4 speed/speedo cable seal question

[George Davis]

Hi All,

I'm hoping someone can tell me how to remove the small metal/rubber lip seal that fits in the transmission rear cover and seals the speedometer drive.

Thanks in advance for any info!



George Davis
'69 280 SL Euro manual

[Benz Dr.]

It's not that easy to do.
You have to remove the speedo drive shaft and gear inside of the rear trans cover. ( Remove the rear cover to do this) To do this the small sealing plug has to be removed first. It can be pulled out using a screw driver. Once you have the plug out you will need to drive the shaft out with a punch. It's a good idea to measure the depth of the shaft in the casting so you can install it in the same place while doing reassembly.
Once you have the shaft and gear out you will be able to remove the seal. It's kind of difficult to remove but with some effort it should come out. The casting may get damaged during the seal removal so repair this by removing any burrs or filling in any missing metal with something like J B weld. Smooth out the hole before installing the new seal.
I use a small socket that will fit into the hole and not damage the seal. A small amount of copper sealer around the outer part of the seal is a good idea. Drive it in until it stops - there's a small ridge in the casting to fix this position. Replace the drive shaft with the slotted end towards the seal and place the speedo drive gear in the casting so that the shaft will slide through it. This is where having the depth of the shaft while removing it becomes handy. It should be just about even with the end of the seal when fully installed. If I remember correctly the meatal part of the seal is facing out while the sealing end goes into the hole first. Make sure of this during removal.
If you have the drive shaft in too far or not out far enough it won't engage in the speedo cable or the cable won't fit into the casting far enough to be locked into place. There really isn't a whole lot of room for error here - it has to be pretty close or it won't work.
Do a trial fit before you decide that you have the shaft set up properly. If it works OK replace the closing plug using a bit of sealer.
 Replace the rear cover using a new gasket. Be sure to use sealer on the rear cover screws or oil could leak by the threads. If the seal for the output flange is worn replace it before installation.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

[George Davis]

Thank you, Dan!  I appreciate the detailed answer, it isn't at all obvious how to do it just by looking at it.

I hope you are doing well, it's good to see you on the forum!

George Davis
'69 280 SL Euro manual

[jeffc280sl]

George,

Please let us know how you're doing with this project.  Good luck!

Jeff C.
1970 280SL 4-speed

[George Davis]

Jeff and All,

I have completed replacement of the speedo drive seal.  It went pretty much as Dan described, but I have added way too much verbage and a couple of pics.

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The closing plug is on the outside/top of the rear transmission cover.  If you want to do this with the trans in the car, the rear cover has to come off.  Watch out for the thin shim washers that are used to control bearing end play.  Also drain the 'box lest ye drown in ATF.

Pry out the closing plug with two screwdrivers; the plug is maybe 5-6 mm long.  Under the plug you'll see the end of the speedo drive shaft.  Measure the depth of the hole to the top of the shaft.  In my case, it was 0.255 inches.

The speedo drive shaft is a tight press fit in the speedo driven gear.  Mark the gear so you'll know which way it goes back in, it has no "up" or "down" that I noticed.

Remove the speedo cable retaining screw if you haven't already.  Knock the shaft out with a 1/4 inch flat-end punch.  This takes some serious pounding, so supporting the transmission cover is critical.  I clamped it in a vice padded with 1/8 inch thick aluminum pads, with the lower end of the speedo drive housing resting on the upper face of the vice so it wouldn't move while pounding.

With the shaft out you can now attack the seal.  I tried to pull it out with a 9/16 bolt screwed into the end of the seal, but that was useless, just not enough bite.  A 5/8 inch tap might work(?).  I have a small milling machine, and used a 5/8 inch end mill to basically grind up the metal part of the seal.  A 5/8 inch mill is just a few thousandths of an inch less than the 16 mm diameter of the hole the seal fits in.  Set it up so the mill turns free inside the hole without scoring the sides of the hole, and use the lowest turning speed you can.  Feed the mill down manually, chewing up the seal until you feel more resistance, then stop.  The increased resistance means you've reached the ledge that the seal seats against.  The metal part of the seal is now gone, the remaining rubber bits can be gotten out with a 1/2 inch drill bit held in the hand.

This method avoids damage to the inside bore of the hole.  This can probably also be done with a good 1/2 inch or larger drill press and a 5/8 inch end mill with a 1/2 inch shank.  Careful alignment of the hole and the mill are the key, plus a decent vice that can be clamped to the mill/drill press table.  Either way, use a low turning speed or you'll never feel the ledge.  I recommend extreme caution if you try this with a 5/8 drill bit, the taper on the end of the drill will damage the ledge and you may go too far; however, if one is very careful, it might be possible to use a drill to get most of the metal part of the seal out.  Again, a good drill press and decent vice clamped to the table are musts.

