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Old 08-22-2007, 12:22 PM
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Swapped out a 5sp for C-6, C-6 acting up

I swapped out a zf-5 for a C-6 the other day and I don't think things are quite right with this tranny.
First problem I'm aware of is the stall. I've got a mildly built 460 with the edelbrock rpm cam. I'm currently running a stock stall which pulls on the brakes and overheats the motor because my commander is trying to keep the motor at 1100 rpms. What stall should I get?

2nd problem I've noticed is it shifts way to fast from 1st into 2nd gear. I pulled out of my drive way this morning and before I got the truck straight it was already in second. I've also noticed that when it's in second and I mash on it, it seems like the tranny won't let the motor rev up. I haven't had a chance to hook up the computer to the commander yet to see what rpm its only letting it go to, but I know it's not right.

3rd is I hear what sounds like gear roll over coming from the tranny. I measured the two trannies and the zf-5 was a 1/4 inch longer that the C-6 so I'm figuring it's coming from my drive shaft since it's sticking out 1/4 more and it's got a nice angle on the CV joint.

One other thing is I've connected the vacuum line from the trans to the manifold tree. Is this right or does it need to be a ported line?

Help Please.

Corey

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Old 08-27-2007, 07:39 AM
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anyone have any idea's?
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Old 08-27-2007, 12:42 PM
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c6

Duallybuster the transmission needs manifold vacuum, 16- 20 inchs of vacuum.

Does this truck have a high numerical differential?

The modulator may have an adjustable screw, in the nipple that the vacuum hose goes onto. If it does, try screwing it in clockwise, to obtain a later upshift.

An upshift that is too early, as you describe, will not let this motor unwind, you will experience poor performance. What are the max 1-2 and 2-3 upshifts at. If you floor it from a stop, at what speeds does it upshift?

I suppose you are going to address the driveshaft problem.

I'm not familiar with this cam, can you post the specs? for converter choice.
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Old 08-28-2007, 11:16 AM
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thanks for the reply, I'm running 4.56 gears in the axles. 1 to 2nd shift happens about 1200 rpm and 2 to 3rd about 2200. When I floor it, it seems like it's slipping and then slowly goes into the next gear. Is that caused by the lack of vaccum the cam produces?

I'll give you the cam specs in the next post, Edelbrock said the rpm range of the cam is 1500 to 6500.
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Old 08-28-2007, 12:14 PM
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c-6

Not by the lack of vacuum when you floor it because, if you were to watch a vacuum gauge as you drive, you would see that at crusin speed,which is very little load on the engine, the vacuum will read the highest.

Under a load, like when you floor it, vacuum may be at o inchs, or close to it.

This is how the trans will raise pressure, as well as serving as a function to help control the shift timing, along with the governor, [speaking of the latter as opposed to the former ].

So anyway, this governor, which is on the output shaft, uses centrifugal force to feed governor pressure to the valve body.

This pressure pushes on the end of the valve to move it in an upshifted position. This causes the transmission to change gears, or shift.

The modulator produces pressure to help oppose this force, along with the shift valve springs.

I think this 4.56 rear end is spinning this governor up way to fast, changing the governor curve and causing this transmission to upshift too quickly.

Robbing you of power and giving you the sensation of a slipping transmission.

That's my story and I'm sticking to it!

I'll wait for your reply and we'll discuss what we can do about it then.
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