C4 shift/RPM question

[msweb]

What should the range of the RPM drop be on a C4/302 when it shifts from 2nd to 3rd?

I get about a 500-700 RPM drop and that's it. With 33" tires and 4.56's I'm turning 3000 RPM at 50 MPH. That just doesn't seem right.

I did notice it at 2400 RPM one night vs. the 3k but no more. I know it is shifting through all gears despite hardly feeling it.

In "D" and starting off casually, the tranny shifts from 1st to 2nd at like 5 mph and you never feel it. 2nd to 3rd is maybe 25mph, just as smooth.

Any ideas?

 

[TJK74]

As far as the RPM and tire combo that sounds about right for 4:56's and 33's
about the early shifts have you tried adjusting the shift modulator? That should help get you where you need to be.
Check the gear calculator for RPM specs.
http://home.comcast.net/~jcmiley/index.html

 

[minimatt]

The amount of rpm drop between shifts will be a function of rpms at the time of shift. The higher the engine speed at the time of shift, the greater the rpm drop should be. As for the 2400 rpm indication one night, I would suspect the tachometer was having issues that night and not giving a proper indication. The shift points at 5 mph and 25 mph do not sound out of line for a light throttle, light load situation, especially when you consider the soft shifts. Doesn't sound to me like you have any trans. problems.

 

[Quick & Dirty]

There will also be some slippage in the torque converter. With a stock converter mine varies 200-300 rpm with the throttle at cruising speed. I.E. going up a hill the rpm is higher than going down a hill at the same mph. With direct gearing the difference between 2nd and 3rd at 50mph should be about 1000 rpm, but with the upshift the load on the converter is higher causing it to slip more. Also, in 3rd at 50 mph the rpm is close to the stall speed so it allows more slip.

Mine also shift into 2nd at very low speeds when not on the throttle. A few times I've dropped it into 2 instead of D and didn't notice until I got up to about 30 and it doesn't upshift. With a torque converter at low throttle it doesn't make much difference what gear it's in. If it's in D the 1-2 shift at 5-10 mph causes almost no rpm change, as the converter is right around the stall speed.

 

[BUCKETOBOLTS]

My rig cruises at 2400 at 55 with 36" tires and 4.56's. I run a 1600-1800 stall and at slow speeds when the convertor is "soft" it is hard to tell when the tranny actually changes gears. But when the hammer is down and the convertor is engaged I get a real firm shift. To help feel the shift I adjusted the modulator to stretch out the gears a bit and get the RPM's up on the shifts. Mine generally shifts to 3rd around 30-35mph.

 

[la77]

don't mean to steal the thread, but which way do you turn the modulator screw to "stretch out the shifts" lefty losey righty tighty?

 

[TJK74]

Its been almost 10 years since ive had to mess with mine but if i remember correct its righty tighty! Anyone confirm??

 

[BUCKETOBOLTS]

Yep, turn the screw in to spread out the shifts.

 

[msweb]

Thanks guys, sorry for absence. I plan to go to 35's as soon as the budget will allow, this should help. I need to measure my current tires to see how close to 33" I really am. We all know that just because it says 33" doesn't mean it is. My buddies 35" boggers are only 33" tall...

The gear calculator says I should be at 64mph at 3000 RPM with 4.56 gears. As mentioned with various stall speeds, this can vary. Who knows.

I'll assume that everything is good but just for good measure, there will be some righty tighty done. Anyone know just how far righty should be? 1 turn? 5 turns? Or is it just ry it and see?

Thanks for always being here to help!