Quote:
Originally Posted by peterhardie
I just completed (well, still waiting for a shift boot actually) a manual conversion on my wagon. Things are ducky. I love it.
But... everyone else here has said they had no change in final drive rpms. I am reading 3000 rpm at 75; with the slush drive it was 3500 at 70. The needles used to be parallel on the highway. Now 60 mph looks in 2000-2500 rpms.
New speedo cable (old 240 style, my trans is from a 79) same rearend, same instrument cluster.
California car, not that I think that means anything.
Any ideas???
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First of all, the speedo drive gearing inside the transmission is different between the manual and the automatic so, the original automatic speedo will indicate a higher speed when it is connected to a manual transmission.
I don't recall anyone ever stating that the speedo indicated correctly after a conversion (Go
here and see posts #119 & 122). My conversion to manual (tranmission only, no change in speedo and the car has 3.07 gears) resulted in an approximate 7-10% error at the speedo ie: an indicated 75mph is actually 68-70mph. Likewise the odometer indicates high.
I assume that your car has a 2.88 rearend so, I suspect that you had/have a couple of things going on:
1) Your speedo was already reading a bit fast. A car with a 2.88 rearend will turn 2750-2850 RPM at 65 MPH. At 70 it will turn a shade over 3000 RPM. For reference, a stock 300D with a 3.07 rearend, an automatic and standard tires running at 3450 RPM would get you 75 MPH as seen below (speed confirmed by GPS in this situation):
2) Your automatic was slipping pretty badly. Per above, 3500 RPM at 70 MPH is higher than the normal revs for either a 2.88 or 3.07.
What's the solution? Well, I'm not sure. I believe that there are three different internal gearings available in the 123 speedo so, one thing might be to use a speedo out of a manual-equipped 123. But, there will still be an error since the manuals have 3.60someting gears and you have 2.88s or 3.07s.