69 GP Rear Diff. question
 

What would have been the most common Rear Diff. for a 69 GP.Model J ? I have the PHS information on my car ,but it doesn't state what rear it has . I thought they all came with a limited slip . If someone can shed some light on this ,I'd really appreciate it .

Owned a '69 GP Model J a while back, it was a 400 auto trans car with A/C. I'm guessing most would have been oedered by the dealer or individuals equipped that way since it was a luxury car.

It had a 3.23 open rear, I opened up the diff and replaced the gear lube so I know it definitely didn't have a Safe-T-Trac posi unit.

69 GP rear end
 

you can find out the rear end on your car one of several ways.

1. get the PHS on the car and see what it came with
2. get the car up in the air and look on the axle housing on the left side. You may need to take a wire brush. You are looking for a two letter code. first letter is either "U" or "V"
V = posi-trac, U = open.
The second letter tells you the gear. Look in the service manual. Example UF = 3.08 open
Also the inside of the brake housing on the drivers side rear will have the code as well.
3. Get the car up and turn the wheels to count the revolutions on the shaft.

Yes, certain rear ends were std with certain engine packages. 428's usually got a higher gear. A 428 HO car with A/C would have likely had a 3.42 or 3.23 rear. I don't think a posi was std on anything. You had to order that.

69GP Rear End
 

Is it on the backing plate ? I read somewhere that it is on the Drum . I checked that and the #'s don't make any sense . Like something is missing ! They have probably been changed out at some point . Thanks for the info !

I've parted out a lot of GPs over the years, mostly 428 cars.

Most of the 428 cars I dismantled had 3.23 rear ends. I live in NC, so most were open rear ends. The limited slip rear ends I've encountered were mostly out of manual transmission cars and 428HO cars.

I found a 69 GP 400 car with a 2.92 limited slip rear end. I also found a 69 428HO 4-spd car with a 3.55 limited slip.

I've seen a lot of 3.08 rear ends in the 70-72 400 cars.

Hope this helps.

Mike

All 69 GTO/GP cars that were optioned with A/C the highest gear Pontiac put in them was 3.23 . This was irregardless of engine 400/428 in the GP. The standard GTO 400 and RA III cars were same too, but on the RAIV GTO they got 3.90 gears were standard .

If the car was not A/C and non optioned for rear gear than standard were 3.55 ratio open.
And could be optioned with 3.23 open or 2.92 open etc.
The Safe-T-Trac could be added to all ratios from 2.92, 3.23,3.55 rear ends.
But even if the Axle performance option( 3.90 gear) was ordered then it still shows the
Safe-T-Trac option on PHS.

Mike is correct the 3.08 is very common 70-72.

I would as blu bomber says look on axle for some codes of try rolling rear wheels to determine.
Ben : Do you have your PHS ?

Dave

It was a sticker if the rear came with that.
(some years had it, but would have to look it up for which ones)

:)

When all else fails you could drop the cover and count the teeth and change lube while at it.
Wipe spot off on R&P and mark a tooth with something for reference.. Done that many a time...;)

Pontiayak,

For some reason, I don't think I ever pulled a 3.08 out of a 69 Grand Prix. I would estimate about 75% of the cars I parted were 428 cars with a/c, and just about all of those came with 3.23s, both open and limited slip.

The few 1969 400 powered cars I picked up had 2.92s. In 1970, the 3.08s were more common than the 3.23s. I think part of the reason is the 455s had 12-bolts, so I didn't part that many 400 cars.

Mike

If you go to the trouble of removing the cover the number of teeth for both of the gears is stamped on the edge of the ring gear. Just divide the smaller into the larger to get ratio.

69 400 Auto with AC, 99% chance it's a 2.93.

69 Rear Diff. question
 

Hey Dave , I do have the PHS Doc. ,but it doesn't have any rear end info on it . I think the inspection cover is going to have to come off to get this solved . Thanks for the info !

69 GP rear Diff. question
 

My 70 4 speed G.P. has 3:31 ratio with a 12 bolt. Have owned several of these cars but this is the 1st one with this rear diff. All others have been 10 bolt with 3:23. Just my 2 cents.

If original pig/rear still in it, I would bet 3.55 if no air . And 3.23 if has cold blowing a/c .