8.75" Diff Housing: Paper Gasket only, or add RTV?

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cudaracer

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My rear diff has been leaking because I took the advice of someone I trusted who said he only seals his diff housings with RTV. Well, that may be so for him, but I had a leak.

So I have it off at the moment, and about to order a gasket.
1st question: Which gasket is best?
2nd question: Should I add RTV in addition to the gasket?
3rd question: Is there a kit that includes the outer paper gaskets at the wheel?

I would like some advice on drive shafts too. I was going to start another thread, but this is as good a place as any. So my e body shimmys and shakes after about 70. While under there for the diff, I spun the drive shaft with the axles removed, with it just barely touching a jack stand underneath it, which I used as a sort of dial indicator, about 2" forward of the rear u-joint. It was certainly out of round. I would guess over 1/16".

1. Is this normal?
2. Can it be rebuilt?
3. U-Joint seemed centered, but is that suspect?

Thanks
 
Rtv is the only thing I have used for the last 25 years. I have had to do it over again if I didn't get enough gear oil out of the third member and it ran down and got into the rtv. Mop out as much as you can put it in quickly shove it all the way and have some nuts ready to run all the way down.
 
Before you take it apart make absolutely certain it isn't the vent bolt leaking and running down looking like it's the differential leaking. Put mine together 3 yrs. ago with just RTV for the first time and for about a year it stayed dry then started dripping. Looked and it was all wet around seal area. Snugged up the bolts. Didn't help. Thinking I didn't get a good seal on the RTV I pulled it back out and this time used a gasket like I had always done in the past and reassembled it. Still leaked. Since I had it cleaned up real good I then saw it was coming down from above at the vent bolt that holds the brake line T


As far as the driveshaft, IMO you'd be better off taking it to a good driveline shop and have them check it. 1/16" = .062" which isn't a bunch and they may be able to balance that out but only they can make the determination after visually inspecting it.
 
I only use RTV in the corners of an oil pan, or intake manifold. Permatex Aviation Gasket Sealer is what I use everywhere else. I've taken engines apart, and found RTV in the oil galleries under main bearings. Perhaps I'm paranoid, and gears don't care about a little RTV getting in their way. Please use black, and not bright blue or orange.
 
Thanks for the advice, all.

Regarding the vent cap, shoot....I did not check it. Is that something I can replace while diff is out?
 
cudaracer said:
Thanks for the advice, all.Regarding the vent cap, shoot....I did not check it. Is that something I can replace while diff is out?
Click to expand...

You can replace it if you want but they don't usually go bad. May just need tightened up. You can get to it real easy even with everything assembled. It's a combination hold down bolt for the brake line tee and vent. If I remember right it takes a 9/16 wrench
 
I always use a gasket on 8 3/4's - with only a light skim of RTV.

My logic is this, and I am probably over thinking things, but the 8 3/4 is not like a diff with a rear cover where you can use just RTV - the gasket is actually engineered into the axle alignment - as it moves the carrier slightly forward, so I always use it. Like I said - probably it is a nil point and I am thinking too much...

Other people have also told me to just put RTV on the housing side of the gasket, then it stays attached to the housing if you change center sections and doesnt tear, so you can re use it.
 
I've been told to use gaskets. I wouldn't get it from anyone but Doctor Diff if you choose to go that way. I haven't used RTV on an 8 3/4 (used it on a golf cart transmission) so I have no opinion there.
 
Only used a gasket once and it leaked....in 30+ years...have only used RTV....no runs..no drips..no errors....and I put it all the way around the housing...LOL
 
gasket-
a little coat of oil, on the gear housing side
- so that the gasket doesn't stick.

We change gear ratios often
re-use gasket,if not torn.
 
cudaracer said:
My rear diff has been leaking because I took the advice of someone I trusted who said he only seals his diff housings with RTV. Well, that may be so for him, but I had a leak.So I have it off at the moment, and about to order a gasket. 1st question: Which gasket is best? 2nd question: Should I add RTV in addition to the gasket?3rd question: Is there a kit that includes the outer paper gaskets at the wheel?I would like some advice on drive shafts too. I was going to start another thread, but this is as good a place as any. So my e body shimmys and shakes after about 70. While under there for the diff, I spun the drive shaft with the axles removed, with it just barely touching a jack stand underneath it, which I used as a sort of dial indicator, about 2" forward of the rear u-joint. It was certainly out of round. I would guess over 1/16". 1. Is this normal?2. Can it be rebuilt?3. U-Joint seemed centered, but is that suspect?Thanks
Click to expand...
I use both
 
Someone makes a good gasket that is a thin metal core sandwiched by gasket. That's what I use!
 
Paper gasket here. I used the red tacky gasket sealer stuff on both sides of it. No leaks so far. Don't over fill and check the vent like said above.

When I worked at the dealer, we used the orange RTV and smeared it all the way around. We did not deal with drop out center sections though, only rear covers so YRMV.
 
Paper gasket only and in swapping center sections with a buddy for a
little weekend action (different gear) several times we have never even
replaced a gasket once. Never a leak of any kind on either vehicle.
 
I had no leaks until the last 3rd member I installed. I had to use RTV and a gasket to fix the leaks. I put RTV on the 3rd member and let it sit for a while to set up and then installed it. No leaks.
 
I bought a gasket the first time I ever did one. After all the trouble of meticulously scraping off the old gasket from around each stud and cleaning with brake clean I decided no more sticky gaskets! I've used RTV ever since and we're talking since 1980. As was mentioned earlier you can't let oil drip from the pumpkin or you will have a problem.
 
there is a special rtv made for rear ends, transfers cases etc
 
What about paper gasket and this...

F14591754.jpg


It says it makes getting the gasket off easier.
 
I use a paper gasket, sprayed with adhesive that I use for the headliner. The gasket is tacky, and seals right up. Never a leak. I have to admit a FORD guy taught me that trick.
 
biggest mistake is installing the gasket to wet surfaces.

next biggest mistake is pinching the gasket during install.

personally i like to use the cork-metal-cork ply gaskets.
 
FelPro gasket with a little grease on both sides. Never a problem to remove even after years of service; easy to remove and reuse if needed and no scraping off dried gasket or RTV.
 
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