Posi rebuild
Thread Starter
Cruising
Joined: Apr 2024
Posts: 13
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Posi rebuild
I opened up my Posi Case/Carrier and am in the process of cleaning and full inspection. What I do notice of the bat is that the cross shaft top & bottom small gears do wobble some when reinstalled on the cross shaft. They obviously ride in the area where the flat spots are on the shaft, but should they have that much play? I understand everything in the case has very close tolerances. Anybody familiar with this or should I go right to Gary? GTR1999
Race Director
Joined: Nov 2006
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From: Sunshine Coast, Queensland, Australia
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You should go right to Gary. Box it all up, send it off.
Melting Slicks
Joined: Nov 2006
Posts: 3,411
Likes: 1,821
From: Apple Valley, MN
You need to be a bit more specific about your concern of “wobble”.
Are you simply sliding the gears onto the shaft or have you assembled the unit, short of installing the spring packs?
Is there any sign of wear or galling on the shaft in the plane where the gears run?
Before you get too deep into a rebuild, have you magnafluxed or FPI’ed the posi case for cracks?
Are you simply sliding the gears onto the shaft or have you assembled the unit, short of installing the spring packs?
Is there any sign of wear or galling on the shaft in the plane where the gears run?
Before you get too deep into a rebuild, have you magnafluxed or FPI’ed the posi case for cracks?
Thread Starter
Cruising
Joined: Apr 2024
Posts: 13
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Yes, I have inspected case for Cracks, and it is in good Shape. It may require an oversized cross shaft from Toms but looks rebuildable. My concern is with the amount of Play with the spider gears and the slight wobble when slid back on existing cross shaft. Could the shaft be that worn?
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Thread Starter
Cruising
Joined: Apr 2024
Posts: 13
Likes: 0
Thread Starter
Cruising
Joined: Apr 2024
Posts: 13
Likes: 0
I Have some measurements.
Bore in carrier with a cheap Harbor freight Digital caliper
Pin Side horizontal - .7535 Vertical - 7515
Opposite Side horizontal - 7550 Vertical - 7510
Shaft measured with a good mechanical micrometer.
Pin Side Bore End - .748 where gear rides - .7475
Opposite Side Bore End - .748 where gear rides - .7475
Bore in carrier with a cheap Harbor freight Digital caliper
Pin Side horizontal - .7535 Vertical - 7515
Opposite Side horizontal - 7550 Vertical - 7510
Shaft measured with a good mechanical micrometer.
Pin Side Bore End - .748 where gear rides - .7475
Opposite Side Bore End - .748 where gear rides - .7475
Old Pro Solo Guy
Joined: Dec 2017
Posts: 8,088
Likes: 4,445
From: Marlton NJ
The pin is tool steel and does not move where it sits on the posi. The pin wear happens where the spiders spin on it.
And I do not believe the spiders fit all that tight.
But the tool steel pin should fit pretty snugly into the cast iron posi case.
And the case typically gets pounded into an oblong hole shape under abuse.
I think you are there. You are at 4 thou oblong. And 7 thou clearance.
An oversized pin, may mean going to a 12 bolt pin, and new 12 bolt spiders.
And boring the posi case.
Get the new hole off-center and you will ruin the posi action / spider fitment.
I would definately send this one to GTR.
I would have the "expert" look this one over.
He is the teacher, he trained other machinists.
If that is all that is wrong, it sounds like he could fix it.
And I do not believe the spiders fit all that tight.
But the tool steel pin should fit pretty snugly into the cast iron posi case.
And the case typically gets pounded into an oblong hole shape under abuse.
I think you are there. You are at 4 thou oblong. And 7 thou clearance.
An oversized pin, may mean going to a 12 bolt pin, and new 12 bolt spiders.
And boring the posi case.
Get the new hole off-center and you will ruin the posi action / spider fitment.
I would definately send this one to GTR.
I would have the "expert" look this one over.
He is the teacher, he trained other machinists.
If that is all that is wrong, it sounds like he could fix it.
Last edited by leigh1322; Dec 5, 2024 at 09:38 PM.