If you have to resort to other methods, I can practically guarantee scoring of the wall of the hole.  In that case, you'll have to do some repairs (as Dan mentioned, maybe using JB Weld), so the seal seats properly and seals on the outside.  It might be worth spending some money to have a machine shop do this, unless there is some tool that can extract that seal(?).

Next, clean things up and then drive the new seal in until it stops against the ledge. I used a deep socket that just fit in the hole.

With the new seal in place, lube the seal lip with ATF, then reinstall the gear, then drop the shaft back into position and hammer it back to its original position.  Don't hammer directly on the top of the shaft, this may distort it and cause it to bind.  I used a piece of aluminum between the shaft and the hammer until it was flush, then used the 1/4 inch punch the rest of the way.  I whacked it one time too many, and the final depth is 0.260 inches.  Close enough, I hope.

I put a couple drops of light oil on top of the shaft and spun it a bit to get the oil down the shaft.  I put a light layer of Permatex No. 2 on the side of the closing plug and tapped it back in.  Seal job done.

This little job is part of a 4-speed transmission rebuild that I'm doing.  I'll post a few pics on that one of these days.  All I can say right now is that rebuilding the transmission is a heck of a lot easier than getting the heater core out!!!

George Davis
'69 280 SL Euro manual

[jeffc280sl]

Thanks George!

It sounds like you tranny is out for service.  This job would appear to be difficult without doing that first.  Correct?

Jeff C.
1970 280SL 4-speed

[George Davis]

Hi Jeff,

replacing the speedo shaft seal can be done with (most of) the tranny in the car, but the tranny rear cover has to be removed to do it.  Removing the rear cover is easy and nothing bad will happen, one just needs to keep track of the shim washers, which can't be mixed up.  Not a trivial job, of course, as driveshaft, trans support plate, and rear motor mount all have to come out to get to the rear cover.

If a special tool exists than can extract the seal without first driving the speedo shaft out, then it wouldn't be necessary to remove the rear cover, but I don't know of such a tool.

George Davis
'69 280 SL Euro manual

[jeffc280sl]

I haven't really had a good look at that area for a while.  Memory tells me its a very tight fit to get to the back of the manual tranny.  I'll take another look next time I'm under the car.

Thanks,


Jeff C.
1970 280SL 4-speed

[Jazn]

quote:Originally posted by Benz Dr.

It's not that easy to do.
You have to remove the speedo drive shaft and gear inside of the rear trans cover. ( Remove the rear cover to do this) To do this the small sealing plug has to be removed first. It can be pulled out using a screw driver. Once you have the plug out you will need to drive the shaft out with a punch. It's a good idea to measure the depth of the shaft in the casting so you can install it in the same place while doing reassembly.
Once you have the shaft and gear out you will be able to remove the seal. It's kind of difficult to remove but with some effort it should come out. The casting may get damaged during the seal removal so repair this by removing any burrs or filling in any missing metal with something like J B weld. Smooth out the hole before installing the new seal.
I use a small socket that will fit into the hole and not damage the seal. A small amount of copper sealer around the outer part of the seal is a good idea. Drive it in until it stops - there's a small ridge in the casting to fix this position. Replace the drive shaft with the slotted end towards the seal and place the speedo drive gear in the casting so that the shaft will slide through it. This is where having the depth of the shaft while removing it becomes handy. It should be just about even with the end of the seal when fully installed. If I remember correctly the meatal part of the seal is facing out while the sealing end goes into the hole first. Make sure of this during removal.
If you have the drive shaft in too far or not out far enough it won't engage in the speedo cable or the cable won't fit into the casting far enough to be locked into place. There really isn't a whole lot of room for error here - it has to be pretty close or it won't work.
Do a trial fit before you decide that you have the shaft set up properly. If it works OK replace the closing plug using a bit of sealer.
 Replace the rear cover using a new gasket. Be sure to use sealer on the rear cover screws or oil could leak by the threads. If the seal for the output flange is worn replace it before installation.

Dan Caron's
 SL Barn
benzbarn@ebtech.net
 slbarn.mbz.org
  1 877 661 6061

I know this might be a bit off topic, but I was wondering how you are doing healthwise?  I hope all is well.
Jason