3K rpm at 50 MPH... What gives?

[charlie challenger]

I just got license plates on my 8 year long project, and I am happy, but...
I can only take it to about 50 mph comfortably, and it's turning about 3,000 rpm. 
I've got a 440 w/ 727, 3.55 gears out back and 275, 65 r 15 tires.  The engine is tuned properly, Shouldn't I be in the 70 mph range at 3,000 rpms? at least according to http://vexer.com/automotive-tools/speed-rpm-calculator
It shifts from 1 to 2 to D just fine manually with the slap stik.  I don't have the kickdown linkage hooked up, but that's just adjusts trans fluid pressure for shifting/passing right?  Also there is a vibration, and I think my drive shaft could be a little too short.  Could that cause it?
What could be going on?  Thanks in advance.
Pat

[tman]

check accuracy with another tach?

[ChallengerHK]

 

[burdar]

I don't have the kickdown linkage hooked up, but that's just adjusts trans fluid pressure for shifting/passing right?

Not correct.  The kickdown linkage increases the trans line pressure in regards to throttle position.  The more you push on the gas pedal, the more the line pressure goes up.  The higher the RPM, the higher the pressure needs are to keep the clutch discs from slipping.  Right now you are burning through the clutches while cruising down the road.  You HAVE to get the kickdown hooked up.  That is your problem.

A good friend of mine smoked two 904s because he didn't have the kickdown hooked up.  His car was a BEAST for about 50 miles, then the trans was junk.  It felt like he had a 3500+ stall convertor in the car.  That's because he was burning through the clutches.  As soon as he rebuilt the trans and hooked up the kickdown, the car was a DOG.  With the proper pressure, the clutch plates didn't slip and the car stalled at the stock rpm.  Do not drive your car until you get it hooked up and adjusted properly.

[anlauto]

  You can't run without the kick down linkage...not for long any way

[charlie challenger]

Ok,  I'll put that on next.  I planned to do it at some point.  Ididn't know it was that crucial.
I've put 450 miles on it without one.  I hope I didn't hurt anything.  It behaved like this from the start.  I figured something was slipping in the transmission, or my torque converter wasn't working right. 
I thought kickdown cables were just for shifting, but I don't know much about transmissions.  If they help build pressure I'd guess that makes sense.  I'm not convinced this will help my problem, but I'll give it a shot.  I have nothing to loose.  I'll let you know if it helps. 

[burdar]

You need line pressure to hold the clutch discs together.  Driving around like grandma doesn't require a lot of pressure to hold the clutch discs together.  As soon as you try to accelerate fast, that puts extra load on the trans.  The pressure needs to increase so the clutch discs stay locked together.  With the kickdown disconnected, you are driving around with very low line pressure.  When you try to accelerate, the clutch discs slip and will eventually burn up.

[roadman5312]

You need line pressure to hold the clutch discs together.  Driving around like grandma doesn't require a lot of pressure to hold the clutch discs together.  As soon as you try to accelerate fast, that puts extra load on the trans.  The pressure needs to increase so the clutch discs stay locked together.  With the kickdown disconnected, you are driving around with very low line pressure.  When you try to accelerate, the clutch discs slip and will eventually burn up.

                    I didn't know this either. So unlike Ford or GM transmissions, which slam you into passing gear, the Torqueflite builds line pressure . Interesting. So does the Torqueflite drop to a lower gear when you floor it in 3rd. ?  ie  passing gear.   

[mopar jack]

Depending on your speed and how far you step on the accelerator the kickdown will shift to second or first gear.

[blown motor]

Yes it does. With mine if I'm doing about 30 to maybe 35 mph and I put it to the floor it will drop right into first. Puts you back in the seat real nice.   

[1 Wild R/T]

Part throttle kick down was used starting around 68-69 for 6 cylinder trans, small blocks & 383 got it in 71 & 440 got it I believe in 73.. It is easy to add to earlier trannies... Also allot of trannies have already had it added....

[734406pk]

Ok,  I'll put that on next.  I planned to do it at some point.  Ididn't know it was that crucial.
I've put 450 miles on it without one.  I hope I didn't hurt anything.  It behaved like this from the start.  I figured something was slipping in the transmission, or my torque converter wasn't working right. 
I thought kickdown cables were just for shifting, but I don't know much about transmissions.  If they help build pressure I'd guess that makes sense.  I'm not convinced this will help my problem, but I'll give it a shot.  I have nothing to loose.  I'll let you know if it helps.

This linkage controls throttle pressure to the transmission valve body. The further you step on the throttle, the more line pressure is created, holding the clutch packs together. Shift timing is delayed and eventually kick down will occur. With the throttle linkage disconnected, the transmission has no sense of throttle position and stays at idle pressure, potentially causing clutch slipping. Check the trans fluid color to see if it's burnt. Hopefully it's ok. The 440 is hard on transmissions...

[69ChargerRT]

learned a lot about auto transmissions just reading in here!

[roadman5312]

So the trans gets its shift timing input from throttle pressure, rather than a vacuum modulator on Ford/GM transmissions. I always wondered about that. 

[GoodysGotaCuda]

So the trans gets its shift timing input from throttle pressure, rather than a vacuum modulator on Ford/GM transmissions. I always wondered about that.

Yep.