Lock-up 904 ?

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J

jeeper

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What is the RPM drop approximately when a 904 locks up?

I'm chewing on some ideas for a real mild street car.

Thanks, ROB
 
Don't believe any versions of the 904 had lock-up torque convertors.
 
The rpm drop is dependent on how close your cruise ropm is to the stall speed of your converter. But it is not an OD gear it just locks up the torque convertor. The reason they were used was with the high gears (2.45) that were in mid 70's cars coupled with the 55mph speed limit it put the convertor in or near stall speed which caused slippage and heat. The cure was to lock up the convertor. Then when the OD trans hit the market the the rear end gears could be lower but with the OD gear the rpm and stall speed was still a problem that's why we still have lock up convertors today. If your cruise rpm is above your stall speed the lock up convertor will not effect your rpm very much if any.
 
OK. So it would be great with smog gears such as 2.76's or something but not good with my 4.10's.

That makes perfect sense.

Thanks for the advice, ROB
 
I won't say it wouldn't be good with the 4.10's. I say you probably wouldn't see as much as a gain as you would with a 2.76 gear.
 
But, did a 904 ever have a lock-up torque converter? I though the only 3 speed trannie with a lock-up converter was a 999. I realize that it was basically the same as the 904 but so is the A500 and 42RH.
 
Here is the problem that I am facing. I have gathered alot of Mopar stuff. I mean whole cars and engines intakes etc. Lots of junk for both BB and SB.

I am coming to the realization that I am going to end up with a single digit mpg car if I don't watch it.

I have an 85 5th avenue transmission which is a 904 variant. I'm sorry for the confusion.

I was looking at putting that in an A body and runnign my 4.10's with some taller tires. If the lock-up would knock a few hundred rpm off I would leave it in there.

Just weighing my options.

Thanks for the help, ROB
 
Technically there were no 904 lock up trannys, the 998 and 999 can be a lock up and are of the 904 family so some people call a 998 or 999 lock up a 904.

I don't think it will knock off a few hundred rpm, more like less that 100.
 
and that 85 tranny has a low gearset in it - i just had one hanged over to a NON lockup - so i could run any converter i wanted....

i saw 400 rpm drop with 3.91's in my other car with lockup 727, hope it helps.
 
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