The Stovebolt Site Forums The Shop Area Driveline TH350 question????

Just aquirred a vehicle with a 350/350 combo. Took it on it's first road trip Sunday and quickly noticed it only shifted once from low to 2nd. Not familiar with a TH350 but Wikipedia says it's a 3-speed tranny. Any idea why it's not shifting into high gear? Runs great but feels comfortable at 50-55 mph and got 19 mpg. Verified shifting by the tach. RPM's dropped only once when it went from 1st to 2nd. Not again.

Any help appreciated!

Are you sure it is a Turbo 350? Sounds like you have a Powerglide.

Sounds like a powerglide to me also. The powerglide will have a vacuum modulator on the back drivers side of the case, while a TH350 has one on the passenger side rear of the case.

Does the spread between shifts seem a bit wide? If so I bet it is a powerglide and not a th350.

I'd say you have a powerglide not a 350turbo. At 50/55mph in second gear you're not going to get 19 mpg. What was the tach reading at 55 mph?

Let me answer a couple of questions to help us along here.......

1. Haven't looked underneath yet to look for a modulator.

2. Spread between 1st and 2nd was pretty quick.

3. Tach reading at 40 mph was appx. 1,600, at 50 mph it was about 2,100, at 55 mph about 2,500 and at 60 mph about 2,700.

I was assured by the seller it was a turbo 350, but I realize the shifting may sound to you guys like it's a powerglide.

Is there a vacuum hose that may be off that is stopping it from shifting into 3rd? Some adjustment that needs made? I've made sure that the shifter is NOT put into 2nd gear and therefore not allowing it to shift into high.

how many dedents on your shifter?
I would think the RPM would be much higher than 2700 @ 60mph if you are in second gear

Still getting used to it, but I do believe it has 3 dedents.

The modulator valve on the back of a 350 is what controls the shifts....right. Inside the nipple is a screw that can be turned in but not sure which way is higher or lower. If its bad then it could be the problem. I checked on one for a guy last week and one of them is about 40-45 bucks at the discount store.

I'm watching to see what others think....because I think I may have the same problem but I just can't get mine up to speed on my street.....will be on the road Feb.

Boyd, I tend to agree with you!

TH350:l-2-3-N-R-P=6
PG:L-D-N-R-P=5
I hope this helps

Boyd

Turn the screw inside clockwise to make the shifts later, turn it counter clockwise to make the shifts sooner.

Be very unlikely the transmission would shift if the vacuum line is bad. If it shifts at all it will be very late and harsh.

There's also a chance you may be taking off in second gear. But I think you would notice that because the engine would have to work a bit harder to take off.

Your rpm readings look like it is in high gear.

Would help to know more about the vehicle, year model, rear end gear ratio.

Just went out to check the shift pattern and this is what it is....

l-2-3-N-R-P=6 (just like Boyd says)

Lokar shifter ball has this printed on it as well.

It does not hesitate at all when taking off from a dead start. No lugging or noticable straining. I guess I'm used to my 2012 Taurus having a very low RPM during hiway operation, appx. 1,600 rpm at 70ish MPH. I realize it has overdrive. I thought 2,600 RPM at 55 mph was quite high though in the vehicle in question.

Nope, rpms sound about right depending on rear end ratio.

Seller told me it has a Ford 9" rear. Have no idea what the gear ratio is.

I'm Googling pics of a TH350 and Powerglide transmissions to help determine what I have.

Count the number of bolts that hold the pan on the transmission.

Modulator on the back of a powerglide is on the driverside of the case while on a th350 it is on the passenger side. There are other visible differences, but that's probably the easiest to spot right off.

No other visible differences? The transmissions look completely different and the pans are different.

There is a cast iron powerglide and an aluminum one. Sounds like it's a TH350 that's not shifting right.

Did I say there were no other visible differences? Or did someone else say that and I missed it?

The modulator position is probably one of the easiest ways to tell whether it is a power glide or TH350. The pan difference is pretty obvious too.

Spot,have you tried manually shifting?Pulling the shifter into first,then watching the tach,or feel,shift into "2"then drive.

Don.....I'll count the number of bolts on the pan tomorrow.

