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1972 V12 Auto - Transmission Problems

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Stuart 1960 Stuart Walker
Richmond Hill, Ontario, Canada   CAN
Hoping someone can point me in the right direction with a problem with the transmission on my 1972 V12 auto. As far as I know the automatic gearbox is the original Borg Warner Model 12.
A month or so ago I was driving the car around the storage area where I keep the car. With no warning, I lost the drive, with a noise (didn't sound catastrophic, but it was there), and the engine revs increased significantly (not as far as redline).
Trying different selector positions, I found that reverse still worked fine. For another few feet, I still had some drive in position 2 on the selector, but then that stopped aswell.
I got the car back into the garage in reverse, with no further issues.
Since then, because I still had motion in reverse, I've been slowly adding transmission fluid to the 'box. So far I've added 2 pints (capacity is 16 pints).
When checking for any progress today, once the car was warmed up, I still have reverse but can only get a creep forward in drive. However, positions 1 & 2 on the selector both give me "normal" positive forward motion (position 2 had stopped originally!).
Reading through the fault diagnosis section of my repair manual, the only check that it suggests for no forward drive in D, other than those suggested for the other selector positions is to check the rear band adjustment. I can't find any detail about how to check this in the manual, so assume it's a transmission strip-down check.
Has anyone experienced anything like this, and, if so, how did you fix it?
Having got drive back in selector positions 1 & 2, I'm tempted to continue topping up the fluid, but I don't want to run the risk of over-filling the 'box, although it is vented through the dipstick/filler tube, so worst case I would only expect it to spit fluid back up through that.

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lmuzza Lindsay Musgrave
Country Victoria, Australia   AUS
perfectpitch Avatar
perfectpitch Charles Windsor (Disabled)
Disabled Account, Antarctica   ATA
Could be something mechanical as mentioned above, no doubt. Those Borg W trannies have a peculiar arrangement in the torque converter that allows fluid to drain out of the torque Conv if it happens to sit for a long time in just the right orientation,without being run. The T-C must be loaded with fluid to work properly, but if seals get dry and the fluid has a chance to drain out, it can be hard to get fluid back into the T-C by just running the engine or driving around the parking lot.

The TH400 GM based transmission in most of the V12 sedans does not suffer this trouble. The solution, if indeed that is the trouble, is to get fluid back into the T-C to swell the seals, etc, and so the trans can operate as designed. Sounds awfully strange, but if you start by adding a drain plug to the tranny pan, remove the pan for that, then fill the transmission with the correct fluid until it starts overflowing, you will be part way there. Be real careful about not spilling fluid while adding. That way you can see if there are any leaks, like at the base of the filler tube. Hopefuly not, but will still work either way. It is important to check for leaks, because what you do is watch the level for the next 24 hours or so and see if the level at the filler tube slowly goes down by checking with a homemade checker and a flashlight at first. Keep topping it up, but as you do measure how much is "disappearing" into the tranny. At least a quart may disappear if the T-C has not been keeping full. After about 24 hours, or when you are sure the tranny is not "absorbing" more fluid, the fun begins. Drain all the fluid out through the drain plug, have multiple drain pans ready. When pan is drained, add the amount they say is the capacity, and start it up and see if that has solved the problem. If the tranny starts working, try and keep her moving around for several hours to help the seals swell. You could even try some "stop leak" tranny fluid, as it is designed to swel seals and the pan gasket. This will save you several thousand dollars if it works, so get down there and start and drive the car as often as possible to avoid in future.

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formercat1 Avatar
formercat1 Mack Besser
Maple Park, IL, USA   USA
Although this is not going to cure no forward speeds, it is worth noting:
There is a vacuum modulator at left hand rear of trans, protected by a large, metal shield.
There is one line & vacuum hose connecting. When the diaphragm in the modulator goes bad,
it allows intake system to suck trans fluid. While you will see no smoke, or leaks for that matter,
over a short period of time your trans will be quite low on fluid. Subsequently, the trans will fail.
Easy to get part at a Napa store, for it's the same as the Chevy part. Mack

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