Transmission Shift Problems after HEI replacement

[conquistador]

Was hoping for some suggestions on how to start diagnosing this problem.

I recently purchased a 1966 C10 with a mildly built 355 and what I was told to be a turbo 250 transmission. The engine and transmission were put in the truck by someone else so I know little about it and with my added lack of overall knowledge, diagnosing problems is hard.

I took my 66 to the local tech school (buddy of mine runs the automotive dept) and he diagnosed the cutting out I was having as a bad HEI distributor. The kids did a great job replacing the HEI and installing the new radiator/electric fan but on the drive home I ran into a problem.

When shifting from first to second, the transmission will stall then surge, stall then surge, stall then the truck runs like a bat out of Hades again. Since it only has to gears it doesnt do it often, but I'm wondering with the new HEI if there is any adjustment to the transmission that needs to be done. The truck has gone from running average to running great but the transmission seems to be the issue now.

Any suggestions out there?

[cg285]

from your description it looks like you need to refocus a little north of the transmission to the engine for your concerns.

[conquistador]

Ok, thanks for the reply. Any ideas what I need to consider looking for?

[bpmcgee]

I'm not familiar with the 250, but with the TH350 I had one time I had shifting problems. That transmission judges shifts based on engine vacuum, and I'd forgotten to hook up the vacuum line.

Is it possibly a similar issue? Perhaps a broken or disconnected vacuum line? It would be running past or possibly connected to the alternator, so maybe it got borked?

[PGSigns]

With just two gears its a powerglide. Sounds like the vacuum line to the modulator is not hooked up or not hooked to the correct port on the carb. If your buddy is teaching this class he needs to teach testing after the work is done before returning it to the customer. Making sure what you did is all good is an important lesson.
Jimmy

[Captainfab]

I agree.........

Originally Posted by PGSigns

With just two gears its a powerglide. Sounds like the vacuum line to the modulator is not hooked up or not hooked to the correct port on the carb. If your buddy is teaching this class he needs to teach testing after the work is done before returning it to the customer. Making sure what you did is all good is an important lesson.
Jimmy

[conquistador]

I guess I should have also said that the issue didn't start with the shifting until later on in the day. I had driven it a couple times before that and perfect shifting, but later in the day I was pulling onto the local interstate and it started acting up. I'm going to check the vacuum hoses this afternoon, possibly one wasn't mounted securely and came loose when my foot go a little heavy on the last trip.

Thanks guys! I appreciate the help!

[jchav62]

I've the vac line isn't the problem... check the fluid level on the trans.

[andyh1956]

Check the diaphragm in the modulator to see if it holds vacuum. Also Power Glides have a linkage from the carb down to the trans, make sure one end or the other hasn't fell off.
It may be you don't have a Power Glide but a 3 spd trans that wasn't shifting properly to begin with. look to see if you have a TP cable coming up from the right side of the trans to the carb, if you do then you may be in for trans work.
Trivia- did you know that you can push off a Power Glide eqpt truck? At about 25 mph or so it will shift into high & turn the engine. They have two pumps, one front & one rear!

[conquistador]

Quick update for everyone, I had a vacuum hose that was split at the far end of the connection causing it to fall off after a few minutes of driving. I was also a little low on fluid. Swapped the hose out and topped off the fluid and things are working well again.

I appreciate the help!!

[PGSigns]

Good to see you got it going.
Jimmy