OK, here's the parts info:
1986 700R4 (early style VB)
Freshly re-built by GMTech
TransGo 2-3 shift kit
Vette Servo
GM 3-4 upshift valve

Main problem is the thing will upshift on it's own to 4th even when I leave it in "D".

Also when it goes to 4th I cannot downshift it to 3rd(stays in 4th) unless I go all the way to 2nd then back to 3rd.

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86 Camaro Sport
LT1 Induction
383 Speed-O-Motive Crate Engine, Raptor 700R4 Tranmission, Trick Flow Twisted Wedge G2's, 58mm Accel TB, 3.73 Auburn Pro, SLP Cold Air Induction and Headers, Hooker Cat-back, Serpentine Belt Setup, Dual IROC Fans, Jamex springs, 16" IROC Rims, 36mm/24mm Sway Bars, Global West Steering Brace. Hotchkis Rear LCA's,Panhard Bar and SFC's.
My Camaro Project
Moderator at SE ThirdGen

 

My guess would be its that 3-4 upshift assembly. I don't think it was intended for early style valvebodies.

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If you live in Southeastern US, check us out!
South East Thirdgen

1987 Trans Am 305
14.88 @ 92.81

 

Ya, your probally right. Now I just wish I still had the old one.


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86 Camaro Sport
LT1 Induction
383 Speed-O-Motive Crate Engine, Raptor 700R4 Tranmission, Trick Flow Twisted Wedge G2's, 58mm Accel TB, 3.73 Auburn Pro, SLP Cold Air Induction and Headers, Hooker Cat-back, Serpentine Belt Setup, Dual IROC Fans, Jamex springs, 16" IROC Rims, 36mm/24mm Sway Bars, Global West Steering Brace. Hotchkis Rear LCA's,Panhard Bar and SFC's.
My Camaro Project
Moderator at SE ThirdGen

 

I'd like to find one other than EOE or C&C. I don't fancy the thought of laying on my back in the sand pulling a trans pan. you know they don't drain the fluids like they are supposed to. You should have seen me getting an oil filter adapter for my cousin's truck. EPA nightmare.

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If you live in Southeastern US, check us out!
South East Thirdgen

1987 Trans Am 305
14.88 @ 92.81

 

It's early and I should be sleeping now so I could be off saying this but I know that the 1-2 Valve train is way different but I thought that the 3-4 is essentially the same. I will look into this when I am awake, remind me if I don't get back on this by @Tuesday. It could be though as right now I can't think of a reason for this problem. How is the 3-4 shift at light, medium and full throttle?

 

It will not shift uncommanded(in "D") into 4th at light throttle, only happens during medium and heavy throttle.


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86 Camaro Sport
LT1 Induction
383 Speed-O-Motive Crate Engine, Raptor 700R4 Tranmission, Trick Flow Twisted Wedge G2's, 58mm Accel TB, 3.73 Auburn Pro, SLP Cold Air Induction and Headers, Hooker Cat-back, Serpentine Belt Setup, Dual IROC Fans, Jamex springs, 16" IROC Rims, 36mm/24mm Sway Bars, Global West Steering Brace. Hotchkis Rear LCA's,Panhard Bar and SFC's.
My Camaro Project
Moderator at SE ThirdGen

 

TTT for Leo.

 

I've got an 86 Camaro with the 3-4 upshift kit from GM and my tranny does not do what yours is doing. If I hold it in D3 in will stay there at light or heavy accelerating until I shift it into OD. Also I am able to downshift it from OD into third at any speed, my point being that I don't believe your problem has anything to do with it being an early style valvebody(I could be wrong).

 

I am thinking along two lines now. One is that the 3# checkball that seals D3 oil to inhibit 4th at the 3-4 shift valve might be leaking. Another is possibly that the roll pin could be in the wrong spot or the valve rotated. I am NOT trying to offend anyone just running through things I have either seen or yes, done! Also, the directions for the Repro Kit IMO leave a little to be desired. It is possible some plug may not be in place in the separator plate or something along those lines.

 

No offense! Damned if I haven't done some stupid stuff in the past! Hehee I think we all do dumb stuff when were learnin. I'll take that stuff into consideration when I check it out.

------------------
If you live in Southeastern US, check us out!
South East Thirdgen

1987 Trans Am 305
14.88 @ 92.81