Roy..... Is the modulator the round protrusion on the tranny? If so I saw one just back from the tranny dip stick on the passenger side.

BC52....... I've not tried shifting manually. That would have been an easy way to tell but I didn't try it last Sunday on the drive. Will do it once I get it back out of the garage.

Here is a good picture of a TH350.

http://www.ebay.com/itm/TCI-Automat...ries&hash=item5aed18ebdb&vxp=mtr

You can see at the rear the shiny vacuum modulator.

Here's one of a power glide. You can see the modulator is on the other side.

http://www.ebay.com/itm/BTE-Powergl...ries&hash=item2577ba5ea7&vxp=mtr

There's lots of other differences too in the way they look.

Roy, based on your pics I've definately got a TH350! The angle on the back right corner of the plate is a giveaway. Also mine does not look like the pic of a Powerglide tranny. So, I've probably got to take it to a tranny shop and get them to look into why my Turbo 350 3-speed isn't shifting from 2nd to 3rd gear. Hope it's a simple fix.

Thanks for your help!!

Roy, based on your pics I've definately got a TH350! The angle on the back right corner of the plate is a giveaway. Also mine does not look like the pic of a Powerglide tranny. So, I've probably got to take it to a tranny shop and get them to look into why my Turbo 350 3-speed isn't shifting from 2nd to 3rd gear. Hope it's a simple fix.

Thanks for your help!!

I think from the rpms you posted it is going into high gear. Maybe skipping second and going into third. I think your engine would be running higher rpms at 55 mph. In the 3,000s depending on rear axle ratio.

About what rpm does it shift from first gear, or what speed are you traveling when it shifts?

Try shifting manually up from 1st to drive from a dead stop using moderate throttle pressure.

Here's a nifty calculator for rpm vs engine speed.

http://vexer.com/automotive-tools/speed-rpm-calculator

Roy, I went to a friends shop today and put it up on the lift. I definately have a TH350. Even the chrome cover says "TURBO 350".

I had my friend ride with me and we pulled the shifter all the way down into 1st and then manually pushed it into 2nd. Kept it there until about 2,200 RPM and then bumped it into 3rd and.......IT SHIFTED! First time I'd felt it go through all 3 gears. My buddy thinks I'm starting off in 2nd gear although there is NO hesitation from a dead start and no lugging. It goes quick. Don't understand it but now we know where we stand. It will go through all 3 gears but I'll have to have someone adjust it so it does it automatically.

Thanks for that nifty calculator too. That is really nice!

I appreciate everyone's help, especially your comments Roy.

Chuck

Now that you are sure it's a 350 turbo, I'll throw something at you. If you look at the transmission, where the dipstick tube goes into the trans case, there should be a cable coming out that goes to the carb. . This if I remember right is called a throttle detent cable. If it is not connected either at the carb. ,or inside the transmission,the shifting could be affected. Inside the trans.the cable is connected to a valve in the valve body which is the brains of the transmission.
Another thing, it sounds like the truck had some other things done, maybe previous owner installed a shift kit in the transmission. If the check balls under the valve body plate are not in the correct position this could also be part of the problem.
good luck and let us know the outcome.

....on a 350 my understanding has always been that the detent cable basically does nothing unless you got to FULL throttle...like passing gear.

....If you have a shift kit in, you should be getting your neck snapped a little..or maybe it depends on the shift kit. I'm taking mine back out of my 37. I hate the tires "chirping" every time it shifts and tired of my neck popping. I have to soft foot it to get going. JUST FYI

Check your pm. I think you have a stuck governor.

Alvin, You're right the detent is what makes passing gear work. It's been 25yrs. since I worked on these, but I think the linkage on the carb activated the cable before full throttle. I may be wrong and don't want to argue, was just throwing it out as a possiblity. As for the shift kit, yes they do snap gears hard, however if you put the check balls in the wrong place, it will affect when the shifts happen if they happen at all.

Roy, the govenor has a plastic gear on it's end. When the gear wears the trans won't shift out of 1st gear till 40/50mph, but as soon as you let off the gas,bangs back into 1st gear. I guess it could be stuck,but I would think it wouldn't shift 2nd to 3rd if it was.

Hope I didn't ruffle any feathers, just expressing some thoughts.

