Rear end Woes...

[aggie97]

So we were almost finished restoring this 87 we bought back in March and I am hearing a pretty good whining coming from the rear, usually while a load is applied and not coasting. Figuring it's the bearings going out so it's time to rebuild the entire rear end and put an eaton in this sucker.

I've figured out we have 2.73's which I think are stock? I want to put in an eaton as I have had good luck with them and the car is destroying one tire at about 25mph and beyond.

Might consider putting in 3.42's but unsure what all will need to change? Will the chip need reburned or do I need to find correct speedo cable gears to swap in? Car has a decent stall, maybe 3000 or so and rolls out very well on the 2.73's but If the ring and pinion are hosed up, we might as well upgrade right?

Thanks!

 

[87GNSteve]

Stock ratio was 3:42.
Did you verify that you have a 8.5 rear or the 7.5?

 

[aggie97]

I'm a ford guy...explain how to identify. I basically turned the driveshaft about 2.75 times to get one rotation on the rear wheel. might explain why the speedo seems off. I've fixed most of the previous owner's hodgepodge of parts and bad fitting exhaust. Rear end and an alignment should have this thing in tip top shape. Would love to go to 3.42's so this thing would get off the line better. It loafs a bit then hauls ass once it build boost.

 

[challengermike]

A whine on and off the gas is going to be a gear noise.So seeing the gears need to be changed i would put the stock ratio of 3.42s in it.

 

[Slow91z]

Look at the cover and match it up Here

Short answer if the cover is round it's a 8.5 if it's kinda squared off it's a 7.5 POS.

 

[87GNSteve]

Its not the cover to look at its at the bottom of the housing under the cover.
The 8.5 has the squared off ends and the 7.5 has little "horns" or "hooks".
The link attached has a picture of them but it is small.

 

[aggie97]

Its not the cover to look at its at the bottom of the housing under the cover.
The 8.5 has the squared off ends and the 7.5 has little "horns" or "hooks".
The link attached has a picture of them but it is small.

based on that description in the link, it looks like the second 10 bolt with the larger "Ears" showing outside the diff cover on the bottom. So it appears it's an 8.5" which is good...now to just find an eaton to fit it. I guess we will go ahead and put the 3.42's back in it... I threw out a set from the camaro.

Were 3.42's standard on ALL 87 GN's? LSD's standard? I know of a wrecked car up in Rowlett that was looking to sell as a whole or part out. Maybe I need to find out if he still has the complete axle with LSD and 3.42's! I probably then need to find out if the speedo is accurate now.

Thanks.

 

[charlief1]

based on that description in the link, it looks like the second 10 bolt with the larger "Ears" showing outside the diff cover on the bottom. So it appears it's an 8.5" which is good...now to just find an eaton to fit it. I guess we will go ahead and put the 3.42's back in it... I threw out a set from the camaro.

Were 3.42's standard on ALL 87 GN's? LSD's standard? I know of a wrecked car up in Rowlett that was looking to sell as a whole or part out. Maybe I need to find out if he still has the complete axle with LSD and 3.42's! I probably then need to find out if the speedo is accurate now.

Thanks.

The 8.5" rear is exclusive to turbo Buick cars from 84 to 87 and the Hurst olds. No other rear will fit unless you buy after market.

All the Camaros after 82 had 7.5" or 7 &5/8" except for the Aussie 9 bolt. They won't fit. You can adapt an early A/B body rear but it will be longer than stock so there's that to consider.

The other option here is to drive up to Hillsboro and buy the ford 9" I've got Made to fit the metric chasis.:biggrin: 3.5 gear and a mini spool so it's just about like having a stock rear. PM me if you're interested.:smile: