Engine/Transmission (1994 - 1998) Stall speed question

[BHaden]

I have a new-to-me 95 3500 4x4 Ext cab auto with 3:54s and 235-85/16 tires. The trans is rebuilt (AAMCO) by previous owner. It shifts nice and firm and seems to be in great shape, but the TC flashes to 2200rpm+ when I hit it moderately. I understand thats "the way they are" and will at some point put in something better when I can afford it and have nothing else to do (HA!). I do not know what type or brand they installed at rebuild; maybe they just cleaned the old one and put it back. My 12 valve is Modded slightly; 4" turbo-back straight-through, AFE-BHAF, #10 plate. Maybe some other p-pump tuning, but I haven't looked further. I have yet to see any visible smoke from the drivers seat, and it is nice and crisp off-idle. I have seen a TC listed, I THINK it was a TCI, that showed a 900rpm stall speed in the specs. I can't find that listing again at the moment, but even with all that diesel torque, 900 seems a little low. This truck will be strictly commuting, hauling and occasionally trailer pulling up to 10,000lbs.



My question is; how low is too low for stall speed? Can you get so low the turbo never gets spooled or is too slow? The current TC is so loose the tach doesn't move when the transmission shifts under load. It just floats around the 2000rpm mark until the TC locks up or I back off!



TIA... .



Went from a 2006 Mega Cab to the 95 12 valve and likin it! Major old-school

basic machine. Feels good to get greasy again!!! And NO PAYMENT BOOK!

 

[Missouri Mule]

900 seems to low you want your stall rpm to be the same as your Max torque (1600 rpm) so a stall speed of 1600 rpm should be good.

The lower the stall speed the more trans fluid pressure at low rpms ( the stock TC is usually putting out pressure at 2000 /2200 rpm much to high for a diesel engine).

 

[JMcCoy]

You want a low stall speed. You want to take advantage of the torque converter after it has reached its stall speed. The stall speed is kinda like the clutch on a manual trannsmission. You wouldn't let of the clutch at 1600 rpm. You would waist all the torque and hp leading up to peek cruising speed. Also, your transmission will over heat around town. That is one of the problems with the stock converter. That said, 900rpm does sound a little low. I would contact a couple "leading" transmission shops that build their own converters. A good triple disk converter will cost at least $1300. 00. It will be one of the best mods you do. It will also extend the life of your transmission. A lock up controller is also nice. Good luck.

 

[fest3er]

The 'stall speed' also depends very much on how much torque/HP you have. What they call a '900 RPM stall' could very well be an 1800 RPM stall if you have, say, twice the torque that TC was designed for. I recall a certain diesel dragster on which the TC was either too tight and wouldn't let the engine move enough air to light the turbos, or it was too loose and couldn't hold the engine at all.

When the ATS TC was install in my truck, the fueling was stock. I could not accelerate, because I could not get the engine to turn fast enough to move enough air to spin up my wheezing HX35. Once I added fuel (slid the plate forward), operation returned to where it used to be: 1800-2200 RPM under full fueling. Only real difference was firm, deliberate TC clutch lockup and perhaps firmer shifts (besides the slightly quicker acceleration; 1/4 miles ET dropped from 18. 1 to 17. 1).