Technical Th400 shift problems

Hello all it's been a while and my car has been running great since break in 350sbc/th400. I drove from Midland down to Galveston for the weekend about 850 miles and all was great it shifted firm and positive as usual it never got above 180 even when I drove a little spirited however this morning when I got ready to come home I ran into trouble....got car up to temp and trans was 160 on the autometer gauge...drove at light throttle and noticed it wasnt shifting as early as it normally would from 1-2 I got on the highway not thinking much of it drove 10 miles at 60mph and got off the highway on a back road and it was stuck in second I pulled over to make sure the vacuum canister was okay and hooked up and everything looked perfect. Now it will shift from 2-3 sometimes under hard acceleration but it will shift manually with the floor shifter into all gears and I do have reverse. while trying to diagnose this problem I took it around the block and sometimes it will work like normal and others it's stuck in second and when I accelerate it won't go into 3rd until about 4000 rpm with a very very hard shift it's intermittent for sure and when it does shift it's hesitant kind of like a flintlock rifle like something is lagging but something is definitely wrong. Also the car now has a slight shudder when I first start it and rpm jumps about 50-75 rpm and is kind of rough...I pulled the vacuum canister off and tested it it looks good no fluid and the spring accuates the line is clean and hole free it's hooked to my Holley on the throttle plate right next to the pcv source. it's got me stumped and I'm not starting it again until I get this solved. The transmission is a FTI transmission new with about 1500 miles on it the converter is stock stall 800-1200 from summit racing any help with this is greatly greatly appreciated.

 

That has an electric switch for kick down, it could be sticking or stuck, or in need of adjustment?

Otherwise I gotta take those problems to the shop

 

I have never hooked up that plug for the kickdown could that be a probem and could it get messed up without it being used?I'm dreading it but I'm by no streach a transmission guy. Thanks for the response

 

Well...you mean you don't have it at all, or is it just laying there? Won't hurt not to use it, it just won't downshift when you step on it.

 

Okay I see what you mean and no it's just hanging there I didn't cut it in case I ever needed it it also wasn't hooked up in the 2 speed so I just left it as was when I did the swap.

 

Could it intermittently be triggered? It'd almost have to be wedged into something, as I recall the spring inside them are not real wimpy. Also, since it just hanging, make sure the wiring isn't chaffed and shorting to anything.

 

Okay so that sounds like it would be a long shot that's what is causing the problem but I will check on that wire to make sure it's not shorting out

 

How could it be intermittently triggered? Can it engage without power to it?

 

Thinking about it, if you don't have 12v going to the switch, it won't matter if it's being made, etc.

Probably not your issue.

But hey...I'm keeping you at the top of the page!

 

If you can manually select all gears the issue could be a sticky governor, but that wouldn't have any affect on the engine itself. Take a look here:

 

Haha that's true thank you much!! Just nice to omit at least I appreciate it

 

That looks like it could be the problem would it keep it in second? These have nylon gears correct??great video I'm going to pull that right now

 

Same as a T350 the governor has a nylon gear. A sticky governor could hold you in second. Jack up the rear of the car to minimise the amount of fluid that comes out and pull the governor to check if its moving freely. It will slide right out with the cover off.

 

Not the govoner this one is working just fine

 

Looks like it's opening

 

Modulator?

 

Okay the govoner may be sticking it will stay open unless gravity pulls the piston back down if I hold it horizontally as it sits in the trans it will not actuate the piston if I hold it vertically it will actuate the piston up and down does this sound like is messed up??

 

Checked it the modulator is good

 

I replaced it but to my disappointment it didn't solve the issue... I got a bottle to lubegard red to soak in overnite in case it's a sticky check valve up there if all else fails Monday to the trans shop!

 

*scratches head* It may be time for throwing chicken bone beads and burning some sage.

 

Haha no kidding

 

Chevy Guy, There's no spring in it . Pressure is what causes it to close. The centrifugal weight force it to open .
Hold it like you did .Move the weights in and out. If the valve moves freely, it's probably okay.

 

Hey there mark thanks for verifying that for me looks like it's in working condition. Is it correct to have 2 different weight springs in there? Thanks again everyone for your input!

 

If that vehicle had a PG in it and you replaced it with a T400, there isn't a kickdown switch in it... unless it had previously had a 400 in it before the PG. Any event, if there are no wires connected to the trans... that isn't the problem.

"Also the car now has a slight shudder when I first start it and rpm jumps about 50-75 rpm and is kind of rough"

Shudder while in park? That is probably a missfire.... missfire can lower the vacuum signal to the modulator which could cause the delayed shift. You have been checking the modulator hose at the trans... what about at the carb? Look at that hose also, it may be cracked. Check for vacuum leak at the carb base near that vacuum port.

 

You said you checked your vacuum to the modulator......what did your vacuum gauge show?

 

I'm replacing the whole line today both steel and rubber to the carb just to make sure but that does make sense to me about the misfire I'll be looking at that and the linkage to my floor shifter is it possible that the gear selector at the trans is caught between 2 gears and then finally selects a gear as I drive it due to misadjusted shift cable??

 

I haven't got my gauge with me but at idle it is ****ing a great deal and it's plugged in front of my Holley next to the pcv port which is full manifold I'm pretty confident it's hooked correctly but I did see someone online mention ported vacuum to the modulator can anyone confirm this for me?

 

I know you DON'T what ported vacuum to your modulator.

 

Okay thank you it's hooked to manifold

 

Yes the cable shifter out of adjustment can cause it. Upshifting thru the gears you say it works ok. I would try putting it in low, shift up to drive and then take off to see if it shifts ok. It may be off just enough that going from park into drive it could cause problems. Look at the cable closely too... if there are any melted looking spots on the housing.... replace it!!! Shifter getting out of adjustment as you drive it is a good indicator the housing has gotten too hot and it allows the cable inside to do strange things. (caused me a race a couple of times)
You have to use manifold vacuum.... high vacuum=early shifts. low vacuum=late shifts (like when you floor it, vacuum drops to make it shift later) If you connect to ported vacuum the vacuum will start out low, go to high at part throttle then low again at WOT.