Help me solve a gearing/transmission problem

[seadog]

I'm still sorting out my Deuce coupe, it's coming along and progress is being made. BUT...'Scratching my head over why it's turning 3,000 revs at 70 when, according to calculations it should be turning 2100 - 2300 at that speed. Here's the set up and what I have done so far...any thoughts/suggestions are appreciated.

ZZ4 crate motor
700 R4 trans from Bow Tie Overdrives, their stage 2 street model, using a converter from Bow Tie OD's, the one they recommended for this tranny. Transmission shifts as it should through all four gears.
26.5 inch tall rear tires
3.50 gear
Stewart Warner electric tach which I believe to be correctly wired; stock HEI distributor

All the on line calculators say this combo should yield approx 2200 rpm at 70.
I have measured 70 mph by GPS and at that speed the tach shows 3000rpm.
The general consensus from others I've talked to about this is that for some reason it's not going into OD, but it sure shifts 4 times (confirmed by seat of the pants).

I have jacked the rear end up and rotated both rear wheels while counting the pinion yoke revolutions and this exercise confirmed the ratio is approx 3.50

I would like to get the revs down into the 2200 range as this car will be driven a lot over long distances and the increased mileage, not to mention less noise, would be a definite plus. Before tearing into the tranny, I'd appreciate any thoughts from you guys as to what's going on here and possible fixes. Thanks -Tom

[kb426]

Only 2 possibles that come to mind quickly: Trans isn't in overdrive. Rear gear isn't 3.50. Not saying you made a mistake just saying that the most obvious would be the trans and something about the overdrive. I have a .69 overdrive and 3.5 gears with 29" tires. 1800 at 70 mph. Is there a chance that the convertor is not locking up?

[Fat Cat]

Another would be that the converter is slipping or not locking up.

[wayne petty]

i will have to ask a question to the 700 gurus....

but i seem to recall that there is a 4 gear pressure switch in some models of the 700 to signal the ecm its in 4th gear...

perhaps what you are feeling is actually the converter locking up in third gear...  and it never shifts to forth..  as that would add up on the tachometer??

just a thought from left field...

just curious..

with the back wheels in the air..   can you watch the speedo and tach as you manually go through gears... pulling it out of overdrive position seeing the tach flair as it drops to third gear..

have you tried driving it with the electric plug unhooked to remove the TCC from the problem... see if you still feel 4 gears shifted ..


also for the gurus.. is there a way ... for an idiot light to be hooked up as a tell tail for the TCC ?  

i know you can see this kind of stuff on some scan tools.. depending on the year of the car and trans..



can you get the date code from above the pan rail on the transmission???  i would imagine everything inside is changed... but it might help...     did you happen to have the pan off at any time... did you snap any photos... i just recall that there were like 15 different wiring harnesses for those.. with slight variations on pressure switches...

and ... did you use the proper throttle valve extension adaptor on the throttle lever of your carb.. so the  TV cable pull ratio to throttle angle is correct...??

[Crosley.In.AZ]

you will not have 4 shifts with  the 700-4l60  trans.

there will be 3 shifts ;  1 to 2nd ,  2 to 3rd, then shift to 4th = three shifts

then the converter clutch should apply , some folks think of it as a shift. It is not


Bow tie should have the trans set up for lock up in 4th gear and they will answer questions.  Most folks are happy with their customer service line.

I suspect tach problems IF the trans is in 4th gear with converter locked or not

[seadog]

Crosley Posted: Thu Jun 17, 2010 11:23 pm    Post subject:  

I suspect tach problems IF the trans is in 4th gear with converter locked or not  
--------------------------------------------------------------------------------

Looks like it is a tach problem.  Thanks for all the input guys.