HT 740 Transmission Lockup, MPG and Shifting techniques question

[neoneddy]

As some of you know, Scott Crosby came out to my place and helped me with a few items, we noticed the transmission bolts were all loose, some so loose you could see daylight between the bolt head and transmission, not good.  This likely explains my loss of transmission fluid over the last year.   Scott also mentioned the transmission oil level can affect MPG by when the torque converter locks up, or my case being 3 gallons low maybe not at all in high gear.

So that got me thinking, would that explain why I seemed to get 7-8 MPG last summer, while this spring I maybe got 6.5 mpg?  We'll be  putting on a few thousand miles this year.

Then in the last post below, TomC mentions  "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. " I'd like to downshift better, What exactly does he mean here?

http://www.busconversions.com/bbs/index.php?topic=6088.msg58238#msg58238

[Iceni John]

TomC has a V730, sort of like an HT740 except without the 740's first gear.   What he can do with it is not automatically ('scuse the pun) what us 740-ites can do.   To smooth the downshifts, especially 3rd to 2nd that is harsh in my transmission, I just manually downshift, and I always manually downshift when climbing and descending hills to keep the revs up.

Can you feel your TC lock up in 2nd gear?   It feels like a shift.   If your TC isn't locking at all, your transmission is dumping a lot of heat into the engine coolant.

John

[neoneddy]

Well after getting the fluid to the right level, shifting is buttery smooth and I feel the lockup, I think so anyway as I count 5 changes with 4 gears.

[Iceni John]

Well after getting the fluid to the right level, shifting is buttery smooth and I feel the lockup, I think so anyway as I count 5 changes with 4 gears.

5 changes?   Including the lockup, you should feel four changes with a typical 740, or five changes with a 5-speed HT.

John

[luvrbus]

740's are 1st C, 2ndC,2nd L,3rd C,3rd L,4th C,and 4th L  C=converter L= lockup, it was locking up in 4th or the engine would over heat like John posted, low fluid or or high fluid levels will also make the transmission heat more also you have a transmission temperature gauge ?

[buswarrior]

The 740 may have "automatic" in its name...

But all the good drivers shifted it manually

Too rough, and upshifts too early under light throttle, to only bang back down again.

So, shifter goes in 2nd for anything undeer 37 mph. The transmission does an adequate job of the 1-2 and 2-1 shifts.

You put it into 3rd above 37mph, and 4th above 50mph

Mph are estimates, it depends where your engine governor is, you shift just ahead of the engine governor effecting acceleration.

Down shift smoothly under hill climbing acceleration, as speed is dropping, 2-3 mph higher than the engine governor, lift throttle, pull the shifter back from 4th to 3rd, and concurrently press throttle back to the floor. It will be smooth as warm butter if you time it right, and the engine is way up high in the power. Not that teeth jarring BANG if you let it drop and shift on its own, and already down the revs.

Same for 3-2 downshift under power.

If slowing down, just pull it back under closed throttle to assist deceleration, and/or having the right gear to resume power.

In context, the arrival of the 740 was lovely, as rowing gears and clutching was the only alternative. Remember, everyone knew how to match revs to gears, so doing the same on downshifts was easy with the automatic.

Happy coaching!
Buswarrior

[luvrbus]

The Stone/Bennett shiftier is a lovey addition to a 740 .PS they make kits for 740's to stop the harsh shifting

[Scott & Heather]

I always shifted my 740 manually. 100% of the time. My 748 ATEC shifts perfectly fine and I rather like it's predefined shift points so I no longer do that but yeah the 740 really should be manually finessed.


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[neoneddy]

Wow, thanks everyone, learning a lot here.   I'll take it out here again and see if I can count the shifts all the way up to speed, maybe record some video.

But in general I don't think I've ever really felt the C to L changes except in 2nd. I wonder if I've been low ever since I bought it, the PO said it leaked a little from the shifter, I never knew the proper method for checking the level.  Correct me if I'm wrong here, shift into all gears including reverse, high idle in Neutral for a minute, back to low idle and check right away on level ground.  Before, I kept checking it while off and the level looked too high.

I did that yesterday over the course of an hour driving a small loop and after 3 gallons got it to be in the proper range for Hot.   I wonder if I've ever had lockup in 4th.  Totally makes sense on the heat in converter mode too.

[luvrbus]

If your 740 is adjusted right, 2nd gear lockup is the only lockup you feel ,always check the transmission when hot at idle 3 gals was low but most 740's hold 10 gals on the average ,when you shift manually you bypass the converter stage and go to the lockup stage   

[lostagain]

neoneddy, you mentioned your transmission leaks a little at the shifter. It is easily fixed by replacing an oring there. Get the oring from the DDA dealer so it is the right size and will take the heat. Then you remove the fork looking retainer that hold the shaft in. Pull the shaft out, replace the oring and reassemble. Trans fluid will pour out of the hole, but you can stuff a clean rag in there for the  minute it takes to do your thing.

JC

[TomC]

Shifting of the HT740 can be different depending on which shifting schedule you have. Older ones and most all trucks have- 1C, 2C, 2L, 3L, 4L. On my truck, they installed a smooth shifting kit which the torque converter drops out of lock up during the shift then locks up immediately eliminating the possible rough shift. As Cliff said- 1C, 2C, 2L, 3C, 3L, 4C, 4L. As with my V730, you can get lockup in 1st is you pull the shifter into 1st, but around 20mph.
Also, unlike the V730, you can install a manual lockup valve on the HT740-meaning you have a switch on the dash with two lines going to a solenoid valve. But-can create rough shifts and stalling if you forget. Good Luck, TomC