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Discussion Starter #1
So I bought this twelve bolt that fits a first gen Camaro or third/fourth gen Nova with multi-leaf pockets and come to find out an open 3.08 gear set, when I opened it up I found this, looks like the drivers side carrier bearing shims came part way out of their spot and got eaten by the axle and turned into C-shapes. The rear cover seems to be the only thing to have kept them in as far as they were still. When I took the carrier out I could'nt really see what holds the shims in place to begin with.

Is it just the tight fit of the carrier bearings against the shims that hold them in? Or is there a missing part here? Why did this happen? Also looks like the drivers side main cap is worn on one side irregularly too. The passenger side had two shims as well but one of them was over a quarter inch thick, these were in place as normal, I think.

Man I'm stoked to get this 12 bolt though! I'm tired of thinking about wether or not to get one.








 

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Discussion Starter #2
to my untrained eyes it appears that the carrier bearings are intact and unharmed and the races appear normal, but here is the main cap off the offending side.


 

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Discussion Starter #3
after reading online about this shim issure, it seems like its a common 12 bolt problem. Some bearing caps have tangs that prevent the shims from coming out. Most articles recommend a very tight carrier to housing preload as well. Then there are "Super Shims" that have a disign that prevents this form happening.
 

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after reading online about this shim issure, it seems like its a common 12 bolt problem. Some bearing caps have tangs that prevent the shims from coming out. Most articles recommend a very tight carrier to housing preload as well. Then there are "Super Shims" that have a disign that prevents this form happening.
The carrier shims are there to adjust the backlash for the R&P once backlash is set the person doing the install should add .005 shim to both sides of the carrier for carrier bearing preload. the shims should be driven in with a shim driver, the pressure between the race and housing should hold the shims in place. it would appear to me that there wasnt enough preload on the races and it allowed the shims to move.
 

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after reading online about this shim issure, it seems like its a common 12 bolt problem. Some bearing caps have tangs that prevent the shims from coming out. Most articles recommend a very tight carrier to housing preload as well. Then there are "Super Shims" that have a disign that prevents this form happening.

I just did my 8.5 a couple months back and like you stated it has the tangs which stop the shims from coming out. I used two thick shims on each side and sandwiched the thin shims between the two and drove the thick shim in tight.
 

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Discussion Starter #7
So the super shim set locks the shims together? but can the shims still come out or does the design of the super shim lock the shims into the start of the axle tube bore??


whats a shim hammer look like?
 

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So the super shim set locks the shims together? but can the shims still come out or does the design of the super shim lock the shims into the start of the axle tube bore??


whats a shim hammer look like?
It can't lock it into the axle tube or you wouldn't be able to get it in there unless using a case spreader perhaps. I am guessing by the design it just keeps the small in between shims from working their way out. Never used them though. I used my thick shims and thin shims in between them. Hammering the thick shim in as you can't tap the thin ones in or they will bend.
 

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Discussion Starter #9
interesting, thanks for the help. gonna look up some aftermarket bearing caps and see if they have this overhanging tang design. I might want to change to billet caps anyways for extra insurance against breakage.

Its funny how the 30 spline twelve bolt axles are basically the same taper as a 28 spline ten bolt axle, the 30 spline axles splined area is just a bit larger
 

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interesting, thanks for the help. gonna look up some aftermarket bearing caps and see if they have this overhanging tang design. I might want to change to billet caps anyways for extra insurance against breakage.

Its funny how the 30 spline twelve bolt axles are basically the same taper as a 28 spline ten bolt axle, the 30 spline axles splined area is just a bit larger
Can you change to billet caps without having a line bore done?

I went with the 30 spline Moser axles as I installed an Eaton posi with 30 spline. These 30 spline axles are nice and beefy compared to the original 28's. Good luck with it.
 

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you would have to have the housing line bored. I would just get a T/A cover for the 12 bolt and not worry about the aftermarket caps. if you have the correct amount of preload on the bearings they should not move around in the housing. The supershim kit does not lock into the housing but locks all the smaller shims together
 

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no line bore but all billet caps have to be fitted by surface grinding the cap to fit. Very time consuming and can get expensive. Sometimes I will take a pointed punch and peen over the edge of the housing next to the shim to make the housing have an overhang to keep the shim from walking out. Also you can figure out what thickness the shims need to be and press them under the bearing instead.

Miles
 

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Discussion Starter #14
well, unfortunately upon further inspection the bearing cap in question appears damaged with a deffinate groove and wear marks in it, and corresponding wear marks in the housing where the bearing race is sposed to live. Will take pictures and post tommorrow. There is a sharp ridge in the housing I'm guessing the roller bearing and or the roller bearing cage rode on the housing itself instead of the race as it backed out of the area it was sposed to be in because the shims walked out. its possible that the bearing race spun in the cap area as well causing the groove.
 

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Yes that can happen as well. A spun housing is never good. Depending on how bad it is you can peen the cap & housing and use bearing retaining locktite but once it's spun... Well it's spun. If you press the shims under the bearing that should move the race out further on the cap so it will contact the good area which may help save it as well.

Miles
 

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Discussion Starter #16
Took the housing to Bill Scribner of Scribner welding and distributing in Kent today. I am thoroughly impressed by his work. His welding examples and fabrication work are top tier. Mr. Scribner advised me that the use of bearing loctite after changing to a different cap on that side would save the housing.

So he is welding the tubes to the center housing, gusseting the spring pockets, fixing the offending bearing cap and sending the housing to his set up guy for 3.73's, 30 spline Moser axles and an Eaton clutch Posi. I decided to stay with C clips for this housing as I have now learned that the GM housing is inferior in almost every way to an aftermarket 12 bolt housing and one of those may be in my future and at that time I hope to have a custom 4 bar style setup and mini tubs to fit a shortend housing with much bigger than the 255mm tires I have now. So a beefed up stock style 12 bolt is good for now.
 
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