Currently we are looking at doing a v8 setup in a Mercedes W115. My one concern is that I want the originals in the cabin to work which includes the Speedometer which is cable driven. No how would you go about ensuring that you can get the same output from the new setup as per the old setup. are there people out there that can make a kit for the actual fit-up and are there engineering houses that may be able to do this??? Please help

  • Welcome to Motor Vehicle Maintenance & Repair! You really aren't giving enough information here for us to help you properly. You state a "V8 setup", but you don't tell use what that setup would be. What does your final configuration look like (what are are the engine/tranny/etc from ... major parts here). Without knowing exactly what you're going to use, it makes it very hard to answer. Handy Howie's answer below is a good start, but I believe there is a lot more which could be answered to help you if we had more information. Sep 15, 2018 at 12:36
  • The current idea is the 1 UZ Lexus V8 setup.with the auto box
    – Ruben
    Sep 16, 2018 at 9:57

2 Answers 2


If it is just an engine conversion you are doing, then the original speedo should work fine, since the speedo drive/sensor comes off the gearbox or final drive.

If you are changing the gearbox and the speedo drive/sensor comes off the gearbox, then you may need to get a conversion done. There are companies that can do this.

  • Also the speedo will be incorrect if they change tire sizes or final drive ratio. Unless they are lucky that the tire change offsets the final drive ratio change...
    – Solar Mike
    Sep 15, 2018 at 8:45
  • Awesome I was thinking the same as I am currently having 18 inch 3 piece custom rims made to take the fintail centre caps,
    – Ruben
    Sep 16, 2018 at 10:00
  • So it looks like the speedo should be the last that I should focus on.
    – Ruben
    Sep 16, 2018 at 10:04
  • @ruben definitely
    – HandyHowie
    Sep 16, 2018 at 12:22

With some Audi conversions, an alternate generation cluster is needed (B6/B7). ECUs need to match the cluster. I'm not familiar with Mercedes in that aspect.

Depending on the swap, if you are changing your ECU to match the engine, you may need to change your cluster. Changing the cluster might make a difference between cable or electronic, or electronic to electronic but with a different signal.

If the engine is the same generation, I expect you won't have any issues. If it's cable driven and you are not changing the transmission, you are good to go.

Edit - I did an Internet search - should have done this first. The W115s were manufactured from 1968 to 1976. As such, you don't have an ECU and associated electronic cluster. Keep the transmission and no problem. Swap the transmission and you may need to swap the speedo gear for correct ratio and perhaps a custom cable (length or connection).

  • Yes correct as in the original post it has a cable drive speedometer that comes of the gearbox. I'm concerned the ratios will be way different and how do I correct this with adaptation.
    – Ruben
    Sep 16, 2018 at 10:02
  • B the way its a 1 UZ Lexus V8 conversion with auto box that we are considering
    – Ruben
    Sep 16, 2018 at 10:05
  • Transmission shops can often help with the gearing. If not, an online search for a speedometer specialist can help. Texas Industrial Electric Co. has gear adapters and cables/tools, but looks like the ends are all SAE. Speedometersolutions appears to be a resource to custom build a cable.
    – David Sain
    Sep 17, 2018 at 0:19

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