Transmission input shaft oil seal on a 69 what's involved in replacing?

[H.G.P.]

What is the process of replacing a transmission input shaft oil seal (on the bell housing end), on a 69? Engine drop?, and then what?

Thank you.

[sayah]

Remove clutch, remove flywheel, knock out bearing, put back new bearing, etc, etc.

Hope this helps

[Zeke]

Removing the old seal is a PITA. Installing the new one is a POC. Just tap it in and flush it up with the rim of the case. One thing to note is where the old bearing is positioned before prying it out. And then note any wear or grooving on the shaft. You can put the new one in just a tiny bit less deep to have the seal lip run on a fresh surface instead of in the old postion. After all, sometimes there is a reason why it leaked. It could be just age and stiffness or it could be wear on the shaft.

[Grady Clay]

First I would confirm that it is transmission oil leaking and not engine oil.
Or is it both?

Yes, you have to remove the engine.

If the leak is transmission oil past the input shaft seal; that is easy.
Remove the shift fork, clean and inspect the plastic cup.
Replace plastic cup if necessary. Clean and inspect the bearing.
Do not get cleaning solvent in the bearing.
Inspect the two plastic pieces, replace if necessary.

Remove throw out bearing guide tube. Clean and inspect.

Remove input shaft seal being careful to not damage input shaft
or the bore in the transmission case.
Inspect the seal surface on the shaft and in the bore.

Clean the input shaft, particularly the clutch splines
and inspect the pilot bearing surfaces

Install new input shaft seal.
Make sure it is flush and square with the transmission surface.
Use a proper drive tool. Do not use the guide tube to push it in place.
I lube the input shaft seal surface and the seal lip with slight amount of trans lube.
I install the seal with “Gaskacinch” sealant.
There are many other good sealants.

Now for a little modification.
Take the guide tube and, using a grinder or Drimmel,
make a small grove in the face that abuts to the transmission case.
This grove should go from the ID bore straight down to the edge of the flange.
The grove should be about the size of half a pencil lead. The purpose of this is to
give any leaking transmission oil an alternate path rather
than going directly into the center of the clutch.

We would install a second seal in the center of the guide tube as a dam.
This forces most leaking oil to go down the new drain grove.
This was just a small commercial seal that did not touch the input shaft.
It was a press fit (about the same fit as the input shaft seal) in the
tube with a press tool “of local manufacture.”




When the input shaft seal leaks all that oil goes directly to the center of the clutch.
You must remove the pressure plate and inspect the disc.

Mark the location of the pressure plate to the flywheel so you can reassemble in the same orientation.
Un-do the pressure plate bolts half turn at a time, going around the circle.
If the disc is oily, replace it.
It is not possible to successfully clean an oily disc.

Clean and inspect the pressure plate and flywheel.
Replace as necessary.
Get the pressure plate perfectly clean and dry and then thoroughly lube with WD-40.
Wipe off all excess and then get the friction surface only perfectly clean with brake clean.

Now is the time to inspect the pilot bearing.
If OK, add a slight amount of molly grease and rotate the bearing needles with your little finger.
Look behind the flywheel (particularly on the bottom side) for any sign of
engine oil leak from the flywheel seal.
Replacing the clutch and flywheel seal are the main “while you are there” issues.
If you must remove the flywheel, I recommend replacing all six flywheel bolts.

While you have the disc out, clean and inspect the splines.
A brass “tooth brush” works well for this.
Test fit the disc onto the input shaft splines.
Add a tiny amount of molly grease to the splines and slide back and forth on the splines.
Remove every bit of excess grease.

Reassemble the clutch, matching your marks, and making sure all the friction
surfaces are absolutely free of any oil or grease.
You will need to align the clutch disc so it is centered.

Install the throw out bearing on the guide tube with molly grease.
Put some molly on the clutch release arm ball and cup and just a tiny swipe
where the fork contacts the bearing.

Reassemble.

Some other “while you are there” are to replace the throttle bell-crank bushings,
inspect the throttle rubber cushion connection, and inspect the clutch cable.
Make sure you have the metal pivot piece (not plastic) where the clutch cable
connects to the clutch release arm.
Keep your eyes open for any other problems.

Best,
Grady

[H.G.P.]

Thanks! Printed out all your comments.

[RWebb]

Grady's diagram is very nice but I thought I'd also post this pic of the groove I ground in the guide tube with my trusty 38 year old Dremel...




I used some fine grit sandpaper also just to be sure there were no stress cracks started.

I also could never find a rubber seal that would fit ovr the trans. drive shaft, so I've given up on that (secondary) safeguard.