What actually breaks?

Reducedfat · 02-21-2011, 08:09 PM

i have always hear the auto dodge trannys are the week link it the drivetrain. But what actually goes bad in the transmission. do they overheat? do clutches slip? so on and so forth. i have always heard temperature is what kills an auto so if i were to turn up the pump and get gauges to keep an eye on all my temps would i be ok? and at this point i dont pull much so i wouldnt be putting a big load on it.

deezall · 02-21-2011, 08:27 PM

Quote:

Originally Posted by Reducedfat

i have always hear the auto dodge trannys are the week link it the drivetrain. But what actually goes bad in the transmission. do they overheat? do clutches slip? so on and so forth. i have always heard temperature is what kills an auto so if i were to turn up the pump and get gauges to keep an eye on all my temps would i be ok? and at this point i dont pull much so i wouldnt be putting a big load on it.

it usually starts lipping in the trans first then the tc starts slipping. well in my case thats how it going.... but yes first thing is gages. then go ahead and spend the cash for a torque converter and probably a valve body if it isnot slipping yet. there are several threads on here i would start with the beginners thread. and yes temp will kill the trans. prolly good to add an external cooler.

Reducedfat · 02-21-2011, 08:33 PM

well the thing is the tranny was recently rebuilt by the PO and it looks like he spent some money on it but i dont know what kind of parts he used. he said he used hard parts and he didnt know much about it but it has one of those fancy billet aluminum pans. so before i go buying a tc im thinking im gonna pull the tranny and see whats inside. unless theres an easier way? it shift perfectly and pretty firm.

deezall · 02-21-2011, 08:42 PM

Quote:

Originally Posted by Reducedfat

well the thing is the tranny was recently rebuilt by the PO and it looks like he spent some money on it but i dont know what kind of parts he used. he said he used hard parts and he didnt know much about it but it has one of those fancy billet aluminum pans. so before i go buying a tc im thinking im gonna pull the tranny and see whats inside. unless theres an easier way? it shift perfectly and pretty firm.

first of all do you know what transmission you have?? 47rh or 47re if not pm me your last 9 of the vin and i can tell you

Reducedfat · 02-21-2011, 10:28 PM

it is a 95 so its the RH.

Art · 02-22-2011, 11:01 AM

The automatic transmissions have clutch plates and bands that are applied using oil pressure. If the oil pressure isn't sufficient enough to prevent slippage, the clutch plates and/or bands will overheat and burn.

Insufficient oil pressure can come from several possibilities. Running the transmission low on oil (or worse yet out of oil) certainly damages a transmission. Vibrations cause the cooler lines to rub against each other, and many diesel trucks have had the lines rub completely through resuling in transmisison failure. Some trucks have a plastic quick-connector on one of the cooler lines - and if overheated - it can soften and/or melt and fail, and that certainly will cause a trans failure. Rust is a very big problem in many states, and that wrecks cooler lines as well. Another cause of insufficient oil pressure is internal leakage. Internal seals do wear. High operating temperatures is very hard on them as well, because the heat hardens them and then they do not seal as well.

Abuse causes transmissions to fail as well. Lack of transmission service (band adjustment checks, filter and fluid changes) shortens transmission life. Lugging the engine in OD causes it to operate at a lower lube pressure, which shortens transmission life as well. Some modifications can contribute to transmission problems as well. The PCM prevents lugging, but some people have a manual lockup switch and that defeats the protection by the PCM. Replacing the TPS with a potentiometer also can be a problem - the PCM makes the OD and TCC shifts when the speeds (RPM difference) are acceptable. Without the PCM making the correct decision, shifts could be made when the speed (and resulting energy) is just too much for the clutches to absorb without damage. Transmission shifts made with the TCC (torque converter clutch, aka lockup clutch) locked do not have the converter cushioning the resulting shock, and then more problems will result. Towing/hauling heavy loads can also be a problem if not done properly. The factory put the 'OD-off' switch on these trucks for a reason.

