passing gear - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Coreyterry · 03-27-2010, 10:44 PM

im having problems with my transmission, its a th400. when it goes to shift from 2nd to 3rd its slips. but it only slips when the rpms are low. when i puut my foot down it shifts fine. i changed the modulator valve and it helped a little bit. also when i manually shift from 2nd to 3rd its shifts fine. what i was wondering is if there is suppost to be a passing gear on the 400s? if this is even the problem then thats great but if someone might know what exactly it is then i would be happy to know.

JimKshortstep4x4 · 03-28-2010, 09:08 AM

The Th-400 has an electric operated passing gear where the detent switch downshifts the transmission to second gear. This would most likely not have anything to do with your upshift from 2 to 3.

Outside of a low fluid level this problem is probably internal as it could involve the pressure regulator valve or the control valve assembly.

I am assuming that you adjusted the modulator valve when you installed it and that there are no vacuum leaks.

Jim

GASoline71 · 03-28-2010, 09:59 AM

"Passing gear" is when the transmission downshifts from 3rd to 2nd when you mash the throttle. If your detent cable isn't hooked to the carb... it won't downshift. I don't know about it being "electric"...

Gary

OhOneWS6 · 03-28-2010, 10:02 AM

Quote:

Originally Posted by GASoline71

"Passing gear" is when the transmission downshifts from 3rd to 2nd when you mash the throttle. If your detent cable isn't hooked to the carb... it won't downshift. I don't know about it being "electric"...

Gary

The Turbo 400 does not use a cable. It is electronic. There is a switch on the gas pedal. There is no detent cable from the carb to the trans. Someone posted a pic recently. I'll see if I can find the thread.

Like Jim already said. Doubtful that is your problem.

GASoline71 · 03-28-2010, 10:13 AM

I learned something new today... which is what is cool about these boards. I had no idea even the old TH400's from back in the day were electronically shifted. Cool...

Still passing gear is a downshift from 3rd to 2nd... not the other way around.

Gary

OhOneWS6 · 03-28-2010, 10:19 AM

Quote:

Originally Posted by GASoline71

Still passing gear is a downshift from 3rd to 2nd... not the other way around.

Gary

LOL. Yep. no way around that.

This is not the thread I was thinking but same info here.
http://67-72chevytrucks.com/vboard/s...d.php?t=350456

GASoline71 · 03-28-2010, 10:23 AM

Awesome! Thanks for the linky!!!

Gary

Longhorn Man · 03-28-2010, 04:37 PM

the TH400 electrick kickdown is for going into first gear. Even if you unplug it, you'll still get the 3 to 2 kickdown.
Either way, fluid level, or clutch wear is about the only thing that'll cause slippage.

Coreyterry · 04-02-2010, 10:54 PM

OK well how would i go about buying a passing gear or whatever its called. im a noob and don't quite know all the terminology. about ok how much will the parts set me back?

Sinister · 04-02-2010, 11:05 PM

Not sure on the price of a stock kickdown setup. Might check out the Parts Board. Somebody on here said you can run a carb mounted nitrous microswitch for the kickdown, which would probably be cheapest. I'm running the Lokar setup which runs about $100.

Chevydude56 · 04-03-2010, 12:11 AM

B&M setup, attaches to carb linkage

http://www.jegs.com/i/B%26M/130/20297/10002/-1?CT=

Installation article for B&M kit (not a truck , but you get the idea ) good pics

http://www.highperformancepontiac.co...all/index.html

original style switch ,mounts near gas pedal

http://www.americanclassic.com/Googl...70NOS-1970.htm

Coreyterry · 04-04-2010, 01:30 AM

ok well heres yet another problem, when i put it to the floor it takes a while to shift, in any gear. but if i have it to the floor its shifts fine from second to third. but at a low rpm like say cruising it slips about three or four times if not more before it decides to shift. like i said before though, when i manualy shift from second to third it shifts fine no slipping or anything.

neba · 04-04-2010, 08:24 AM

have you checked your fluid? in park, engine running, pull dipstick, wipe clean and check level. what color is it? should be red to pink. if its brown your trans is toast. also check engine oil. radiators can break internally and mix trans fluid and antifreeze. passing gear/downshift has nothing to do with trans slipping. you can also drop trans pan. as clutches wear material collects in bottom of pan. if there is a large amount in pan also a bad sign.

