: Rear End

02-20-05, 04:40 PM
How do you change the gear oil in the rear end of a 69 Fleetwood (Hearse)? Are they even servicable? My service manual talks about wheel bearings and such but nothing about the differentials gear oil? Thanks

lux hauler
02-20-05, 05:24 PM
If I'm not mistaken, your car has a 12-bolt rear.

Unbolt the cover to drain and refill it through the removable plug. Be sure, if it's a posi rear (as I understand it, all commercial chassis cars were), to add the posi additive with the new differential oil.

02-20-05, 06:52 PM
Just got under the car and looked. Could only get so far under it. Did find the add/check plug. It is located on the rear of the differential. So loosen all the nuts on the front of the diff. then "crack the seal between the two parts and that is how to drain? What about pumping it out with a hand pump through the plug? The front is a big piece that ties into the yoke for the driveshart. looks like it's all one piece. Any way to tell if it's posi? When I have both wheels off the ground and turn one wheel they both turn? Can't remember.

lux hauler
02-20-05, 07:30 PM
is there a cover bolted to the back-side?

02-20-05, 07:31 PM
Ok I was looking a little deeper in my service manual and came up with this regarding the diff. and the two types in 1969.


and also this regarding the fluid change.

Hope this helps others with the same question. My car is a 698 series. Commercial Chassis. Thanks.

02-20-05, 07:37 PM
No cover bolted to the backside. Tomorrow I'll jack it up and see if it is a controlled diff. or not. Remove the drain plug and check the level and go from there. Just routine maintenance. I don't know the last time it was checked before I owned it. I've had it for 10 or 11 months now. Thanks.

lux hauler
02-20-05, 07:42 PM
I was under the impression that all late 60's through '76 or so Cadillacs had 12 bolt rears.....looks like that may not be so.

Can anyone ID that carrier?

02-20-05, 07:47 PM
If you read in the general description I posted these were the carriers used in 69. The only difference was gear ratio designated by a number 1 or number 2. Also whether it was a Standard or Controlled diff. designated by the letter G before the number 1 or 2. The letter G denotes a Controlled Diff. That's what I'm looking for. According to the chart I posted in the 698 series the number "2" diff was used which was a gear ratio of 3.21-1. All I need to know now is if there is a G stamped in front of it or not. Then I'll know which lubricant is needed.

03-04-05, 03:04 PM
I was wrong in my last post the number "1" differential was used in the 698 series and had the gear ratio of 3.21-1. Got under my car today and there is no letter G stamped in front of the "1" so therefor I have a standard differential and can use SAE 90 multi purpose type gear lubricant conforming to MIL-L-2105-B.

03-07-05, 05:32 PM
I think GM started putting the 12 bolt rear covers on in 1969. My 1968 is a solid stell housing, inly one fill plug at the top. You have to pump out the old fluid to replace it.

There are no identifiers that I can see as to whether or not it has controlled diff, but I think i remember spinning one weel and the other going in the opposite direction, indicating a "regular" diff, not the controlled or limited slip one.

03-09-05, 06:44 AM
My service manual is issued by GM and covers all 69 Cadillacs including Eldorados. According to it this is the only diff. used in 69 other than the 693 series. Check the diagram I posted it shows where there should be a number 1 or 2 stamped on the diff. If proceeded by the letter G it is controlled. Mine was a little hard to see but it was there.

Night Wolf
03-09-05, 11:27 AM
The 1969 Eldorado (or any Eldo since 1967) did NOT have a rear diff....

03-09-05, 03:31 PM
That is correct. I meant that the service manual I have covers the Eldo not that it had that diff. As a matter of fact if you look at the last picture I posted from my manual titled 11. Differential (except 693) The 693 series was the Fleetwood Eldorado.


[url="http://www.theimagehosting.com/"]http://images5.theimagehosting.com/CadillacSeries0002.jpg (http://www.theimagehosting.com/)
http://images5.theimagehosting.com/CadillacSeries0001.2.jpg (http://www.theimagehosting.com)

03-17-05, 10:56 AM
When it comes to Positraction Rear Differentials , on GM Products, in my shop, the only thing we use in there for Posi-Lube is the GM rear end treatment. I tried some of the other stuff from a Western Auto store, and it worked ok for 3 weeks and then the positraction would scream when engaged. The customer, a relative of mine, took the car back, and the ONLY thing different that I did that day was instead of driving 20 miles to the nearest GM dealer, I bought it at the parts house down the street. I regretted that so much I drove to the a Chevy dealer that day and got it straigtened out.
Thanks, Dave

03-17-05, 03:52 PM
That damn thing..... I'm interested in finding out if a 12 bolt from a later deville will bolt up. Back in '68 they didnt make parts for it (a non-servicable unit) and im sure they didnt start anytime lately. Want to change ratios? Can't. Want to upgrade to a Posi or a locker? Can't. (though I have the factory one :nyanya: )