"Late" 915 Input Shaft Dam Seal

[rhk109]

So I'm in the process of replacing my 915 input shaft seal. I've read the dozen or so posts recommending the addition of a dam seal in the guide tube to prevent any future leakage from finding its way to the clutch.

I went out and got the CR 8620 dam seal but it is way too small. I think it only fits the early 915's without the removable guide tube.

Has anyone performed this mod on a late 915? What dam seal is required?

Here's a pic of the CR 8620 and my guide tube. As you can see, it isn't going to work.

[rhk109]

bump

[Porsche_monkey]

Free bump. I took mine apart yesterday, I need to do the same thing. If no-one posts I'll figure it out next week and reply.

[rhk109]

Well, I just got back from my local seal distributor. They didn't have anything in stock in the 36mm OD we need.

I was thinking about just running a bead of high temp RTV sealant around the inside of the tube to act as the dam.

[rhk109]

Bump.

Grady you out there?

[Chuck Moreland]

Can't you use a second factory input shaft seal?

[MBEngineering]

HI rhk109 the seal you require is 23-35-8/11 RO1 and depending on the bearing sleeve a tool to fit it in square, see below,



lube the seal when fitting and do not force the seal over the input shaft where the clutch splines are, when re-fitting.
The seal you have is not for a early box.

regards mike

[rhk109]

Originally posted by Chuck Moreland
Can't you use a second factory input shaft seal?

Nope, that was was my first idea too. The guide tube ID is larger in region where the dam seal gets installed and necked down in the area where the factory shaft seal gets pressed in.

[rhk109]

Mike,

That looks like the factory shaft seal. Is it?

I'm trying to install the 915 "dam seal" mod discussed in other posts.

For example.
http://forums.pelicanparts.com/showthread.php?threadid=196173

It is essentionaly another seal that gets installed behind the factory shaft seal to stop leaking fluid from making its way to the clutch. A hole is then drilled between the two seals so the fluid drains harmlessly out of the bottom of the bell housing.

There are quite a few people who have done this mod. I'm hoping someone has a part number for a seal that works with the later 915 removable guide tube.

[Grady Clay]

Here is part of a draft I’m working on. As you can see, it still needs work.

An important feature is a “dam seal” should not tough the input shaft. It should be slightly toward the clutch from the ground input shaft seal surface. Test fit the disc on the input shaft and make sure the splined hub can’t touch the dam seal.


4)There is the later 915 seal used with the removable guide tube with the O-ring.
The input shaft seal is 999.113.327.40 and is 23x35x8/11 mm size.
The O-ring is 999. is 43x1.5 size.

IMG

To remove the tube (and seal) it takes a 5 mm steel loop to grab the tube. The Factory recommended a loop that seems to be about 3 mm. Occasionally it takes a lot of force to pull the guide tube. Some light lateral tapping helps.

IMG

Installation uses P381 to install the seal in the clutch release bearing guide tube. Then protection guide tube P382 is installed over the input shaft and use a pipe tool (40+ mm OD, 26.7+ mm ID) to install the assembled part in the transmission.

IMG

The “dam seal” is 36x22x6 mm. There is a CR 8690 that is 1.437”x0.875. I haven't test-fit yet.
To install a dam seal the tool “of local manufacture” measures:

IMG

Best,
Grady

[Shawn 357]

Originally posted by rhk109
Well, I just got back from my local seal distributor. They didn't have anything in stock in the 36mm OD we need.

I was thinking about just running a bead of high temp RTV sealant around the inside of the tube to act as the dam.

I just resealed my trans, the PO had used RTV, it didn't work

[rhk109]

Grady,

Any thoughts on just running a bead on high temp, oil resistant RTV, silicon sealant around the inside of the tube to act as the dam?

Ryan

[rhk109]

Shawn,

What didn't work about it? RTV didn't adhere?

[Porsche_monkey]

Pictures?

[Shawn 357]

Originally posted by rhk109
Shawn,

What didn't work about it? RTV didn't adhere?

The RTV did adhere but it wasn't stopping anything from leaking. Unfortunately I don't have a picture of it. Part of the problem was that the actual input shaft seal was leaking but the RTV didn't help slow it down enough. Maybe it could be made to work with RTV but if there is another alternative I would look for it.
-Shawn

[rhk109]

Originally posted by Shawn 357
Part of the problem was that the actual input shaft seal was leaking but the RTV didn't help slow it down enough.
-Shawn

Did the PO have a drain hole between the shaft seal and the RTV dam drilled in the tube?

[Porsche_monkey]

For a late model the relevant sizes are 36mm OD and 23 mm ID. that is nowhere near the 8620 seal. The 8620 is only 28.5 mm OD.

I have to question the practicality of this solution. A seal like this needs lubrication, which the outer seal won't be getting. By the time the inner seal fails it is likely that the outer seal will be chewed up from lack of oil.

CR doesn't make a 36/23 seal. So you would need to make a sleeve (and use a 35/23 or 34/23) or buy one somewhere else.

I think I'll stick to the factory design.

[Grady Clay]

PBH,

The “dam seal” doesn’t function as a seal. It is simply a dam that prevents oil from draining out the guide tube and into the clutch. It is important that the lip of the seam NOT contact the input shaft as there shouldn’t be any lubrication there.

The very important other half of this is to drill a drain hole in the guide tube.

Any oil that gets past the input shaft seal would drain into the unsealed cavity between the input shaft seal and the dam seal. The drain hole in the guide tube allows the oil to drain out and dribble down the surface of the bell housing and make a spot on the floor.

It is important the dam seal be located slightly toward the clutch from the edge of the ground surface of the input shaft for the input shaft seal. The reason for this is to allow any oil that would travel along the ground surface to drip into the cavity. On the other hand, the dam cannot be so close to the clutch to have the hub of the disc ever contact it.

The dam could just as well be a machined ring of aluminum or steel. A press-fit commercial seal is an inexpensive solution. I’m not comfortable with simply gluing in some RTV that doesn’t have a real interference fit. The consequences of the RTV going into the clutch aren’t good.

I developed this in ’72 with the poor design of the early 915 where the input shaft seal installs from the INSIDE of the transmission and the gearbox is assembled around the seal. The whole point of the dam seal is to prevent oil contamination of the clutch IF the input shaft seal leaks.

I think later seals are better and more long-lived material. The biggest feature is you can easily (without disassembling the transmission) replace the seal whenever the engine is out. That said, I look at the dam seal as simply an inexpensive added level of protection. One of the insidious aspects of getting oil on a clutch disc is it starts to fail to release completely and damages the syncros.


I’ll get back to work on a through post.

Best,
Grady

[Porsche_monkey]

Okay, that makes sense. I'll try and do mine this week and post some pictures.