1957 Transmission slips from 2nd to 3rd upshift

[Rex]

'57 Thunderbird Fordomatic: I get a slip or 'flare' when the transmission upshifts from 2nd to 3rd gear . It happens only after the transmission warms up: When cold, starting out, it shifts perfectly, no slip. So I changed the fluid, replaced with same that I drained out, A/T type 'F' fluid. It still slips, 2 to 3 upshift after it gets warm.

 

[cokefirst]

it may be time for an overhaul. Type F or Dexron will both work. The most correct fluid is Dexron, non synthetic. Many people think that type F means Ford, which it does not. You can read the information from the API on this, but lots of folks will tell you that you should only use Type F. Since either seems to work on this older style transmission, there is no sense in starting an argument. Back in the 60;s and 70;s there was a trick to add about 8-10 oz of brake fluid to the transmission and that worked in many cases. It is NOT a cure, but you may get a couple of more years out of it before doing an overhaul.

 

[Rex]

it may be time for an overhaul. Type F or Dexron will both work. The most correct fluid is Dexron, non synthetic. Many people think that type F means Ford, which it does not. You can read the information from the API on this, but lots of folks will tell you that you should only use Type F. Since either seems to work on this older style transmission, there is no sense in starting an argument. Back in the 60;s and 70;s there was a trick to add about 8-10 oz of brake fluid to the transmission and that worked in many cases. It is NOT a cure, but you may get a couple of more years out of it before doing an overhaul.

Thanks for the reply. About a year ago, that large square o-ring torque converter seal started leaking so I put a seal stop-leak. After a time, it worked, no more leak. But about two months ago it started that 2nd-to-3rd gear slip after reaching operating temperature. I thought maybe the ATF viscosity was thinning when reaching operating temperature. So I changed the fluid, using Type 'F': My understanding is that Type 'F' has higher frictional properties than Dexron and others, so I thought that might help the situation. But no luck. Something is happening after it warms up.

 

[74 Harley]

Have you done a band adjustment?

 

[Tom Alpers]

If a band adjustment doesn't fix it here are some other thoughts.
Since it's happening after it warms up (when the fluid has warmed up and thinned out) it's likely the primary cause is too much fluid leakage past the internal seals inside the drums and/or servos. The only way to actually fix that is new seals which means a rebuild. But before you contemplate going that route there are a couple of things worth trying. It's possible it's just a misadjusted transmission rod (between the carb linkage and the trans) Per the Ford Manual, if you are getting flare you can try to fix it by adjusting the rod to the transmission. Presuming it's already adjusted per the basic spec the recommended adjustment is to "lengthen" the rod. In practice you lengthen it by disconnecting the swivel and unscrewing the adjustment link. Ford Recommends trying 3 turns and not more than 4 turns. I had a small flare occasionally (cold or warm) at low throttle openings so I lengthened the rod 4 turns and it almost completely eliminated the occasional flare. Lengthening the rod increases the internal pressure of the transmission... higher pressure results in more fluid flow to help overcome leaking seals. But you might want to start with checking the basic adjustment and see if your car is where it's supposed to be with that rod adjustment before adjusting it more. Maybe someone has got it out of whack by past miss-adjustments. I only have my own car to go by but here is a suggestion. Before I made the adjustment if I pushed the throttle to the floor so the carburetor was open all the way, that linkage with the slot would move so the "pin" moved to the center of the slot. (engine off of course). After I lengthened it the 4 turns it moved the pin about half an inch toward one of the ends, don't recall which, but not all the way to the end. So you should check that before adjusting anything and make sure when it's floored the pin isn't bumping into the end of the slot, I'd say ideally it will be in the middle as the starting point. Ditto after you adjust it, make sure the pin isn't hitting the slot end.

The second thing you can do if the adjustment doesn't fix it is something I have done a couple of times over the years for transmissions with leaking internal seals. It helps without hurting anything. Put some STP oil treatment in, the classic stuff that's like honey. Start with one 16 oz can. It's really thick, you may want to heat it in the over to make it easier to pour thru the dipstick tube. I've added as much as two cans of the stuff. You may need to suck some ATF out first if the trans is filled to the top already. The STP will increase the viscosity of the ATF which will help keep so much of the oil from leaking past those worn-out seals.