**kwmech** · 04-04-2010, 01:12 PM

On the pass side of the trans near the tailshaft there is a 4 bolt cover. That is where the governor is. Remove the cover and pull the gov out with a slight twisting motion. Inspect the nylon gear on the end for wear

03-27-2010, 10:44 PM	#1
Coreyterry Registered User Join Date: Dec 2009 Location: bakersfild ca Posts: 115	passing gear im having problems with my transmission, its a th400. when it goes to shift from 2nd to 3rd its slips. but it only slips when the rpms are low. when i puut my foot down it shifts fine. i changed the modulator valve and it helped a little bit. also when i manually shift from 2nd to 3rd its shifts fine. what i was wondering is if there is suppost to be a passing gear on the 400s? if this is even the problem then thats great but if someone might know what exactly it is then i would be happy to know.

03-28-2010, 09:08 AM	#2
JimKshortstep4x4 Senior Member Join Date: Jul 2001 Location: Muskegon,MI,USA Posts: 6,026	Re: passing gear The Th-400 has an electric operated passing gear where the detent switch downshifts the transmission to second gear. This would most likely not have anything to do with your upshift from 2 to 3. Outside of a low fluid level this problem is probably internal as it could involve the pressure regulator valve or the control valve assembly. I am assuming that you adjusted the modulator valve when you installed it and that there are no vacuum leaks. Jim __________________ 1971 Shortbox step side 4x4, 350 sbc, 3:07 rear end 1965 Impala SS 400 sbc, Muncie rock crusher 1966 Impala SS 396 bbc, TH 400 1969 El Camino, 350 sbc, TH 350 1971 Snowplow built on a Blazer frame 1972 GMC Short bed, stepside, TH 400, 427 BBC

03-28-2010, 04:37 PM	#8
Longhorn Man its all about the +6 inches Join Date: Jan 2001 Location: Hilliard Ohio Posts: 2,693	Re: passing gear the TH400 electrick kickdown is for going into first gear. Even if you unplug it, you'll still get the 3 to 2 kickdown. Either way, fluid level, or clutch wear is about the only thing that'll cause slippage.

04-02-2010, 10:54 PM	#9
Coreyterry Registered User Join Date: Dec 2009 Location: bakersfild ca Posts: 115	Re: passing gear OK well how would i go about buying a passing gear or whatever its called. im a noob and don't quite know all the terminology. about ok how much will the parts set me back?

04-02-2010, 11:05 PM	#10
Sinister Between Trucks... Join Date: Mar 2002 Location: Los Angeles, CA. Posts: 3,830	Re: passing gear Not sure on the price of a stock kickdown setup. Might check out the Parts Board. Somebody on here said you can run a carb mounted nitrous microswitch for the kickdown, which would probably be cheapest. I'm running the Lokar setup which runs about $100. __________________ Beat it to fit, Paint it to match... Last edited by Sinister; 04-02-2010 at 11:06 PM.

04-03-2010, 12:11 AM	#11
Chevydude56 Registered User Join Date: Sep 2009 Location: Syracuse NY Posts: 110	Re: passing gear B&M setup, attaches to carb linkage http://www.jegs.com/i/B%26M/130/20297/10002/-1?CT= Installation article for B&M kit (not a truck , but you get the idea ) good pics http://www.highperformancepontiac.co...all/index.html original style switch ,mounts near gas pedal http://www.americanclassic.com/Googl...70NOS-1970.htm __________________ 1967 Suburban 292 3spd 1964 Chevy II wagon 1971 Monte Carlo 402BB 1964 Cadillac series 62 2dr 1964 Bonneville 2dr/ht 1967 GTO 1978 Chevy Van 30 1989 R30 Crew Dually Bonus Cab

04-04-2010, 01:30 AM	#12
Coreyterry Registered User Join Date: Dec 2009 Location: bakersfild ca Posts: 115	Re: passing gear ok well heres yet another problem, when i put it to the floor it takes a while to shift, in any gear. but if i have it to the floor its shifts fine from second to third. but at a low rpm like say cruising it slips about three or four times if not more before it decides to shift. like i said before though, when i manualy shift from second to third it shifts fine no slipping or anything.

04-04-2010, 08:24 AM	#13
neba Registered User Join Date: Feb 2010 Location: duluth mn Posts: 108	Re: passing gear have you checked your fluid? in park, engine running, pull dipstick, wipe clean and check level. what color is it? should be red to pink. if its brown your trans is toast. also check engine oil. radiators can break internally and mix trans fluid and antifreeze. passing gear/downshift has nothing to do with trans slipping. you can also drop trans pan. as clutches wear material collects in bottom of pan. if there is a large amount in pan also a bad sign.

04-04-2010, 01:12 PM	#14
kwmech Senior Member Join Date: Mar 2003 Location: Colfax-California Posts: 8,596	Re: passing gear On the pass side of the trans near the tailshaft there is a 4 bolt cover. That is where the governor is. Remove the cover and pull the gov out with a slight twisting motion. Inspect the nylon gear on the end for wear



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