Transmission pops out of park - The 1947 - Present Chevrolet & GMC Truck Message Board Network

FL71C10 · 08-30-2010, 10:41 PM

I'm looking at a 76 GMC with a 350 and a turbo 400 to use for the motor. The transmission won't stay in park! You have to hold the shift lever in park and tgen if you let go, it will slip into reverse. When I dropped it into neutral it stayed there, but then wouldn't start in neutral, but if I dropped it into drive it started (in gear!). Is this a linkage problem, or something inside the transmission. If it's just a minor adjustment or worn out linkage, that's no problem, but I don't want to have to do any internal work on the transmission.

Can anyone give me some advice on the severity of this problem?

Thanks!

ChevLoRay · 08-30-2010, 11:19 PM

A part, called the parking pawl, is what holds the transmission in that position. If it won't stay in Park, the pawl is probably bad.

The starting in gear is the Neutral Start Safety switch, which is probably out of adjustment.

FL71C10 · 08-30-2010, 11:23 PM

Can the pawl be replaced with just the pan off?

ChevLoRay · 08-30-2010, 11:26 PM

Someone else will have to answer that question.

68K30 · 08-31-2010, 09:26 AM

I have seen lots of Turbo 350's do this and it may be the nut on the manual linkage inside the pan came loose, this allows the internal linkage to be out of sync with what the indicator on the column says. It's easy to pull the pan to check, when I overhaul these I put Loctite 271 [red] on the internal threads.

Good Luck
Bill

storm9c1 · 08-31-2010, 12:29 PM

Check the shifter linkage first. Sounds like it needs adjustment to match up the indicator on the column with the clicks in the transmission. The linkage only has so much travel, so it could be at the end position in the linkage at the column before it actually engages park fully, so it easily pops back out. Could also explain why the PRN saftey switch is out of alignment. The switch can be adjusted independently, but first I would make sure the travel is right in the linkage and match it up to the clicks in the transmission, and make sure that when you are in P or "low 1" you aren't hitting the end of travel in the column.

FL71C10 · 08-31-2010, 12:35 PM

First of all, thank you everyone for your replies. It sounds like a linkage problem. This truck is very rusty and one of the leaf springs in the rear is broken. I'm wondering if the frame is flexing and causing the linkage to not line up properly.

propanemudtruck · 08-31-2010, 12:49 PM

If it's that rusty, the sagging body mounts could do it too.

08-30-2010, 10:41 PM	#1
FL71C10 Registered User Join Date: Jun 2010 Location: Orlando, Florida Posts: 2,508	Transmission pops out of park I'm looking at a 76 GMC with a 350 and a turbo 400 to use for the motor. The transmission won't stay in park! You have to hold the shift lever in park and tgen if you let go, it will slip into reverse. When I dropped it into neutral it stayed there, but then wouldn't start in neutral, but if I dropped it into drive it started (in gear!). Is this a linkage problem, or something inside the transmission. If it's just a minor adjustment or worn out linkage, that's no problem, but I don't want to have to do any internal work on the transmission. Can anyone give me some advice on the severity of this problem? Thanks! __________________ 71 Chevy C10 Shortbed Stepside. LT1 with 4l60E. Just got back from painter, in assembly now.

08-30-2010, 11:19 PM	#2
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Transmission pops out of park A part, called the parking pawl, is what holds the transmission in that position. If it won't stay in Park, the pawl is probably bad. The starting in gear is the Neutral Start Safety switch, which is probably out of adjustment. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

08-30-2010, 11:23 PM	#3
FL71C10 Registered User Join Date: Jun 2010 Location: Orlando, Florida Posts: 2,508	Re: Transmission pops out of park Can the pawl be replaced with just the pan off? __________________ 71 Chevy C10 Shortbed Stepside. LT1 with 4l60E. Just got back from painter, in assembly now.

08-30-2010, 11:26 PM	#4
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	Re: Transmission pops out of park Someone else will have to answer that question. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

08-31-2010, 09:26 AM	#5
68K30 Registered User Join Date: May 2007 Location: Pennsylvania Posts: 99	Re: Transmission pops out of park I have seen lots of Turbo 350's do this and it may be the nut on the manual linkage inside the pan came loose, this allows the internal linkage to be out of sync with what the indicator on the column says. It's easy to pull the pan to check, when I overhaul these I put Loctite 271 [red] on the internal threads. Good Luck Bill

08-31-2010, 12:29 PM	#6
storm9c1 * That's interesting * Join Date: Oct 2008 Location: Pittsburgh, PA Posts: 2,772	Re: Transmission pops out of park Check the shifter linkage first. Sounds like it needs adjustment to match up the indicator on the column with the clicks in the transmission. The linkage only has so much travel, so it could be at the end position in the linkage at the column before it actually engages park fully, so it easily pops back out. Could also explain why the PRN saftey switch is out of alignment. The switch can be adjusted independently, but first I would make sure the travel is right in the linkage and match it up to the clicks in the transmission, and make sure that when you are in P or "low 1" you aren't hitting the end of travel in the column. __________________ Tom Chevy by day... 1969 Chevy C30 Rollback Tow Truck -- 383 stroker, 4L80E 2011 Chevy Caprice PPV 9C3 6.0L 1995 Chevy Caprice 9C1 1994 Chevy Caprice 9C1 #3 1995 Chevy Caprice Wagon #2 1995 Chevy Impala SS Mopar by night... 1969 Dodge Charger 1972 Chrysler Newport 2dr Hardtop (27K miles) Plus others...

08-31-2010, 12:35 PM	#7
FL71C10 Registered User Join Date: Jun 2010 Location: Orlando, Florida Posts: 2,508	Re: Transmission pops out of park First of all, thank you everyone for your replies. It sounds like a linkage problem. This truck is very rusty and one of the leaf springs in the rear is broken. I'm wondering if the frame is flexing and causing the linkage to not line up properly. __________________ 71 Chevy C10 Shortbed Stepside. LT1 with 4l60E. Just got back from painter, in assembly now.

08-31-2010, 12:49 PM	#8
propanemudtruck Local Redneck Authority Join Date: Mar 2009 Location: Grand Rapids, MI Posts: 584	Re: Transmission pops out of park If it's that rusty, the sagging body mounts could do it too. __________________ -Kevin four on the floor feel the beat in your soul movin to the rhythym pumpin til ya cant take no more dance if you want to do what you came to you cant ignore the feeling of that four on the floor

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