Engine/Transmission (1994 - 1998) 47re basic questions.

[Crowhurst]

I've spent 45 years as a shadetree mechanic in the U. K, but solely on manual gearbox vehicles. I've rebuilt engines and gearboxes, but the auto transmission is a new box of tricks, and, even having studied the schematics of the 47RE auto,and having driven and maintained it for ten years, I still have a great amount of ignorance of the simplest issues. Here are a few of my queries, which mainly relate to keeping the transmission operating for as many miles as possible, with the highest reliability:



1. Waiting at stop lights, my inclination is to shift to P. If I leave it in D, will this shorten the life of the transmisssion, or will it just generate heat, which might be a good or a bad thing? ( I have a trans temperature guage on the output line, and I keep below 200 degrees. )



2. I have altered the overdrive switching so that default is "no O. D", and I have to select O. D manually. I prefer this, particularly when towing, to avoid lugging. I tend to accelerate in 3rd up to perhaps 50 mph, and only then drop into O. D. Is this reasonable?



3. When towing, the '98 Dodge Owner's manual at Page 123 says not to use O. D. (I may be misinterpreting the manual) Also, the engine defuels at about 2600 rpm. In theory, then, the truck should not pull a trailer over about 65 mph. If I'm towing my 6500 pound Airstream travel trailer on a level highway, with no strong headwind, am I truly risking my clutches by going into O. D, and back to top on the slightest grade? I have a BD torque-lock, which increases the line pressure at low rpms. I get 13 mph towing in 3rd, and 15 mph in OD, with far less noise to disturb the passengers. Speed is about 63 mph.



4. Although I change the transmission fluid and filter regularly, I have avoided adjusting the bands. I feel that, even with the information from my full Chrysler workshop manual, this is a risky procedure when the transmission is always shifting correctly. I have read contrary views. One is that the band adjustments can be ignored on a 47RE, and the other is that regular band adjustment is important. What do the TDR gurus recommend?



5. I'd rather replace a unit before it leaves me stranded at the roadside. Am I likely to get warning of a failing transmission? Mine has 160. 000 miles and it operates perfectly. I aim to keep this truck for the rest of my driving days. The torque converter seems loose, but I understand this is to protect the transmission from the Cummins torque. What would be the warning signs? More TC slippage?



6. The '98 shop manual at pages 21-99 and 21-100 describes a stall test for the TC. This seems a brutal procedure, and hence I have avoided it as a means of assessing the slippage of the TC. Should I be wary of this procedure?



7. I am accustomed to hauling heavy loads, and we all know that at the beginning of a down grade when hauling heavy, one should shift to a low gear to use engine braking. Hence I was stunned to discover that the 47RE unlocks the TC under these circumstances, and the truck can freewheel to its doom down the grade. I immediately had a BD exhaust brake and Auto-lock fitted to the truck. Why would anyone think that forcing a TC unlock in these circumstances in a heavy duty truck was a good idea? Was this to meet a fuel consumption government target? By making the truck less safe? Really?



8. Fitting an exhaust brake to these trannies is a contentious issue. I like to use mine all the time, even when running empty. This suits my driving style, as I try to avoid using the foot brake unless coming to a stop. This gives the passengers a smooth ride, helps fuel economy, and prolongs brake life. However, am I risking wearing out the auto transmission clutches by always using the exhaust brake?



9. Does one get faster acceleration with or without TC lockup in a stock 98 12 valve in everyday driving? Intuitively I would have thought that a locked TC would avoid slippage, and thus be better for acceleration. However, there is the torque multiplication effect of the slipping TC. Also, there is the issue of fluid temperature with the unlocked TC. I have fitted a red LED in the dash to indicate TC lockup, and a transmission temperature gauge.



I'd be very interested to know the answers to these questions.



Nick.

 

[cerberusiam]

1. Waiting at stop lights, my inclination is to shift to P. If I leave it in D, will this shorten the life of the transmisssion, or will it just generate heat, which might be a good or a bad thing? ( I have a trans temperature guage on the output line, and I keep below 200 degrees. )

One could theoretically make a case that sitting at lights too long in gear could eventually cause a problem. Just not sure that it would cause a problem in the life time of the trans under normal use. I mean it would take HOURS in high temps to materially effect anything meaningful, aside from an early hard part failure. Kicking it into neutral is much more effective as it will circulate fluid where park does not, nuless that was addressed in a shift\build.

2. I have altered the overdrive switching so that default is "no O. D", and I have to select O. D manually. I prefer this, particularly when towing, to avoid lugging. I tend to accelerate in 3rd up to perhaps 50 mph, and only then drop into O. D. Is this reasonable?

Perfectly reasonable mod to make driving it more effective when towing. They always shifted too fast for my liking so I always figured out ways to extend the shift points as much as possible when I tweaked them.

3. When towing, the '98 Dodge Owner's manual at Page 123 says not to use O. D. (I may be misinterpreting the manual) Also, the engine defuels at about 2600 rpm. In theory, then, the truck should not pull a trailer over about 65 mph. If I'm towing my 6500 pound Airstream travel trailer on a level highway, with no strong headwind, am I truly risking my clutches by going into O. D, and back to top on the slightest grade? I have a BD torque-lock, which increases the line pressure at low rpms. I get 13 mph towing in 3rd, and 15 mph in OD, with far less noise to disturb the passengers. Speed is about 63 mph.

