I previously asked about tires/wheels as my 940 has 205/65R15s on it. I finally got out my wife GPS and drove around testing and, darned if my speedo isn't spot on! (Speedometer - not the thing I was wearing while driving :)

I would have expected my odometer and speedometer to be reading low (says 70 when doing 75, etc).

Is my thinking wrong? What might be the cause of this accuracy? Do I have to now spend more money on tires to keep the speedo working (since this is "my son's car" if I ever let him have it)?

Transmission Issues: Kickdown, overdrive and jerking.

I think I can follow the FAQ and get the kickdown sorted out, but the other two issues I need a couple of hints.

Overdrive works. Is the little button at the back of the shifter nob supposed to disable OD? If that is not working is it possibly something simple like a burned out wire or do I have to take lots of stuff apart?

My biggest concern, saved for last, is that the car thumbs pretty hard when I go from Park to D or R or from R to D.

I do not know when the tranny was serviced last (if ever). I am thinking about going the Auto-Rx route but want to know if there are any mechanical things I should check first.

Thanks

The only issue you will have with the tires is rubbing in the tire well on sharp tuns.

Kickdown is easily adjustable so long as the ferrule/cable connection is properly crimped, if not, you will not be able to adjust it where it will hold. An undone ferrule usually necessitates a new cable. Adjustments should be made in increments of partial (60 degrees) turns of the adj. nuts ( go by the flats on the nuts). Small adjustments translate to big changes in kickdown. Look in FAQs for initial adjustment but then fiddle with it until it shifts properly.

Your OD, if not electrical is probably the valve unit. External on tranny & attaches with 2 bolts. Follow the FAQ's for checking it out.

Jerking (thumps?) could be as easy as a fluid change/cleaning as Steve said.
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1999 E320 1994 F150 1989 560 SL 1986 560 SL (deceased) 1988 300 TE (departed) 1994 945T (daughter's) 1988 244DL (it lives!) 1986 242Ti (fallow) 1968 GT500KR (under restoration)

IMHO - Unless the wide tires really bother you I wouldn't worry about them. They should improve the ride, handling and stability of the car. 185's seem pretty narrow to me for a 940. That is the same width as on my 240 and they seemed narrow on that car too. However, the 240 had smaller 185/70-14's. I have 195/60-15's on my 850 and those seem a little narrow for that car too...

I can't remember the specifics, but there is a tire principle I believe is called "plus 2". It states if you widen your tires by a certain size and aspect ratio the speedo will stay accurate. Perhaps that's what the previous owner did?

When you say "thumbs" do you mean it bangs going into gear? A flush is a good idea but you might also want to check your shift linkage (and its little bushings) and your driveshaft u-joints. As Steve mentioned it could be worn tranny or engine mounts.

Is the engine still occasionally knocking?

The thump is really just a surge. There's not much of a noise associated with it.

I had some SeaFoam and tried that in the gas. Only a 1/4 tank through that. If anything it has made the knocking/tapping worse (but not massively).

Between tweaks to the timing belt and snugging up the kickdown cable it seems to behave better at high speeds (other than the knock), but I have not had time to do the kickdown properly and follow the FAQ.

I have, unfortunately, been devoting time to my Chrysler T&C (now nicknamed "Satan"). It has 206K on it and I decided the spark plugs needed changing. The only good out of that is I think I am afraid of NO task on the 940. I'd like to find a Chrysler engineer and ...

Anyhoo, thanks for the input. I leave for a week's "vacation" tomorrow and when I get back there is a "new" 1994 940 wagon at my favorite junk yard. I must go scavenge.

The small switch at the back of the shifter shuts off the OD unit and downshifts into third gear. If it is not working, look at the FAQ diagnostics for relay, wiring, switch.
Try the easy stuff first: drain, flush, AutoRx etc. Look at both the tranny and engine mounts to see if they have compressed. More in the FAQ.
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See the 700/900 "FAQ" at the menu bar top screen left side.