th350 1st gear manual shift problem - Hot Rod Forum : Hotrodders Bulletin Board
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Old 07-07-2003, 06:03 PM
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th350 1st gear manual shift problem

Hi, I just rebuilt a th350 (with the help of this site!) and installed it in my 68 firebird. While rebuilding it I also put in a B&M shift improver kit . When in "drive" it operates just fine. Upshifts and downshifts all gears perfectly. The problem is that when I try to manually downshift to 1st (from 2nd) , it doesn't downshift, even at very slow speeds. It does manually downshift from 3rd to 2nd just fine, but it does not manually downshift 2nd to 1st. It will also not hold 1st gear when I manually put it there when taking off from a stop, it will just shift nicely to 2nd (the point it shifts varies with acceleration as I would expect it to) It does hold 2nd gear when manually placed there. I checked and verified that the manual linkage on the tranny is in the position it should be when the gearshift in the car is in 1st. Can anyone tell me if there is some kind of rpm override ( the governer?)that prevents downshifts to 1st? Could this be a manual valve adjustment, affecting only one gear like this? I'm used to an old powerglide and am not sure if this how a th350 normally operates. I could just leave it in "drive" and go with it, but, well, it's awfully fun shifting it manually! Thanks!

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Old 07-07-2003, 07:56 PM
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there is an over ride shift valve in the valve body. You can block that in place to have manual first at any speed. A piece of 5/16 steel brake/fuel line or a stronger spring.

The only other thing that comes to my mind is that you may have the valve body gaskets swapped positions?

I am un familar with the B&M products, so I do not know if they adress the over-ride valve in all / any of their kits.


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Old 07-08-2003, 08:18 AM
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I'm pretty sure I have the gaskets in correct position for the B&M, one of the gaskets was quite distinct with a "Z" cut in and the directions that came with the kit were very clear. However in this kit they did not address the override valve so I'll follow your thoughts on that. Thanks for getting me on the right path. Paul
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Old 07-08-2003, 08:21 AM
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There is a difference in the B&M shift improver kit and the B&M transpak. The shift improver kit does not have the manual valve body conversion parts. The Transpak does.
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Old 07-08-2003, 09:18 AM
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Are you sure your shifter linkage(s) are adjusted properly to get 1st gear in the tranny?

Go under the car and have someone shift down through the gears. You should get a distinct "clink" from the tranny for each gear. You may have an indicated 1st gear at the shifter, but only 2nd at the tranny.
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Old 02-08-2004, 03:10 PM
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I am having the exact same problems as desman. As far as I know, my tranny is stock, no shift kits installed or anything. The most I've done to it are a filter and fluid change (not recently) It use to work just fine, I could manually shift up/down into any gear I wanted at any speed. I have checked, visually and audibly that the tranny is "clicked" into first gear. When I start off, it will shift into second on it's own, regardless of the fact that the gear selector and lever on the side of the tranny are indeed in the 1st gear position. And, I cannot downshift into 1st gear either.

I know this thread is kinda old, but any new insights/revelations would be appreciated.

Thanks
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Old 02-08-2004, 03:15 PM
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This used to happen with my turbo400 in my 70 Chevelle. If held in 1st, it would shift into 2nd at about 5000rpm, even though shifter wasw still in 1st. When I put a shift kit in it, don't remember the brand, it stopped doing that. It would stay in 1st no matter what.
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