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C-6 Gearing???

1080 Views 10 Replies 8 Participants Last post by  BARTnRED
Okay, I've been crunching numbers and I'm still at a loss...
This all pertains to the '89 351W with a C-6 (rebuilt 15k and 3 years ago).

-Which is a 3-speed with top gear being 1:1 ratio, yes?
-With 32x11.5's
-with an axle code of H9, which is a 3.55 limited slip

With that, I should be doing @ 2200rpm at 60mph

Now, I don't have a tach, but there's no way I'm doing that. It's more like 3500-4000rpm. My shifts occur at 25mph for 2nd and 35mph for 3rd.

Wiskey Tango Foxtrot?
Is something slipping? Did the tranny place hose something up when they put in a rebuilt?
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Sound's like something isn't right,there's no way you should be spinning that much rpm with 3.55 gear's 32" tire's.I have 4.56 gear's and 35's and I'm not spinning that much rpm.
Sounds like you're stuck in 2nd maybe? Are you sure you're grabbing 3rd at 35mph? I had this happen on a '79 F-250 with a C6 and had a bad vacuum modulator. You're right on the 2200 RPM guess. Calcs can be done here:

there are some specs to some trannys. i tried to copy-paste but my computer is a POS and wouldnt let me
Sounds like the problem I have, at present mine is all stock, just bought it, 85 351W, C6, and I run about 3000 rpm at 70 mph, with factory 3.50 ratio. Does this sound normal?
"Sounds like you're stuck in 2nd maybe?"
That's what I thought when my wife told me about it. (The '89 is her Bronco)
No such luck. It's a firm shift, with noticable RPM change...only it's at 35mph.
Night and day compared to the 5.0L and E4OD in the '94.
Im guessing thats normal. My bronco, with an AOD does around 2000rpm at 60mph. IIRC the overdrive gear on the AOD is .67:1. With a bit of math your rpm's should be at 3340
i have the same setup as you 351w c6 and 3.50 gears with 32's and run around 3k if not higher at 70 if i remember right!
How accurate is your tach as I need to find out how accurate mine is. I run a 351 with ac6 355 gears and 35 tires and when I do 60mph my tach says 2800 and I know Iam in 3rd as I have a shift kit the trans is only aprox 2 years old.
dunno how accurate it is. so it could be way off.
It's a Custom trim level, so no stock tach. Just going by ears and feel. Not in the mood to install an aftermarket just so I can see my 351W spinning like a hamster on crank. It'll probably never have to go over 45 when we move to Maine anyways.
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