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C4 hanging 1-2 shift???

latrucker

Contributor
Sr. Member
Joined
Jul 19, 2010
Messages
614
I have a c4 built by Jay at Broader performance. Was built 3 years ago but was just installed a couple of months ago. Once at operating temp the 1-2 shift will hang till late in the rpm' during normal easy driving. Take off in D and it will stay in 1st until I stomp the throttle then it will shift to 2nd and shifts to 3rd as normal with no problems. If a don't stomp it, it won't shift into 2nd, it will stay in 1st at 3000 rpm's all day until I stomp the throttle then it will shift into 2nd. If I manual shift it it will shift great. It's not a modulator adjustment issue. I tried that. It will just make my 2-3 shift change but 1-2 is still hanging. Anyone have any idea what would cause this?
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
Do you have a single port modulator or a dual port modulator? have you checked that you have good manifold vacuum at the modulator.

Next area of concern it down shift lever at idle the lever needs to be pulled up to the engine. there should be a light spring at the carb pulling on this lever in addition to the spring inside the transmission. The throttle linkage should not be pushing this lever down until after 3/4 of the way to full throttle.

After looking at those issue then I worry about the small pin that is behind the vacuum modulator. It falls out when you remove the modulator as you get the red arm pit as the tranny fluid rushes out.

At idle when cold the the tranny fluid level needs to be at the tip of the dipstick.

After that its an issue between you and Broader.
 
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latrucker

latrucker

Contributor
Sr. Member
Joined
Jul 19, 2010
Messages
614
Thanks Rusty, really appreciate the help. I will check all the things you listed hoping one of them will cure the issue. Funny thing is once it finally shifts into 2nd, it will make the 2-3 shift when it is supposed to with no issues. Its only the 1-2 shift. Also, it shift great when it is cold. Only have this issue when it gets to operating temp.
 

Rustytruck

Bronco Guru
Joined
Feb 24, 2002
Messages
10,875
The only outside issue I can think of would be the valve in the valve body or the valve in the governor sticking but you can still induce the shift. How hot is hot? Any restrictions in the cooling system for the tranny?

After the basic checks I suggested this problem needs to go to the professionals to sort out as it is beyond my capabilities.
 

DJs74

Bronco Guru
Joined
Apr 1, 2014
Messages
1,135
Sounds like a kickdown lever issue to me too. If the rod is not far enough forward (toward the radiator), you are continuously getting a "passing gear" situation because the lever arm on the side of the case is engaging too early... or all the time.

Jay is a good guy, he built a VB for me a few years back - I'm sure he will try to walk you through some troubleshooting on the phone if you are not able to dial it in.


DJs74
 

c0astie31

Jr. Member
Joined
Jun 27, 2015
Messages
157
I am having some issues on my c4 and I can tell you, on mine if I lock the kick down level to the kick down my trans shifts into 2nd at 20mph and 3rd at 45 mph, it works better that way. if I let the lever sit regular my trans will not go into 1st at stop lights or signs. if locked out it will down shift into second off throttle and into 1st at full stops.
I am leaning toward a new valve body from performance automatics, their street strip valve body
 

B RON CO

Contributor
Bronco Guru
Joined
Jun 29, 2016
Messages
2,412
Loc.
Statesville, NC
Hi, X2 on the kick down lever. Make sure you can move it up and down freely from the throttle on the carb, and the spring pulls it forward. It needs it own spring. The throttle should only engage the kick down near full throttle.
What kind of modulater adjustment did you do. There are different length pins, and adjustable modulaters.
How is the vacuum source.
Can you post a pic of the throttle and kick down linkage?
Good luck
 

BroncoKelley

Jr. Member
Joined
Aug 18, 2011
Messages
131
Loc.
Billings, Montana
I just had my C4 rebuilt and had a similar issue, 1-2 shift was delayed and mine would not downshift to 1st when pulling out. There was debris floating around and was stuck in the governor. I pulled the TC out and cleaned out the governor and polished the valves. It was good for about 20 miles and started again. I pulled the transmission out again and sent it back to the guy that overhauled it. I have it back now and its been good. Make sure you flush the cooler or coolers. I also installed an inline filter on the return cooler line.
 
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latrucker

latrucker

Contributor
Sr. Member
Joined
Jul 19, 2010
Messages
614
Fixed it....

I have resolved my problem. Looks like the guy that did my Fitech connected the modulator hose to ported vacuum instead of manifold vacuum. Switched it over and she shifts like a new transmission. Thank you for all the help and guidance.
 

Broncobowsher

Total hack
Joined
Jun 4, 2002
Messages
34,833
Ported vacuum came to mind about halfway through this. It was about to be my suggestion.
 
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