Depends on where the valve is stuck in the governor housing I think. It's been a long time since I have worked on one too. LOL

And if the gear is stripped, you're right, it won't shift at all.

But he should be able to tell whether he is starting out in first or second.

He can start off at a low speed with it in drive or second and see how the engine acts, then do the same thing by manually putting it in low he can see if it's a bit easier for the engine to start the vehicle off.

He could also take off in drive or second and get about 5 - 10mph and manually down shift to low. If it down shifts manually into low then he would be starting off in second. He would be able to tell this because it would act like he hit the brakes.

My bet is the govenor has some trash stuck in the bore.

Tommy, noooo problem. I learn from you guys! Thats why its called a "discussion board" I like reading all about folks experience and hope I avoid some pitfalls! Thanks to EVERYONE who contributes to these discussions.

Tommy, Roy and Alvin,

I appreciate all your input!! I'm learning just like everyone else.

Good idea Roy about starting off and then dropping it into low to see if I'm starting off in 2nd. Also a good idea to start off in both drive and low to see if it takes off any differently. Like I've said before, it takes off rather nicely in drive making me think it's starting in low. I'll check one day this week and report back. I'll get to a point where I'm going to drive it to a Transmission shop and let them do some diagnostics and an estimate of repair costs. It may take that to solve this mystery since I don't know anything about automatic transmissions.

Thanks!

If you can get it to shift into third gear, then you should know whether it was in third before based on your rpm's. Then if you figure out if it's starting in low or not, you know if it's only shifting 1-2, 2-3, or 1-3. Then you can ask your local transmission guy what to check.

Spot,anything new on this?

Nothing new to report except that I've confirmed what Roy suggested and that I can drop it into 2nd gear after getting up to speed and it down shifts, which means I've been starting off in 2nd gear all this time. Also, it won't let me drop down in low from the get go. I have to drive it and then come to a stop before the shifter lets me go all the way down to first gear. Don't know why. Not worried because it does not strain to start off in second gear. I'm not hard on it from a dead start and certainly am not racing it. I'll budget some time and money so I can drop by a transmission shop to ask for some diagnostic help. Thanks for asking for the update BC52.

Is or was this a rebuilt transmission? And how many miles on it since it was rebuilt?

Is it starting out in second even if you manually move the shifter to low?

I would look very close at the governor valve being stuck in the bore of the governor. Transmission shop can do that very easily and quickly. Or you can too. I think I sent you a pm on how to check it.

Once at a stop, if you manually put the transmission in low, does it start out in low? If so, I think the governor is going to be the first thing you should look at. I bet the valve is stuck.

Good luck and let us know what you find.

When my valve body had a sticking problem, i was not even able to manually shift through the gears. Is it possible that 1st is just really short and soft? I have a 4.11 rear end and my TH350 generally shifts from first to second around 10mph and from second to third around 20mph. His RPMs seem about spot on for the speeds and setup that he is running.

20 MPH per 1000 RPM IS ABOUT RIGHT DEPENDING ON THE
REAREND GEAR RATIO. IT FOLLOWS:
20 MPH X 3000 RPM = 60 MPH.
ISN'T THAT WHAT YOU ARE GETTING?
IF SO, YOU ARE IN HIGH [DIRECT] GEAR.

Roy, Don't know if it is a rebuilt tranny, but if it was it was done 12 years ago. 13,000 since the build. Once I've backed it out of the drive and drop it down into what I think is low gear it starts off and then shifts itself into the next gear. Obviously it's not going down low enough to get into 1st. So, after I drive it a while and stop THEN it allows me to drop the Lokar shifter WAY down and it goes into 1st gear and STAYS there until I shift it into 2nd. This is what Al and I did the day I reported to you all that I had determined that the tranny was in fact capable of shifting through all the gears. Don't know why it won't let me shift it down into 1st when it's first started.

Thanks again everyone for your interest in my problem.

If you try to manually shift the linkage into the lowest setting without the engine running will it go through all the detents then?

Should be able to count the stops as you go from park to low.

Should feel a stop for N then for D then for D2(or2) then finally L.

If it won't shift from Park through each of those stops (detents) with the engine not running, then perhaps the linkage is out of adjustment.