I have an 83 F-150 4x4 with a 351W and C6 transmission. It was wrecked in the front end hard and the engine didn't run when I bought it. I put a new front clip on it and got the engine running. That turned out to be the timing chain. Then the first time I drove it, it shimmied like all get out (33x12.50's). I couldn't drive it past 35 mph. I put all new tie rods on it and a shimmy shock. And it also didn't have good brakes. I put a junkyard booster and master cylinder on it and bled all 4 wheels. So now it's driveable but it won't shift past 2nd gear. Ok, no biggie. I changed the fluid and filter and put in a new modulator. This should have done the trick. But it didn't. I have good vacuum at the modulator and the old one was not sucking fluid. I have two questions about this. The new modulator is a little different from the old one. The pin sticks in the old modulator like it has a socket that it is supposed to fit in. The pin does not fit the new one like this, therefore the pin sticks out further. If you were to turn the old one with the pin in it sticking down, it will not fall out. The pin will fall out of the new one. Do you reckon this could be a problem? I have not adjusted the modulator yet since they are usually pretty close to where the need to be. I don't know exactly how much vacuum it has at the modulator, but when I disconnect it from the modulator and put my finger over the line, it pulls on my finger pretty good. And the modulator makes a really fast clicking noise. I have never heard this before. The vacuum source is from the vacuum tree on the firewall. My other question is can someone tell me what this electronic thing on the side of my transmission is? I have a picture to show what I am asking about. The shift linkage from the steering column connects to it and the kickdown rod does too. Thanks for any insight on this problem.

 

No one knows?

 

the thing in the picture is the neutral safety switch and the reverse light switch. the modulator should have full manifold vacuum

 

Thanks, 84-250. I don't know why I didn't think of that being the neutral safety switch. Apparently, the guy who had it before me was driving it with the modulator connected to the tree. I will try to connect it straight to the manifold and see what that does. At idle, that hose has pretty stong vacuum. I'd say it's comparable to when you stick your finger over the pcv valve. Man I need a vacuum gauge!

 

just trace the vac lines from the tree to the manifold, there are only two kinds of vacuum, ported and manifold. if you have strong suction at idle, then its manifold vacuum.

 

Well, then if it has good vacuum, what do you suggest could be wrong with the transmission? Or do you think I just need to adjust the modulator?

 

I should add that the transmission shifts fine from first to second. Then it just stays in second. I have went as fast as 70mph to see if it would shift into third. It downshifts to first like it's supposed to when you slow down or stop.

 

If it shifts 1-2 at the proper speeds the modulator is not the culprit.

3rd. gear uses the same clutch as reverse. If reverse is a bit slow engaging the direct seals or clutches are worn.

The only reason reverse would be stronger is from increased oil pressure.

 

Reverse is not slow at engaging at all. I had disconnected the kickdown rod to see if it was keeping me in 2nd. No luck. So, thought I'd change the location where the modulator gets its vacuum. I hooked it to where I had a plug on the manifold. Now my transmission is shifting fine. Thanks for the replies.