Turning up the injection pump creates another transmission problem - the resulting increase in engine torque can exceed the torque capacity of the transmission as well as the TCC. Increasing the line pressure helps increase torque capacity, but the increased line pressure is harder on the seals, especially those in the rotating applications. Everything has its limits, including the seals. The transmissions were designed with enough line pressure to survive behind a stock engine, but not much more in order to get more life out of the seals.

The TCC is another failure mode. A billet front cover is much more durable than the (cheap) stamped cover used on the OEM converters. The TCC friction plate operates against the front cover, and wears much faster if the front cover is not flat. A single plate TCC cannot hold the torque of a really turned-up engine, and then a triple plate converter is required. The next weak link then is the strength of the shafts.

In the tech articles section 'stickied' to the top of this forum, there are a couple tech articles written about automatic transmissions like this one:

Chrysler Automatics 101, revised 08 Mar 2010

That linked article discusses the importance of the TV linkage, another possible cause of transmission failure.

The strength of a drivetrain is just like a chain - every chain has its weakest link. In order to make the drivetrain stronger, its weakest link need to be strengthened. Then the next weakest link needs to be improved, and it goes on and on and on...

God prefers Diesels · 02-22-2011, 07:15 PM

But at the same time, don't let Art's post let you think this tranny is a piece of junk. Those weak links are the weak links in 99% of autos. Once built, this RH is a sought after work of art.(no, not the forum member.

)

After driving mine, I'll never go back to a stick shift.

o6smoker · 02-22-2011, 08:36 PM

I'm no genius on all the internals on automatics, but my transmission slips under full throttle and feels kind of "sloppy". Do I need to upgrade all the clutch packs and everything or just a new torque converter? The transmission was just rebuilt by the previous owner with alto red eagle clutches and koleen steals.

smken u · 02-22-2011, 08:49 PM

Quote:

Originally Posted by o6smoker

I'm no genius on all the internals on automatics, but my transmission slips under full throttle and feels kind of "sloppy". Do I need to upgrade all the clutch packs and everything or just a new torque converter? The transmission was just rebuilt by the previous owner with alto red eagle clutches and koleen steals.

yes clutch packs and VB.converter be nice also..you could also have someone drill the holes in your VB to increase pressure but u have to no wht ur doin thts wht my buddy does,u prob may need seals also could be leaking past them prob.if it has those clutches n stuff not knowing everything bout wht else was done it sounds like he lied to u bout rebuild or it was a terrible rebuild or ya got some big hp

smken u · 02-22-2011, 08:52 PM

there no point in doing just the converter n not the internals cause when the clutches start slippin, if ya just do converter all the junk is gonna go n the converter n ruin the costly round slush box..not ruin but def. not be good for it

o6smoker · 02-22-2011, 08:53 PM

Its got a billet single and a custom vb and I called the guy that owns the transmission shop and he read me all the stuff that was done to the transmission so I don't know, but there is a leak somewhere on the transmission that I can't seem to find but the oil level is fine so far. I was really hoping I wasn't going to have to buy a whole rebuild kit. I'm guessing I have somewhere around 500hp also.

Art · 02-22-2011, 10:36 PM

Quote:

Originally Posted by God prefers Diesels

But at the same time, don't let Art's post let you think this tranny is a piece of junk. Those weak links are the weak links in 99% of autos. Once built, this RH is a sought after work of art.(no, not the forum member.

)

After driving mine, I'll never go back to a stick shift.

Don't misunderstand me - I really like the 727s and RH transmissions. I like them much better than the other brands of transmissions. I was just listing the failure modes I could think of off the top of my head. I have a 727 in each of my 1967 Coronets, including the one I beat on at the dragstrip. I put a 47RH in my 6BT conversion project. I have rebuilt dozens of these transmissions for locals in the area. When properly rebuilt, they are great. When neglected or abused, no trans is going to be good...