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Old 10-31-2011, 11:53 AM   #1
30 A coupe
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Post Pinion gear and Mitchell Overdrive

Hi guys,
I'm putting a Mitchell overdrive in my coupe. I did not take the rear end apart, I just pulled out the pinion gear out of the axle from the torque tube side end. I want to put in new bearings and bearing race. I know the first bearing is a press fit but it doesn't even slides over the dirst part of the pinion. So I think I'm going to use the old bearings because they felt like a better fit.
But I have another question, all the pinion gear preload measurements are made with a dismantled rear end. What are the preload values needed with an assembled rear end. Plus I don't have a dial indicator inch pound torque wrench!!!! How do measure the preload then?
Thanks,
Eddy
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Old 10-31-2011, 12:39 PM   #2
Fred A
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Default Re: Pinion gear and Mitchell Overdrive

So, what was the first question? Read it again and clarify. I doubt that the factory went through the care and measurment that we must because of doing so many by feel with repeatable parts supply as in a factory. The mix of parts, damage by years of poor service and various bearing suppliers makes it a bit tougher to get it right without being very cautious. The popular preload recommendations seems to be around 20 IP. Don't chase any threads if possible. Years ago when I knew far less I would take a low mileage component and replace the gaskets, feel the bearings to an expected preload and go... Recent A rears that I have seen have been obviously redone to unknown standards. The safety wire job is most obvious clue. Read the article by Tom Endy at the Orange As site for a wonderful explanation. Good Luck: Fred A
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Old 10-31-2011, 01:04 PM   #3
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Default Re: Pinion gear and Mitchell Overdrive

Thanks Fred,


I did read the Tom Endy article but it only talks about the preload values with the carrier out of the banjo but I didn't take the rear end apart. I was told when buying the Mitchell I could leave the rear end together. So I would like to now the preload measurements with the carrier inside the banjo.
I would like to use the new bearings but I understand that the second bearing on the pinion gear has to slide on to be able to set the preload. And it really doesn't.

Eddy
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Old 10-31-2011, 05:13 PM   #4
Fred A
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Default Re: Pinion gear and Mitchell Overdrive

When the driveshaft and pinion are removed without splitting the axle housings, a puller is used to access the pinion nut and bearing assembly. That allows the optimistic claim that the rear axle disassembly is not required. Many take the whole rear axle apart to inspect the parts and replace the bearings and seals. Some also change the axle ratio to maximize the advantage of available overdrive. I prefer the 4.11 ratio with modified four cylinder engines. With my V8-60, the 4.56 ratio with V8 passenger car(15/28) is my choice. Many choices are available and just as many are poor choices are commony praised wrongly. I believe in my choices without reservation. Good Luck: Fred A
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Old 10-31-2011, 07:25 PM   #5
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Default Re: Pinion gear and Mitchell Overdrive

You can install a Mitchell without pulling the rear end. If you plan to do it that way, pull the pinion assembly without disturbing the two large nuts. They hold the pinion pre-load in tact if there was one there to begin with. You need a proper tool that clamps onto the drive shaft. Mitchell can loan you one. All you need do then is remove the drive shaft from the pinion assembly and replace it with the Mitchell stub shaft. The assembly is then reinserted into the banjo. You can pull it into place using the torque tube flange and some studs with nuts on them.

Since it sounds like you already distrubed the two nuts you will have to reset the pre-load. You can do this by feel. Clamp the stub shaft into the pipe grabbers of a vice. Rotate the bearing pack and tighten the nuts until it feels reasonably snug.

The outer bearing on the pinion sleeve is not always a slip fit by hand. However it does need to slide and should not be a press fit. Many of the repos are not machined correctly and both bearings are a press fit unless you machine the outer part of the sleeve.

Tom Endy
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Old 10-31-2011, 07:53 PM   #6
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Default Re: Pinion gear and Mitchell Overdrive

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We just put a Mitchell in my coupe. I rebuilt the rear end a couple of years ago and set the pre-load in the process.
When we installed the Mitchell used a special Mitchell tool that allowed us to remove the pinion and bearings without disturbing the pre-load (2-large nuts on the pinion) then removed the axle and replaced with the Mitchell axle and unit. Tom is right, if you disturbed the nuts you will need to re-set the pre-load.
I am running 3:54's with the OD and works just fine.
Steve
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Old 10-31-2011, 08:13 PM   #7
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Default Re: Pinion gear and Mitchell Overdrive

Quote:
Originally Posted by Smitty View Post
We just put a Mitchell in my coupe. I rebuilt the rear end a couple of years ago and set the pre-load in the process.
When we installed the Mitchell used a special Mitchell tool that allowed us to remove the pinion and bearings without disturbing the pre-load (2-large nuts on the pinion) then removed the axle and replaced with the Mitchell axle and unit. Tom is right, if you disturbed the nuts you will need to re-set the pre-load.
I am running 3:54's with the OD and works just fine.
Steve
When you say "Axle", are you by chance referring to the drive shaft?
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Old 10-31-2011, 10:56 PM   #8
Jerry Parr WI
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Default Re: Pinion gear and Mitchell Overdrive

The pinion preload cannot be set with an assembled differential because the drag from the carrier bearings and axle seals add an unknown amount of load. The preload can be set before the pinion is installed. With the bearings assembled hold the bearing race and measure the force to turn the pinion. If you don't have an inch/lb torque wrench the bearing should be snug but you should be able to turn it with your hand.
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Old 11-01-2011, 12:16 PM   #9
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Default Re: Pinion gear and Mitchell Overdrive

Thanks for all the info

I will put the pinion assembly together and put it on the Mitchell drive shaft and adjust the preload by hand as told here because I haven't got an inch-lbs torque wrench. And then mount it in the banjo. It is possible that the preload in my set up was not correct because the second lock nut was loose when I took of the torque tube. I did not notice anything wrong with it when I drove the car, it wasn't noisy or anything so!
Hope everythings turns out OK, I also put in a syncro trans from Mitchell in my coupe. I have a touring engine in it also. I have the stock 3.78 gearing.

Thanks,

Eddy
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