"67, D4D, 78A7177, direct drive. Guess it was bound to happen, It has been just sitting there since spring but for a couple hours of use two weeks ago. There is now a small but growing spot of oil on the inner track below the left hand rear drive sprocket. The shop manual I have does not indicate what is involved in replacing a final drive outer seal(s). How big a deal is this?
Bumping this up in the hopes someone with first hand experience will lend their insight into what is involved in replacing this seal.
If the sprocket it tight I wouldn't worry about it to much. You can wedge a bar between the case and sprocket to see if there is play in the bearing. I have one doing the same thing, it doesn't leak while running but leaves a spot on the tracks after it sits. I'll take the spot rather than open a can of worms on a limited use machine. If the sprocket it loose you may be able to tighten, check your service manual.
DPete-- Does the weight need to be off the track to check for sprocket wiggle?
No, you need a fairly long bar though, 4 or 5'
The right sprocket on my D4D 78A has lots of play, moves 1 1/2" or so. No leak at all, checked preload and is OK. I think the play is between the shaft and the splines inside the sprocket. The manual shows removal and installation with special press and puller available from Cat.
Do those have the old bellows seal on them instead of the metal to metal ones. I recall those old seals could develop a slight seep that showed up the same way.
Boy, you got me, John. My $70 repo manual is not a lot of help.
Now that you had better look into before it ruins everything inside.
Currently dealing with similar issue on an old Allis, sprocket nut shoulders up to the axle stub before the sprocket draws tight to spline shaft. I know it is a weak spot and have parts to repair so am careful with that for now paying close attention to it as a lot of stresses not designed for are working there.
Scott it is quite a while since I have pulled a final drive on a D4D to bits but if my memory serves me correctly I was under the impression the outer seal was quite simple you just pull the outer hub off and there it is, I am sure someone will correct me if I am mistaken, it is the inner one that is the big problem to get at you have to basically pull the sprocket and if you have done that then you may as well go though and check out the whole final drive. If there was no play much in the sprocket I wouldn't worry too much just keep checking the oil level
That, would be a treat, thanks! Think I'll call the ex-shop foreman at the local CAT house to see if he can verify what you describe. He works half days and has been a good info source in the past.
Your original post states the leak is in the inner track side. If the sprocket adjustment is tight I wouldn't get to concerned unless it become a major leak. Old Cat's, Driptroits and old Harley and British motorcycles all like to mark their turf with oil leaks. The 78A's use the floating ring seals and seldom have complete failures. An outer seal job is not to bad once you get the track roller support removed. May require splitting the track to get the elevation needed. Process is explained and detailed very well in the Cat Service Manual
Sorry, OM, outside is leaking. Nothing shows on the sprocket while in operation but a spot developed on the outer track pad while sitting. Whew, those nasty Detroits. Early eighties I worked in an industrial engine machine shop. My co-worker and I would alternate hot tanking Detroits they were so filthy. Even your socks and underwear got ruined. Turbo'd, intercooled 93's were the worst. HD's are the poster child for an internal combustion engine oxymoron.