Out driving the truck today and out of knowwhere....it starts having trouble shifting. It really waits to upshift until RPM is pretty high...unless i lift off the throttle then it will shift fine. On some shifts, it realy labors to get to the next gear, pauses between gears and then slips into the next.

Just bought this thing a couple months ago so not sure of the history of the tranny.

Checked the fluid level and it is fine. Fluid is nice and bright red and don't smell burned.

Could this be a modulator causing this or something more serious?

 

Make sure the vacuum line for the modulator is hooked up on both ends. At the engine, it should be hooked to a manifold vacuum port.
If it appears to be hooked up on both ends, pull it loose from the modulator. If fluid drips out, the modulator is bad. If no fluid drips out, check for vacuum getting to the modulator.
A bad modulator, or one not getting any vacuum, can really make the trans shift odd, and late.

 

Thanks for the tip...just had new exhaust ran so will get up there and make sure they didn't yank the line off the modulator...and make sure it's not up against a pipe and melting

 

Also make sure there is no trans fluid in it, as that indicates a bad diaphragm, replacement needed.

 

And, make sure the hose is good. One of the guys on here, although I don't remember which, had a hose that was collapsing under vacuum. And lots of us have had hoses that cracked or split, dumping the vacuum before it gets to the business end.

 

Well disconnected the hose from the modulator...no transmission fluid there. Checked all the hoses and connections and they all seem to be good. I guess that rules out the modulator as being the issue and leaves me with something is drastically going wrong with the transmission. Guess it's time to take it to a transmission shop.

 

I'm not sure if a blown diaphragm in a vacuum modulator always shows up as ATF in the hose, but if it were mine I would check to see that the modulator isn't blown before taking it to a pro. I'd put a clean piece of vacuum hose on it and suck on it to see if it is blown or not. (Actually, I'd put my Mityvac on it, but you may not have one so...)

 

Yeah I think for $15 I'm just gonna replace it

 

Good plan, Stan. If it fixes it you'll have saved a lot from the tranny shop. If it doesn't you now know it is good and can move on to other possible prob's.

 

Have you check the band adjustments? If they are loose, the trans will have bad shifting characteristics. The bands will not grab the drums hard enough and slip.

Intermediate adjustment: On drivers side - Loosen lock nut and back out stud about 1/2-3/4 turn. Tighten stud to 120 inch pounds. Back out stud exactly 1 1/2 turns. While holding stud, tighten lock nut. Remember, the torque value in inch-pounds, NOT foot-pounds.
If it's going into first and reverse just fine, don't worry about the other one.

If the band is just stretched or worn a little, this may fix it. It may be possible that the band or other parts are worn past their life.

 

Bands have nothing to do with shift points, and if they did, it would only affect 2nd gear. There is only one band, intermediate. The intermediate clutches do most of the work, the band helps them. If the band was the issue, it would actually slip going into 2nd, then go to 3rd normal. Only 3 things affect shift points across the board: governor, throttle valve, and modulator valve.

Need a little more qualifying info here. When it shifts,does it shift hard or soft? Also, another simple check is to be sure the downshift rod is connected, not all that uncommon for them to come off at the carb. If it does, it will settle downward and back, which will move the tv into position as if you are standing on the gas, delaying the shift points.

 

ok gentlemen...here's some more information on what this thing is doing. I'm pretty limited on the automatics so I'm going solely on what makes common sense to me.

Today when I was driving it, had it in "D" and just drove off the line gently. When it was trying to go to second it just kinda stays there and then eventually, very slowly goes into second....with a delay between gears. Like it's not real sure it wants to go there. Des the same thing going into third. Next time when it got to the point where it was about to go to second, I pulled the shifter down into 2 and it shifted no problem. Went back to D and it went right into 3rd.

From there I did a little driving around the block a few times manually shifting it the whole time. If I manually shift it, it shifts great. Nice solid, not harsh, shifts right to the next gear. That's shifting up and down.

To me, this tells me everything internally is ok...as long as you tell it what gear to be in. If you leave it on it's own...it don't know what gear to be in. That tells me modulator just not telling it what gear to be in. If the transmission (clutches, bands) where going bad, would it not still have problems shifting manually?

Not sure if my reasoning is valid...but I'm sure lots of you know much, much more then I do on these automatics.

Another queston, not related...any of you have experience with these 460's not wanting to be timed to factory setting? I've retimed this thing to factory setting several times, with the vacuum advance off. When I hook the vacuum back up it settles in at about 12 degrees advanced. The thing just don't like it there. It sputters and backfires. I got it at about 20 advanced now (with the vacuum connected) and it's ready to go!!! Loves it up there. Not sure if it's the carb / manifold making a difference or not. The way I see it, set it where it likes to run and leave it alone

 

From that description, it could well be a bad modulator. And, no, they don't have to suck fluid to have failed. You do add a little bit of line pressure by shifting manually, which will engage the clutches a bit better. Basically, shift points are a balancing act between two sides of a valve, you have pressure to the governor, which controls how much fluid gets through. Then you have pressure from the throttle valve ( controls line pressure) and modulator valve. this balancing act moves the shift valves according the the varying pressures. The governor pressure does not change per gear, it is a steady pressure changed in relation to drive shaft speed. Only the throttle valve and modulator valve change pressure per gear.

The reason I asked about hard vs soft is that a hard shift indicates throttle or modulator trouble, while a soft shift indicates governor trouble. When you stomp on the throttle you want more pressure on the clutches to try to prevent slippage due to torque, it increases the frictional resistance by increasing the pressure. This is by design.

Governor trouble will cause late but soft shifts, as the pressure from that side is not as high, so the line pressure does not get raised.

 

About your timing, I'd be suspicious of a harmonic balancer that's slipping (the rubber in between the two rings) and that's throwing you off....

 

that's a great explanation...thank you. What I plan on doing is replacing the modulator because it's so easy and cheap to do. If that does nothing, then it sounds like from your decription it might be the governor.

in this picture...what am I looking at and do those numbers mean anything to you? Now you know how little I know about automatics .
I'm trying to see what year this tranny is but can see the VIN on the top.