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81 Sedan DeVille 8-6-4
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Discussion Starter #1
I pulled the cover off my differential to inspect a suspect leak. Should I replace it with a new gasket with gasket glue or go the silicone route with no gasket at all, or combo of the two. What is the capacity of the differential anyway, as I only have purchased one bottle of fluid and cannot find a spec. anywhere in the Haynes manual I have for the car. Thanks in advance for the feedback.
KC.
 

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94 Fleetwood Brougham
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My 85 Cutlass (7.5") had gasket goo, my 94 Cadillac, 80 T/A and 96 Suburban (all 8.5") had gaskets. I used Ultra Grey for it, which is supposedly spec'd the same as GM spec'd new.

I have had good results with both. I like the NAPA premium gasket best (3/16" thick cork, not thin like paper), but it is $10.

The 8.5" takes around 2.5 quarts of fluid.

kc81cadman said:
I pulled the cover off my differential to inspect a suspect leak. Should I replace it with a new gasket with gasket glue or go the silicone route with no gasket at all, or combo of the two. What is the capacity of the differential anyway, as I only have purchased one bottle of fluid and cannot find a spec. anywhere in the Haynes manual I have for the car. Thanks in advance for the feedback.
KC.
In this weather (cold, 0 degrees F here!) you will need to have the oil sit inside to get warm enough to flow through the pump if you use one. Probably 2-3 hours to warm up to 70F to make it somewhat usable.
 

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81 Sedan DeVille 8-6-4
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Discussion Starter #3
How can you tell if it is a 8.5" diff or the larger one. I got a paper gasket from Part Source in Toronto, but the bolt pattern was different, they took it back, OK service. The bolts on mine seem evenly spaced where as the gasket they gave me had to short pieces opposite each other that had no holes.
KC.


*edit*Its pretty cold here too, 0 deg celsius and lower. I will probably have to heat up the case with a propane torch before the install.
 

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94 Fleetwood Brougham
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http://www.coloradok5.com/axleguide.shtml for drawings

8.5" real picture
http://www.accuautoparts.com/axledescription.jsp?axleid=G85PROREAR

7.5" real picture
http://www.accuautoparts.com/axledescription.jsp?axleid=G75REAR26

And good gasket page:
http://usgear.com/tl/gm2.htm 8.5
http://usgear.com/tl/gm1.htm 7.5


kc81cadman said:
How can you tell if it is a 8.5" diff or the larger one. I got a paper gasket from Part Source in Toronto, but the bolt pattern was different, they took it back, OK service. The bolts on mine seem evenly spaced where as the gasket they gave me had to short pieces opposite each other that had no holes.
KC.


*edit*Its pretty cold here too, 0 deg celsius and lower. I will probably have to heat up the case with a propane torch before the install.
Just drive it, don't torch cast iron, and with it that cold it won't do much to it anyway. Driving 20 miles will warm it up nicely (with oil in in it !!!!)

what year car is it?
 

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'86 Brougham
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I went to the dealer with the same question on an 86 Brougham. Guy walked to the car popped the trunk lid and looked at a paper pasted to the trunk lid underside. It had a series of numeric codes which he copied about two or three. Took them to his computer screen and compared. Told me "here's your gasket, and you don't need RTV. That'll be $ 12.95. Clean it good."
Gasket fit perfectly, the clean was an easy job even though the fluid drained for a long period of time. (Make sure its warm)
I suggest removing the fill plug before you drain. (In case it's siezed.)
The twenty year fluid had seen its day but was still liquid. Kinda.
New fluid went in, quiet and smooth ride, no leaks. 8 months 10k miles.:)
 

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81 Sedan DeVille 8-6-4
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Discussion Starter #6
Unfortunately I have the cover off already and the fluid is out, and the car is out of town. So the general idea is use a gasket as opposed to using the RTV. The car is an 81 SDV with the 8-6-4 368 in it. I will follow the links that were posted. I have to work outside in the cold, so I hope the gaasket goop does not suffer any cold weather defects. Thanks for the info.
KC.
 

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Where there was a gasket, put a gasket! Be it paper or rubber i always put a thin coat of RTV on either side of the gasket and then install. Be sure you clean the gasket surface well... I usually use a diegrinder with a scotch-brite pad.
 

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Gaskets are easier in my book to install, more of a pain to remove. I have had success with both. The 8.5" needs to have the holes in the sides of the gasket to allow oil to get to the axle tubes. Some OEM were missing and caused early axle failures. Odd, my 94 FWB was missing the holes and no issues @ 173K miles. I added new oil and new gasket with holes, and my left axle is now whining in right hand turns some.... Go figure....

kc81cadman said:
Unfortunately I have the cover off already and the fluid is out, and the car is out of town. So the general idea is use a gasket as opposed to using the RTV. The car is an 81 SDV with the 8-6-4 368 in it. I will follow the links that were posted. I have to work outside in the cold, so I hope the gaasket goop does not suffer any cold weather defects. Thanks for the info.
KC.
With a 81 SDV, you might have the "O" Pontiac 8.875" axle. This one is an oddity, not related to the 8.5" or 7.5". Was same axle center as the 71-76 B/C/D cars. Continued on in Cadillac from 77-8? with the BB Cad engines. But I don't know the actual breakout of them.
 

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Discussion Starter #9
Thanks again for the additional info, never thought they would use a Pontiac axle assy. but you learn something new everyday.

KC.
 

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In 77-83 or so, the Pontiac axle was exclusive to Cadillac.... Go figure.....

kc81cadman said:
Thanks again for the additional info, never thought they would use a Pontiac axle assy. but you learn something new everyday.

KC.
 

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By all means, whatever factory did, I do. But all too often people who owned it previously changed it for whatever reason. The 10 bolt 7.5" axles that I have seen all were goo, 10 bolts (Pontiac (8.875") and Chevy (8.5") have been gaksets.

JTraik said:
Where there was a gasket, put a gasket! Be it paper or rubber i always put a thin coat of RTV on either side of the gasket and then install. Be sure you clean the gasket surface well... I usually use a diegrinder with a scotch-brite pad.
 
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Rule of thumb, always use sealant to one side of gasket. Put the sealant on the part or cover that is removable. It will seal and if you ever have to remove this part again the gasket will stay in tact and will be reusable.

Please update your profile to show correct age, car owned, and time zone.
 

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Rule of thumb, always use sealant to one side of gasket. Put the sealant on the part or cover that is removable. It will seal and if you ever have to remove this part again the gasket will stay in tact and will be reusable.

Please update your profile to show correct age, car owned, and time zone.
Does anybody else use this as a rule of thumb? Put sealant on the removable side of the part?
 

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I do, though not for the same reason. Paper or cork gaskets should never be reused. (that said, I recommend RTV on the diff cover - not a gasket)

I really don't like to use both RTV and a gasket on the same application (only one or the other), but if I have to, it's because I use this method in certain situations where the part in question is in a tight spot, and I need some "glue" to help keep things in place during assembly. I RTV only the removeable side because it cuts down on cleaning time if it's ever taken apart again. That way, I don't have to spend much time picking and scraping RTV from the said tight space under the hood - if the removeable part is defective, it just gets tossed, and if it is being reused, it can be cleaned on the bench quickly and easily.
 
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