turns without a click unless I put a little more pressure on the wrench. Is this close enough to where I need to be, or will I need to go get a beam/dial torque wrench?
 
As My68barracuda said, you need a dial type torque wrench, and measure actual turning torque. A clicker (if accurate at that low of a setting) is only measuring "breakaway" torque, which is always higher than turning torque. IMO 16 in/lb is too low for new bearings even for turning torque. Most preload specs for new bearings are in the 20~30 in/lb range.
The specs say 14-19 in lbs for new bearings on a 489 case, so that’s what I was going by.
 
As My68barracuda said, you need a dial type torque wrench, and measure actual turning torque. A clicker (if accurate at that low of a setting) is only measuring "breakaway" torque, which is always higher than turning torque. IMO 16 in/lb is too low for new bearings even for turning torque. Most preload specs for new bearings are in the 20~30 in/lb range.
Hopefully my reply didn’t sound arrogant as it wasn’t intended to be. In my naivety I was merely going by what the Chrysler specs were for the 489. The 741, and 742 are different specs. Wasn’t sure if I should go with different since I eliminated the crush sleeve, or stick to their specs. Decided to stick to 489 specs, and I guess we’ll see what happens.

Here’s my gear pattern
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I just changed the yoke on a set of 2.76s and used my “Grunt” style torque wrench for bearing preload. Lol
Going on a 400 mile road trip and just couldn't live with my 3.55s @ 85 mph !
 
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