t400 tranny sticking between gears @ low rpm? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

WinDancer · 11-06-2009, 03:11 AM

I have a 396 in my truck. Under feathered throttle conditions my tranny reaches a point where it constantly [like 40-50 times per minute ] keeps changing from 1st to 2nd and then back again, over and over and over.
With moderate throttle it works perfectly.
Had a new B&M adjustable modulator put in with no change- the mechanic says the 400 has no carb-to-tranny cable to adjust it correctly like the t350's do.
Has anyone actually had this problem? Were you able to get it corrected? What did you do?
Thanks,
Dave

mtdave2 · 11-06-2009, 12:58 PM

still sounds like a modulator to me.. id crank the sensitivity down a bunch and see if it stops. What tells the trany to shift is the modulator.

chevy_mike · 11-06-2009, 01:18 PM

The TH400 does have a vacuum line that hooks to the modulator. Make sure there is not a leak in that line.

I am assuming you don't have some wild cam installed in the 396 that is lowering the vacuum signal too low. You should be seeing 14"+ at idle.

11-06-2009, 03:11 AM	#1
WinDancer The Original HotRod KnifeMaker Join Date: Jan 2007 Location: Tenino, Washington Posts: 811	t400 tranny sticking between gears @ low rpm? I have a 396 in my truck. Under feathered throttle conditions my tranny reaches a point where it constantly [like 40-50 times per minute ] keeps changing from 1st to 2nd and then back again, over and over and over. With moderate throttle it works perfectly. Had a new B&M adjustable modulator put in with no change- the mechanic says the 400 has no carb-to-tranny cable to adjust it correctly like the t350's do. Has anyone actually had this problem? Were you able to get it corrected? What did you do? Thanks, Dave __________________ Dave 69 GMC SWB 2WD 454 Turbo 400

11-06-2009, 12:58 PM	#2
mtdave2 newly minted old timer Join Date: Dec 1999 Location: Hudson WI Posts: 3,518	Re: t400 tranny sticking between gears @ low rpm? still sounds like a modulator to me.. id crank the sensitivity down a bunch and see if it stops. What tells the trany to shift is the modulator. __________________ ____________________________________________ 72 c20 longhorn 65k org miles and counting! 69 k10 Suburban

11-06-2009, 01:18 PM	#3
chevy_mike Never Ending Projects Join Date: Jul 2006 Location: San Diego, CA Posts: 3,836	Re: t400 tranny sticking between gears @ low rpm? The TH400 does have a vacuum line that hooks to the modulator. Make sure there is not a leak in that line. I am assuming you don't have some wild cam installed in the 396 that is lowering the vacuum signal too low. You should be seeing 14"+ at idle. __________________ . 1965 C10 Panel, Tiki Express http://www.67-72chevytrucks.com/vboa...d.php?t=506580 SOLD 1968 Chevy C10, Long, Fleetside, Hot Rod Hauler http://67-72chevytrucks.com/vboard/s...d.php?t=313233 SOLD 1965 Chevy C10, Long, Fleetside, Hot Rod C10 http://67-72chevytrucks.com/vboard/s...d.php?t=415702 SOLD We were given two ears and one mouth for a reason... listen twice as much and speak half as often...



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