Well this is a problem that has been around for me for awhile but I would like some opinions on a better solution.

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It would help if we knew what tranny ya had...
If it's the factory 350, it's a simple pressure switch change to move the LU speed higher. I like using a 56 psi switch on them, myself. The pressure switches are rated by the psi at which they close, which corresponds to the MPH it will go into LU. If you have LU at 45, you have a 45psi switch. Just get a 56psi switch, swap them, and then see how a 56mph LU feels.
If you have a 700 or 2004R overdrive, we would need to know if it is set up for a hydraulic LU apply, or if it is set up with an electrical switch for LU. If it is a hydraulic system, it's a simple matter of changing one spring in the valve body to raise/lower the LU application speed.


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Joel Adams
C3VR Lifetime Member #56    
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"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Thanks Adam.

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The pressure switch is simple to change, but you will need to drain the fluid, and drop the trans pan. On the valve body you will see the only switch there. Simply unplug it, and unscrew the switch, screw the new one in, plug in the connector, and put the pan back on with a new gasket.
You MAY be able to get or order the switch from your local parts house...don't know, but it's worth a shot. A trans shop would be a better place to go for one. If they do not have one in stock, they can get it easily. If not, let me know, and I'll send ya one.

With the 350 trans, and 3.08 gears, it's going to be a little doggy off the line. I would suggest a change to a 3.36, or 3.55 rear gear for that. It's gunna lower your mpg somewhat, but it'll definitely have a little more get-up-and-go. Your cruise RPM will also be a bit higher with the lower gears, so that's something to think about.


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

In 1980 lock up is done at the firewall with a vac switch that is adjustable . It can be found to the left of the break booster and has an adjustment by taking off the vac hose and turning the screw in the vac pod not sure if it is allen head it may be. 

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1980 , ZZ430 , 3.92 rear , 700R4 2400 stall NEW EZ EFI 

Hmmmm...that's interesting. Are you sure that is not the switch to dis-engage the LU on acceleration? I'll have to look that thing up...ya got me curious now!

I see the switch in the wiring diagram. It is tied in with the Neutral safety switch, and the brake light switch. It appears that that vacuum switch is used to cancel the LU on acceleration(under a load). If it is adjustable, it looks like it could change the timing of when it un-locks, but I'm not sure if it would make it lock up later or not. Certainly worth a try.
The pressure switch on the VB still has to close before lock up applies. The most common switch rating is, believe it or not, 35psi, where lock-up would apply at 35 mph! Just a simple matter of changing the switch to get the apply speed up. The switches are available up to 62psi, iirc.



|UPDATED|3/18/2013 10:24:37 AM (AZT)|/UPDATED|


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Joel Adams
C3VR Lifetime Member #56    
My Link


(click for Texas-sized view!)             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Thanks for the replies. I will see if I can find the switch this weekend on the firewall and play with the adjustment. I don't remember seeing one there. If there is not one on my year, I will likely go to the trany shop that did the rebuild and have them bump up the lockup setpoint to 62 or something higher than I currently have with the switch that is inside the trany.

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On my 1980 the wires go from that vac switch to the transmission , I think the break switch cuts off elec power to it and because it is vac operated anytime you change engine speed while driving the vac signal will drop the elec signal. 

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1980 , ZZ430 , 3.92 rear , 700R4 2400 stall NEW EZ EFI