Please help hard shifting! Can't figure it out!

[nckmsn]

I'm sorry to add another hard shift thread, but I have researched pervious post and still dont undertand my problem.

I have concluded that I dont have a vacuum leak that is causing the shifting problem. According to other posts I should now look at the vacuum modulator on the transmission. I understand that it is under a cap. I cant find the location of the modulator for the life of me. My vehicle is a 1980 300sd.

I guess my main question is where the hell is the modulator so I can adjust it with the "T".

Also, The car seems to shift normally from 1-2, but hard from 2-3 and harder from 3-4 with a clunk.

Thanks

[kerry]

Have you T'd in a MityVac to the transmission vacuum line and monitored the vacuum as the car shifts? I would get those numbers before adjusting the modulator.

[nckmsn]

Originally Posted by kerry

Have you T'd in a MityVac to the transmission vacuum line and monitored the vacuum as the car shifts? I would get those numbers before adjusting the modulator.

No I have not. I don't own one of them. How much are they and where can you buy one?

I have seen many people solving their problems w/0 the mityvac. Not to say that is the correct way, but it might be my only option as I don't own a mityvac.

I need to know the location of the vac modulator.

Thanks

[kerry]

MityVac's are available at lots of auto parts stores, Harbor Freight, Sears etc. You could also use a vacuum gauge. The reason I suggest it is that upstream of the transmission vacuum modulator is the vacuum control valve on the back of the IP. Until you know how much vacuum is going in and out of that vacuum control valve, I don't see a good reason to adjust the transmission modulator.
You can follow the vacuum line from the VCV to the modulator on the transmission.

[nckmsn]

Originally Posted by kerry

MityVac's are available at lots of auto parts stores, Harbor Freight, Sears etc. You could also use a vacuum gauge. The reason I suggest it is that upstream of the transmission vacuum modulator is the vacuum control valve on the back of the IP. Until you know how much vacuum is going in and out of that vacuum control valve, I don't see a good reason to adjust the transmission modulator.
You can follow the vacuum line from the VCV to the modulator on the transmission.

I have followed the line from the vcv to the transmission. It hooks to the transmission on a white plastic piece somewhat similiar to the vcv but with no linkage. If this is the modulator then how do you adjust it? I dont see anythingon it that resembles the "T" adjuster that other talk about.


I really do appreciate your help Kerry!

[kerry]

I believe there is a cover that needs to be removed to access the T. But I wouldn't mess with it until I knew how much vacuum it was getting. It could be that one of the reducer orfices is missing in the system and the VCV is sending too much vacuum to the modulator.

[nckmsn]

Okay. Is this the mityvac you speak of?

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=39522

Tell me yes and I am going to go get it right now!!

[kerry]

Sorry, I had that reversed. Hard shifts are caused by too little vacuum. The orfice could be plugged

[kerry]

Yes, that's it.

[nckmsn]

Originally Posted by kerry

Yes, that's it.

Okay Im going to get it right now. How when and where to I test the vac on vcv? Thanks man

[kerry]

T into the line coming from the VCV to the transmission, run the vacuum hose out of the cowl and lay the MityVac in front of the windshield so you can see the guage. Go for a drive and monitor the vacuum for the shifts in a variety of accelerator positions. It should start at some number (to be found in the big vacuum thread) and reduce to almost zero under full acceleration.

[nckmsn]

Originally Posted by kerry

T into the line coming from the VCV to the transmission, run the vacuum hose out of the cowl and lay the MityVac in front of the windshield so you can see the guage. Go for a drive and monitor the vacuum for the shifts in a variety of accelerator positions. It should start at some number (to be found in the big vacuum thread) and reduce to almost zero under full acceleration.

Just went for a short drive and only got to 3rd gear. The gauge read 0 the whole time!!!!

[nckmsn]

I am going to try again tomorrow when it is light out and I can assure good connections and no pinching of the line on the mityvac. Be back tomorrow!

[layback40]

Sounds like you have no vac getting to modulator. When you fix that, problem may go away! T adjustments are not something you just do without getting everything else correct first. They should only be done by some one with experience with autos & chances are they would want a gauge on the trans fluid pressure when they did it.
10/10 for kerry !!!

[kerry]

Originally Posted by nckmsn

Just went for a short drive and only got to 3rd gear. The gauge read 0 the whole time!!!!

That's why you're getting hard shifts. Could be as simple as a plugged orfice.