marlinspike

The car was working fine one moment, parked, driven again a couple of hours later, and this problem was present: shifts were suddenly very firm and occurring about 500-750rpm later than one would expect for the throttle position. I loosened the bowden cable thinking this will help, but it doesn't really - I can loosen it so much the car spends no time at all in 3rd, but it will still spend more time than it should (albeit by less) in 2nd. Also, it does the 1-2 shift late at full throttle and the 2-3 shift doesn't even want to happen at full throttle (will just keep banging off the rev limiter). If I unplug the kickdown switch under the pedal, the full throttle shifts will be fine. Ideas?

Landseer

Maybe something simple.
Emergence of a vac leak, source being the modulator valve, possibly cracks its rubber cap, or the line running to it.

The modulator valve regulates mainly the hardess of the shift, with no vac meaning very hard.

Bowden adjustment affects primarily when the unit shifts.

I realize you are seeing both behaviors, but you might start by performing a vac test at mod valve.
Hookup the vac line to a vac gauge (like an acton from Advance auto, or mighty vac) and see if it pulls solid vac with engine running. Then, instead, connect the device to the mod valve and, pump it down an see if valve holds vac.

marlinspike

Vacuum admittedly confuses me. By any chance do you live in the Tidewater and feel like exchanging your vac testing equipment and some time for a meal?

Landseer

I'm pretty far away from there.
The vac check work is fairly simple and the equipment is trivial in cost.

But is this the transmission youve posted about before, the one in the Mercedes Benz with engine mods?
If so, based on history, I'd probably opt to ask a real transmission shop to assess it more fully, measuring the circuits with pressure gauges. If the mod valve was ever adjusted, say to address 2-3 flare, then my understanding is a flare reduction kit should be put into the valve body and the mod valve reset using pressure gauges to guide.

marlinspike

Yep, that's the one. The thing that gets me is why it would work fine for so long, then suddenly not work properly after being parked. And yes, the modulator valve was adjusted pretty much to the max, not just for 2-3 flare (even after the flare reduction kit) but also to get firmer shifts in general. I tried reeling that back a bit last night and it did seem to help, but even if I made the pressure so low that the 1-2 shift would flare, it still exhibited symptoms.

I don't hear any clicking from under the car if I hit the kickdown with the ignition on and the engine off, so maybe the kickdown solenoid is sticking given that if I unplug the kickdown the 2-3 shift will occur without banging off the rev-limiter? I did notice one time just driving around normally it wanted to hold 2nd, not just longer than normal, but seemingly until redline.

Landseer

So its got some squirrely intermittent behaviors?
Time to take the empirical DIY hat off and get it to a pro.

marlinspike

Yea, based on my drive to work I would say intermittent. Problem with getting to a pro is I'd have to take a day off work. If I had a shop I'd close sunday and monday.

Landseer

Me too !!!!

WallyP

If unplugging the kickdown solenoid makes a difference, it sounds more like an intermittent electrical problem than a sticking valve. I would start by seeing if there is power on the solenoid without the pedal being all the way down. If there is, find out why.

Cosmo Kramer

You have to set the modulator back down. Too high of line pressure at WOT will cause a no-shift condition from 2-3. I had this exact problem with my 85 when I added the supercharger, the boost pressure (instead of 0 vacuum) was causing the modulator valve to increase the line pressure to the point that it wouldn't upshift 2-3 and slam the limiter at WOT. If I lifted just enough to release the kickdown switch it would shift. In my case I installed a bleed valve to my modulator so it would not see boost (0 vacuum like stock) and adjusted the modulator until my shift firmness was where I wanted it. After that shift points were restored and I was actually able to put my bowden cable back to normal adjustment.

In your case, the modulator has been cranked up to hide another problem but has created a new one.

marlinspike

The weird thing is that I've been driving with the modulator set that way for 20k miles. Maybe since it's a fairly new modulator it never seated right until now or something.

marlinspike

Does it mean anything if twice today it was physically hard to put the shifter into R from D, like it was caught on something?

Cosmo Kramer

Could be a sticky linkage.

BTW when was the last time you changed the fluid/checked fluid level?

marlinspike

The fluid has about 20k on it. I'm going to change it, but it looks/feels/smells good. And the level is fine.

marlinspike

And today I got on the highway after getting gas and found I couldn't get 4th gear. I was picking someone up from something of an emergency situation, so I just pulled over and put a ton of slack in the bowden cable to get 4th again, but sheesh. I think this trans may just be on it's way out, but I had to replace a trans when there is probably one particular thing wrong with it. I checked the fluid again and it's about 0.3 liters high. No idea how that would happen, but it's not foaming either so I have my doubts that it's related. It will work fine more or less without the kickdown, but hit that kickdown and something will fail (either it won't give me 1st when it should or it won't let me make it past 2nd gear and 1-2 will work but be later than normal).