What is a "shift kit?"

Question

What is a "shift kit?"

Silverado (Computer)

(OP)

6 Sep 01 10:36

I recently bought a Chevy Silverado with a "shift kit" on it. Now, the only thing I know about this thing, is that it makes my automatic transmission shift at a higher rpm than normally and makes in-town gas milage really bad. I have looked at a couple of these online and I think I have a pretty good idea of what it looks like, what I want to know is this: What is it attached to, and how should I go about getting rid of/replacing it to return to normal automatic shifting? Thanks ahead of time for your response.

TheBlacksmith (Mechanical) · Answer 1 · 2001-09-06 16:33:51

Traditionally, the auto trans, used a "hydraulic computer", AKA, the "valve body", that would measure the engine RPM, vehicle speed, engine load (vacuum) and throttle position, then determine the optimum shift points and hydraulic pressures for economy, smoothness and efficient power transfer (no slippage). Shift kits replace portions or all of the valve body with modified orifices, springs, diaphragms, etc, that shift the balance towards power (hence the higher shift RPM, when the engine is making more power) and more pressure on the clutches and bands to preclude slippage. If your truck is a late model, many of these functions are now done by the electronic computer, still measures and controls the same things, but the changes are made in the EEPROM or "chip". If the change is in the valve body, you probably need the instructions from the kit to identify the springs and orifices that need to be restored to stock, if its electronic, you need to put a stock chip or program back in (some are chips, some are programs, which need security codes to overwrite the existing program) Good luck.

Blacksmith

Silverado (Computer) · Answer 2 · 2001-09-06 18:48:39

Blacksmith,

Thank you very much for your response. It seems from your reply that I will need professional assistance. Thanks again.

Silverado

JayMaechtlen (Industrial) · Answer 3 · 2001-09-07 14:12:29

depending on specific model of transmission, it may have something called a "vacuum modulator".
This is a device (mounts to the case of the transmission) that uses engine manifold vacuum to signal engine load to the transmision.
Less vacuum=more load.

some of these are adjustable.
if a vacuum leak exists, it will "see" less vacuum, and shift "later" as if you had a higher load than you really have.

check it out...

Jay

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What is a "shift kit?"