toomanygasfumes

Need a little help yall. Got a 85 TA rear I would like to know what size it is. I dont really care what the ratio is due to the fact I will be changing the ring and pinion. I am almost sure the size is GM 8.875. Am I correct on that size. Also give me some ideas on a decent mid range ratio. Motor is a 355 Carbureted (screw the v6, OLD SCHOOL BABY) and trans is a th350, I am thingking about a 3.73:1. Thanks!!!

sofakingdom

iTrader: (1)

No, absolutely not.

It's either a 7½" 10-bolt or a Borg-Warner 9-bolt.

Count the cover bolts. If there's 10, it's a 10-bolt. If there's 9, .... you do the math.

JamesC

iTrader: (5)

[QUOTE=toomanygasfumes;5088079Also give me some ideas on a decent mid range ratio.[/QUOTE]

Welcome to TGO, toomany.

Mid-range? Probably 3.23's or 3.42's (both are 10-bolt gearing, though the 9-bolt is close). Should the rear prove to be a 10-bolt, the FAQ below may answer any questions you may have:

https://www.thirdgen.org/forums/tran...-10-bolts.html

Info on the 9-bolt:

https://www.thirdgen.org/forums/faq-...now-about.html

JamesC

toomanygasfumes

James, thank you great to be here, and thanks for the info.

Sofa, Ok thank you. I could have made an ordering mess up there.

Another question when it comes to a rear diff is there a way to messure it to see what size the rear is ie 7.5", 8.8", ect. (meaning what to mesure and from what point to what point)

Drew

iTrader: (58)

No need... If it's a 10 bolt, it's a 7.5", if it's a 9 bolt is 7.75". There were no other rears used in 85. The measurement is of the ring gear inside the differential.

sofakingdom

iTrader: (1)

The 8.875" is the old 12-bolt; last year for that was around 1972. You definitely won't have that.

There was a 8.2" 10-bolt. Last year for that was about the same. You won't have that either.

There was/is a 8.5"/8.6" 10-bolt. That came in ALOT of cars including 2nd gen F-bodies and is still used in trucks, but was never used in these cars. You won't have that either.

The only 2 rears ever used in these cars were the 7½" 10-bolt (starting in about 87 or so they upped the OD to 7.625", but all parts interchange, and all replacement gears are 7.625" nowadays, so for all practical purposes it's the same rear) and the B-W 9-bolt which has a 7.75" ring gear as stated.

There's no need to actually physically measure anything to identify what parts you need, other than knowing whether your current ratio is in the 2 series range or the 3 series range. Pop the cover off, count the teeth or look on the edge of the ring to get the ratio.

Most likely you will find you have the 9-bolt and most likely a 2 series, but the only way to know for sure is to look.

toomanygasfumes

Sofa,
thank you for all the info I appreciate you going over the older rears also that will help me when I start me 79 z. The only reason I was asking was just in general for any rear there are so many diff sizes out there that if there was a way to mesure them or be able too know what they are just by doing x that would be a cool thing to know. But still thanks for helping a young buck out.

sofakingdom

iTrader: (1)

Easiest way to identify a rear is not by measuring, anyway; it's by looking at the cover gasket. For example http://www.drivetrainspecialists.com/categories/gm/

A 79 Camaro would have come with the 8½" 10-bolt. That's the only rear they used in those.