Engine/Transmission (1994 - 1998) My transmission shop buddy is stumped on this 47re!

[SRay]

Hello all, I'm looking for advice on a 1998 12v 47re transmission for my buddy that runs a Dodge diesel shop.

He does all kinds of repairs from body, engine, transmission etc and even mega cab long box conversions.

Another buddy of mine dropped off his 1998 for a trans rebuild.

But one problem that for some reason won't get fixed and that's the transmission couldn't hold the engines power in lock up, overdrive.

He's rebuilt the trans 3 times, redid the valve body 3 times, replaced the torque converter 3 times. (Torque converter is an upgraded unit that's handled 600 hp in other trucks he's done)

All his gauges that hook up to the trans read good for transmission operation and pressure but in lock up mode, won't show why the slush box won't hold the engine power.

The recent valve body has been modified so much, it should be shifting so hard that the input shaft should snap under load. But still behaves like stock auto.

Theres only 25 psi of boost, (approx 250 hp)

Takes only a little throttle travel and the trans slips.

Only thing done to this truck is a "0" plate.

My buddy has decided to try doing up a different transmission, (case, valve body, hard parts, all)

He is about to give up if this complete different transmission doesn't solve the issue.

Any help would be appreciated.

 

[fest3er]

Does it hold out of overdrive (in Direct)? Has the throttle valve cable been correctly adjusted?

 

[Ozymandias]

Which line pressure has he measured within the gears?
How does the throttle position change the pressures?

 

[Tuesdak]

Is it a triple disc TC? Who makes the TC? I suspect a poor quality or limited ability of the TC clutch. Perhaps it's trying to lock up too early aka more throttle than it can handle locked up.

It's not the HP rating that matters it's the torque. (Low RPM high torque vs. high RPM high HP example below.)

I found that locking the TCC up early then pulling a grade unloaded will slip a factory converter clutch so bad the ECM unlocks it to prevent burn up. Replaced it with a high stall Yank triple disc billet and can lock it up anytime I like including lugging the engine up the 7% grade. Yes this is on the GM 6.2 hot rod. Normal lock up is 45 MPH and I was attempting (now I am) locking it up at 35 MPH.

Edit:
What kind of oil is being used and is there a break in procedure for the TC clutch? I know some TC companies don't recommend synthetic oil and have a 25 1/2 throttle lockup break in period.

 

[cerberusiam]

There are 4 different points that would cause slip when locked up in OD, which one is actually slippping? Until that is determined it is like playing darts blindfolded.

 

[SRay]

Cerberusiam: what are the four points in the trans? Then I'll check with the trans buddy to see if he covered all of them.

Is there a good torque converter for these 12v trucks that are good with the 1-3 gears that would be more useful?

The converter he installed he said is good for holding 600 hp but the 1,2,3 gears the engine is up at governed rpm (2,250 rpm) with foot to the floor, but truck doesn't seem to be moving fast.

Once in overdrive, the engine finally gets loaded down and moves good.

Once boost reaches 20 psi, the slippage occurs. So no good there either.

 

[SRay]

JDoremire: it's supposedly a upgraded 48re single disk converter.

The engine put out 300 hp with 700 tq at the wheels at 2,100 rpms on the dyno last year.

My truck with manual trans, same p-pump setup, made 283 hp 1,000 tq before burning up the clutch at 1,450 rpms.

 

[cerberusiam]

In lockup the 4 points are TCC, direct clutch pack, forward clutch pack, OD clutch pack. If it is actually slipping one of those is going to show issues.

Being rated at 600 HP is totally meaningless when they get hammered with the TQ. I have a TC rated at 600 HP but at 400 I can drive right thru the fluid coupling and bounce the tach off the rev limiter until it shifts. The clutch is holding 1000 ft\lbs of TQ becasue it is running +220 psi at 3200 plus rpms. If he is only getting 2200 rpms and the PR valve is not tight enough, pump is not putting out the pressure it is entirely possible it is slipping cluthces. Need to know what the apply pressures are at the rpm to see if they are high enough. A gauge on th emiddle port on the passenger side will tell you apply pressures at slip point and go from there.

It is also possible there is a cracked internla passage that is opening under high TQ load and dropping pressures. The 47's were not as stiff as a 48 and one could mess the 48's with too much TQ applied too hard and crack the case internally. He needs to do pressure tests under load conditions to see if hsi build is good or there is a problem internally.

 

[SRay]

The builder has been wondering if the case cracked internally.

He is currently building another 47re to see if that fixes the issues.