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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: joelsplace ()
Date: November 02, 2017 10:26PM

Where do you buy the shims?

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: Murphy ()
Date: November 03, 2017 02:16AM

joelsplace Wrote:
-------------------------------------------------------
> Where do you buy the shims?

California Corvairs, Clarks, Corvair ranch. Take your pick. Unless someone has some to sell.

65 Monza Coupe
61 500 Coupe (under Construction) Getting REALclose.

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: joelsplace ()
Date: November 03, 2017 07:07AM

I couldn't find them on Clark's site.

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: Murphy ()
Date: November 03, 2017 09:51AM

joelsplace Wrote:
-------------------------------------------------------
> I couldn't find them on Clark's site.

I think you're correct. Check CC or the ranch, I know they both have them.

65 Monza Coupe
61 500 Coupe (under Construction) Getting REALclose.

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: dryenko ()
Date: November 03, 2017 07:00PM

Just a question.
Doesn't adding a gasket for final assembly change the clearance required as measured above?
Or does the shop manual specify no gasket?

Bob C aka Dryenko
Dobson, NC 27017

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: davemotohead ()
Date: November 03, 2017 07:20PM

dryenko Wrote:
-------------------------------------------------------
> Just a question.
> Doesn't adding a gasket for final assembly change
> the clearance required as measured above?
> Or does the shop manual specify no gasket?
------------------------------------------------------
Shop manual specifies taking all measurements with no gasket.





Email me at: Dave Motohead

1960 4dr sedan caveman car
1961 Rampside (Chetside)
1962 Rampside (Barnside)
1962 Short Rampside (Shortside)
1962 Monza 700 Wagon
1963 Monza 900 coup (General Nader)

-----------------------------------
Rust Free Lancaster Ca

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: dryenko ()
Date: November 04, 2017 02:52AM

So the actual clearance is what is specified plus the thickness of the factory gasket.
Anyone know what that thickness is?

Bob C aka Dryenko
Dobson, NC 27017

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: joelsplace ()
Date: November 04, 2017 04:05AM

Clamped factory gasket so you can't measure a new one.

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: dryenko ()
Date: November 04, 2017 05:41AM

So maybe measure a used one???

Bob C aka Dryenko
Dobson, NC 27017

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: davemotohead ()
Date: November 04, 2017 06:59AM

I just took one apart and can measure the squashed gasket, But if the manual says to do the measurements with no gasket then they must have taken into consideration the gasket compressed thickness when figuring out the Shim stack tolerances.





Email me at: Dave Motohead

1960 4dr sedan caveman car
1961 Rampside (Chetside)
1962 Rampside (Barnside)
1962 Short Rampside (Shortside)
1962 Monza 700 Wagon
1963 Monza 900 coup (General Nader)

-----------------------------------
Rust Free Lancaster Ca

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: GWLee ()
Date: November 04, 2017 07:06AM

I could have given you the old gasket measurement, but I disposed of it last week. I just did this to my transaxle a month or so ago and was going to keep the old gasket but decided there was no reason too!

On the shims needed, check your measurements first, you may not need anymore. If you do, then find some. You will then know what thickness you will need, since they come in different sizes.

Lee Adkins

A Cave Man car
1960 2dr Coupe with pg
Color Tasco Turq.
With Ermine white top.

Catlettsburg,
In the Beautiful state of
North/East KY!

Not the best pic, but the only I had from then, 1997!

2016!

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: Darrin ()
Date: April 17, 2018 04:52AM

Excellent write up and pics Dave.

I have a question about outcomes. I have made this measurement three times now and every time the factory stack of two shims measuring .032 in. each brought the assembly to spec. I checked the remaining four pg differentials I have sitting around and all had two shims same size.

The danger seems to be too little clearance and the factory stack addresses that and seems to work in every case.

Do any of you have experience checking this measurement and found that the factory stack of two shims was not in range?

I always check, but think that maybe this is not much of a risk as long as factory shims are in place. I have never had to replace with thinner or thicker shims, but have only looked at a few of these. Maybe that is why Clark’s does not sell them in multiple thicknesses?

Any horror stories when factory shims were used and problems followed?

Darrin Hartzler
Bethesda, MD

Corvairs in two states of the Union and varying states of disarray.

Northern Virginia Corvairs & Group Corvair

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: davemotohead ()
Date: April 17, 2018 08:03AM

Hello Darrin, if you read the shop manual it gives over 7 specs for shim stacks, from .025-.046 needing no shims to .143-.155 needing 7 -.016 thickness shim spacers to bring into spec, I agree most you take apart have 2 shims of a mixture of .016 and .032 shims, BUT, I have taken a lot of these apart, and have found some have 1 shim and have found some that have up to 4 shims, There are a lot of factors involved including the diff shims that affect how far the diff pinion shaft protrudes, AND the selective thrust washer on the front clutch hub as noted below the shim chart in the manual, the clutch hub thrust washer comes in either a .050 or .075 thickness and affects the over all internal running clearance as well, so as noted in the manual, if your reading is below the .025 spec your running clearance is too tight and you need to change the front thrust washer from a .075 to a .050 or if your running clearance is above the max of .155, you need to change the front thrust washer from a .050 to a .075 to tighten up the clearance needed to get within spec, Also I have found when swapping diffs or transmissions the spec will change, or rebuilding a diff with new gears and bearings the specs will change as well as rebuilding a PG the specs will change, I recently did a diff swap and found 1 shim from factory but needed 3 shims with the new diff, and When I recently rebuilt both a trans and diff with new parts the original 2 shims would put me way too tight and in fact with all new internals on both the diff and trans the spec was too tight with no shims, so I changed the front thrust washer from the NOS .075 that I installed when building the trans to the smaller .050 thrust washer and that brought me into spec and needed 1 shim, I think the factory measured the specs and marked them and mixed and matched diffs and transmissions to fall within the 2 shim range, but when you start swapping diffs and trans, AND when things start wearing out the spec will change, AND remember the shims are 2 different sizes, so if it has 2 .016 shims you have a total of .032 clearance, and if you have 2 .032 shims you have a total of .064, so even though there are only 2 shims, the spec will be different because the shims are not the same size. Also, there is another J-Tool used when preforming a rebuild without removing the trans from the car, that measures the clearance from the other end of the trans and tells you what selective thrust washer is needed to maintain the correct clearance on the other end that is still bolted to the car, GM would not have gone into such detail and had 2 different tools made to check this clearance from either end of the Transmission, and made different thrust washers on one end and selective spacers on the other end and a chart of 7 different specs and shim stacks if this was not very important, Hope that clears things up. smoking smiley





Email me at: Dave Motohead

1960 4dr sedan caveman car
1961 Rampside (Chetside)
1962 Rampside (Barnside)
1962 Short Rampside (Shortside)
1962 Monza 700 Wagon
1963 Monza 900 coup (General Nader)

-----------------------------------
Rust Free Lancaster Ca



Edited 1 time(s). Last edit at 04/17/2018 08:04AM by davemotohead.

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Re: HOW TO : Figure out the correct shim stack for a PG to Diff mating.
Posted by: Darrin ()
Date: April 17, 2018 01:24PM

Thanks Dave, exactly what I wanted to learn...based on your experience. Will keep measuring when I do a new PG/Diff mating ceremony!

Clearer to me now where the variation comes from.

Much appreciated.

Darrin Hartzler
Bethesda, MD

Corvairs in two states of the Union and varying states of disarray.

Northern Virginia Corvairs & Group Corvair

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