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differential problems.. HELP PLease

Joined
Oct 7, 2006
Messages
295
Location
South Dakota
Corvette
76 Coupe
Several problems with my differential.

1) 3 of the 4 bolt holes for the strut rod mounting plate are stripped and will not tighten securely. they are 3/8 16 thread bolts. It appear to me to be a fairly beefy pad where the bolts go,(drill out and helicoil back to the 3/8 bolt size) so was wondering if using a heli-coil would hold sufficiently rather than buying a new diff carrier case.

2) What is my gear ratio? original equipment was 4 speed, L48. I am not sure if I still have the original guts in the differential. I counted 37 teeth on ring gear and 12 pinion. the book says i should have 355 with manual tranny, i think is 3.08, picture has the GM numbers on the ring gear.

3) how can you tell if the side yokes need replacing? they do slide in and out less than 1/8 inch. there is some play in the splines (about the same as you feel for backlash between the pinion and ring gear when you turn the front yoke.)

4) Is there anything else i should consider since i have it all shredded apart?
 

GTR1999

Well-known member
Joined
Sep 4, 2003
Messages
1,146
Location
New Haven CT
Corvette
1969,1972,1975
Several problems with my differential.

1) 3 of the 4 bolt holes for the strut rod mounting plate are stripped and will not tighten securely. they are 3/8 16 thread bolts. It appear to me to be a fairly beefy pad where the bolts go,(drill out and helicoil back to the 3/8 bolt size) so was wondering if using a heli-coil would hold sufficiently rather than buying a new diff carrier case. You have to check close to see if you can repair them if they are stripped out. I'm not crazy about Heli-Coils but sometimes they're the only game in town. If there is room I like the solid inserts better. I would have to really see the housing to determine.

2) What is my gear ratio? original equipment was 4 speed, L48. I am not sure if I still have the original guts in the differential. I counted 37 teeth on ring gear and 12 pinion. the book says i should have 355 with manual tranny, i think is 3.08, picture has the GM numbers on the ring gear.You have a 308 gear ration. A 336 or 355 would be better off the line then 08's but they offer about 200-300 RPM better crusing. I setup a 273 for a 76 L48 and ST-10. The guy really likes it too.

3) how can you tell if the side yokes need replacing? they do slide in and out less than 1/8 inch. there is some play in the splines (about the same as you feel for backlash between the pinion and ring gear when you turn the front yoke.)1/8 is .125 and way too much. The yoke ends should be measured from the end to the clip, should be .180-.187. Doubt they are, if you have more then 030 endplay in the yoke,not the posi side gear, replace them. They were case hardened to 030 only and the mid 70's were poorly done.

4) Is there anything else i should consider since i have it all shredded apart?
You should check the posi case for cracks,replace the clutches with solid steels at a minimum. Me, I would rebuild it and polish & tune the posi,fit the yokes to 005 endplay, tap it for a drain, fit the caps,use ARP RG Bolts,and install new gears if you have more then 010 lash. GM gears were set to 005-006. Richmonds are set to 008-010.
Exchange units don't offer a lot of those things so I would read my thread on the job if you are thinking about doing it at home.
Me, without a lathe, surface grinder, and Bridgeport wouldn't do one~ but many do.:eek:hnoes
 
Joined
Oct 7, 2006
Messages
295
Location
South Dakota
Corvette
76 Coupe
I was hoping to only have to spend about 6 or 7 hundred bucks for this. Budget is so tight at my house. I do not have all the special tools and equipment, but I am adventureous SOMETIMES !!!!!
 

Hib Halverson

Technical Writer for Internet & Print Media
Joined
Jan 10, 2001
Messages
13,453
Location
CenCoast CA
Corvette
71 04 12 19
First, don't use Helicoil on that. I'd use a product called "TimeSert". For that applcation is a much stronger thread repair.

Second, a 3.08 axle is extremely rare with a manual in any C3 and was not offered in 76 at all. At sometime in the car's life it must have had the axle ratio changed. You'll see a hube improvement in performance if you go back to the stock 3.55 ratio.

Third, an 1/8" end play for the side yokes way large. The axles or the diff housing is toast. Since you have the wrong ratio, anyway, you might as well overhaul the axle.
 

GTR1999

Well-known member
Joined
Sep 4, 2003
Messages
1,146
Location
New Haven CT
Corvette
1969,1972,1975
$600-$700 isn't going to get you much. Look at the cost of the parts alone and you're in your budget range. You can buy an exchange unit, they consist of a master kit and clutches,nothing else and are in the budget range you want. They are fast rebuilds so don't expect much other then a stock job. Add in the cost of gears, yokes and you're into $1000 for base work. You can take a chance on a used diff but that spinning the wheel of luck. If your housing is bad, and chances are a rebuilder will not take in a housing with stripped out holes, you'll have to add another $300-$500 core charge to the mix.
From the sound of it, a good used diff then maybe a master kit and posi kit are your best option to stay in your budget but you'll have to do the work. Be sure to look it over real close and follow my thread on the work.
Good luck
 

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