Down shifting an Allison 740

[IMABUSBOY]

My question is two fold:1. Is it safe, or will it damage the transmission to use it to help hold back on long or steep hills or to slow down on off ramps.
2. Does anyone see an advantage to manually upshifting the Allison 740 auto or just put it in 1-4 and go?
Thanks, Danny

[RJ]

Danny -

1)  No, it won't hurt the transmission.  Be aware, however, that it WILL upshift on it's own to keep from self-destructing if your downhill speed holds it against the governor for more than a few seconds.  If you have a jake brake, use that.  It's a great additional safety tool for descending grades.

2) Depends on the conditions and if the driver's lazy.  For best performance, shift manually, both up and down.  When working in city traffic, sometimes just leaving it in 2nd or 3rd fits better, and avoids "hunting" back and forth if in D.

Get out some of mama's white nail polish and go for a ride.  Find yourself an area with very light traffic.  Starting with first gear, wind the engine to the governor and note the maximum road speed in that gear.  Do the same for each intermediate gear (1, 2, 3).  Now take the white nail polish and put a dab on the speedometer face indicating the speeds you determined from your testing.  Bingo! You have an instant visual guide for being in the right gear at the right time. 

There is a complete article about shifting over on busnut.com in the articles of interest tab off the main menu.

FWIW & HTH. . .

[blue_goose]

RJ is right on with what he said.  Jake brake doesn't do much in 4th gear.  If you are trying to hold back on a hill down shift and then you get lots of help from the jake.
Jack

[eagle19952]

i accelerate up to 4th gear and as soon as it engages i shift right back into 3rd. and when i approach a grade i lose less road speed. not sure that's best but it works well for me.

Generally I always manually shift my 740.

[IMABUSBOY]

RJ, blue_goose I wish I had a jake but I don't. I drove tri-axle local and over the road tractor trailer with 10 and 13/15 spd road rangers, but have no experience at all with automatics. I have been shifting manually coming onto the HI way so it don't shift to soon and down shifting as far as 3rd on a grade, so far with no problems. I just wanted to be sure I wouldn't blow a seal or worse by letting the tranny hold me back.  As suggested, I hold 3rd in town traffic. RJ, I haven't checked 1st-2nd gear yet, but it shifts from 2 to 3rd @ about 40 mph and from 3rd to 4th at 50 mph. Going uphill, it downshifts to 3rd @ 50 and 2nd@ about 40 mph.
Thanks eagle 19952, I'll try that
Thanks again fellows! Danny 

[RJ]

Danny -

Also be aware, if you haven't noticed already, that your 4-spd 740 feels like a 5-spd as it upshifts, especially in Drive.  That extra shift is actually the torque converter locking up.  The pattern thus is 1U - 2U - 2L -3L - 4L.

FWIW & HTH. . .

[TomC]

RJ-How're Doin? On my truck conversion, when I had the 13spd taken out and the Allison HT740 installed, they (Pedco) installed a soft shift transmission. This is the first I've ever experienced with this-on every shift, the torque converter comes out of lockup, then after the transmission shifts, re locks up. Makes for very smooth almost undetectable shifts. Only thing I don't like, is that going to wear out the torque converter clutch?
On HT740's, pulling the gear shift down into 1st, you hold the transmission in 1st, and can get lockup in 1st-albeit at 20mph and up near the governor. Just in case you're pulling that really steep hill. Good Luck, TomC

[luvrbus]

TomC I ran the soft shift setup on my FS 740 Allison for 15 years no problems what so ever and FS is not a typo 

[TomC]

Thanks Clifford-glad to hear that!

[IMABUSBOY]

Thanks RJ, I did count 5. You answered a question that I had before I even ask it. haha
What a wealth of knowledge! 

[Lin]

Generally, on the flats I let the automatic do its job.  I manually shift going up grades to keep the engine rpm above 1500, or as I feel needed for appropriate power.  Go downhill, I will downshift to maximize the Jakes if necessary. 

[Oonrahnjay]

... and FS is not a typo 

    OK, just for curiosity, what's the difference between the FS and HT versions?

[luvrbus]

The FS was a fuel saving transmission mostly found behind the 8v92,different valve body and trimmer valves made for a smooth shift up or down and they used a different ratio torque converter it was a nice transmission but now you cannot buy parts to build one. The highly publicized Transynd fluid did mine in, the clutch linings were not compatible with the Transynd     

[Oonrahnjay]

The FS was a fuel saving transmission ...       

    Thanks!  Interesting to know.