| Author |
Message |
Timnvt (Timnvt)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 24, 2005 - 7:45 am: | |
Hi folks.
I’m still not fully satisfied with the $3000 valve body job DDAllison did to my HT740D equipped MCI5A last week.
They put in a group 16-1107 valve body supposedly for a coach application. The trick of it is, after installing it the coach wouldn’t downshift from 4 to3 until 40 mph. I expressed my concerns that a highway coach shouldn’t have to put the 4-way flashers on before the rig will downshift on the interstate hills.
They dropped the pan and adjusted the new valve body to its maximum shift speed which brought the downshift up to 43mph.
Is 43mph the correct downshift speed? I’d like to know what speed your HT740D equipped coaches downshift from 4 to 3. Also, does anyone have specific information on whether the Group 16-1107 is the correct valve body for a 6V92 335hp coach or what they should have installed?
I know I can down shift it manually, and I do, but it’s an automatic and for the $3000 I’d like it to be repaired correctly.
Second gear lock-up seems very late in coming on as well. Should I be concerned about prematurely wearing out the 2nd gear clutches? It literally shifts like 5 complete shifts now. Going up a hill second gear doesn’t necessarily lock up!
Thanks,
Tim
ps It is shifting firmly now which I can live with. No more violent downshifts ;) |
Jim Ashworth (Jimnh)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 24, 2005 - 8:11 am: | |
My 740 upshifted at 51 and down at 47. Lockup is often mistaken for a shift with those unfamiliar with the transmission. Sounds like you did ok except you may need a stronger spring in the 4-3 downshift valve. As I understand it, that is do-able.
Good luck
Jim |
David Dulmage (Daved)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 24, 2005 - 8:16 am: | |
43 mph doesn't sound too far off. I generally always downshift manually on steep hills so that the engine doesn't start to lug. It's typical to feel the lock-up; makes it seem like you are going through five gears.
FWIW
DaveD
(MC-8) |
RJL
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 24, 2005 - 10:20 am: | |
Tim - Can't remember at the moment, but does your coach have a tachometer?
RJ
PD4106-2784
Fresno CA |
Timnvt (Timnvt)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 24, 2005 - 11:11 am: | |
RJ, Yes I have a tach. What are you thinking?
Jim, do you know whether replacing with a stronger spring would result in a harsher downshift? Is changing that spring a fairly straight forward swap out that I might do myself rather than pay DDAllison another $500 plus to experiment with my coach? At this point I'm not persuaded they're serving me as anything more than parts swappers anyway. I can do that.
If I do drop the pan again, is there adjustment that can be made to quicken the second gear lockup?
Tim. |
Gary Carter
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 24, 2005 - 1:55 pm: | |
Under full throttle my 740 downshifts in th 50mph range. This is with 3.33 RE and 24" tires. |
john w. roan (Chessie4905)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 24, 2005 - 5:18 pm: | |
You need to carefully record your tach readings for each gear full throttle upshift and down shift...going by MPH is going to be different with others if tire size/ axle ratio is different.Harshness of up-down shift will be affected by weight of coach, horsepower and torque of engine used,rpm of shift points and axle ratio to lesser extent.With patience and time, you can adjust or change springs, to get it a lot closer.If you look at valve body breakdowns for different models of your trans, different springs are specified and sometimes valves are different diameters. If you are considering on attempting this, you should obtain an automatic transmission theory of operation book so you have some understanding of how the hydraulic circuits work.GM car manuals cover this and explain how some of the valves work also.I think the Allison shop manual for your trans might explain how or what the different valves do. I'm pretty sure my V-730 manual does, but it is at work....will check it tomorrow.BTW I have done this on car trans and AT540 Allisons, so I'm not talking through my hat. |
Jim Ashworth (Jimnh)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Wednesday, August 24, 2005 - 6:47 pm: | |
I had my 740 rebuilt and they tweaked it until I was happy, including changing springs and adjusting shift points. Never done it myself, just was there when they did it. But that was 12 years ago at a cost then of $3000. However, it is still running great today with a new owner for the last 5 years.
Wish I could be more help.
Jim |
Buswarrior (Buswarrior)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, August 25, 2005 - 6:41 pm: | |
Hello Tim.
Mine is the same as Jim's, upshift at 50-51 and downshift at 47.
I'd like it if I could get mine to shift at 43. Gives you a little more flexibility in what you are doing as you just top a hill and it won't hold the gear. I'll shift down manually earlier on a steep hill, and I'd like to be able to just torque it over the top.
And I keep my eye on the temp gauge, etc, so the primary danger of lugging is covered. The opportunity to get the revs down earlier in light throttle situations on flat ground would also be of advantage for fuel economy
Perhaps we should trade? :-)
happy coaching!
buswarrior |
john w. roan (Chessie4905)
Rating: N/A
Votes: 0 (Vote!) | | Posted on Thursday, August 25, 2005 - 9:09 pm: | |
the shift valves have a stepped ring in the end of the valve body..something like the adjustable rear shocks on some smaller dirt bikes. Pushing in and rotating the ring cw or ccw to different steps increases spring pressure and upshift- downshift speed or lowers spring pressure and decreases upshift-downshift speed. usually varies speed 2-7mph depending on gear.Sometimes you run out of steps before you achieve the desired result which will require a slightly stiffer or weaker spring change and then re-adjust stepped ring. Allison shop manuals list color, coils, diameter,wire thickness and length for the different springs. |
Doug McCartney
Rating: N/A
Votes: 0 (Vote!) | | Posted on Friday, August 26, 2005 - 1:12 pm: | |
I would be careful about using other coaches to determine the proper shift point. The shift points should be set to keep the engine RPM’s in the proper working range. If someone has a different axle ratio or torque curve on the engine, the desired shift point may occur at a different road speed.
I would want to know what RPMs it shifted at and a little bit about the engine performance when evaluating the shift point. If you have lost performance, it’s probably safe to say that it is not occurring at the most ideal point. Later engines generally have peak torque at lower RPM’s, so pulling them down a bit more is appropriate.
It’s not a big deal to change the shift point. John described it perfectly. You will have to take the pan off again.
It is not unusual for a valve body to need some fine-tuning and the dealer knows this. I personally would think for a $3000 bill, the price would include some minor fine-tuning of the valve body and I would push them to do it as part of the job.
Good Luck,
Doug |