Speedo year / gear ratio info - PeachParts Mercedes-Benz Forum

BIGRED · #1 11-21-2007, 01:56 AM

Our wagon is a 1980 and had 3.46 gears. A turbo motor was dropped in it and a couple of years ago I changed the rear end to 2.88 gears. That caused our 80 MPH speedo to be off about 10 mph.

I came across a cluster that has a newer speedo in it. I have not been able to reference any numbers on it to any numbers I can find on the EPC to see if installed, will it but back into place the proper speed. Or, do the gears in the speedo have some identification that ties them to the difference ratio?

The face of the speedo has 123 542 27 57 between the MPH and VDO and goes to 120 mph.

Thanks for the help
Don

DeliveryValve · #2 11-21-2007, 02:20 AM

Quote:

Originally Posted by BIGRED

....The face of the speedo has 123 542 27 57 between the MPH and VDO and goes to 120 mph.

Thanks for the help
Don

I believe that is the correct speedo for the 2.88 diff.

winmutt · #3 11-21-2007, 09:05 AM

How does the 2.88 in a non turbo feel?

BIGRED · #4 11-21-2007, 09:11 AM

No idea...

When it was a non turbo it had 3.46. Then the turbo engine and finally the 2.88's.

BIGRED · #5 11-21-2007, 09:12 AM

Quote:

Originally Posted by DeliveryValve

I believe that is the correct speedo for the 2.88 diff.

Well... I suppose I can go for it and see what the result is.
Thanks
Don

BIGRED · #6 11-21-2007, 11:56 PM

Installed the newer Speedo....
It works...but..
By the seat of the pants feel, it seems that the speed being reported is higher than actual.

I don't see how that is possible as I (at least what I had) am running the highest gear ratio. If that's the case, then it shouldn't be possible.

KAdams4458 · #7 11-22-2007, 12:26 AM

Quote:

Originally Posted by BIGRED

Installed the newer Speedo....
It works...but..
By the seat of the pants feel, it seems that the speed being reported is higher than actual.

I don't see how that is possible as I (at least what I had) am running the highest gear ratio. If that's the case, then it shouldn't be possible.

That does seem more than a little strange. I think I'd do some verification using mile markers.

Off topic, but I'm curious to know how the car felt with the turbo engine installed while it still had the 3.46 rear end in it.

BIGRED · #8 11-22-2007, 12:53 AM

It chirped tires going into 2nd...and the shifts were even harder than what is a typical - already hard shift.

Would have been OK for a in town car. On the highway it was always revving way up there..I would guess at least 500 RPM higher.

We so much prefer it now.. and I am going to begin running some fuel consumption tests and am guessing it has gone north a fair amount.

Yet to be seen, checked and verified...

Assuming with the lower gears at 60 mph...I was getting 21 MPG, I used 2.8 GPH and was running at 3000 RPM.

Then at 70 mph I should get 25 miles per gal on the same 2.8 GPH running at 3000 RPM with the taller gears. Of course the torque needs to be there to pull it or I will be increasing throttle and everything I stated is mute.

KAdams4458 · #9 11-22-2007, 01:46 PM

Quote:

Originally Posted by BIGRED

It chirped tires going into 2nd...and the shifts were even harder than what is a typical - already hard shift.

Would have been OK for a in town car. On the highway it was always revving way up there..I would guess at least 500 RPM higher.

We so much prefer it now.. and I am going to begin running some fuel consumption tests and am guessing it has gone north a fair amount.

Yet to be seen, checked and verified...

Assuming with the lower gears at 60 mph...I was getting 21 MPG, I used 2.8 GPH and was running at 3000 RPM.

Then at 70 mph I should get 25 miles per gal on the same 2.8 GPH running at 3000 RPM with the taller gears. Of course the torque needs to be there to pull it or I will be increasing throttle and everything I stated is mute.

Well, that's good information. I may well end up swapping a turbo motor in to my '77, since N/A motors are apparently not easy to find at a reasonable price in this part of the country. Turbos, on the other hand, are plentiful and far less cash. This says to me that if I do the motor swap, I should also keep an eye out for a 2.88 rear end. 3000 RPM at 60 MPH? Holy crap! Great for hauling a boat, maybe, but I'd rather not eat so much fuel.

Thank you for your insight!

BIGRED · #10 11-22-2007, 03:09 PM

Quote:

Originally Posted by KAdams4458

Well, that's good information. I may well end up swapping a turbo motor in to my '77, since N/A motors are apparently not easy to find at a reasonable price in this part of the country. Turbos, on the other hand, are plentiful and far less cash. This says to me that if I do the motor swap, I should also keep an eye out for a 2.88 rear end. 3000 RPM at 60 MPH? Holy crap! Great for hauling a boat, maybe, but I'd rather not eat so much fuel.

Thank you for your insight!

Maybe.. they had a 85 mph speedo in there for a reason.... top speed at redline..

KAdams4458 · #11 11-22-2007, 03:28 PM

Quote:

Originally Posted by BIGRED

Maybe.. they had a 85 mph speedo in there for a reason.... top speed at redline..

Heh. Amusing though. Too bad the 85 MPH speedometer was a "brilliant" Federal Government stipulation in those days. Interestingly enough, my '77 300D speedometer reads to 110... As if that would ever happen. Ha!

#12 11-22-2007, 05:38 PM

The 110mph speedo is perfect for the 3.46 ratio. The top speed limited by RPM is 107-109mph.