speedometer needle jumps around PONTON
 

My speedometer needle is erratic as hell. At low speed it seems to work but at higher speeds it starts jumping around.


I took the cable out and inspected. Looks fine not worn or spun. (replaced with a old spare same results)


Took the speedo out of dash , ran it with a drill motor, works fine .


I have the tranny out right now. Should I take apart the bronze worm gear? Does anyone have any experience with this? Hard to believe the worm could wear out.


THANKS!!!!!

The problem is most likey the output flange nut on the transmission. If it is not torqued properly, or loose, the speedo will act as you have described. The socket you need is large and notched, and I can't remember the size. As a last resort, or fisrt resort, you can use a punch and hammer to tighten the nut. Probably the correct torque is not as important as just being tight enough. This is a common problem that is usually mis-diagnosed. Good Luck.

I always found on cars from the 50's and 60's, not just Mercedes but all cars, this was caused by one of two things: The aforementioned loose connection and a cable that needed lube.

There was once a graphite in powder form that you could coat the cable in. Or you could just pour it down the cable housing without even removing the cable.

It would take a bit for the graphite to work it's way down the cable but this would usually smooth things out.

There is also the outside chance that the cable has worn away a hole in the cable housing and is jumping around outside the housing where the hole is worn though. Inspect the cable housing and see if it is still sound.

Correct info...

Not many get this one right............Dan, The Man !!!!


https://classicmotorsports.com/project-cars/1966-mercedes-benz-230-s/a-cheap-fix-for-our-transmission/

loose connection at speedo cable fastening point
 

Hi Arthur and Dan-
Thanks for the help! Arthur, I think you are correct. The attachment hole on my gearbox is warn. When I was checking this on the car the cable was loose even though the fastening was tight. Attached are two pictures. The first 'called warn" shows a wear ring on the inside of the receiving hole in the transmission. You have to look closely.
The second picture is of a spare aluminum transmission end plate I have, showing a clean smooth hole. (called 'not warn" and has a blue flashlight in the picture)

So when I took the cable end piece and put it into the "not warn" end plate, it sits in the hole firmly and doesn't move around. It'll be even better when the screw is in place.

My plan is to put the spare endplate onto the existing gearbox. and this should fix my problem. I can pull the cable out of the housing so I should be able to put a generous amount of graphite into the cable. ( I did try greasing it earlier but the graphite should be better)

OK! Thanks so much! Angus

thanks to Mr Idle too!
 

sorry Didn't include you in my last message

This is a topic that others are bound to find useful in the future. And the photos are a massive help when it comes to pinpointing such a problem.

speedo drive
 

>>>>My plan is to put the spare endplate onto the existing gearbox. and this should fix my problem.<<<


You are missing the point.

The problem on these speedo drives is the large gear inside the tail of the trans. That gear turns tyhe little gear on the speedo shaft.
That gear is driven by CLAMP FORCE FRICTION....it is sandwiched between the rear flange and the rear tailshaft bearing. If the flange nut loosens [ and they all do], then the gear is slipping around the tailshaft.....like if you had a washer between 2 nuts...when the nut are loose, you can easily turn the waher...when they are tight, you can't and the washer will turn only when the shaft turns.
In other words, there is no locking device on that gear...it is locked to the output shaft by the pressure clamping force put on it by the flange nut ]]

Loose nut = jumping speedo...

Go reread the article in the Magazine I posted. Or go over to 113 forum...the archieves has all that info from me and other Techs.
This is a common problem....it is an uncommonly known fix.

Your remedy of the" Warn" housing is NOT the remedy .
The remedy is to lock the drive gear in the trans by tightening the flange nut.
Which is another procedure all together.


PIC of the gear in question...... #137. Self explainatory

https://www.sls-hh-shop.de/main/en/mercedes-230-280sl-w113-/25-26-clutch-4-speed-box/26-a-gearbox-manual-

Arthur-
OK, Yes!! I finally do understand you. After looking at the articles you mentioned , I went out to look at the gearbox I took out of the car. The flange nut is actually loose! As is the flange itself!
The drive gear being held by clamp force friction seems an odd way to do things but now I know! Thank you for following up. I'll work on this and report back. Thanks Again ,Angus

You're Welcome .

They went with that clamp design b/c a speed head takes very little force to be driven.....

..and knowing this allows the experienced tech to know when the flange nut is loose.

Easy way to test for a loose flange nut is to remove the speedo cable from the trans and stick a flat bladed screw driver into where the cable would go. Turn the drive shaft and see if that will twist the screw driver handle out of your hand. If it doesn't, the flange nut is loose.