Speedo showing 10% lower with new 5 speed gearbox

[Merc_Girl]

Calling on all my genius pagoda owners, help!

So folks, another issue, not too bad, more annoying

So Bessie has her lovely Getrag gearbox that was recommended on the forum, with the mechanical speedo drive.
When first installed it registered approx 10% off, ie when showing 70mph, she was doing around 80!
I’ve had the speedo recalibrated, but the issue remains

Any thoughts on whet is needed so that the correct speed shows?

Thank you! 🥰

[WRe]

Hi,
The gear ratio of the speedo drive of the Getrag gearbox is different from that of the Pagoda gearbox, which is certainly not surprising. The gear ratio in the speedometer must be adjusted for adaptation.
A somewhat unusual “adjustment” would be to replace the rear axle gearbox (3.69), which “coincidentally” leads to an approximate result.
Another option: https://www.sl113.org/forums/index.php?topic=19312.msg135535#msg135535 .
There are several posts on this here in the forum and perhaps also suitable experiences.
...WRe

[Davek1]

Hi Merc girl, I put a 3.27 rear end in my 280sl, and had the same problem, unfortunately could not work out how to alter the speedo. I went down the route of getting a speedo from a w108 which had this rear axle and hoped to change the insides but this could not be done. Will be interested to see if you find a answer.

[BobH]

Why not speak to Colin Ferns, and or Speedy Cables

https://www.sl113.org/forums/index.php?topic=23203.msg165899#msg165899

https://www.speedycables.com/speedometer-calibration/

[Merc_Girl]

Thank you!

[RAY]

Hi Katy,

I have the same issue with my speedo reading about the same difference after a diff change and have never got round to getting the speedo recalibrated.

Would be interested in knowing where you got yours done if it was somewhere different from Speedy Cables ?

Ray

[Merc_Girl]

Hi Ray
The company that refurbs speedos and other such things, is JDO Instruments
http://www.jdo1.com/clocks.html
Don’t be put off by rubbish website, they are really good and ‘honest’, no rip off pricing. Ie SL shop refurbed my speedo and charged over £800! These guys did it and took out all gunk that been had been put it and properly refurbed, under £100!!!?
Still chatting to mechanic to decide to go down recalibration or try Speedycables’ that you mentioned
Katie