ZF 12 speed Transmission vs Allison 6 speed

[MarkofSJC]

I had the opportunity to drive a Newell with the ZF 12 speed transmission, and in many ways it was truely like driving a manual (with a "virtual" clutch). At a stop sign, if you didn't keep your foot on the brake, the coach would roll. It was a little harder to "creep" as small throtte inputs had that "slipping the clutch" feel.

We climbed a significant grade, and it was really amazing to see the transmission shift into what ever gear would keep it at the RPM sweet spot - at times I assumed it was down shifting when it was actually up shifting!

I would really be interested in anyone who has driven significant miles on the ZF 10 or ZF 12 transmissions. With significantly more gears, have you found fuel milage to be any different? In climbing mountain grades can you maintain speed better? Or decending a long grade using the Jake brake do you have more control? I'm told the first service is at 250,000 miles, have they been that robust? Are there things you don't like about the transmission?

I would love any an all comments. Thanks in advance!

Mark

[rheavn]

Mark,
I can't give you any first hand experience with the ZF 10 or ZF 12 speeds. I have spoken with John Clark at Newell who drives many of the coaches extensively. Last time I spoke with him he had driven a coach back from Indio. He seems very knowledgeable. Give him a call and see if he can answer your questions.

[Barry Rooker]

I've driven a few ZF coaches and my own coach has the Allison. The ZF was a temporary transmission for Newell until Allison would warranty their transmission with the increased horsepower & torque after the Detroit 60 was replaced with Cats & Cummins engines. Current Newells come only with the Allison, I believe.

That said, the ZF is great for mountain driving as the Jake Brake is awesome. Otherwise, I've no use for it: slower accelerating; roll back at stop signs; lurching between gears.

[MarkofSJC]

Steve,
Thanks for the great suggestion! I reached John Clark and had a really nice chat with him. I thought I'd share the key points, as they were surprising.

An Allison equipted coach will be 4 ~ 5 seconds faster than a ZF to 60mph, as the drive train is always engaged, while the ZF clutches between gears (actually using the brake retarder on the engine to bring the rpms down to shift faster). The Allison will also have service outlets throughout the U.S., where the ZF will be much more limited in servicing options.

The ZF will perform better on grades (up and down), as it has so many more gears to choose from and the "jake brake" is much more powerful as a result. Mileage advantage may be a bit better on the ZF, but the Allison does lock up the torque converter on overdrive gears, so it's not a huge difference.

As for that rolling back at stop signs on a ZF, that's a driver controlled option. If they push hard on the brakes at the stop and then let up slowly and completely, the front brakes lock "on" and will remain on until you accelerate, which takes them "off" -- but if you don't push hard, they won't lock.

So it kinda comes back to what type of driving style you're most comfortable with. If you like driving a stick with a lot of control, or climb a lot of steep grades, you may be most happy with a ZF. On the other hand, if you live/travel in the flat lands, or like drag racing off red lights, the Allison is your best bet.

[JohnC]

Steve,
Thanks for the great suggestion! I reached John Clark and had a really nice chat with him. I thought I'd share the key points, as they were surprising.


As for that rolling back at stop signs on a ZF, that's a driver controlled option. If they push hard on the brakes at the stop and then let up slowly and completely, the front brakes lock "on" and will remain on until you accelerate, which takes them "off" -- but if you don't push hard, they won't lock.

So it kinda comes back to what type of driving style you're most comfortable with. If you like driving a stick with a lot of control, or climb a lot of steep grades, you may be most happy with a ZF. On the other hand, if you live/travel in the flat lands, or like drag racing off red lights, the Allison is your best bet.

A couple of clarifications:

1. When stopping on an uphill grade with a ZF, apply the brakes sufficiently so that the front brakes alone could keep the coach from rolling backwards, then release the brake pedal pressure to what is comfortable and will hold the coach in place. Do not release the brakes completely as the coach will roll back with no pressure on the brake pedal.

2. The Allison transmission is also very good on steep grades, and depending upon steepness and length of the grade, may actually ouperform the ZF because of shifting lag on the ZF

[MarkofSJC]

Thanks John!
That's an important clarification.
Recently I happened to drive the ZF-12 against an Allison 6 speed, back to back on the identical coach. The ZF was (obviously) in a Newell, while the Allison was in a 45' Beaver Marquis with the identical engine. Even though the Beaver was considerably lighter, it was interesting to see that coach struggle a bit to work up a slightly inclined hill at 50 while the Newell just dropped a gear and pulled right through it.

I guess it's sorta like a bicycle vs a mountain bike ~ they both work, but when you start having a lot of differences in terrain, you want more gears!