My 85 300D won't downshift at Highway speed unless I back off the gas (well, actually Diesel) pedal.

The tach climbs to 4000 rpm as I hit the 45 to 50 mph range, even if I floor it. If I let up on the accelerator pedal, or back off on it, I get the downshift, which seems to be smooth and well modulated.

In troubleshooting, I always check the last thing I touched. I recently pulled the IP to retime the engine and I disconnected a lot of linkages and hoses. I may have bent some linkages unwittingly. One question I have is why the tach won't climb higher if I floor it. For some reason I think there is more RPM available bu the travel in the linkage may be misadjusted so when I floor it, I can't get full travel at the IP.

The other point is the car sat idle for three months while I repainted it. During that time i would only take it around the block once a week to keep everything "moving". but I rarely went over 20mph.

..........won't downshift??


or, more likely..........


..........won't upshift??

Glad to see I got your attention Brian, I know you know transmissions! She won't downshift to kickdown the RPM...

If you want the RPMs to go down you are actually upshifting, downshifting would be going into a lower gear with more RPMs. Did you reconnect your bowden cable? That seems like it has the most effect on shift timing, the vacuum modulator is more so how hard or soft not so much when.

There is an adjustment for the throttle linkage as the rod comes through the firewall. Have an assistant or wedge something on your accelerator to see if it does actually go all the way, if not you should be able to adjust it out with the bolt by the firewall or worst case pop one of the ends off and make the linkage longer.

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Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

What Jeff said.

It appears that she won't upshift. When you lift your foot, the trans. upshifts and the rpm's drop.........correct?

I guess it should want to kick to a higher gear, say 2nd to 3rd ( I am totally clueless about automatics and I don't know how many gears she has )so that the RPM drops, but instead it stays at the lower gear, in this case 2nd.

It was working fine before I painted her, so I guess I must have bent the linkage or something when I pulled the Injection Pump. I took a peek under the hood and it looks like something is bent.

Its raining Elephants outside, I got to wait some time

You have a four speed automatic. If your engine is turning 4000 rpm in the 45-50 mph range, I would say you're stuck in 3rd gear. This could be a lack of vacuum or a cable adjustment. Are your upshifts to that point okay? Paul.

__________________
1984 300CD red/blk 290,000 partial resto
1980 240D 4 sp Brn/palomino gone
1997 Mazda Miata STO edition wife's baby
1988 Lincoln Mark VII LSC next resto
1986 Subaru GL wagon daily
1993 Isuzu pickup field beater
2008 Honda Civic EX-L 5sp wife's new car
1978 Honda XL350
1974 Honda XL70 my Calif. ride in HS

I would say it is pretty safe to rule vacuum out of the equation, I've drove around before with my modulator line completely off. It only caused abrupt shifting. If you had bent accelerator linkage it'd be making the car go faster or slower for the same pedal angle, not really dealing with the shift point just where your foot is. I'd say it is very likely the bowden cable is your issue.

You are correct it would be in second waiting to shift into third as third doesn't get into those RPMs until upper 60s. Remember hash marks on cluster.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

Thats the other thing I disconnected was my vacuum lines. For some reason my car has "California EGR 85" Vacuum configuration in the engine compartment and its a real spider web compared to the simpler vacuum configuration of other models. It has a Vacuum Amplifier on the fender for the Feed to the transmission instead of a direct feed from the modulator and it also has an EGR. When i pulled my Injection Pump I had to drop my oil filter tower and to get to those 27 mm oil hose nuts, I simply disconnected all the vacuum lines to avoid anything getting broken. I followed the diagram carefully when I put it back together...but I know somewhere something is leaking.
However its my understanding theat the Vaccum modulator only causes smoother shifting, not missed shifting. Rebyuilding an Automatic Trans was always a "Next Year" project because personally I love 5 speed manual...

I know that cable well, its a pain to hook up a new one, you have to disconnect a lot of stuff to get to the "hook" where it feeds in. when I did my valves I took the linkage off and my cable was hooked to the linkage and could be tangled when I put it back on............

Exactly.

I've never had to put on a new bowden but their influence on shift timing is huge. If it is indeed the cable it would be pulled out to far as it being further in would cause early shifting.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k

Possible clogged fuel filter???

__________________
-disav

99 E300 TURBODIESEL Astral Silver 282K - AMG brakes, suspension, monoblocks, speedo & interior - Full Load Maxed on IP by custom Speed Tuning USA Chip - T3/T4 Garrett - EGR/MAF delete
98 E300 TURBODIESEL Alexandrite Green on black leather 289K
95 E300 DIESEL Green Queen 267K SOLD
84 300D 216k SOLD
87 300D 299K #22 head - intercooler - full load adj. - 8sec 0-60mph - SOLD
76 300D 214K SOLD

It was routed "tight" ie taut around the automatic transmission fill stick. I rerouted it. It shifts properly but still a little too slowly.

So to make it shift a bit quicker, do I have to turn it (turn the plastic threaded part ) to make it shorter or longer.

I went through this whole scenario in 2002 and I forgot already. Boy I got a lousy memory.

And I did part of an auto trans rebuild, but it was a FWD on a Honda

It cannot shift "slowly".

Either is shifts "early" or it shifts "late".

If it's late on it's shifts, you need to put a bit more slack in the cable. Turn the plastic adjusting nut inward (clockwise, IIRC).

Well it can actually shift slowly, but that doesn't have anything to do with the Bowden cable. If it is literally shifting slowly the modulator is getting a high vacuum.

If you want it to shift at a higher RPM you want to back the plastic piece out, if you want it to shift at a lower RPM turn the plastic piece in.

__________________
Jeff M.
Mercedes W123 DIY pages are now located here.
1983 / 1984 300D Sold
2000 CLK430 Cabriolet ~58k Sold
2005 Avalanche 4x4 ~66k