transmission choice ?

[sledhead]

hello I have a 1990 mci 102c with a fresh rebuilt 6v92ta .Iam thinking of changing my transmission ht740 . at present 83 mph at 2150 rpm ,I think 333 rear end 315 80 r 22.5 firestone fs 400 tires. would like to go to a ht754 for extra gear between 3rd,4th for the hills or what about a ultra $#!% plus 13 speed for 4th through 13 with 2 over drives ?? please help thanks dave

[hargreaves]

Hi Dave, I have a 1987 Mci 102A3 36,000 lbs, with a 6V92 330hp, 740 trans , 3:73 gears , top speed 78mph.  It climbs hills pretty good in third.The 754 has an extra low first gear. I don't think it will help third gear. I think changing the diff would be a better way to go.  Cheers, Gerry.

[AndyG]

What problem are you trying to solve?  What do you NOT like about the current set up?

[bevans6]

My sense is that he feels he is geared too high, and not getting mid range gears that suit his needs.  Hence the comment that he is doing 83 mph at 2150, which suggests a 3.34 gear ratio, and wanting an extra gear between 3 and 4.  Now, I thought the five speeds were usually an overdrive, which probably isn't what he wants. 

Brian

[luvrbus]

He is wanting a 750 CR final is same as a 740 the DR is the one with the low gear

740              750CR      754CR
3:69             3:19       3:69             1st
2:07             1:89       2:00             2nd
1:40             1:55       1:58             3rd
1:1               1:24       1:25             4th
                   1:1         1:1               5th  


good luck

[sledhead]

sorry I forgot ht754__cr__ . probably would work with less expence and modifacations .but would like to hear if any one has a altrashift plus  10 speed or 13 speed . how well do they work,what price ?? thanks dave

[buswarrior]

Can we get a newer two pedal automated transmission to communicate with a 6V92ta of 1990 vintage?

What version of DDEC do we need?

Anything is possible, with enough ca$h and perseverance.

happy coaching!
buswarrior

[TomC]

Climbing a hill is a function of torque.  Adding extra gears will get you into a better torque area of your engine, but don't expect much more then a 2-4mph increase at best.  If you really want better hill climbing, use that HT740 with the 8V-92TA pumped up to 500hp.  Then your torque will go from around 950lb/ft to 1550lb/ft.  Then you will REALLY notice a difference in hill climbing.  Good Luck, TomC

[rv_safetyman]

I do not have direct information on the UltraShift (two pedal transmission).  However, I have a lot of experience with the AutoShift.

To obtain the automated shifting, the transmission needs to communicate with the engine via SAE J1939 technology.  Supposedly DDEC III will communicate, as it has a J1939 port (as well as the normal J1708).  However, the DD folks could not activate my 1939 port - even with a lot of discussion with the DD headquarters.  I ended up having to buy a DDEC IV ECM.

The AutoShift can be made to work with an earlier DDEC or mechanical engine by reverting to what they call the AutoSelect mode.  Here the driver has to work the throttle to break the torque and match the engine speed to the transmission speed for the gear selected on the control system.  Once that is done, the transmission will make the shift.  The gear selector display tells you which way vary the engine speed for the gear selected.  I have not tried that mode, but I think it would become pretty easy to operate with practice - at least while shifting up. 

For the AutoShift/AutoSelect, you would need the clutch, but would not need the shift linkage.  You would have to make and run the cable to the front.  That is about 6-8 wires and two shielded twisted pair.  Making the cable is pretty straight forward.

There are quite a few AutoShift/AutoSelect transmissions in the wrecking yards, but the Ultrashift is too new to be easily found.  The two that I know that are going into buses were obtained by buying the whole truck. 

I am told that the Ultrashift demands more space in the area that connects to the engine. 

The AutoShift is a bit shorter than an HT740 as I recall.  I think it is wider than the HT740.

Jim

[HB of CJ]

I did not know the 750 CR had close-close gear ratios.  How about that!  Thank you.  Also good knowledge on getting an auto-shift manual to work with an old mechanical Big Cam Cummins.  Thank you.  HB of CJ (old coot)

[sledhead]

wow thanks for your help guys . I think the the 754 cr is the transmission to look for or mabe I should have my trans. rebuilt. As to repower, I like the mpg the 6v92ta ddec 2 has to offer.I use cruise alot and its the hills on I 77,79 on the way to florida each year to visit  my wifes sister that I would like more gears. Bus runs great now , trans. is about the last thing left to redo.  Thanks alot Jim for your help . I could not find much on the ultra shift, any more thoughts would be great       thanks dave                                                                                                                                                                                                   

[TomC]

Keep the HT740-is more reliable (stronger) then the HT754CR.  I hope you believe me when I tell you you WON'T gain much in speed with the 5spd over the 4spd. Enjoy the country side and the 2-4mph slower you might have to go over the hill. Besides-you're only on the east coast-not like the 5-15 mile long grades we have out west.  Save your money.  Good Luck, TomC

[luvrbus]

 Are you sure that bus doesn't have a 741 electronic transmission ?

[kyle4501]

A friend has a MCI with a 8V92. He had the 740 but it was a dog on the hills. Didn't have enough torque to stay in 4th gear & 3rd gear was required, along with the drastic reduction in speed. He replaced it with a 7series close ratio & LOVES it. He told me that it is so much more fun to drive now having the option to drop 'half a gear' when you need to.

The HT754 is rated for 465HP, so you should be just fine with your 6V92. It is also rated at something like 165,000 lbs GVCW, so weight won't be an issue either.

From my own experience, I like the CR transmissions better. 

[luvrbus]

 If you have a DDEC with a 741 the 755 would be the transmission for you