help - 47rh slipping like crazy - not sure why???

[30dodgeboy]

I just recently had major problems with the 47RH in my completely stock 94 4WD Ram. Put ~40,000 miles on this truck since I got it without any trans trouble so far (was told the trans was previously rebuilt at some point). I use it for daily driving and occasional towing of a 7000# car trailer (I don't use OD below 55mph when towing, and not at all if the terrain isn't flat).

I was pulling my car trailer with a car on it, and when pulling out of a toll booth I noticed the trans was slipping pretty bad at higher throttle. There was no place to pull over safely, so I continued driving it at less throttle - knowing that I was still inflicting more damage. In the next 20 miles the slipping got severe enough that the truck needed to be towed the rest of the way home. At that point, the truck would not move at all forward or reverse without 2000 RPM. So I pulled the trans out and tore it all apart...

The oil is black like engine drain oil and really stinks like burned oil.
No metal in pan, only a few flakes of clutch lining, magnet has some fuzz but overall pan is rather clean compared to the others I have been inside.
Front clutch plates look great, clearance is good, seals all intact.
Rear (forward) clutch plates look great, clearance is good, seals all intact.
Intermediate band is overall burned and about one square inch of lining flaked off.
Rear (lo/rev) band looks like new.
Sprag behind rear band is intact.
Intermediate clutch plates are smoked completely black and worn ~0.010" each. This pack was bottoming out against the OD piston (thickest OD piston shim was installed by previous rebuilder) preventing the spring from applying them properly.
OD (brake) plates somewhat burned, but should have still worked. OD piston seals intact. OD clutch pressure plate and backing plate were installed in wrong positions (by previous rebuilder).
Sprag in OD section is intact.
Both servos' seals are good, as well as the accumulator seals.

Sprag in torque coverter is operating correctly.

I blew compressed air into the front cooler line (in direction of flow) and (burned) oil came out cooler return line.

I am scratching my head on this one :nail: Slipping direct clutches would prevent reverse, but the OD sprag should still make the truck move forward...

Anyone have any suggestions???

 

[30dodgeboy]

Intermediate clutch plates are smoked completely black and worn ~0.010" each. This pack was bottoming out against the OD piston (thickest OD piston shim was installed by previous rebuilder) preventing the spring from applying them properly.

I meant to say DIRECT clutch plates

 

[HightechRedneck]

Could it be your fluid pump that has gone bad? It would cause the black everything issue.

 

[30dodgeboy]

Thanks for the reply.

The pump looks really really good. No nicks or scoring on the rotors or teeth.

 

[Big Blue24]

If all the clutch packs and sprags required for forward movement looked good, I would suspect the torque converter is broken.

There are race trucks that run fewer overdrive/direct clutches than the 9-10 found in stock transmissions and work just fine other than slipping a little in reverse because the sprag only holds in the forward direction. If the sprag is working correctly, it can't slip in the tail housing/overdrive portion of the transmission.

 

[30dodgeboy]

If all the clutch packs and sprags required for forward movement looked good, I would suspect the torque converter is broken.

There are race trucks that run fewer overdrive/direct clutches than the 9-10 found in stock transmissions and work just fine other than slipping a little in reverse because the sprag only holds in the forward direction. If the sprag is working correctly, it can't slip in the tail housing/overdrive portion of the transmission.

Thanks for the reply and yes, I hear ya 100%.

The torque converter sprag seems OK, but I am going to have the converter opened up and inspected by an TC expert.

When I have it all back together I will be checking the trans pressures thoroughly.

Edit: When I looked for the check valve ball located in the one cooler line I saw it was previously removed.

 

[fox]

The filter was plugged up, so all the pressures were down. This explains why it slipped in both directions.

Before removing it, you needed to check pressures. But at that point it needed the direct clutches. These fail the most often.

 

[30dodgeboy]

The filter was plugged up, so all the pressures were down. This explains why it slipped in both directions.

Before removing it, you needed to check pressures. But at that point it needed the direct clutches. These fail the most often.

Thank you for replying.

Actually, the filter was amost perfectly clean. No sludge and only a few flakes of friction material that were from the itermediate band. Remember that the pan was remarkably clean... The filter's dacron media had come out of the crimp at one edge for about 1/2" and I sortof expected to see debris jamming the valvebody somewhere - but the filter in the VB stopped the small amount that actually entered and every single valve spool was able to move freely in its bore. Not the cause either...

I agree that I made a mistake by not checking the pressures before removing and disassembling, but I really expected to find the front and rear clutches smoked - so I just removed it and tore it down in a hurry. In hindsight you are right, I should have checked the pressures.

I will check the pressures when it is all back together... before the wheels touch the ground.