1977 GMC stalls when put into gear

Tiny
BAKS
  • MEMBER
  • 1977 GMC
1977 GMC silverado, shortbox stepside. 454 engine w/(i assume) the original TH400 auto transmission. Mileage.A lot! I recently aquired this truck as a project. It's been sitting in a guys yard for a few years and hasn't been moved, but was running and driven there to be parked. Before I did anything I changed all the fluids (other than the transmission, silly me). I will be puting the carb back together today as I tore it apart on the weekend to rebuild it. It started and idled fine however when put into any gear the engine dies. It will start again but die when shifted. I thought perhaps the torque converter might be locked up but with more research I've found that the transmission isn't supposed to have a lockup torque converter. Any thoughts or ideas?
Wednesday, June 20th, 2007 AT 9:50 AM

2 Replies

Tiny
DANIMALGMC
  • MEMBER
  • 33 POSTS
If the torque converter was locked up, the vehicle would lurch forward when you shifted into drive.
There is a device that was called a dashpot that was behind the throttle connection (on the carb). It should look like a cylinder about an inch in diameter and about 2 inches long. This was supposed to provide a slight idle increase when shifted into gear. They also used this to increase idle speed when you turned on the A/C. This device might be bad.
However, with a 454 you should not have this problem unless the idle is to low (less than 500).
I would check the idle and maybe adjust it to around 800 in park. It should drop to 500ish when in gear.
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Monday, June 25th, 2007 AT 10:14 AM
Tiny
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I think you were right. I mentioned that I was going to rebuild the Carb. Well I did that and I found that someone in the past had been in there before but neglected to attach the needle to the float. The clip was missing all together. Put in new needle/seat, float etc. Fiddled with the air mixture/idle speed until it was idling ok then put it into gear. Voila! Movement! Tee hee.I drove it home on sunday. I've still got a vacuum leak somewhere though. It sounds like someone's blowing on a saxaphone as hard as they can. Quite annoying. Thanx!
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Monday, June 25th, 2007 AT 3:50 PM

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