found gear oil in manual trans. NOW WHAT?

[n/a]

I just recently bought my car and while changing the fluids I found gear oil in my manual transmission. I do not appear to have any metal in the drained fluid but I do appear to have a fluctuating speedometer which seems to indicate a loose output shaft nut mentioned in other threads.

My two questions are this.
1) Do I need to flush this gear oil out of the transmission before adding Type F ATF? If so with what? Does anyone think that removal and rebuilding of the transmission bearings and seals is now necessary?

2) The plate that holds the transmission into place would indicate that I need to support the transmission and remove the plate to get to the front driveshaft and ultimately the output nut. Is this the case or can I do this job without removing this plate?

John
Davis, CA, USA

66 230SL

[Ricardo]

John
I  did remove the lower transmission plate to tighten the nut and I don't think you could easily tighten it without doing so.
You can undo the flex disc without removing the plate, but the plate isn't difficult and I just supported the transmission with blocks of wood. You may encounter a large washer between the plate and the mount, that has to be slid in place after the  plate goes back on, but before you cinch up the bolts. Otherwise you have to lift the tranny. The output nut requires pretty good torque, can't remember exactly what and it is tight working on ramps or stands, a hoist would help.
Ricardo

[bayleif]

John,
A loose nut on the output shaft is not the only reason that our speedometers fluctuate. Often times, it is just the speedometer. Do a search, I think there are symptoms related to the fluctuation getting worse when you take your foot of the gas that indicate the source of the problem being the output nut.

Chuck Bartlett
1969 Signal Red 4 Speed

[Ricardo]

John
Chuck is right...my speedo originally fluctuated because of worn parts in the speedo itself. The speedo bounce caused by the output nut coming loose looks similar and at first I thought my  speedo repairs hadn't lasted. What I noticed  different is that when I clutched in, the speedo got nice and steady. I also started hearing the occasional "click" coming from under the car, that coincided with the speedo bouncing. Nut was finger loose. Joe Alexander has warned that if it goes too long like that, parts can fall into the tranny, that require complete disassembly to fish out and I'm sure things can get broken too.
Ricardo

[n/a]

I've been under the car working on getting to the flange nut to tighten it.  Hope it will solve my bouncy speedometer.  I have a related question, is there supposed to be a cover plate for the driveshaft access in the middle of the driveshaft (rearward from the trans/shaft connection)?  I noticed that there was a threaded hole back there, but there is no cover to speak of.  Thanks for any response, and, of course, special thanks to the useful ones!



Dan

1965 230 SL Euro 4 speed
2004 230 SLK

[Benz Dr.]

Lots of them come loose and the symptoms are VERY specific. Bouncing needle at speed and at the road speed that your're tavelling isn't a loose output shaft nut but is more likely a speedo cable or in the guage.
Loose nut usually will give you a much lower than road speed reading that seems to get worse as the trans warms up. This is caused by the oil in the trans getting thinner as it warms up and having less drag between the gear and the shaft it sits on.The speedo drive gear sits on a splined shaft but is not splined to it - it just slides on and the tightened assembly makes it turn with everything else.
 Speeding up quickly may cause the needle to drop down to 20MPH while sharp braking or slowing should make the needle jump to actual speed being travelled.
There's a reason for this, anyone care to play detective?

Daniel G Caron

[Naj ✝︎]

My guess is it depends on who's driving the speedo:
The engine or the rear wheels?
naj

65 230SL
68 280SL

[Benz Dr.]

ummmmm sort of.... the engine moves the car but I'm asking about why it jumps up to speed or falls off to almost no speed, or at least far less than what you're actually tavelling.

Daniel G Caron

[George Davis]

Doc,

I'm guessing the speed reading falls off because the speedo drive gear moves far enough when power is on to partially disengage from the driven gear.  The movement is caused by thrust from the helical gears.  When coasting, this thrust is either removed or reversed, causing the speedo drive gear to move back to where it should be, thus giving the correct reading again.

If I'm right, I want a ride in the Red Rocket, but you have to bring it to Oregon!

George Davis
'69 280 SL Euro manual

[Benz Dr.]

Wellll..... no. OK, sort of, but not really how it works. Keep trying.

Daniel G Caron

[George Davis]

Yreka!  OK, the speedo drive gear is not keyed in place, it's just held tight by the output flange nut.  Under load (with a loose flange nut), gear thrust reduces the clamping effect so the drive gear is no longer held tightly.  It still turns from friction/drag, but it slows down giving a false low reading.  When coasting, gear thrust reverses and the stack tightens up on the drive gear so it turns at shaft speed again.

Don't come to Oregon in late August/early September, we won't be here, but any other time is OK!

George Davis
'69 280 SL Euro manual

[Benz Dr.]

( he thinks he has the answer )
George:
It's really quite simple and pyhisics comes into play. Think of kinetic energy.

 The gear lube can be dained and replaced with ATF. It would have been better if it had ATF all along but, hey, you found it so don't worry too much and just change it out.

That was the original question, I believe.

Daniel G Caron

[Naj ✝︎]

The output shaft nut is locked in place with a lock tab - right?
So how does it manage to become loose?

naj

65 230SL
68 280SL

[Benz Dr.]

The locking plate is shaped like a cup and only keeps the nut from falling off once it does come loose. There's no way it will actually keep it tight.
The nut comes loose because it wasn't tight enough to begin wih and like I said, lots of them go loose. On newer cars the nut has an improved locking part on it that helps to keep them from backing off.
Part of how the speedo works when the nut comes loose is also why it works loose in the first place.

Daniel G Caron

[Naj ✝︎]

Thanks, Doc.

naj

65 230SL
68 280SL

[n/a]

Doc,

Thanks for finally giving me a reply to the original question about the lube. I also appreciate all the other posts for the insight into things to look at for the speedo problem.

John
Davis, CA, USA

66 230SL