C4 Auto Downshift Problem.

[064 PNY]

Auto will not downshift back to 1st when stop at lights, etc. When start in 'D' gear it will shift up to 2nd and 3rd ok but will not shift back down when stopped. Auto shifts fine if used manually, i.e. manual shift to 1st then move up to 2nd & 3rd via T-bar shifter. Shifts back down through gears manually also with no problem. Manual shift up & down through gears is smooth. The kick down rod is OK and working. If cuising in 3rd & hit the gas it drops back to 2nd no problem then shifts back up to 3rd smoothly. Same for kick down from 2nd to 1st when step on the gas, so no problem with kick down linkage/adjustment.

So, only problem is in 'D' gear and not coming back to 1st when stopped. Is this a modulator or govenor problem? How do I check?

Comments welcomed....thanks.

P.S. have already checked vacuum line frominlet maniflod to rear of modulator valve in back of transmission. No splits, etc and is connected properly. Also, auto is full of fluid.

[VIBE 65]

dont have a c4 but im pretty sure what your describing is normal. If you start in D it takes off in second. Kinda stupid system if you ask me but I think thats normal.

[BLKPNY]

Vibe, that system is for Snow affected area's, I believe. Not too stupid, if you're on an icy road. I think it's optional though, and you should be able to tell somehow, if your cars got it, or not.

[064 PNY]

dont have a c4 but im pretty sure what your describing is normal. If you start in D it takes off in second. Kinda stupid system if you ask me but I think thats normal.

Was not doing this a few months ago. Used to operate normally in 'D' before. There is no 'crawl' gear in this auto.

[FST68]

might be worth replacing the Modulator valve, I have had this problem in the past and this fixed it.

Cheers

[064 PNY]

just went for a drive. It drove perfectly........shifted up and down smoothly while in 'D' gear. Went right back to 1st every time the vehicle was stopped. I'm thinking a sticky modulator valve may be the cause. Will go with your suggestion FST68 to replace. Sticky valve would explain intermintent problem I am seeing.

Thanks for replies.

[064 PNY]

latest update......still have issues. Replace modulator. The downshift problem has gone away. Shift from 1-2 is fine. Shift from 2-3 slips real bad. Upshift/sip is very bad and engine revs right up. Have to back off throttle and let it engage 3rd then can drive along in 3rd ok. Has been slipping occasionally from 2-3 for a while but not very bad like now. Even tried putting old modulator valve back in....same problem. Thinking modulator is not the issue. Also checked vacuum hose from modulator valve all the way to intake manifold, no leaks.splits, all looks fine. Now thinking intermediate band adjustment or Govenor problem?? Any ideas out there?? thanks in advance.

[MustangNut]

bands maybe need adjusting. They can wear quickly.

[IGALOP]

Inter band adjust!:thumb:

[FST68]

if its slipping then the issue is definatly internal.

Its worth taking it to get serviced they will adjust the bands and fix the issue if they know what they are doing.

My sugggestion is get it shift kitted at the same time will be a little harsher on changes but less likely to slip.

If your interested Try Precise Automatics they seemed to know what they where doing with mine, not the cheapest around though.

Cheers

[064 PNY]

thanks for advice guys. Will check out the band adjust option and go from there.