general auto transmission question

[AMink]

I think my transmission (47re) slips too much before converter lock. You know, many revs, not much go. When I step on it while cruising unlocked, the rpm's go way up before anything interesting starts to happen. Converter lock is great, instant speed gain. What part of the transmission is most responsible for unlocked acceleration? Right now, the only comparisons I have are gassers at work and my wife's Expedition. Step on the gas in that, the rpms go up a little, things tighten up, and off you go. tia

 

[TBurow]

sounds like the tork converter is going bad(too high stall speed) when it locks there is no slip in the converter and it pulls fine. time for a new one and a trans cooler.

 

[Joe G.]

The whole thing runs on hydraulic pressure. The faster the torque convertor turns the more pressure the pump can make. That's a general answer to understand what is going on. In the case of the gassers the engine will turn a lot faster so all things being equal you have more pressure thus less slippage. Our trucks are a lot heavier than the cars so it takes more to move the truck. Ok, there are compensations for all this supposed to be included in the transmission design. Basically we are using a torque converter that works pretty good behind a V10. Not so hot behind a slow turning Cummins. Lots of slippage. If you think that the slippage is excessive you might want to take it to a reputable (if you can find one) transmission shop for a pressure test. When my '95 was stock and I stood on it what I got was more noise, not much in the way of go.

 

[Greenleaf]

The FSM has the tests outlined. If you can, buy the corect gauge or guages and hook 'em in to perform the readings yourself.



The color and smell of the fluid say a lot too. Espessially if you have had the truck for some time and keep tabs on the oil changes or oil condition.

 

[fox]

The torque converter is similar to two fans (air) facing each other. One is powered, one is connected to the input shaft of the trans. Turn the powered one, and the other will begin to turn. Instead of air, they use trans fluid. The factory set-up is far too loose for the torque we can produce. ( some say the factory sets them up like this to get the pump turning faster to build pressure to - rather than fixing the internal leaks).

A correctly built trans addresses the internal leaks and builds a converter to MATCH the torque of the Cummins.

If yours has gotten looser, the it is failing.

 

[AMink]

Thanks Fox. I did have a rebuild, but have never thought it worked like it should. Should have spent the extra and gone with one of the big, proven names found on here. Supposedly, the internal leaks have been fixed and a new converter and vb were installed. They raised the line pressure. The shifts are definately firm, but it is still mushy between gears. I'm wondering if it comes to it, if a new tc would be the ticket. And if I put in a new tc, is it something I can do myself? I don't think I want to get into dropping the transmission etc. Any other suggestions out there? Adjustments? Thanks!

 

[Joe G.]

The TC is between the trans and the engine so the trans has to come out to replace it. If you are not comfortable doing a job like that you might be able to find a shop to do it without charging you too much. They have all the necessary tools so it does not take them very long.

 

[McLaughlin]

Can a bad/leaky seal where the transmission valve body mates to the transmission also cause this due to lower fluid pressure or does that just affect the transmission clutch plate operation?

 

[nps]

Can a bad/leaky seal where the transmission valve body mates to the transmission also cause this due to lower fluid pressure or does that just affect the transmission clutch plate operation?

Too low of pressure on the clutches can cause slippage. In this case the fluid will be dark reddish-brown and smell burned due to the friction heat that is built up between the clutch plates when they slip.



If the fluid is bright red and smells good, then the TC is loose.

 

[Tom W]

I think what you are describing is normal operation of the Dodge transmission ( described as a slushbox ) The torque convertor is good in a gas engine but not suitable for a diesel. The only way to to make a silk purse out of this sows ear is to get a torque convertor with a low stall stator. There are several good ones, I have DTT and couldn't be happier.