TH350 that won't shift into 2nd - The 1947 - Present Chevrolet & GMC Truck Message Board Network

**nlped** · 11-21-2009, 06:23 PM

Okay, a quick question. I have just bought this old beater, which I was told wouldn't run, that now runs. It was a bit low on trans fluid so I added 2 quarts and it would pull like normal in 1st and Reverse. But when I took it out on its "Maiden" voyage, come to find out it won't pull in 2nd, nor will it shift into 3rd. When the trans shifts into 2nd it pulls the motor down and will actually try to lock up the rear tires. Is this something major, or is there something simple that I can check first? It does great in 1st and Reverse, and the fluid looks nice and red, but beyond that, I have no knowledge when it comes to an automatic.

Any help would be appreciated.

Ed

**lolife99** · 11-21-2009, 07:01 PM

It's not something as simple as the vacuum modulator line being disconnected?
Maybe a cracked/dry rotted vacuum line?

SGTHohensee · 11-21-2009, 07:31 PM

Quote:

Originally Posted by lolife99

It's not something as simple as the vacuum modulator line being disconnected?
Maybe a cracked/dry rotted vacuum line?

Probably not. Usually if it's that it will shift very hard and very late. Kinda sounds like something is stuck inside causing hydraulic pressure in places it shouldn't. You might try some Trans Tune from Seafoam to try and unstick whatever is stuck. Either that, or something is broke inside, and that's why the truck was parked. Good luck.

cableguy0 · 11-21-2009, 08:46 PM

could be a bad 2nd gear sprag. the only thing to do is yank the trans and tear it apart to find the problem. if its locking up most likely you got broken hard parts.

midnite · 11-21-2009, 09:22 PM

i had a problem where mimne wouldnt shift at all but 1st and reverse worked, i forgot the vaccum line on the transmission when i put it all back together

**old Rusty C10** · 11-22-2009, 12:25 AM

im thirding the vacuum line or the modulator on the trans

68 TT · 11-22-2009, 10:00 AM

Quote:

Originally Posted by nlped

Okay, a quick question. I have just bought this old beater, which I was told wouldn't run, that now runs. It was a bit low on trans fluid so I added 2 quarts and it would pull like normal in 1st and Reverse. But when I took it out on its "Maiden" voyage, come to find out it won't pull in 2nd, nor will it shift into 3rd. When the trans shifts into 2nd it pulls the motor down and will actually try to lock up the rear tires. Is this something major, or is there something simple that I can check first? It does great in 1st and Reverse, and the fluid looks nice and red, but beyond that, I have no knowledge when it comes to an automatic.

Any help would be appreciated.

Ed

When I have had the vacuum modulator line come off at the trans it would not shift into second but maybe I wasn't staying in it long enough to force it to shift.

Dragging the engine down doesn't sound like anything normal unless you are getting a little compression braking from being high up in rpm in 2nd and letting off on the gas like at the end of a drag strip but I have never had enough of that with an unmodified valve body to actually try to lock up the tires.

You can have a valve body modified for more compression braking but usually that is done to race cars not old trucks.

I say check the vacuum modulator line all the way from the engine to the trans to make sure it is not damaged / unhooked first then call a transmission shop and give them your symptoms. They may be able to tell you what it is over the phone if it is a common problem.

James McClure · 11-22-2009, 10:46 AM

Hay all.33 years with Chevy. Modulator will not cause this problem. Modulators job is to regulate shift points by changing control pressure. The governor does the same thing based on road speed. Now, 1st gear is forward clutch & low\reverse clutch, second gear is intermediate clutch and band, third gear is forward clutch and direct clutch, reverse is direct clutch and low\reverse clutch which gives you a second gear ratio in reverse. You could have a stuck sprag but I am of the mind you have an internal oil leak requireing ovehaul, especially if it was that low on fluid. 350's are dependable IF they are built right. Find a good mechanic who knows them.

**nlped** · 11-22-2009, 12:08 PM

I replaced the hammered vacuum line from the intake to the hardline going down to the trans. I assume that is the modulator line everyone is talking about.

Well, I took it out and drove it a bit and it was still "locking" up when it shifted up to second, so I slipped it into neutral then back to drive a couple of times and wahlah, it is now shifting into all gears. Don't know if something inside the trans was just stuck or what, but it now shift perfectly.

I'm gonna get some more trans fluid and a filter kit and change them next. The rear seal needs to be replaced as it leaks, but maybe that will be all ole Blue needs.

joe231 · 11-22-2009, 12:29 PM

maybe it was something sticking in the valve body, just needed some persuasion

**nlped** · 11-22-2009, 12:37 PM

Must have been, that made my Sunday!!!

68 TT · 11-23-2009, 01:34 PM

Being so low on fluid probably exposed it to some corrosion that worked its way clean after a little use. Glad it is working again. Tranny swaps suck.

I think I would do a filter & fluid change on it now.

11-21-2009, 06:23 PM	#1
nlped Senior Member Join Date: Jul 2009 Location: Hayden, Al. Posts: 4,147	TH350 that won't shift into 2nd Okay, a quick question. I have just bought this old beater, which I was told wouldn't run, that now runs. It was a bit low on trans fluid so I added 2 quarts and it would pull like normal in 1st and Reverse. But when I took it out on its "Maiden" voyage, come to find out it won't pull in 2nd, nor will it shift into 3rd. When the trans shifts into 2nd it pulls the motor down and will actually try to lock up the rear tires. Is this something major, or is there something simple that I can check first? It does great in 1st and Reverse, and the fluid looks nice and red, but beyond that, I have no knowledge when it comes to an automatic. Any help would be appreciated. Ed __________________ Carter 1968 Chevy SWB Fleet... Walt 1963-1/2 Ford Falcon Futura...Martha

11-21-2009, 07:01 PM	#2
lolife99 67-72 parts collector,… Join Date: Nov 2002 Location: Mid-MO Posts: 22,691	Re: TH350 that won't shift into 2nd It's not something as simple as the vacuum modulator line being disconnected? Maybe a cracked/dry rotted vacuum line? __________________ Keith Convert to disc brakes. http://67-72chevytrucks.com/vboard/s...d.php?t=444823 Last edited by lolife99; 11-21-2009 at 07:04 PM.

