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Old 09-09-2008, 12:10 PM
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th350 delayed manual 1-2 upshift

OK, I am having a problem with my turbo 350 trans. I've been fighting delayed 1-2 manual upshifts at wide open throttle (WOT). Sorry for the long post, just trying to provide plenty of info for a diagnosis.

Some basic info about the car: I'm running my th350 (which does have a shift kit in it) behind a 355 small block. I've got a 2400 - 2800 stall converter in it. I'm running a 4:10 12 bolt and the car ran 12.92 last week in the quarter. The car has about 12in of vacuum at the manifold.

When bracket racing, I shift at about 5800, but the trans from 1-2 doesn't then shift until about 6200-6300, there is a delay. The delay from 2-3 isn't much at all, so I can shift at 6000 going from 2-3 and it shifts right away.

To fight a heat problem with the carb, I just put in a .5 inch edelbrock wood carb spacer...to act as an isolator between the intake and the carb. I know this probably doesn't sound related, but apparently it may be.

After putting in the carb spacer and taking the car out for a test drive, the car doesn't want to shift manually at WOT from 1-2. As soon as I let up on the throttle a bit it will complete the shift to 2nd. Now, partial throttle acceleration manual shifts from 1-2 seems to work pretty well without delay. It seems to be primarily a WOT manual upshift issue from 1-2.

I also noticed just going down the road in drive (3rd gear) doing about 35 mph, and then manually downshifting to 2nd with no change in the throttle (just a partial throtlle maintaining current speed) there is a pronounced delay in that manual downshift....I'm talking a couple of seconds before it happens.

This leads me to a couple of questions that I'm hoping someone here with transmission knowledge can help with:

1) does vacuum play a role during WOT manual 1-2 upshifts?
2) does the downshift linkage attached to the carb affect anything other than downshifts while in drive due to a WOT condition?
3) does vacuum play a role for 3-2 downshifts at an even (partial) throttle?
4) If kickdown cable or shift linkage is off just a tad, can this cause these delayed up and down shifts?
5) I checked vacuum in neutral at the modulator, and going into it is the same reading of 12 as I have up at the manifold...so no apparent leaks on the line to the modulator. Does a vacuum modulator even have any impact on a WOT manual upshift?

Thanks in advance for any assistance you can provide.

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Old 09-13-2008, 09:04 AM
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bump it. 1 for the experts.
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Old 09-13-2008, 10:06 AM
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Quote:
Originally Posted by olympic73


This leads me to a couple of questions that I'm hoping someone here with transmission knowledge can help with:

1) does vacuum play a role during WOT manual 1-2 upshifts?
2) does the downshift linkage attached to the carb affect anything other than downshifts while in drive due to a WOT condition?
3) does vacuum play a role for 3-2 downshifts at an even (partial) throttle?
4) If kickdown cable or shift linkage is off just a tad, can this cause these delayed up and down shifts?
5) I checked vacuum in neutral at the modulator, and going into it is the same reading of 12 as I have up at the manifold...so no apparent leaks on the line to the modulator. Does a vacuum modulator even have any impact on a WOT manual upshift?

Thanks in advance for any assistance you can provide.
1. not really. At WOT the vacuum on the modulator is minimum if not at ZERO.

2. You answered your own question IF I understand the question. At WOT the cable should be fully pulled out. This tells the trans you want maximum pressure and maximum RPM shift points..... do not forget the vacuum modulator has told the trans the engine is under a high load condition with no vacuum at the modulator.

3. A little bit. Not a large factor.

4. A cable pulling too much can cause delayed shift points under light throttle. The cable on a t-350 can have some slack in it at a closed throttle.

5. See answer number 1. The governor will over ride an upshift if the road speed is not high enough for the upshift. Unless you have a trans that is modified for full manual shifts only.


====== you do not mention what shift mods or kit was installed... only that a shift modifier kit was installed. there are different levels of kits

I would suggest dropping the valve body and see how many check balls are installed.

IF there are 4 check balls. Please remove 3 check balls. Retain the check ball that is near the modulator valve. That would be the valve behind the vacuum modulator . This will quicken the upshift 1-2 .
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