Need tranny help.... Not shifting out of first...

[PhoenixZorn]

We put the 350 and 208 in the 1980 blazer yesterday, and after realizing that the little rubber gasket was not on the kickdown cable and thus was leaking all over the place, I repaired the blunder and drove it around a bit. It was in 4-Low at first, then we fixed that, and I drove it some more. I realized after hitting the street for a quick gas run, that the tranny wouldn't shift out of first. I checked everything I could see, but by that point, the exhaust was too hot for me to get very close to the tranny. I could get it up to around 35 or so in first gear, let off the gas, and it would stay in first. The tranny came off a working truck, and I know it was shifting properly before... so what am I missing??

Both the replacement and original trannys were actually TH350s, but the original one has a short output and an NP205, while the replacement has a long output and an NP208, making the rear driveshaft 3.25 inches too long after everything was said and done... I had it cut and balanced by a driveline shop, and installed it myself. The front driveshaft is currently locked in a stuffed position, and is for now, about 6 inches too short to reach the front pumpkin in it's current configuration. I'll either need to get the front shaft from the tranny donor truck, or from a yard, since I don't want to pay out my ass for a new one. Everything works except the shifting part... it is definitely gripping the tranny, nearly spinning the 32 inch tires just putting it in drive and reverse, and I just can't figure out what else could be wrong.

Can anyone help me out with a few ideas for what to check next time I have a chance to work on the truck?

 

[mudhog]

plug in the vacuum line to the carb and to the modulator on the tranny. if it wont shift normal after that try manually shifting it if it manually shifts then its the governer

 

[mrk5]

plug in the vacuum line to the carb and to the modulator on the tranny.

That was going to be my suggestion. I've forgotten that one twice before in the past.

 

[PhoenixZorn]

Well, I know for sure the vacuum line is connected to the modulator, but not sure about the carb... I'll check that first... actually... if I can get there today, I may do that... but I'll have to wait for a friend to arrive before I do that...

 

[Blue85]

plug in the vacuum line to the carb and to the modulator on the tranny. if it wont shift normal after that try manually shifting it if it manually shifts then its the governer

Yeah, what he said...

 

[diesel4me]

Modulator...

It might be the modulator..either bad,or not getting any vacuum--on a small block,the vacuum hose for the modulator goes to the intake manifold right behind the carb...not to the carb itself--it needs manifold vacuum to work properly..(strong suction at idle)..

If the govener is not working due to a stripped nylon drive gear,it wont upshift out of first gear,no matter WHAT you do as far as manually shifting it!..if the modulator is the reason,you may be able to coax it to upshift by manually shifting from first to second..and it will feel like neutral when you let off the gas when coasting..

A maladjusted detent cable can hold the tranny in low or second gear constantly too...needs more "slack" in the cable...hope you find its an easy fix..good luck!