18 spd vs 15spd/9LL

The main problem with an 18 in a dump is the constant shifting that most dump trucks see every day. This is rough on the splitter gears unless you drive it like a 9 speed and split only when necessary. Some people want to split practically every gear, which is totally unnecessary. They are really handy though with being able to split upper and lower gears.

The 8LL will give a very low crawling gear, but I don't especially like the wide gear spacing. An 8LL is a 9 speed with deep reduction like a 15 spd.

With a 15 speed the gear spacing is not that wide, and you have a low crawling gear in deep reduction, with progressive shifting all the way up if you know how to drive one.

Just have to make up your mind which way you want to go.

With any transmission you decide on, get the model number and check the lowest gear ratio to make sure you are getting something that will move a load around on soft ground without tearing something out of the driveline.

 

There is a reason why most dump trucks that go off road have 8LL transmissions, they are the strongest set up for that type of application, pit to pit its not a necessity.

 

I like the idea of an 18 speed. I have an 8LL now and love it.
You'd never need to split lower gears I mean you could in boggy ground grab another gear with the flip of the button.

I was hauling 20 tons of rock to a job one day when LowLow didn't seem quite low enough in boggy ground with my 8LL. The 18 speed goes just almost as low as the 8LL. The 18 Speed is 14.40:1 in LowLow and 8LL is 14.56:1 in LowLow.

Then there are long up hill grades I find it would be nice to split the last gears in the 8LL but can't and the 18 will do that.

There's an 8LL hidden inside the 18 speed. The 18 just gives a lot more possibilities throughout the entire range.

I think dump trucks might be a bit harder on transmissions and don't last as long as a road tractor's transmissions. Dump trucks are always delivering in soft boggy or rough ground and over curb's and lots of starting and stopping at lights all day long. Some days not so much.

8LL is my favorite so far but Id trade for an 18.

I skip all unnecessary gears.
If I'm taking off downhill empty ill do 5th, 7th and 8th with Jakes to speed up the shift. Loaded Id do 3rd 5th 7th.or 4th 6th 8th depending on the down hill. The trick to that is let the truck roll far enough to ease out the clutch without ever loading the motor.

There's no way I'm Gonna shift 18 or even all 8 if not needed.

 

550 hp kitty in a gravel truck has enough power to pull almost any gearing IMO. The 15 and 15 rto are different transmissions...an rto will handle an insane amount of torque and abuse, better than 18 speed IMO. I have lots of trucks with a 15 rto, no fancy splitter or bs, just a solid transmission, grab an entire gear at a time, and let the big kitty pull it, it can and will. I heavy haul with trucks with a 550 kitty and 15 rto, pulling 9 axles and gross weights 190k lbs. That is a marvelous engine and stout tranny. You will twist the input shaft in an 18 doing what will never hurt an 15 rto....even if some website claims the 18 can take more than an rto, real life experience has taught me differently.

 

Are you refering to the RTO-14/16915 at the bottom of this link? Versatile 15 Speed

Our Pete 379 Lowboy tractor in my avatar had a 3406E 475 hp Cat and 10 speed tranny that was rock solid.
Looks like the 15 is pretty much the same except it has 5 lower?

 

All the ones i have are old, and the rto version, so could be different than that, not sure.
I was taught how to drive on a 15, and drove them a lot for many years, before the fad was to get an 18. Not saying an 18 is bad, just more problems with them than a 15, and also i think that they are just easier for people to drive is why they like them. Also can be helpful in an under powered truck, since you can split the gears to help it stay right in the meat of the power band. In a 15 you just shift a couple hundred rpm higher if making it pull hard. I still like a 15, don't see the need for an 18 either. But again I may be biased growing up learning how to drive on a 15.

 

It all depends on the input torque rating of the transmission. That being said, a 15 or 8LL can be more reliable just because it doesn't have all the synchro wear an 18 speed would experience from splitting between direct and overdrive all the time.

Me, I prefer the ratio coverage an 18 speed provides off road.

 

On those you only split the lower gears is that right?
Our first lowboy tractor was a 78 International, 350 Cummins and a 13 Speed Roadranger. That's what I learned to drive. That tranny was an 8 H pattern with a low back and left. The top 4 could be split. I've never driven another one of those since we sold that one.

How does over all ratio play into the mix when choosing a different transmission?

19.68 is my overall ratio in the 8LL in my dump truck. I'm thinking if I change transmissions that I'm gonna have to go back with something very close to that over all ratio so I don't have to change the rear end. My rear axel ratio is 4.33. Its slow as a snail in double low and will darn near do 90MPH in OD. I haven't tested that because I don't want a super speeder ticket. I just know how easy it does 75MPH.

My low low forward is 14.56 and believe it or not turning in soft boggy ground with 20 tons without some throttle will stall the engine. That was the 1st time I'd ever double checked to make sure I was in Low Low.

 

I like the low of the 18 as well plus all the options throughout the entire range. Its almost identical to an 8LL but has way more options.

 

Yes, you can split the low gears (one through four). It just comes in handy sometimes when you are loaded on real soft ground where you can't get enough momentum to get rolling fast enough to grab a full gear.

I've had a few trucks with 8LL's but I don't like the big spacings between gears when you are in soft ground or big hills.

The 15 over was one of my favorite transmissions though, I ran quite of few of them behind Mack E6 350 and E9 500's. Those trucks had 4.44 ratio,
My current truck has an 18 double low, double over with 4.30 gears on 22.5 rubber. Will top out at 81 MPH.