68 Mustang c4 not shifting right after engine work

[jerthemost]

I recently had a good bit of work done on my 68 Mustang coupe engine. I had new intake, carb, heads and cam installed. All parts by Edelbrock. After upgrades I had over heat issue explained elsewhere in this forum. After the engine work my c4 auto trans is shifting weird. If I am cruising along the street at about 35 mph the trans will shift up if I speed up just a bit and then shift down iimmediately if I slow down just a bit. And it jerks real hard when it down shifts. The trans was just rebuilt a year ago and the car has been driven very little over the past year because of problems. It’s very irritating to be driving down the street with the trans shifting up and down abruptly. The trans was perfect before the work. The mechanic must have done something to cause this since it was perect when it went in had this problem after the work was done. It took 3 months for the mechanic to get the work done because he kept screwing up. When I got the car back the second time it ran fine trans and all but it was getting to hot so went back to shop to see if he drilled the steam vent holes. When it came back out of the shop I had the trans problem.

I thought maybe a vacuum line problem or something of that sort. I am thinking they didn’t connect something back up right maybe. They had to pull intake and carb and one head back off to see if the holes were under the heads so they had to disconnect some things. I know the trans shifts on vacuum but I don’t know what to look for. The trans vac line is connected at base of carb where edelbrock says to connect it. Any help would be greatly appreciated.

 

[JonK]

They shouldn't have touched the rear hose but i'd check it anyway. It is a 90* hose at the rear half of the trans on the pass. side, the metal line runs from the top of the motor to down there. The hose may need replacement and you'll need a 90* formed hose or it'll kink. While you're there pull the hose off the trans modulator it's plugged to and make sure no fluid is coming out of the modulator into the hose. If it is leaking it's bad and they have a color stripe on them to get the right one. I see you have verified that the trans vac line on the carb goes to a FULL vacuum nipple on the carb vs. the ported nipple which changes with engine RPM. I would double check this as you can see if it were on ported it would change with engine speed which is what you are experiencing.

There is also a kickdown rod on the drivers side of the trans that hooks to the carb linkage near the throttle rod, if it is in the wrong place on the lever it could also cause what you are describing. If I remember correctly my kickdown was hooked to the bottom half of the carb lever while the throttle rod is connected to the top half. The kickdown lever would need to be connected properly when installing an aftermarket carb as the levers aren't the same. Maybe someone with a C4 and Edel. carb. can post a pic of their carb linkage, you might request that in a post.

Lastly, have you checked the trans fluid level while in park at idle?
Jon

 

[jerthemost]

don't seem to have kickdown rod

the carb was changed prior to this work and there was no rod going to the trans then. so i don't seem to have a kickdown rod.

fluid was good.

i will try all you suggest. adding 100 hp would not cause this would it?

thanks for your help

 

[jerthemost]

checked vac lines

the trans is connected to the port on front passenger side of carb base, distributor to the other side, pcv valve to center. edelbrock calls the one the trans is on timed vac is that the same as constant vac? they call the other one manifold vac. i coulld swear that the trans was connected to a tee sticking out of the old intake manifold before it was changed to edelbrock performer. it was a tee right behind the carb. haven't checked the other things yet.

 

[Hwyman]

My performer intake has a vacuum port in about the same place the old one did. Also, I think the trans. vacuum pick up on an Ed. carb is on the back of the carb, if you don't use the manifold. The front of the carb. gives you two choices for dist. vacuum. Timed or full. One on each side of center port where the PCV goes.

 

[jerthemost]

problem solved

moved trans vac connetion to an intake runner on intake manifold and trans works perfectly. case closed