Author Topic: 1985 GMC Sierra 350 700r4 Trans lack of power  (Read 344 times)

Offline 1985GMCSierra

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1985 GMC Sierra 350 700r4 Trans lack of power
« on: December 10, 2018, 03:27:31 PM »
Hello,

I have a 1985 GMC Sierra with a Chevy 350 crate motor and 700r4 transmission. Lately I have been having a series of issues which are as follows:

-Spark plugs keep getting fouled and contributing to loss of engine power, I tried leaning out the carb mixture a but (Edelbrock 1406) but it doesn't seem to be doing anything. (Any tips on tuning carb air-fuel mixture from scratch would be greatly appreciated.

-Trans won't shift from 2-3 unless I take my foot off the gas and then usually won't shift into 4 at all. Changed filter and trans fluid over the summer and replaced the TV cable twice, but it is just not shifting like it should at all and I'm at a loss of where to begin. I'll be home from school soon and will analyze it again and post as much detail as I can, just can't remember all of it right now.

-Lack of power from engine and transmission; extremely sluggish acceleration and occasional coughing from engine while driving down road

Engine starts up fine and idles fine, but once it gets put into drive these issues occur. Any and all help is appreciated, would really like to get this thing in driveable condition again. Thank you!

Offline Rapid Roy

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Re: 1985 GMC Sierra 350 700r4 Trans lack of power
« Reply #1 on: December 10, 2018, 04:00:22 PM »
Welcome
1974 Cheyenne 10 LWB 350/TH350/AC/4 BBL Quadrajet

Offline JohnnyPopper

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Re: 1985 GMC Sierra 350 700r4 Trans lack of power
« Reply #2 on: January 02, 2019, 01:29:28 PM »
What do your spark plug look like? Soot or oil?

Is your timing correct? is your timing advance working?

I got nuthin on the trans, but I would use some good flushing cleaner and then change the oil again.

Then leave some room to treat it with Seafoam Trans Treatment. Works well.

Offline VileZambonie

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Re: 1985 GMC Sierra 350 700r4 Trans lack of power
« Reply #3 on: January 02, 2019, 04:03:33 PM »
I would suggest you recheck the firing order. Make sure #5 and #7 aren't crossed. Adjust the timing and once it's running good tune the carburetor. How did you lean it out? As far as the trans not upshifting, where is the TV cable connected? Post a pic? How did you set it? Is it properly adjusted? Sounds too tight or governor is either stuck or not spinning.
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