HT 740 torque converter lock up postpone

NewbeeMC9 · October 22, 2007, 06:03:22 PM

Whilst climing some hills this weekend around and on the blue ridge parkway( fun & lovely ride) , some times it was in first gear and would shift into second while climbing which it would have been doing good but the torque converter would lock up too early and kill the rpm.

Is there a way to postpone the lock-up until the revs are back up?

I'm also pretty sure that the ht 740 seems like a 5 speed because the lock up between 2nd & 3rd seems like an extra gear on flat ground. it is even timed that way.

thanks for the help

niles500 · October 23, 2007, 12:28:07 AM

MC9 - if you put your foot in it and it still shifts too early you have other problems - what rpm is it shifting at?

DrivingMissLazy · October 23, 2007, 05:21:25 AM

Lots of good info here. It is posted on the Help board.
http://www.busconversions.com/bbs/index.php?topic=883.msg12267#msg12267
Richard

HB of CJ · October 23, 2007, 01:31:24 PM

First thing check the tranny oil level. As a last ditch thing, you can manually select the highest gear you want and lock it in that gear--the granny should progress from converter mode to lockup mode in a normal feeling manner--if it still lockups too fast, then other problems, but perhaps still adjustable/correctable outside the box. Good luck.

NewbeeMC9 · October 23, 2007, 04:54:33 PM

it locked at about 1950 and which imediately dropped it to about 1500 which was is right outside where i wanted to be on RPM. really lugged

I had it in first and shifted in to second. it went to second then strait to lock-up. I was feathering the throttle a little to keep the black smoke out.

Checked level upon leaving and again when leaving there. level was same.

I noticed i am springing a little leak on the hose at the cooler. I believe a snugging will fix that.

thanks for searching that thread Richard, I guess if you can overide the unlock, you can overide the lock. I will get the book out and see what i have. I like the 1C-2C-2L-3C-3L-4C-4L, (i have that 1C-2C-2L-3L-4L now i believe).
the 4L-4C downshift would be nice on the rolling hills of the interstate around here. Can you switch the programming?

I have been speculating that the Modulater linkage needs adusting. I think it is too tight and causing another leak at the modulater linkage.

TomC · October 24, 2007, 09:03:42 AM

I would highly recommend you keep with the 1C-2C-2L-3L-4L setup. Each time you go into converter you loose power through slip and create a tremendous amount of heat. If you can't get lockup when you pull the gear shift into 1st for 1st gear lock up, there are solenoids and valves you can install in the transmission for manual lockup. The idea is to keep the transmission locked up as much as possible. The only reason Allison made the 1C-2C-2L-3C-3L-4C-4L was for truckers with heavy loads to keep the engines revved up more-not needed in a bus. Good Luck, TomC

HB of CJ · October 24, 2007, 12:52:00 PM

TomC is right. In a Bus/Coach, getting into lockup mode the quickest is the bestest. Marginal tranny cooling systems to begin with, making the problem worse is worser which leads to the worestestest.

Years ago, we had a 740 in a 8V71N fire engine ladder truck that shifted that way. Sounded cool, but when we told the master mechanic about it; he quickly corrected the lockup mode. Oh, well.

NewbeeMC9 · October 24, 2007, 04:24:23 PM

Quote from: TomC on October 24, 2007, 09:03:42 AM
I would highly recommend you keep with the 1C-2C-2L-3L-4L setup. Each time you go into converter you loose power through slip and create a tremendous amount of heat. If you can't get lockup when you pull the gear shift into 1st for 1st gear lock up, there are solenoids and valves you can install in the transmission for manual lockup. The idea is to keep the transmission locked up as much as possible. The only reason Allison made the 1C-2C-2L-3C-3L-4C-4L was for truckers with heavy loads to keep the engines revved up more-not needed in a bus. Good Luck, TomC

Interesting Tom & HB, I think the 1C-2C-2L-3C-3L-4C-4L would be something I would like on a hill climb occasions, i see what you mean about the heat.

But as it is now, if I start off with the lever in 1, Should I get a shift from 1C-1L ? Or is it supposed to be 1C from start and 1L when downshift from 2L?

Thanks for helping me out on this.

TomC · October 25, 2007, 05:20:58 PM

When you pull the shifter into 1st, you should get lockup on no fuel for going down hill, and should be able to get all but the last 1 inch of gas pedal with fueling. On mine, if I go down all the way on the pedal, it will slip back into converter-which I do right before shifting to 2nd to make the shift smoother. Good Luck, TomC