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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Peter
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K

If you were really at 3500 at 70 mph with the auto tranny, something was wrong. At 3500, you should have been in the 80-85 mph range with an '85 (2.88 ratio). 3000 rpm at 75 sounds just about right with no slipping.

I agree what craig said. I think maybe your torque converter was slipping.

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1983 123.133 California
- GreaseCar Veg System

Torque converter = a few hundred RPM slip between the engine and the tranny.
Clutch = 1:1 RPM transfer from the engine to the tranny.

The auto trans was failing, and I suspected slippage. Moving off a stop would produce major groaning if I leaned into it. Hence the swap.

What is interesting is that I was getting a consistent 24 mpg with that auto, which led me to believe that it wasn't slipping that much on the highway, since that did not seem particularly low mileage.

I know some folks have claimed upwards of 30mpg. I never believed them. Maybe I'll change my opinion.

I'll post some results my next fill-up. Thanks for the replies

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Peter
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K

I predict 26 or 7 based on your previous experience.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

That sounds about right, getting over 30 mpg would require some serious effort, even with '85 gears.

just curious how she is off the line w/ 2.88 and a turbo? Is 1st gear deep enough for a fast launch if you want it?

is there another thread where these questions have been answered?

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Cheers,
Robert

No fast launch! I am still getting used to this clutch and the response of the 617, so it may be that it gets better. I tend to baby clutches, and not ride them. My gut is that it will never be deep enough for fast launch, unless I want to go through clutches.

I plan on experimenting a bit with it, since I have 205-15's and the stock rear. I do LOTS of highway miles, and will take slowness off the line for the better highway mileage.

I haven't studied the diff issue; has anyone swapped in a higher (lower??) ratio diff? Is one available? Seems I remember a discussion of this on one of the 4-sp swap threads.

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Peter
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K

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.

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Never a dull moment at Berry Hill Farm.

In my 300cd with four speed and 307 rear, the gearing is fine. We don't try for drag strip starts though.

In my 83 240/300d non turbo, it feels kindof tall but still workable, definately no drag starts with it.

Tom W

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Thanks for the data, RLeo. I thought that the speedo gears in the instrument cluster correspond to the diff, and that all the speed gears in the trans are reading exit rpm. Ergo, diff and cluster stay same, readings stay same.

That said, if the evidence is to the contrary, then maybe I am wrong.

Which cars got the 2.88 rear?

I'll have to do a GPS check. I am not worried too much about an inaccurate speedo, at least at that ratio. If what you are saying is true, then manual trans may differ as well, no? Trying to figure out how to match my hybridized car may be too much!

If it is reading high, my wife will like that. I have a heavy foot.

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Peter
1985 300TD 4-speed 212K
1992 400E 343K
2001 E320 72K

The 85 300D and 300SD came with the 2.88 gearing. 84 on down to 81-82, IIRC came with 3.07. I believe the non turbo 617 had different gearing than the 3.07.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

I have an 85 300 SD with a 2.88 rear end. With an automatic 70-75 mph is 3000 rpm (note it moves around a bit depending on the torque converter's mood at the moment). I would love a manual transmission. I dream about a CVT though.

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green 85 300SD 200K miles "Das Schlepper Frog" With a OM603 TBO360 turbo ( To be intercooled someday )( Kalifornistani emissons )
white 79 300SD 200K'ish miles "Farfegnugen" (RIP - cracked crank)
desert storm primer 63 T-bird "The Undead" (long term hibernation)

http://ecomodder.com/forum/fe-graphs/sig692a.png

Methinks N/A engined cars have 3.69:1 ratios.


And, I can state without a doubt, the speedo drive gearing differs between the manual and automatic transmissions. I don't know about all manual transmissions but, the speedo outputs on the old cast iron 4-speed I had and, the Getrag 5-speed that's in the car now are both the same.

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Never a dull moment at Berry Hill Farm.