Hi,

I am currently in the market for a used Peterbilt. I came across one I liked on truckpaper, and in the details, it was stated that the transmission was a 10 speed but could be converted to a 13 speed? Anybody, now if there is any truth to this, and if so, what is involved in converting the transmission to 13 speed, and the associated costs? Thank You.

I do believe you can add the overdrive section from a 13 speed onto a ten,I know when I had mine(13) worked on my mechanico pulled the OD unit off and vaugly remember him saying how easy it was to convert a 10 to a 13, I am sure there are details involved try a gear shop or pick up a trade magazine and find a trans shop and call. If you like the truck and it's all good except the trans get it, I am actually kind of sick of my 13, I drive local so I split em alot,and it howels in OD on the freeway. I know that some guys have a dampner on their shifter to cut some of the noise.

You can convert a 9 speed to a 13, or a 13 to a 9 speed.

To change a 9 speed to a 13, you add an overdrive splitter box onto the rear of the transmission, add a splitter button and air lines, and shorten the drive shaft.

You do the opposite to make a 13 a nine.

It won't work with a 10 speed. You either have a 10 speed direct, or a 10 speed overdrive.

You can drive a 13 exactly like a 9 speed, and never split any gear except the highest gear.

You can get an extra gear out of a 13 speed that a lot of people don't know about. When changing from 3rd, instead of going to fourth, change the range selector to high, and go into the low position(where 6th is on a 10 speed). Then you can split that gear to overdrive, and split each gear all the way out.

Most people won't need the extra gear, but in the old 318's and 250's you needed every gear you could get taking off up a hill.

Stranger, your post actually got me to go out to my truck and drive it around the block to try that "new" gear. Ironic, but I never thought about it before.

Now for my hijack.....

Can you convert a 13 into an 18 speed?

Eaton's convertible 9 speed transmissions (RTOC-1X909A) can be converted to either a traditional 13 speed (RTLO-1X913A) or a 9 speed "Top 2" (RTLOC-1X909A-T2) that shifts like a 9 speed but automatically splits between 2 O/D gears on 9th (.88 or .73). The 9 and 9 Top 2 transmissions have 14.38:1 overall ratio coverage while the 13 has wider 16.86:1 overall ratio coverage.

Probably could but you wouldn't have the same ratio coverage as you'd get with a traditional 18 speed.