JollyGreen
Metalworking Madman
Yeah, it just depends on what part(s) are going bad. Mine wouldn't start slipping until it was warm.
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A trans that shifts soft is slipping slightly between gears.
Most transmissions were designed with this so that the masses get a vehicle that shifts 'smooth'. But it's that slippage that creates heat, & heat kills transmissions. Smell the trans fluid. If it smells burnt, then the rest of the tranny is too.
The less time the transmission spends going from one gear to the next, means that there is a lot less heat being generated. Those firmer shifts can be a little harder on the rest of the drivetrain, though. Probably why the PO swapped the posi unit. Gov-locks don't like to be hammered like that. They go Boom!
If you think that the auto with an s-kit shifts hard, go for a ride in a vehicle with a high HP engine, a stick, & someone that can bang shifts! Now that's hard on a vehicle!
An automatic can shift faster, (constantly in gear) & it's a lot easier on the rest of the drivetrain!
If that 'clunk is pretty bad, or gets worse, I'd be checking those u-joints, the u-bolts, shackle & hanger bolts, & the engine & tranny mounts.
A little clarification: hard, fast shifts are good for the life of the clutches due to decreased slippage and heat generation. HOWEVER, tire chirping, neck snapping shifts kill hard parts, period. You may save the clutches, but take out the reaction shell, forward sprag, input drum, planetaries, or any combination of those in the process. If your buddy likes to drive with his foot in it, he may need that spare trans sooner than he thinks. You didn't mention what kind of truck he bought, but 400's can and do break reaction shells and planetaries when completely stock. With lockers and bigger/wider wheels and tires it's even easier. Food for thought.
To answer your question, yes, it sounds like a shift kit. Most kits will have you make several changes to the valve body to change shift timing and firmness. Automatic transmissions have accumulators in the valve body that cause a delay between the time a valve opens and when the clutches are applied. This serves several purposes, but primarily acts to make the shift smoother and to ease clutch engagement to reduce shock loading of the transmission and driveline. By opening up the metering orifices in the separator plate and/or changing the accumulator piston spring, you can reduce the delay and create a quicker, firmer shift. The problem is that too little delay serves no purpose but to make the shift feel harder and tear up hard parts without any performance benefit.
A little clarification: hard, fast shifts are good for the life of the clutches due to decreased slippage and heat generation. HOWEVER, tire chirping, neck snapping shifts kill hard parts, period. You may save the clutches, but take out the reaction shell, forward sprag, input drum, planetaries, or any combination of those in the process. If your buddy likes to drive with his foot in it, he may need that spare trans sooner than he thinks. You didn't mention what kind of truck he bought, but 400's can and do break reaction shells and planetaries when completely stock. With lockers and bigger/wider wheels and tires it's even easier. Food for thought.
To answer your question, yes, it sounds like a shift kit. Most kits will have you make several changes to the valve body to change shift timing and firmness. Automatic transmissions have accumulators in the valve body that cause a delay between the time a valve opens and when the clutches are applied. This serves several purposes, but primarily acts to make the shift smoother and to ease clutch engagement to reduce shock loading of the transmission and driveline. By opening up the metering orifices in the separator plate and/or changing the accumulator piston spring, you can reduce the delay and create a quicker, firmer shift. The problem is that too little delay serves no purpose but to make the shift feel harder and tear up hard parts without any performance benefit.