i heard a pitch about the truck having a convertible 9 speed and its very much like a straight 10.

What is a convertible 9? And is it like a straight 10?

 

A convertible 9 speed is a transmission that can be converted to a 13 speed without much fuss. The 17% splitter gear unit is already built into it, it's just not hooked up. Essentially, it's a 13 speed transmission that you can't drive as a 13 speed unless the extra required parts (airlines, shift knob, etc) have been installed.

 

So this is what the shift pattern is?


R/R 1/6 3/8
--------------------
Lo/5 2/7 4/9

 

Almost. With a 9 or 13 you don't get to use the high range of the low hole, or you can but it may only work once. :lol:

R/R 1/5 3/7
LO 2/6 4/8

Or as a 13 speed
R/R 1/ 5L/5H 3/7L/7H
LO 2/6L/6H 4/8L/8H

 

AHHHHHH :shock:

at the school I went to they called it the 8 speed.

or is there actually a 8 speed transmission?

 

A traditional 9 speed is more of an "8 speed plus low". Nearly all 9 speeds follow that pattern, however Eaton at one time made an R ratio "performance 9 speed" that was a true 9 speed, you repeated 4 gears for the first 8 speeds and had a 9th gear that only worked in high range which was overdrive.

Here's the pattern:

R/R 3/4 7/8
1/2 5/6 9

There are 8 speed transmissions which are like traditional 9 speeds without the low hole, just 4 forward positions with range change and reverse. Those kind of 8 speeds are popular in medium duty European trucks and buses. Scania, for example, offers both an 8 speed and an 8 + 1 that is like our traditional 9 speed. ZF offers an 8 speed that is based on a non-repeating pattern, meaning it has 8 positions plus reverse.

R 1 2 3 4
- 5 6 7 8

The ZF box is popular with bus manufacturers.

Dual range 8 speed transmissions are available in the US as well but you don't see them very often. Most fleets just went with a single pattern 7 speed if they didn't need the coverage of a 9 or 10 speed.

 

There is also the 8LL which is just like a regula "9 speed" but it also has a super low reduction box (instead of a splitter). The naming of these transmisisons follows no set rule, it is more of just a given name to identify it than anything.

Birken

 

That's a good way to put it.

Two more examples:

Eaton used to make the 6613 which was a 10 speed with double reduction on low which gave 15 separate ratios but only yielded 13 succesive ratios due to the overlapping of ratios. OTOH, they also made their "15 speed transmission" the same way (10 speed with double reduction) that yielded only 12 successive ratios. :lol: