Does anyone know if the tach on the left (no red line) is a OEM W108/109 MB part. If so which engine or engines was this used in. The one on the right is from a W109 6.3.

It looks like it'd be for a 3.5, since it goes to nearly 7k and the 3.5 redlined @ 6800. I imagine it may have also been used on 4.5s with the 6k redline, as the line isn't marked like the 6.3's is.

__________________
Current:
2021 Charger Scat Pack Widebody "Sinabee"
2018 Durango R/T

Previous:
1972 280SE 4.5
2014 Jeep Grand Cherokee Limited "Hefe", 1992 Jeep Cherokee Laredo "Jeepy", 2006 Charger R/T "Hemi"
1999 Chrysler 300M - RIP @ 221k

Can you shoot a picture of the back?

I have looked through all of my manuals and cannot find any mention of a factory tach for the 108/109 besides the 6.3 tach.

It could be a tach VDO offered if the owner wished to swap out their clock for a tach. One that might have been sold and installed by a dealer but never offered by Mercedes as a factory approved option. I have run across a number of such dealer installed 'options' over the years. You could even get a rear A/C set up from the factory if you wished to pony up the big bucks. Or a dealer could install one for about $1,000.

It might also be a marine tach. VDO made those and back then they were all about the same size as the ones you would find in autos.

I will post more pics later today of the 7k tach.

Okay here the pics.

The back of the 7k tach.



The back of the 6.3 tach.



This is a side view of both. The only difference between the two other than the rpm scale is the chrome ring. The 7k tach (on left) has a beveled lip where it would touch the instrument cover.

You might need to post this to the M-100 board or change the name of your thread to 'Is this a 6.3 tach?'

Because from what I can see I think you have two 6.3 tachs but of different styles. The color code of the wires is the same and both of them allow you to go to 6,000 rpm but not much more.

The bright screws in the face of one of them does not fit with the overall mode of the 6.3 interior but it could have been rebuilt along the way.

The only way to really know is to contact VOD with the catalog number which is the 230/29/4 on the back.

Note the codes of 24000 and 28000, respectively, on the two instruments.
6000RPM x 4 pulses/revolution = 24000
7000 x 4 = 28000
Both tachs are for 8 cylinder engines.

I checked the M-100 board doing a search and came up with this thread.

M-100 Message Board - 6.3 gauge in a 3.5

Looks like as Tom suggested in his reply this is a tach for the 3.5 M116. From that thread the 4.5 had its own tach.

I will contact VDO with the part number to see what they have.

Thank you all for the responses and info.

Idle, any chance you can provide more info on the factory rear ac MB offered. I have seen a photo of a Japan market W108 with a really old rear AC system. That was said to be after market though.

From what I have found the only factory rear air offered during the 60's and 70's was from the factory and then they were usually found only in the 600.

You can tell a factory installation from an aftermarket by the air inlets for the rear unit. The Factory units had air intakes on the outside of the car; small air scoops mounted on the sides of the car just behind the rear doors.

There were also large scoops you could get if the factory thought you needed them.

The after market units were box shipped units that mounted in the trunk in the space under the package tray and between the real wheels. This must have made getting to the bolt that holds the rear axle support to the car quite a chore.

These units were heavy, usually about 45 pounds, and their air intake was in the middle of the package tray where a 6x9 speaker could be mounted. The air outlets were to either side of the package tray where 3.5 inch speakers could be mounted. The outlets had grills that covered them to keep you from dropping things in there and air vents that directed the air away from the back glass and into the interior.

The controls for the unit were mounted under the dash where the driver could reach them.

The whole thing was secured by pieces of usually angle iron that had to be cut to fit. Supports under the units helped to keep it off the floor and up against the the package tray.

The whole thing was tied into the front under the dash AC. The front AC was to keep the front passengers cool and the rear was to keep the entire car cool. The theory was you would have the car's interior cool without air blowing on your face or hands. Older people are known to dislike the cold air blowing on them so this was the solution.

There were normally two blower motors with easy to obtain motors. This way the owner could be sure of finding a replacement blower motor if they were away from home.

These come up on Ebay now and then, and I don't know of any additional value a factory unit would have over an aftermarket unit. With a factory unit you would need to cut holes in the side of the car for the inlets since there is no central intake through the center speaker hole.

By the way, this takes up so much room in the trunk that there is no way to install rear speakers unless they are mounted above the package tray.

This installation also requires a drain hole be drilled in the floor for the drain hose to go through. This is no big deal but it is something you would want to do before mounting the unit. Space between the wheels is tight after the unit is installed.

One last thing.... These aftermarket units were built to fit a large number of cars and none were built to be Mercedes specific. If you start looking for one then I would recommend an ARA as they seemed to build one of the strongest units for this type of application.

Thanks Idle.

That rear OEM AC system seems like a real PIA to retro fit assuming one can even find one for sale.

Here is another link to variations on these tachs.

M-100 Message Board - Mystery quiz.

I have a 3.5 with a 6.3 tach that i'm in the process of bring back.

__________________
With best regards

Al