Odd speedometer activities

[Joe]

Still working my way through a 1965 230SL. The speedometer needle flopper around a lot and wouldn't get above 50 mph, regardless of how fast I went, so I swapped it out with a spare Euro speedo of unknown condition. This one acts differently. It is slow to rise, and seems to run a bit slow, but may not. Can't check since I don't have a cigar lighter socket for the GPS, and I hate to ask a cop to clock me. Anyway, when running at a somewhat constant speed, the needle varies 10 - 15 kph. Oddly enough, when I put in the clutch, the needle is steady on, and appears to read the correct speed. As soon as I release the clutch, the needle drops about 10kph and then proceeds to bounce again.
The odometer seems to be accurate.
I hope this is not a problem internal to the transmission. Any advice is appreciated.
Joe

[Naj ✝︎]

quote:I hope this is not a problem internal to the transmission. Any advice is appreciated.
Joe

It seems to be a problem external to the transmission. The rear propshaft (drive shaft) flange nut on the gearbox output shaft has probly come loose. The speedo drive gear is friction driven and slips when the flange nut is loose.
You need to drop the prop and tighten the slotted nut and relock it.
You can make your own tool or buy one.



naj

[Joe]

Thanks, Naj. Can that be checked without dropping the prop shaft?
Joe

[waqas]

quote:Originally posted by Joe

Thanks, Naj. Can that be checked without dropping the prop shaft?
Joe

The nut holds the transmission output flange at the center axis, and is hidden behind the drive-shaft flex disk. You'll need to:
- First support the transmission, and then remove the transmission support plate (16 or so bolts, with the center mount bolt).
- This will allow you to disconnect the flex disc from the transmission flange.
- If you loosen the center driveshaft coupling nuts, you can simply compress the driveshaft toward the rear.
- THEN you get to check if the nut is loose or not!

The tool Naj has shown was actually made by me, and I'd offer to lend it to you, but I actually made it to fit the differential nut instead of the transmission nut. (you're free to borrow it if you need to work on the differential side though   )

The differential side also has the same kind of setup as the transmission, but for some reason, Mercedes made the nuts different! You can make your own, or purchase a proper one from the tool vendor Samstag. I can get you the dimensions if you're interested in making your own.

This would be a great time to replace the flex disc and/or transmission mount, if necessary.

Hope this helps!

[Raymond]

To add to Waqas' good description:
To loosen the driveshaft (prop) center coupling you will need 42mm and 46mm open end wrenches. The jam nuts aren't real tight, just too tight for bare hands.  Hydaullic service wrenches are the cheapest in that size.  

Then, if you have never messed with a flex disc, you need to search the forum for good advice with photos.  It is a good time to replace the flex disc if it shows any kind of wear.  It is critical that pay attention to disc orientation and centering and get bolt alignment and torque right.  

The torquing of the output flange is easy with the Samstag socket which costs around $90.

[Joe]

Maybe I really don't need a speedometer that badly....

[waqas]

quote:Originally posted by Joe

Maybe I really don't need a speedometer that badly....

This nut also holds the entire gear cluster together, so letting it get too loose is not a very good idea...

Quoting from this thread: http://index.php?topic=3923,gear,cluster[/url]

quote:On a standard transmission the tightness of the nut keeps the entire main gear cluster tight. If the nut should come loose so does the gear cluster, causing a bouncy speedometer (especially under acceleration and de-acceleration). Often some shifting problems will follow (slight nipping when going into gears or hard shifting). The problem on the standard transmissions is once the cluster becomes loose enough it will shift a key out of place and then just tightening the slotted nut may not completely solve the problem.

[waqas]

quote:Originally posted by Raymond

The torquing of the output flange is easy with the Samstag socket which costs around $90.

You can also buy both differential and transmission tools as a set from ZDmak tools on flea-bay for $95 (item number 180219899757).