Failed 240D Modulator?
 

I bought an 82 240D automatic and it was underpowered. I figured out some of the linkage rods were bent and it wasn't getting full throttle. It shifted really early and a little soft, but well enough. Adjusted the valves and changed the filters, runs really nice now.

I straightened the rods and adjusted the linkage so now it gets full throttle. At full throttle it still shifts low but will flare if you've got it floored. At half throttle it shifts at about the same places but doesn't flare.

Fluid level is right and the fluid is nice and red.

I removed the EGR and simplified the vacuum system, no changes. At this point I have the VCV, 3/2 valve, and modulator drawing from one T on the main vacuum line, and the shutoff drawing from the other. The car shuts off and the brakes feel fine, so I should have vacuum.

Messed with the VCV on the pump, from correctly adjusting, to excessive tension or very weak preload on the coil (exhausting random possibilities out of frustration last night). No change.

I ran vacuum straight to the modulator, no change.

Unplugged the modulator entirely, no change.

Turned the modulator up a turn, no change.

So, to me full vacuum or no vacuum to the modulator making no difference means the modulator is bad. I've never seen a modulator totally fail, does this happen? I believe its a 722.118. A new modulator from the dealer is $50 so if people have also experienced total modulator failure I'll order one Monday.

Since the .118 doesn't have a bowden cable and the modulator controls the shifts entirely, I would think its fairly critical.

As you have a 240 it's more likely a .117.

You have done very comprehensive troubleshooting, but one thing I did not see: did you test that the modulator cap is holding vacuum?

I also did not see that you checked whether you are getting good vacuum in the main line (at the brake booster connection) from the pump. My pump diaphragm was defective (and had been installed backwards) and I still had good brakes, shutoff and door locks.

I find it odd the VCV adjustments did nothing. If your main vacuum supply is indeed ok, my vote would be on swapping that out before messing with the modulator. I had more or less your issues with my .117 and adjusting the VCV spring tension made a world of difference.

Put it this way: they sell modulators as replacement parts, so I guess at least in theory they can go bad. More often it's the cap or something else.

Agreed - it should be a 722.117 for a 240D

I think it is worth checking to see if there is vacuum at each point along the line to the dashpot before you replace it.

Scientific I know but I pulled vacuum on the 4' line going to the modulator with my mouth and the line and modulator held vacuum.

I should probably go buy a mighty vac.

The VCV spring tension adjustment made such a difference on my dads automatic 83 240D taking it from undrivably quick upshifts to a a 240D that surprises other previous 240 owners because it will hold each gear out.

Thanks for the correction on the .117/.118 I think I came up with .118 reading various threads last night on my iPhone, pissed off that my car wouldn't shift right.

I was thinking zero vacuum or full vacuum would have made the transmission shift like a dump truck but since it did nothing I was thinking the modulator was the culprit.

I had a modulator diaphragm go bad on my W114 once. It would occasionally send a nice bit of ATF into the intake resulting in a huge cloud of white smoke. I think you can imagine what could have happened if I decided to test it by mouth:eek:

I can't speak much as to the other troubleshooting, since my stock answer to automatic transmission problems is to put a manual in it.

I found a spare .117 in my cache of engines and trans. I'll probably try a used modulator first.

Need to find my modulator pressure gauge.

If memory serves correctly. reading vacuum off the line leading to the transmission, it should be -.4 Bar or -11 HG of vacuum at idle. The whole shifting mechanism works by controlled leaks in vacuum which causes shifting for the 240D's didn't use a bowden cable. Vacuum off the pump should be around 21 HG.