NP203 rear output seal leak

[77 K20]

So I drove my truck for 10 years without it leaking. I bought a new driveshaft and instead of a yoke it came with a flange for the transfer case. I had always heard after having a seal that old it will leak when you disturb it. So since the driveshaft came with a new seal I installed it.

200 miles later I notice it is leaking. Crossmembers and skid plate below it are very wet. Maybe it was a bad seal- or damaged in shipping. So I go buy another one and install it.

30 miles later and I can see it is starting to seep. The motor oil has made a trail 3-4" down the cone of the output shaft.

I contacted the manufacturer of the driveshaft and yoke asking for measurements of the flange. When I get around to working on it I'll use some dial calipers on it to make sure it was the right size.

When I installed both seals I used a bit of grease on the rubber seal part and used some oil on the flange and assembled it that way. The flange is perfectly smooth- no nicks/gouges on it. I use a bit of RTV on the splines also so it doesn't leak out thru there.

Is there room to use 2 seals on the output of the 203? I didn't inspect it that close last time as I really thought replacing it would take care of that.

My vent line looks fine- I really doubt it suddenly got clogged a few days after replacing the driveshaft.

Any other causes of a leak? Does anyone know how much end play is allowed for a flange/yoke? I heard that there is supposed to be some but no exact spec is ever given.

Nothing irritates me more when I try to improve or fix the truck and somehow it comes back to bite me. A seal should be nice and easy!

 

[bucket]

The grease could be attacking the seal, but I doubt it would happen that fast.

Before installing the second seal, did you see how well it fit the yoke? Should slip on and fit just slightly snug.

 

[77 K20]

It fit the yoke well- snug but not too tight.

I've been trying to read up on the 203. Seems maybe sometimes the rear shaft gearing part can get worn out. If the yoke has any movement at all can this cause a leak?

 

[bucket]

It just seems odd since you never had trouble before with it leaking. I've had a lot of output shafts that are a little loose and it never hurt the seal, I don't know why a 203 would be any different?

 

[77 K20]

Yeah- that is what has me so confused also. Just wondered if I was missing or overlooking something.

 

[firebane]

Is the new seal the same size as the old seal? I've heard on the NP203 the output shafts on the front and rear used a seal that was thicker than normal and sometimes require two new seals to replace the 1 old one.

I haven't tackled this yet on my truck for the very reasons you are having troubles with.

 

[77 K20]

The part number of the new seal they sent is the seal that any autoparts store says should be in there.

So when you say "two new seals" is there room to stack 2 seals in there back to back?

 

[firebane]

The part number of the new seal they sent is the seal that any autoparts store says should be in there.

So when you say "two new seals" is there room to stack 2 seals in there back to back?

It is just something I have read from time to time so I am not sure. What was the thickness of the old seal compared to the new? Or did you throw the old one away already?

 

[77 K20]

The old seal has been thrown away now, but when I was replacing it I compared them side by side and they looked identical.
I too have heard on some transfer cases you can stack 2 seals back to back but haven't been able to read online if that is true on the 203.