Turbo 400 Shifting Soft!

[savatreatabvr]

My mid 70's Turbo 400 shifts out of 1st to 2nd fine but 2nd to 3rd shifts soft, it's not really slipping it's just soft. Plus it shifts to soon throughout the gears, at 20 mph I'm in 3rd but it's not bogging down it just takes a while to get up to speed so 90% of the time I shift it manually from 2nd to 3rd so I've got more RPMs going into 3rd. I've got the transmission modulator (I think that's what it's called) hooked directly to manifold vacuum, should it be hooked to ported vacuum?

[notyo_cheez]

Modulator should draw vacuum from its own dedicated port on the manifold, starboard next to the carburetor.

[savatreatabvr]

Yeah, it's hooked up to manifold vacuum behind the carb but also is the vacuum advance. Should I hook the vacuum advance somewhere else?

Originally Posted by notyo_cheez

Modulator should draw vacuum from its own dedicated port on the manifold, starboard next to the carburetor.

[notyo_cheez]

Vacuum advance should be sourced from a port on the carburetor if I'm not mistaken.

[savatreatabvr]

75% of people say manifold vacuum and the rest say ported vacuum, I've tried both and can't say I've seen much of a noticeable difference.

Originally Posted by notyo_cheez

Vacuum advance should be sourced from a port on the carburetor if I'm not mistaken.

[geester]

vacuum advance should come from ported vaccum. you dont want advance to start kicking in till about 1000 rpm and above.

[notyo_cheez]

Checking cheap and simple stuff first take a look at your vacuum hoses. If they all look okay I'll guess that perhaps the modulator is beginning to fail, although if this were the case it would be like not having any vacuum to the modulator at all and no/erratic shift pattern.

If it's feeling sluggish going through the gears it may be an internal issue. You can try a fluid flush with a new filter to see if that makes an improvement, if that's already been done you might be looking at a rebuild/overhaul in a worst case situation as the forward fluid pump could be heading south among other things. Auto trannies are pretty complex components and unfortunately many of us are at the mercy of the specialists when it comes to them.

Good luck.

[savatreatabvr]

Not sure why 1000rpm and above?

Originally Posted by geester

vacuum advance should come from ported vaccum. you dont want advance to start kicking in till about 1000 rpm and above.

[INSIDIOUS '86]

Originally Posted by geester

vacuum advance should come from ported vaccum. you dont want advance to start kicking in till about 1000 rpm and above.

are you a ford guy?

[kikkegek]

Originally Posted by savatreatabvr

Not sure why 1000rpm and above?

the amount of vacuum has nothing to do with rpm. It is determined by how far you open the throttle. So biggest vacuum is at idle and during cruising. and lowest vacuum is at WOT (Wide Open Throttle).

that means you could have max OR least vacuum at 1000 rpm depending on how far you have opened up the throttle.

vacuum advance is connected to ported vacuum on SMOG engines and on manifold on non-smog engines.

you can read up on that one these two great pages:

ignition timing 101:
http://www.73-87.com/7387garage/driv...timing101s.htm

HEI tuning secrets
http://www.73-87.com/7387garage/drivetrain/hei.htm

[savatreatabvr]

BITE YOUR TONGUE! However I did own an 85 Bronco at one time and will admit it was a great truck!

Originally Posted by INSIDIOUS '86

are you a ford guy?

[savatreatabvr]

So there's no adjustments other than the vacuum source?

Originally Posted by kikkegek

the amount of vacuum has nothing to do with rpm. It is determined by how far you open the throttle. So biggest vacuum is at idle and during cruising. and lowest vacuum is at WOT (Wide Open Throttle).

that means you could have max OR least vacuum at 1000 rpm depending on how far you have opened up the throttle.

vacuum advance is connected to ported vacuum on SMOG engines and on manifold on non-smog engines.

you can read up on that one these two great pages:

ignition timing 101:
http://www.73-87.com/7387garage/driv...timing101s.htm

HEI tuning secrets
http://www.73-87.com/7387garage/drivetrain/hei.htm

[Wrecked1982]

you might want to check for kick down cable ajustment if it is equiped with

[kikkegek]

Originally Posted by savatreatabvr

So there's no adjustments other than the vacuum source?

? are you referring to the ignition or the transmission? I am no transmission expert. Sorry. I just wanted to set things straight about the ignition.

good luck...and I'll be watching this cause I am also interested in your question.

[savatreatabvr]

Yeah, I'm talking about my transmission.

Originally Posted by kikkegek

? are you referring to the ignition or the transmission? I am no transmission expert. Sorry. I just wanted to set things straight about the ignition.

good luck...and I'll be watching this cause I am also interested in your question.

[savatreatabvr]

It's a turbo 400 so no kick down cable.

Originally Posted by Wrecked1982

you might want to check for kick down cable ajustment if it is equiped with

[Wrecked1982]

i knew some tubro 400 didnt have kickdown cable but now i know they all dont have

[savatreatabvr]

I believe the turbo 350 was the one with the kick down cable, turbo 400 has the modulator.

Originally Posted by Wrecked1982

i knew some tubro 400 didnt have kickdown cable but now i know they all dont have

[beamn7]

THM350 = kickdown cable. THM400 has the kickdown solenoid which is the electrical conneciton on the drivers side of the case. Connects to the switch mounted in the accelerator pedal assy bracket....

Pull the vaccum hose off the modulator and see if you have an adjusting screw inside the vaccum port. (not all had adjustable modulators) If you tighten it up, it will shift later and harder. If you loosen it up, it will shift sooner and softer.

If you don't have an adjustable one, I'd pick one up.... easy install.

[savatreatabvr]

I'm assuming adjusting the modulator will effect 2nd & 3rd gear correct? Since 2nd gear in my truck shifts normal the big question now is will the adjustment make 2nd gear shift too hard and 3rd gear shift normal or does it even them out?

Originally Posted by beamn7

THM350 = kickdown cable. THM400 has the kickdown solenoid which is the electrical conneciton on the drivers side of the case. Connects to the switch mounted in the accelerator pedal assy bracket....

Pull the vaccum hose off the modulator and see if you have an adjusting screw inside the vaccum port. (not all had adjustable modulators) If you tighten it up, it will shift later and harder. If you loosen it up, it will shift sooner and softer.

If you don't have an adjustable one, I'd pick one up.... easy install.