If none of that works the last thing you can try as a hail mary is a can of Seal Sweller. I don't recommend the seal swellers unless you have tried everything else, I've seen some seals that were turned to mush by them. But if it doesn't mess up the seals it may soften and swell them enough to slow down the leaking enough to stop the flare.

 

[Rex]

If a band adjustment doesn't fix it here are some other thoughts.
Since it's happening after it warms up (when the fluid has warmed up and thinned out) it's likely the primary cause is too much fluid leakage past the internal seals inside the drums and/or servos. The only way to actually fix that is new seals which means a rebuild. But before you contemplate going that route there are a couple of things worth trying. It's possible it's just a misadjusted transmission rod (between the carb linkage and the trans) Per the Ford Manual, if you are getting flare you can try to fix it by adjusting the rod to the transmission. Presuming it's already adjusted per the basic spec the recommended adjustment is to "lengthen" the rod. In practice you lengthen it by disconnecting the swivel and unscrewing the adjustment link. Ford Recommends trying 3 turns and not more than 4 turns. I had a small flare occasionally (cold or warm) at low throttle openings so I lengthened the rod 4 turns and it almost completely eliminated the occasional flare. Lengthening the rod increases the internal pressure of the transmission... higher pressure results in more fluid flow to help overcome leaking seals. But you might want to start with checking the basic adjustment and see if your car is where it's supposed to be with that rod adjustment before adjusting it more. Maybe someone has got it out of whack by past miss-adjustments. I only have my own car to go by but here is a suggestion. Before I made the adjustment if I pushed the throttle to the floor so the carburetor was open all the way, that linkage with the slot would move so the "pin" moved to the center of the slot. (engine off of course). After I lengthened it the 4 turns it moved the pin about half an inch toward one of the ends, don't recall which, but not all the way to the end. So you should check that before adjusting anything and make sure when it's floored the pin isn't bumping into the end of the slot, I'd say ideally it will be in the middle as the starting point. Ditto after you adjust it, make sure the pin isn't hitting the slot end.

The second thing you can do if the adjustment doesn't fix it is something I have done a couple of times over the years for transmissions with leaking internal seals. It helps without hurting anything. Put some STP oil treatment in, the classic stuff that's like honey. Start with one 16 oz can. It's really thick, you may want to heat it in the over to make it easier to pour thru the dipstick tube. I've added as much as two cans of the stuff. You may need to suck some ATF out first if the trans is filled to the top already. The STP will increase the viscosity of the ATF which will help keep so much of the oil from leaking past those worn-out seals.

If none of that works the last thing you can try as a hail mary is a can of Seal Sweller. I don't recommend the seal swellers unless you have tried everything else, I've seen some seals that were turned to mush by them. But if it doesn't mess up the seals it may soften and swell them enough to slow down the leaking enough to stop the flare.

Hey Tom, problem solved, thanks! I had never adjusted that transmission rod before. So I adjusted a little on the long side: now it 2 to 3 upshifts at around 32-35 mph vs. factory spec of 28 mph, but no more flare! I'll play with the adjustment a little more in the next few days to get just the right length: eliminate flare vs. upshift mph. But I appreciate the advice, thanks again! -Rex.

 

[Tom Alpers]

Great. Its unavoidable that lengthening it will raise the shift speed a bit. That rod is called the TV rod, throttle valve rod. Internally what it's doing is acting as the balance against the fluid pressure that comes from the governor. The balance is measured by the Throttle Valve in the transmission. The faster the car goes (and hence faster the governor spins) the higher the governor pressure is. The TV pressure is how the transmission knows how much "load" is on the transmission for the speed you are going. The more you open the throttle the higher the pressure is. The higher the pressure, the harder the clutch packs and servos apply. And the more load, the harder you want them to apply so they don't slip. But you don't want high pressure all the time, that would waste power, wear out the trans oil pump, and make hard shifts. So the TV takes care of all that. In more modern transmissions they added a vacuum modulator as another way to sense how much load there was, the lower the vacuum, the more load and the higher the pressure in the system.