68 tempest
68 tempest
Im looking to up grade rear end on my 68 tempest. It was a 6 cyl car originaly and now has a 455 in it. So i believe the 10 bolt thats in it now would be a 8.2? would like to have a posi 8.5 or a 12 bolt posi in it. was wondering what you would suggest. Also are the posi units changable between 8.2 ,8.5, or the 12 bolts? Thanks Mike
Re: 68 tempest rear diff swap questions
Mike, Glad to see you using the site...
Ok, so first thing is if your NOT going to be do any track time the 8.2 10 bolt freshen up with new bearings and posi etc will more than do the job on the street and even some trac duty as long as the car does not get the clutch dumped above 3500 rpms with slicks on a sticky track.
-10 bolt 8.5 is an excellent choice and will also give you that almost same look as a tempest rear...If your trying to keep it looking stock.
-10 bolt 8.5 uses the same size pinion shaft as the 12 bolt Chevy diff which is what makes it one of the strongest GM rears for cars and light trucks.
-10 bolt 8.5 also has the desirable BOLT IN axle system as your Pontiac rear (28 spline stock can be upgraded with MoSER axles to 30 spline WE STOCK THESE... )giving you the confidence that if a axle does snap the axle will be retained in the housing and NOT ruin a 1/4 panel.
-10 bolt 8.5 has 10 bolts holding the ring gear to the carrier unit (larger 7/16" x 20 thread count per inch)
-12 bolt chevy is again a great choice...getting more expensive and harder to find in unmolested conditions.
-12 bolt has a slightly bigger ring gear at 8.875 which will keep the heat down on long hauling and freeway driving.
-12 bolt has an extra 2 bolts holding the ring gear steady too (3/8 x 24thread count) smaller than the 8.5
-12 bolt has the 30 spline axles and held in with c-clips (can be bad news if the axle breaks because the axle will slide out of the housing and tear up a rear 1/4 panel and maybe cause a accident too.)
So all in all the 8.5 10 bolt will be cheaper to build and will give you good strength for the street and strip applications
The 12 bolt will be more expensive and give you good resale value to your car and of course be strong.
10 bolt 8.2 - we can get you 3.36 3.55 3.73 3.90 gears and posi units to build up that rear also if you really do not think your ever going to need the strip strength. I have had GUYs test the 10 bolt 8.2 with 455 Buick and Pontiacs even at the track with NO issues. 12.0 cars that were mostly street bound but have had the slicks on to race.
Ultimately it is your choice on the rear and what you think you will need. We can guide you the best we can with the info given.
Ask yourself what you will be doing mostly with the car...you should not be too far in wish mode when answering this question but be realistic in the time spent RACING...lol. Everyone thinks they will race ever weekend but end up only getting there a few times in the cars life.
I hope some of this info has helped and keep the questions coming if you need more help figuring the right rear to choose. Jim
Ok, so first thing is if your NOT going to be do any track time the 8.2 10 bolt freshen up with new bearings and posi etc will more than do the job on the street and even some trac duty as long as the car does not get the clutch dumped above 3500 rpms with slicks on a sticky track.
-10 bolt 8.5 is an excellent choice and will also give you that almost same look as a tempest rear...If your trying to keep it looking stock.
-10 bolt 8.5 uses the same size pinion shaft as the 12 bolt Chevy diff which is what makes it one of the strongest GM rears for cars and light trucks.
-10 bolt 8.5 also has the desirable BOLT IN axle system as your Pontiac rear (28 spline stock can be upgraded with MoSER axles to 30 spline WE STOCK THESE... )giving you the confidence that if a axle does snap the axle will be retained in the housing and NOT ruin a 1/4 panel.
-10 bolt 8.5 has 10 bolts holding the ring gear to the carrier unit (larger 7/16" x 20 thread count per inch)
-12 bolt chevy is again a great choice...getting more expensive and harder to find in unmolested conditions.
-12 bolt has a slightly bigger ring gear at 8.875 which will keep the heat down on long hauling and freeway driving.
-12 bolt has an extra 2 bolts holding the ring gear steady too (3/8 x 24thread count) smaller than the 8.5
-12 bolt has the 30 spline axles and held in with c-clips (can be bad news if the axle breaks because the axle will slide out of the housing and tear up a rear 1/4 panel and maybe cause a accident too.)