Yeah, thats one of the great mysteries of the owners manual. Said that on the first gens too and it generally got ignored. I got 240k out of the trans and it spent most of its time with a trailer on it. You may not get 400k if you tow a lot because of the OD pinion wearing out but it beats the amount of extra fuel and noise. Tow in OD and fix any problems that develop.

4. Although I change the transmission fluid and filter regularly, I have avoided adjusting the bands. I feel that, even with the information from my full Chrysler workshop manual, this is a risky procedure when the transmission is always shifting correctly. I have read contrary views. One is that the band adjustments can be ignored on a 47RE, and the other is that regular band adjustment is important. What do the TDR gurus recommend?

Yes and no. Checking the band adjustmnet is a good way to monitor wear and stop a potential catastrophic failure. On the other hand, if you don't do correctly and the same way every time it can negate the benfits. Just make sure to follow the recommended procedure and do the same way every time and you will be fine. If your towing a lot and using and EB, check it frequently to be pro-active.

5. I'd rather replace a unit before it leaves me stranded at the roadside. Am I likely to get warning of a failing transmission? Mine has 160. 000 miles and it operates perfectly. I aim to keep this truck for the rest of my driving days. The torque converter seems loose, but I understand this is to protect the transmission from the Cummins torque. What would be the warning signs? More TC slippage?

You could see warnings like lockup not holding, flare shifts, etc, or, no sign of problems and you put it in gear one day and it will barely move. There is no warning of a lig seal in the forward clutches tearing, leaking pressure and hlding ability, and welding the clutch pack. The first indication is that all you have is one forward gear, even in reverse. All you can really do is change the fluid regularly while understanding the limits of the trans build and driving accordingly. That would make 20 psi boosted launches a big non-no. :-laf



Yes, the stock TC is loose. This was Dodges way of not having to retool for the diesel so they just used all the gasser parts and dais don't tow in OD. Took them until 2003 and doubling the engine HP output to figure out it needed to be designed differently. Go figure.

6. The '98 shop manual at pages 21-99 and 21-100 describes a stall test for the TC. This seems a brutal procedure, and hence I have avoided it as a means of assessing the slippage of the TC. Should I be wary of this procedure?

What? Don't you test this at a minimum of one stop light every day??? Oh, but you DID say you wanted the trans to last, my bad.



Yeah, thats as bad as putting it in reverse and backing a heavy load up a grade. Once in a while is fine but make a habit of it and your trans guy sends you birthday and christmas cards.

7. I am accustomed to hauling heavy loads, and we all know that at the beginning of a down grade when hauling heavy, one should shift to a low gear to use engine braking. Hence I was stunned to discover that the 47RE unlocks the TC under these circumstances, and the truck can freewheel to its doom down the grade. I immediately had a BD exhaust brake and Auto-lock fitted to the truck. Why would anyone think that forcing a TC unlock in these circumstances in a heavy duty truck was a good idea? Was this to meet a fuel consumption government target? By making the truck less safe? Really?

Thats cuz its a gasser TC and it won't take the load locked up under power or on coast. Much better to spin in fluid coupling than hurt the equipment.

Like anything else, we can just wonder at the reasons some of these devisions were made.



The OD has an over running clutch in it so it may not be the TC unlocking but just free wheel in OD. However, the lockup strategy in OD in these trucks leaves a LOT to be desired. Thats why the addtion of the TQ-Loc, lockup controllers, etc, were so effective at making the trans and truck much better. Thats comes at a price though as the stock components simpl will not take the added load.

8. Fitting an exhaust brake to these trannies is a contentious issue. I like to use mine all the time, even when running empty. This suits my driving style, as I try to avoid using the foot brake unless coming to a stop. This gives the passengers a smooth ride, helps fuel economy, and prolongs brake life. However, am I risking wearing out the auto transmission clutches by always using the exhaust brake?

Not so much gear clutch packs but the TC is definitely at risk unless you have beefed it up and added a shift kit and some internal parts. The stock TC has a tendency to warp the cover if it slips too much and even under heavy loads without slipping. Then the clutch slips and its downhill, literally, from there. Back loading sone of the thrust washers is also hard on them because they were never designed run with a load from that direction. Add to that the lack of cooling and lube in key places and it is a bit of a risk without a build to address the shortcomings.



Without a shift kit to raise OE line pressures it definitely puts more strain on the clutch packs both accelerating and decelerating.

9. Does one get faster acceleration with or without TC lockup in a stock 98 12 valve in everyday driving? Intuitively I would have thought that a locked TC would avoid slippage, and thus be better for acceleration. However, there is the torque multiplication effect of the slipping TC. Also, there is the issue of fluid temperature with the unlocked TC. I have fitted a red LED in the dash to indicate TC lockup, and a transmission temperature gauge.

Yep, mystery switch time. The difference in acceleration when the TQ hits and locked\unlocked TC is dramatic. Even better when you add a little fuel and turn the wick up. But, here comes the slippery slope. Make work better and you start breaking things, like input shafts, TC's, output shafts, pinions, etc. A TC that is better at TQ multiplication and has lower stall is the best compromise to a locked TC. Even a stock 180 HP Cummins B will snap a 47RE input like a twig in the right conditions.

 

[Crowhurst]

cerberusiam, that's excellent information, thank you. Just what I needed to know. I'll be reading your post several times.

Nick.