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Old 06-07-2018, 04:54 PM   #1
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Turbo 350 - Possible Issues

Folks; need some advice before I pull out the money gun and pull the trigger.

I've got a 350/195 GM replacement engine, with a Turbo 350 behind it. I just got this recently, so it's history is lost, but both seem to be very low mileage and fresh from about 7 years ago when the truck was built out.

The truck came with a flexible aluminum fan on it, which sounded like a turbine spinning up from a dead stop, so I swapped that out for a 6 blade steel with thermal clutch. Well, the turbine sound is the same as ever, so it's not the fan. Also, if the truck sits a day or two, I fire it up, wait about 1 minute (always let older vehicles sit for a few before heading out), then drop it into "D" and nothing - no movement. Back up to "R" and the same - nothing. Go from park to "L1", and it goes right into gear. After this routine, it drives out fine, with firm shifts. The fluid is full, bright pink/red and has zero odor to it.

Finally, I don't know if this is trans related, but from a dead stop, the thing takes forever to get up to speed if you mash the go pedal - no slippage, just the worst dog I've ever driven. I do have crazy tall gears (3.08 max), but with the timing at 12 degrees, a new 500 carb and true dual exhaust, it just seems something is way off. Automatic transmissions are all black magic to me anyhow, so I don't know if it could be the converter, etc.

Thoughts are appreciated!
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Old 06-07-2018, 05:43 PM   #2
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Re: Turbo 350 - Possible Issues

With those symptoms the torque converter is suspect. The manual low comment is strange. I am not sure why that would entice the converter to engage.
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Old 06-07-2018, 06:28 PM   #3
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Re: Turbo 350 - Possible Issues

I'd drop the pan and remove the filter. Look to make sure somebody didn't leave some old O-rings up there also make sure the filter is good and properly attached. Make sure the linkage is tight and working properly. The whining could be the pump in the trans being starved of fluid. I would not run it AT ALL until you get that pan off and check. Also could be a bad pump.
'69 GMC C2500 Custom Camper, 8 1/2' bed (same as Chevy "Longhorn"), 350 ci. mild RV cam, NP 435 CR 4spd. Trans., 3.73 Dana-60 open.Camper and Trailer wiring, PS, PB, AC, tach , three gas tanks, 2nd owner, Work-Truck supreme. Best $300 I ever spent.
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Old 06-07-2018, 06:36 PM   #4
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Re: Turbo 350 - Possible Issues

If you got the heavy duty fan clutch, could explain the fan turbo sound. Go to the standard duty. Not sure how cold a HD clutch has to get before it free spins but it is lower then average temps around here.

Make sure the transmission vacuum modulator is hooked up to manifold vacuum.

Is the cam stock or or a PO's idea of a 'performance monster' that needs 4000+ rpm to start working?

2nd on the check the filter. Installer might have skipped the install new O-ring step.
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Old 06-07-2018, 09:23 PM   #5
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Re: Turbo 350 - Possible Issues

I had a 350 with a TH350 and 3.08 gears in my 69 and it ran great. Hauled my full size tractor and shredder with it and other than gas mileage it was good setup for what I used it for. It has plenty of get up and go but I didn't use it for racing or burning rubber. It was strictly a work and cruise truck.
68 GMC 250/3 speed Saginaw p/b p/s
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I just want a vehicle that I can work on, that won't talk to me, leave error msgs or keep track of how I drive...
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Old 06-07-2018, 10:22 PM   #6
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Re: Turbo 350 - Possible Issues

The stator/sprag is bad in the torque converter, with a bad stator/sprag you dont have a true "torque" converter, its now just a fluid coupler my guess, why the vehicle is sluggish on take off........... .

could be your noise as well....take the three bolts out of the TC and fire the truck up and see if noise goes away....just a thought....

Last edited by YoungPup1977; 06-07-2018 at 10:33 PM.
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