So all in all the 8.5 10 bolt will be cheaper to build and will give you good strength for the street and strip applications
The 12 bolt will be more expensive and give you good resale value to your car and of course be strong.
10 bolt 8.2 - we can get you 3.36 3.55 3.73 3.90 gears and posi units to build up that rear also if you really do not think your ever going to need the strip strength. I have had GUYs test the 10 bolt 8.2 with 455 Buick and Pontiacs even at the track with NO issues. 12.0 cars that were mostly street bound but have had the slicks on to race.
Ultimately it is your choice on the rear and what you think you will need. We can guide you the best we can with the info given.
Ask yourself what you will be doing mostly with the car...you should not be too far in wish mode when answering this question but be realistic in the time spent RACING...lol. Everyone thinks they will race ever weekend but end up only getting there a few times in the cars life.
I hope some of this info has helped and keep the questions coming if you need more help figuring the right rear to choose. Jim
J D Race
Re: 68 tempest
Jim thanks for all the info, and from what it sounds like I'm just going to stick with 8.2. I dont have any plans at the moment to use the car at the strip. Can you put 8.5 posi in a 8.2?? And what gears would you suggest. Mike P.S. Jim are you guys in northern Ohio?
Re: 68 tempest
Oops forgot that question.
The 8.5 posi does not fit the 8.2 housing. You will need a 8.2 buick olds or pontiac posi unit.
Reasons for the 8.5 NOT working.
-carrier is too wide
-the series ring gear flange is not correct
-axle splines are different...60 degree compared to 45 degree 8.5 axle shafts will be loose in the 8.5 posi unit
-ring gear bolts are different 3/8" 8.2 compared to the 7/16" 8.5
Hope this helps.
I have Auburn and Eaton posi units in stock and gears too
Question is what do you do with the car most freeway cruise burnouts light to light action??? What transmission do you have 350th 400th overdrive manual etc. What size tires overall diameter ex. 26 27 28 " etc. Then we can help pick a gear ratio
The 8.5 posi does not fit the 8.2 housing. You will need a 8.2 buick olds or pontiac posi unit.
Reasons for the 8.5 NOT working.
-carrier is too wide
-the series ring gear flange is not correct
-axle splines are different...60 degree compared to 45 degree 8.5 axle shafts will be loose in the 8.5 posi unit
-ring gear bolts are different 3/8" 8.2 compared to the 7/16" 8.5
Hope this helps.
I have Auburn and Eaton posi units in stock and gears too
Question is what do you do with the car most freeway cruise burnouts light to light action??? What transmission do you have 350th 400th overdrive manual etc. What size tires overall diameter ex. 26 27 28 " etc. Then we can help pick a gear ratio
J D Race
Re: 68 tempest
yikes sorry, Its has 400th 26 dia tires. Cant say it wont get on the freeway but will mostly be around town/weekender.
Re: 68 tempest
Jim also forgot to ask how much parts would be?
Re: 68 tempest
POSI UNITS ARE IN THE STORE AND GEARS SHOULD BE LISTED TOO.
Posi is 389.00 (2.93-3.23 or the 3.36 -4.33 carrier)
gears are 199.99 (3.36, 3.55, 3.73, 3.90)
rebuild kit is - 74.99
Rebuild kit includes as follows:
2 carrier bearings and races
1 inner pinion bearing and race
1 outer pinion bearing and race
1 Pinion seal
1 pinion crush sleeve
1 pinion nut
1 rear inspection cover gasket
1 carrier pack of carrier shims
1 pinion pack of shims
1 marking compound and applicator brush
10 ring gear bolts
1 booklet to help you with your set-up pattern and torque specs.
Posi is 389.00 (2.93-3.23 or the 3.36 -4.33 carrier)
gears are 199.99 (3.36, 3.55, 3.73, 3.90)
rebuild kit is - 74.99
Rebuild kit includes as follows:
2 carrier bearings and races
1 inner pinion bearing and race
1 outer pinion bearing and race
1 Pinion seal
1 pinion crush sleeve
1 pinion nut
1 rear inspection cover gasket
1 carrier pack of carrier shims
1 pinion pack of shims
1 marking compound and applicator brush
10 ring gear bolts
1 booklet to help you with your set-up pattern and torque specs.
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J D Race