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18 speed

7K views 28 replies 10 participants last post by  Oxbow12 
#1 ·
my Peterbilt dealer is telling me that my '90 Pete came from the factory with the 18 speed transmission. I always thought that the 18's didn't come out until mid-90's. who is right??
 
#2 ·
I could very well be wrong here, but I think they came out before that. However, the higher foot/lb ratings I am sure didn't come out till the mid 90's when the electronic engines came out and started having higher torque ratings.
 
#5 ·
Have the parts dept run the serial number....remove all doubt
 
#7 ·
There should also be a sticker on the cab in the left door frame that shows the drive train specs for the truck, there is nothing majic about 18 speeds, they are just a 13 that splits the bottom range. water haulers and gravel haulers had built their own by pass for the splitter back in the late seventies, I saw them work. A 2050 torque in 1990 I would doubt, a 1650 would have been a lot more common. it may have a 2050 or 2150 clutch that was special ordered. See what the tags say and post the numbers.
 
#8 ·
R series 18618 came out in Nov. '88 production in trucks late summer '89. Rating was 1650ftlbs and short lived. 51/2 years later came 18918 and rated 1850 but held well over 2000lbs with next to no flaws. Big staple to building four digit HP engines. No other trans would hold, and Spicers said good bye ;)
 
#12 ·
Yes it does, just not in current production information,
http://www.roadranger.com/rr/CustomerSupport/Support/LiteratureCenter/index.htm
Click on Interchange Manual - Heavy-Duty Manual Transmissions
when it comes up asking for a pass word ,click on read only then scroll down to 18 speeds the first entry is RTLO14618A. a few rows down is the RTO15618 which would indicat that it was prolly an old style (pre low inertia) fixed main aux type transmission. Also prolly among the first 18 speeds available.
 
#14 ·
You should be ok as long as you keep the revs above 1600 under heavy load in low range. It should be as strong as a 13speed of the same era, My 15715 seems to handle a turned up 3ZJ just fine, the 146 series was common behind 7FB,4MG engines and they would make more power,when the pump was played with.
 
#17 ·
Wonder how tuff it would be to get parts for one. Never seen one in an '85 or even the few years after. Bet it would be quite q find to have a 14618. Woundn't trust it much but behind a 3176 or Detroit 50 it'd be cool. But like you said, have to drive it out of those motors R range. Still cool to know :rock
 
#22 · (Edited)
I now that this is an old thread, but I thought I would just add that I have an RTOF15618 that came stock in my 89 378. I believe that the F must refer to the shifter position, possibly because the 378 is a short hood, and I have a brakesaver? I am going to replace it with an 18918B in order to gain the double overdrive with 4.11 rears. It still works well though. I will probably get dinged on the core charge. The case length is the same on both, but I suspect that the guts are not interchangeable.
 
#23 ·
Yes the "F" is the forward shift opening, you would need a RTLOF to have the shifter opening in the same location.
 
#24 ·
Thanks SmokinCat. So to put in a non-F 18 speed such as an 18918B, would I have to find an F series, or could I just modify the stick. I have a fair bit of room on the floorboard plate where the shifter comes through, but would likely have to modify the stick so that it ends up where it is now and not too far back.
 
#26 ·
Swap your F top cover to the 18918. Problem solved. But shift pattern will be backwards. Against the dash.
 
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#25 ·
The shift bar housing can be changed, better doing that then trying to bend and modify the shifter.
 
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#27 ·
The other truck has a 15 with an against the dash pattern, so I could probably get used to that. After all these years with the eighteen/thirteens I still find myself lost in the fifteen occasionally.

The old 18 has a fair bit of slop in it that I was hoping to cure. Does that come from the parts in the cover?
 
#28 · (Edited)
Most of the time roadranger shifter slop is caused by worn isolators in the shifter coupler outside of the box on the shifter it's self (does that make sense?: the rod that the shift knob threads onto)

the top gear in a RTLO is 0.73, one split taller than a RTO, the down split is close to 0.86 , the same as the over split in a RTO.
 
#29 ·
Thanks Longhood!

So I should be able to rebuild the shifter.

Yea, the .73 is what I am looking for. 1800 @ 65 mph is a bit slow for today's speed limit.

I see that the RTLO 18918A and B are geared the same, with the same case length (33.1 inches). Do you know what the difference is? Just a newer version?
 
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