Author Topic: Needing more insight from you gurus; this time Th350 tranny  (Read 2965 times)

Offline 1976er

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Needing more insight from you gurus; this time Th350 tranny
« on: March 27, 2012, 12:10:50 PM »
Finished my rebuild of the Tcase-NP203; BTW, 76 Chev 3/4 ton, 350/Th350,NP203.  After tcase rebuild and install initial trial run was great; everything worked as should.  I went out the next morning to put on a few miles, put the truck in reverse and nothing.  I thought what the heck now.  After a couple minutes of going from reverse to drive (nothing in drive either by the way) she took hold and worked fine for the remainder of the drive.  Ever come across something like that?  Weak pump in tranny cause slow build-up of pressure or .....??  I do know the TV cable is not hooked up; never has been and I have never had any issues with the tranny prior to the Tcase rebuild.  I am going to find the required brackets to hook up the cable to the carb.  Could this be the issue?  Suggestions and ideas needed; Thanks

Offline Lt.Del

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Re: Needing more insight from you gurus; this time Th350 tranny
« Reply #1 on: March 27, 2012, 12:24:34 PM »
you are checking the trans fluid when engine is warm and in park, right?

Offline ehjorten

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Re: Needing more insight from you gurus; this time Th350 tranny
« Reply #2 on: March 27, 2012, 02:36:12 PM »
Sounds like the most likely culprit is that you are low on transmission fluid!  There is also not a TV cable on a TH350.  It is a Kickdown cable and it plays a different role.  If you don't have the kickdown cable attached you will not notice anything except that it will not downshift when you floor the accelerator pedal.

A TV Cable such as in a TH700R-4 is responsible for controlling transmission fluid pressure.  Never drive without a TV cable attached!  You will burn-up your transmission in short order!
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline 1976er

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Re: Needing more insight from you gurus; this time Th350 tranny
« Reply #3 on: March 27, 2012, 07:55:34 PM »
Well, now I feel like a complete idiot.  Must have a slow leak in tranny as the last time I checked it was OK; but it is now low, me bad.  Of course no fluid on hand.  Kickdown cable, I was wondering about that.  Is there an adjustment for it or just hook it up and go.  I noticed it is attached with the bracket to the manifold and I have the link to attach to the carb; just wondering now about any adjustments to be made??  Thanks everyone for the feedback

Offline ehjorten

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Re: Needing more insight from you gurus; this time Th350 tranny
« Reply #4 on: March 28, 2012, 08:51:15 AM »
Depends on what kind of setup you have for cable and brackets if there is adjustment or not.  Usually there is a large diameter plastic cylinder behind the bracket where the kickdown attaches to the engine.  There is a slide lock piece in there that you can push up on from the bottom of that cylinder and release it.  Now with that piece released you have someone step on the accelerator and put it to the WOT (foot to the floor).  With the pedal to the floor you then push that piece back down and it locks the adjustment into place (do not release the throttle from WOT until you push that piece down).  You want the cable to be at it's full travel when the pedal is at WOT.

Also...while you are there, check to be sure that your butterfly valves in the carburetor are at WOT when the person pushing on the pedal is at max pedal travel.  Sometimes because of various reasons (for example: extra thick carpeting and insulation) you are not reaching full open on the carburetor.  The reason you have someone step on the pedal and not just cycle the throttle by hand is to account for that difference in throttle opening between the pedal and cycling it by hand.  If you confirm that you are getting full throttle with the pedal you can forgo the guy stepping on the throttle and just do it by hand at the carburetor.
-Erik-
1991 V3500 - Gen V TBI 454, 4L80E, NP205, 14 bolt FF, D60, 8" Lift on 35s
1977 K20 Silverado - 350, THM350, NP203, 14 bolt FF, D44, Stock Lift on 31s
1969 Chevelle Malibu Sport Coupe - EFI350, THM350
1968 Chevrolet Step-side Pickup - 300HP L6

Offline 1976er

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Re: Needing more insight from you gurus; this time Th350 tranny
« Reply #5 on: March 28, 2012, 06:32:01 PM »
As always; Thank You much