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Old 07-23-2021, 04:30 PM   #1
Bob/AZ
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I'm in day 3 of installing my Mitchell overdrive (by myself!). It is going very well. Paul Shinns video has been very helpful. I welded up a homemade spring spreader but just used it as a safety, I left the spring on the rear end and not in the car. I'm amazed at the quality of the entire Mitchell package that they send, right down to the way they package it for shipping
So...today I bent the washer tabs down and removed the top large nut on the pinion. Then I discovered that I could jiggle the tabbed washer and the lower nut at least 1/8 inch with the tabbed washer on there. After I lifted the tabbed washer I could tighten the lower nut by fingers at least 3/8 inch in the clockwise direction. I understand that there should be 20 inch pounds preload on the pinion bearing. Obviously there was none. So my question is how can I do this preload setting. I have an inch pound torque wrench but don't see any way to use one on that large nut. Thanks, Bob
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Old 07-23-2021, 04:39 PM   #2
john in illinois
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Did you remove pinion and driveshaft from the center to put in OD drive shaft?
I do not see how a working rear end could be that much out of spec.

John
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Old 07-23-2021, 05:03 PM   #3
Bob/AZ
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Quote:
Originally Posted by john in illinois View Post
Did you remove pinion and driveshaft from the center to put in OD drive shaft?
I do not see how a working rear end could be that much out of spec.

John
No, I haven't removed it from the banjo yet.
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Old 07-23-2021, 06:19 PM   #4
nkaminar
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Les Andrews' Mechanics Handbook says 20 inch-pounds of drag with a new bearings and 12 to 15 inch-pounds with old bearings. You can buy adapters that go from 3/8 square to 1/2 square drive for the larger socket at any automotive store or McMasters-Carr. Or if need be an adapter to go to 3/4 square drive.

So, tighten the nut then measure the drag on the bearings using the torque wrench. After installing the locking plate and locking nut, recheck the drag. 12 to 15 inch-pounds of drag is not much. You can get a feeling for how much it is by just clamping the drive of your torque wrench in a vice and torquing to 12 to 15 inch-lbs. It is about one foot-pound so if you have 16 ounce hammer with a one foot handle you can clamp the handle to the drive shaft to get the approximate drag torque.
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Old 07-23-2021, 06:25 PM   #5
Kurt in NJ
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When you loosen the outer nut the inner nut moves to the other side of the threads and moves away from the pinnion bearing, the preload can only be checked when both nuts are tight to each other
Usually if you can turn turn the pinion with 2 fingers---not easily but not so tight it can't keep it turning , new bearings get set up tighter than used bearings
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Old 07-23-2021, 08:21 PM   #6
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I don't think you will be able to re-set the pinion bearing pre-load with a dial indicator torque wrench with the rear axle assembly fully assembled. The pre-load on both the carrier bearings and the pinion bearings is done when you are measuring only those elements separately. With a full assembly you have to take into consideration the combination of both pre-loads, drag on the axles by the seals, drag created by the spider gears. Used bearings also give erroneous readings.

When we install a Mitchell overdrive we leave the spring installed in the car where it can do no damage and we use a pinion puller that does not destroy the pre-load. Removing the front large nut destroys the pre-load it there actually is any.

When installing a Mitchell overdrive if we have to replace unserviceable pinion bearings it is possible to set the preload by clamping the stub shaft in a vice and rotating the assembly with the drive shaft nut and using the dial wrench. With used bearings I re-set the pinion pre-load by feel. I have done enough to have a good feel for a proper pre-load.

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Old 07-24-2021, 11:23 AM   #7
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Setting the drag by feel works very well. I would tighten the inner nut just enough to eliminate the slop, then install the front nut tightly and bend the tab. drag slight should be felt.
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Old 07-24-2021, 11:56 AM   #8
Bob/AZ
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Thanks to all for your thoughts on this. I'm getting the impression that pinion preload leans a little more to art than science. Tom, I went back into the archives (which I should have done before I posted this) and found a wealth of information you have posted over the years on this and other rear end issues. I loved your story about the one you rebuilt where someone had tightened the preload nut so tight they had frozen the bearing and the entire pinion assembly had been spinning in the banjo housing for many years. After the initial heat-up I guess it got enough lube to keep working although a little noisy.

Bob
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Old 07-24-2021, 04:09 PM   #9
john in illinois
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As Tom and Charly said doit by feel. Just a slight drag because it will probably get tighter from the press fit in the banjo.

Also you will probably have to try a couple of times with the nuts as tightenig thr lock nut increases preload.

Do you have wrenches that will fit the nuts. The suppliers have special wrenches for the nuts.
John
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Last edited by john in illinois; 07-24-2021 at 04:26 PM.
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Old 07-24-2021, 09:21 PM   #10
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As Tom says and he and I have done hundreds of rear axles it is very important you get this right. If the pinion isn’t right my guess is the carrier bearings and preload may also be in question. You can attempt this yourself with the correctly used tools to do the job. If you don’t have them and also the understanding anc knowledge of it I would suggest seeing if here is someone knowledgeable of them in your area with a local A club.
Disassemble the drivers side and remove the carrier anc axle assembly and inspect the bearings and races. Ensure the bearings aren’t spinning on the id of the bearings against the carrier. A common problem.

Your going to go faster with the overdrive so you must have everything in top notch order.
Read Les’s and Tom’s rear axle info and tackle or find someone who can assist with proper knowledge, tools, and assistance.

No it’s not brain surgery but it is all about process and proper at that .
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Old 07-25-2021, 04:35 PM   #11
john in illinois
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There you go Bob. Very good suggestions to get it going as is or spend time and money to restore it properly. If you wNt to drive a lot and keep the car that is best solution.

John
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Old 07-25-2021, 09:54 PM   #12
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I'd be checking the whole thing. Restoration knowledge in past years wasn't all that great. There is some good background info on banjo's in this little booklet.
https://www.verntardel.com/store/p30...ook_%2310.html
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