1983 300CD

My speedo is off a bit. I sure could use a few reference points to keep me out of trouble until I can get it fixed or replace it.

For example, tach reading at 55mph and at 65mph,

or mph for tach at 3000rpm.

Something like that or whatever is convenient. I'm running stock tire size.

Thanks.

I think I am running 2100 RPM at 55 in my 300D-T automatic

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1983 300D-Turbo - Deep Blue w Palomino MB Tex (total loss in fire 1/5/09 RIP)
1995 E320 W124 Polar White/Grey Mushroom MB Tex
2005 F150 Supercrew - Arizona Beige - Lear topper
1985 Piaggio Vespa T5 - Black and Chrome

www.cphilip.com

I noticed that mine was off too. Then I remembered that my hand held GPS that I use for geocaching has a MPH setting. It is slow by about 3mph. Just a thought, if you have one or can borrow one to test it.

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"Any sufficiently advanced technology is indistinguishable from magic"
-Arthur C. Clarke

"I won't be wronged. I won't be insulted. I won't be laid a hand on. I don't do these things to other people. I require the same from them."
--John Wayne.

OBK member#16
77 300D
75 300D (rusty parts car)
73 220D (Dad's)
98 Jeep Grand Cherokee
82 Kawasaki M1

I'll take note tonight on the way home and post up.

45mph = 2000 rpm.

MPH X GEAR RATIO X 331 = RPM
TIRE DIAMETER

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82 300SD 202K
82 300SD 233K
83 300TD 340K
82 300TD 98k euro (parts on the hoof)
85 300TD 282K
83 300TD 197K

so... (45 X 3.07 X 331)/195? 14? now we need a chart to compute tire diameter ...
((section width)(aspect ratio)/25.4)(2)+rim diameter... 195/70/14 = (((195*.70)/25.4) *2)+14=24.75" diameter...


sooooo.... at 45MPH and with 195/70/14 tires on the car... you are traveling at 1847.73RPM... now that assumes 0 Torque converter slip... so say 5% slip... brings up the RPM's to ...1940

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Try this:

http://www.miata.net/garage/tirecalc.html

I saw that site... but it's not a formula... I found the formula... see above.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

It also depends on what gear the tranny is in at any given RPM. This looks like it assumes the car is in high gear.

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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

The SD's have a different rear end gear, I'll check the CD later today.

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83 SD

84 CD

75 MPH at approx. 3100 RPM

Wow! Thanks for all the replies.

I can see that my speedo is quite a bit off.

The car is new to me, and compared to my 300SD, this little CD just wants to go fast.

no, they do not.
year to year same as the 300D and CD/TD...
the 240 has a lower gear (numerically higher) but the SD is same as same year counterparts.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Exhibit A. See pic.
In my '84 CD, 55 mph registered 2500 rpm.

Attached Thumbnails

 

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83 SD

84 CD