11-21-2009, 08:46 PM	#4
cableguy0 Senior Member Join Date: Apr 2000 Location: Delta,Pa Posts: 14,950	Re: TH350 that won't shift into 2nd could be a bad 2nd gear sprag. the only thing to do is yank the trans and tear it apart to find the problem. if its locking up most likely you got broken hard parts. __________________ Owner of North Point Car Care in Dundalk Md. We specialize in custom exhaust on both modern and classic vehicles. We are a full service auto shop from classics to modern vehicles. Feel free to contact me with questions. I will give a 10% discount to any board member.

11-21-2009, 09:22 PM	#5
midnite Registered User Join Date: Oct 2009 Location: Edmonton Alberta Canada Posts: 107	Re: TH350 that won't shift into 2nd i had a problem where mimne wouldnt shift at all but 1st and reverse worked, i forgot the vaccum line on the transmission when i put it all back together

11-22-2009, 12:25 AM	#6
old Rusty C10 Robert Olson Transport Join Date: Oct 2002 Location: recent transplant to NC USA Posts: 20,277	Re: TH350 that won't shift into 2nd im thirding the vacuum line or the modulator on the trans __________________ Bob 1951 International running on a squarebody chassis "If a man's worth is judged by the people he associates himself with, then i am the richest man in the world knowing some of the fine people of this board" http://67-72chevytrucks.com/vboard/a...t.php?f=25&a=9 (you can review the site rules here!) PM Me for your vehicle/parts hauling needs in the North East US or see my Facebook page Robert Olson Transport Live each day to the fullest.. you never know when fate is going to pull the rug out from under you... I hate cancer!!

11-22-2009, 10:46 AM	#8
James McClure One shot, one kill. Join Date: Dec 2007 Location: Saratoga Springs NY Posts: 859	Re: TH350 that won't shift into 2nd Hay all.33 years with Chevy. Modulator will not cause this problem. Modulators job is to regulate shift points by changing control pressure. The governor does the same thing based on road speed. Now, 1st gear is forward clutch & low\reverse clutch, second gear is intermediate clutch and band, third gear is forward clutch and direct clutch, reverse is direct clutch and low\reverse clutch which gives you a second gear ratio in reverse. You could have a stuck sprag but I am of the mind you have an internal oil leak requireing ovehaul, especially if it was that low on fluid. 350's are dependable IF they are built right. Find a good mechanic who knows them. __________________ 1984 K20 350M engine with 465,000 miles. Well, it's finally done!! Almost 2 years of work, but it was really worth the effort. Little stuff left to do is mount winch, wet sand & buff out and build belly pan\running boards. Body work takes lots and LOTS of beer!!!! God, Guts and Guns made America and God, Guts and Guns will preserve it! The worst thing you could do is get into my sights, but that don't matter, you'll never know it, cause you'll never hear the shotJim or Paladin whichever you choose.

11-22-2009, 12:08 PM	#9
nlped Senior Member Join Date: Jul 2009 Location: Hayden, Al. Posts: 4,147	Re: TH350 that won't shift into 2nd I replaced the hammered vacuum line from the intake to the hardline going down to the trans. I assume that is the modulator line everyone is talking about. Well, I took it out and drove it a bit and it was still "locking" up when it shifted up to second, so I slipped it into neutral then back to drive a couple of times and wahlah, it is now shifting into all gears. Don't know if something inside the trans was just stuck or what, but it now shift perfectly. I'm gonna get some more trans fluid and a filter kit and change them next. The rear seal needs to be replaced as it leaks, but maybe that will be all ole Blue needs. __________________ Carter 1968 Chevy SWB Fleet... Walt 1963-1/2 Ford Falcon Futura...Martha

11-22-2009, 12:29 PM	#10
joe231 Registered User Join Date: Dec 2007 Location: Palmer, Alaska Posts: 13,821	Re: TH350 that won't shift into 2nd maybe it was something sticking in the valve body, just needed some persuasion __________________ *CHEVY ONLY*

11-22-2009, 12:37 PM	#11
nlped Senior Member Join Date: Jul 2009 Location: Hayden, Al. Posts: 4,147	Re: TH350 that won't shift into 2nd Must have been, that made my Sunday!!! __________________ Carter 1968 Chevy SWB Fleet... Walt 1963-1/2 Ford Falcon Futura...Martha

11-23-2009, 01:34 PM	#12
68 TT Still plays with trucks Join Date: Jul 2009 Location: Spokane, WA Posts: 3,556	Re: TH350 that won't shift into 2nd Being so low on fluid probably exposed it to some corrosion that worked its way clean after a little use. Glad it is working again. Tranny swaps suck. I think I would do a filter & fluid change on it now. __________________ miSSed opportunity - ground up creation of an AWD 1994 454 SS that never was http://67-72chevytrucks.com/vboard/s...d.php?t=795577 69 C10 shortbed stepside 400 small block - built like what a super sport truck could have been 69 K20 lwb TBI 350 4L60E NP208 14-bolt Dana-44 w/disc 68 Camaro SS / RS 500hp 439 inch roller cam big block 4L80E 79 Malibu TPI 350 4L60 w/ Z28 steering & sway bars



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