First I am not a third gen owner, but I have a bunch of third gen. parts in my 1955 Chevy 2Dr Sedan.

I am running a 406 SBC with computer controlled MAP TPI, Painless wiring harness, 700R4 from a 1989 blazer and a IROC posi rear axle. After the initial install the transmission worked great, but the TC would not lockup in any gear. The problem was no 12 volt signal from the brake switch. Corrected that problem and now directly after the shift from 1-2, 2-3 & 3-4 the TC goes into lockup. After lockup it does lug the engine down somewhat before it will unlock.

Thanks in advance for your help.

 

What speed are you doing in 1st?
May be below the TCC settings in the tune

" A minimum road speed is required before the TCC will lock. The actual speed threshold can vary depending upon which gear the transmission is in. To keep the TCC from chattering the required road speed will use two values.
If the TCC is currently locked the unlock road speed threshold will be a value lower than if the TCC
is not currently locked. This action is called hysteresis.

These values are typically a couple of MPH apart. An example would be the road speed values of 38 mph & 36 mph.
If the TCC is unlocked it will stay unlocked as long as the road speed is below 38 mph.

Once the TCC locks the unlock road speed will be the 36 mph threshold.
In this manner if the vehicle speed is held at 38 mph the TCC will not continuously lock/unlock causing chatter.
If vehicle road speed falls below 36 mph the TCC will be unlocked."

 

I don't know the exact speed, but normal acceleration would probably indicate a shift from 1st to 2nd at about 15-20 mph range.

 

So you are well below the speed needed for TCC to activate ?

 

Your post is confusing like your wanting the tcc too lockup in 1st ?

 

You're wired wrong or running the wrong pressure switch.

Further very similar discussion:

https://www.thirdgen.org/forums/tran...-selenoid.html

 

Not at all. The initial shift points appear to be correct for all gears. My concern is that after each shift, there is a drop in engine rpm that to me indicates the TC has locked.This happens for all shifts. It does not lockup while in first and I understand that is as designed.