Im looking at a 1996 379 peterbilt with 850,000 miles. Took it for a drive today and its a nice riding truck. It all heavy spec with a drop axle. My question for you is that it has a 8 speed transmission. Is this going to be geared too low or too high for me. im use to 18 speeds and I currently run a mack superliner with a 350. I just need a bigger truck due to heavier equipment . What you guys think. the peter built has a cat 3406 in it.
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Peterbuilt question
- Thread starter cfd511
- Start date
Truck Shop
Senior Member
8LL I take it? Some like'm some don't. If your in the need to move heavier loads--big power or even
medium power the 18 spd are hard to beat for low & slow plus still having road speed. The 8LL is
not a trans for any real road speed, all depending on final drive gearing.
Truck Shop
Senior Member
Depends on rear axle ratios, but I'll guess in the 55 to 62 area.
Tenwheeler
Senior Member
Need transmission model number, axle ratio, tire size and engine rated speed.
Just drive it again and find out.
Truck Shop
Senior Member
Those gear boxes are normally direct in top hole and a few are under. But for generality sake
the 8LL was for dumps/inner city/suburb. Although I know you know that.
cuttin edge
Senior Member
I remember driving an 8LL with high gear towards the dash. Would that make it an overdrive?
Truck Shop
Senior Member
Eaton made a mainly on highway version that did have .74 top gear with a low low of 14.5.
It didn't sell all that well. The standard version was low low of 19.5 with direct in high.
The first model I posted is basically a high torque 13 spd with no top splits, and the bottom
ratios of a 18 spd with no splits, it was not popular because in the middle gears the ratios
between were wide, 450-500 plus rpm drops. The second one had closer ratios, more friendly.
BC Placer gold
Senior Member
Our dump has an 8LL with the high gear - over & back- the tag has been ripped off the tranny so unfortunately don’t know model number.
It is pretty slow for sure…max about 90km/h (52-55 mph). 22.5’s & 5.38 rears.
It is pretty slow for sure…max about 90km/h (52-55 mph). 22.5’s & 5.38 rears.
cfherrman
Senior Member
I've driven a few 8ll and they are a nice trans, not as good as a 13/18 but easy to drive.
Depending on gearing they are nice to drive till you hit the last two holes, which is highway speeds, so if you highway a lot they suck, if not it's not that big of deal. Deep reduction is nice in soft ground going slow.
Higher Gears might have 400 rpm shifts instead of 200 like a 13/18 which at highway matter a lot.
Depending on gearing they are nice to drive till you hit the last two holes, which is highway speeds, so if you highway a lot they suck, if not it's not that big of deal. Deep reduction is nice in soft ground going slow.
Higher Gears might have 400 rpm shifts instead of 200 like a 13/18 which at highway matter a lot.
cuttin edge
Senior Member
I worked for a small company that had 10 or 11 359 Petes. Highway trucks, 400 Cat, 13 speed, don't remember the gearing, but they were a typical highway speed and power truck at the time. Their first 379 had a head gasket crazy 425 Cat, the 8LL with high gear towards the dash, and the same gear ratio as the 359s had. She was a 100 plus mile an hour truck, but still hauled 79,000 pounds of OSB without missing a beat. You almost never used high gear. Next one they bought, went with a different gear set, and I think the 3rd purchase went to the standard shift pattern.
cfherrman
Senior Member
I've driven 10 speeds that had high side towards the dash as well as 8ll, I was always told that meant it was a double overdrive.
Tenwheeler
Senior Member
To have a double over you have to have a back box that is OD. Then the gears in the front of the main case are installed to be OD in high. That makes a double OD. An LL is deep reduction ( Low Low ) in the back. Old ten speeds did not have compound auxiliary boxes, no over drive there.
High was originally toward the dash but then they came out with the X top. That top on those trans made high over and back. Still had to skip a gear on some or all of them. Some were factory and some were made. 9513, 12513, 14613 and mongoloid OD boxes put on 10 speeds and such. Factory ones would have a tag that started something like this RTOO ( Roadranger Twin Countershaft, OD, OD ).
This old dog has a factory Cat and Fuller with a Shaker cut off. Man bought it used and thought the transmission was trash. Nobody could shift it. Did the math on it and it should be able to run out about 120 MPH.
Late 80's Autocars with deep reduction 7 speed OD, 5:17 rears and 11R22.5 tires would run out 68ish? Those 7 speed Fullers, deep reduction with over drive were factory. There is strange stuff out there.
Attachments
cfherrman
Senior Member
Pretty cool info, I've called most of them a 7 speed as you skip low side high gear. I told a bunch of people that and they would use that gear then shift into high side and only go a few mph faster, whatever drive it your way then. Newest was a 94 I think.
In my service a 8ll is better than a 13 because of deep reduction, but a 18 beats every transmission except allisons
Tenwheeler
Senior Member
Cannot drive like that anymore unless you out west. Your still 14 over out there. I became allergic to that when I only had one point left.You fellows and your slow dump trucks ours has a 13 with .74 od I think with 3.73s bout 94 if I recall right. I haven't tried it .... yet
Thought you folks would be more interested in those LL gears for backing up with asphalt or being in the mud and such.
Those deep reduction 7 speeds with OD were actually pretty cool after one figured out how to shift them. You could actually shift 10 gears in progression. Come out of the muck in the landfill and still get along on the interstate.
Tenwheeler
Senior Member
I thought they were 14 series but about the closest I can find is a RTOF13707MLL. That is a 7 speed with a o.76 OD
It was not the pattern on the dash ( which said 7 speed ) but you could start in LL behind R, shift top center, straight back, preselect and shift straight forward, then straight back, horse shoe back to the bottom right. The preselect and go back to the top center, shift straight back, another horse shoe and then shift straight forward.
Some of those 8 LL's will shift out of deep reduction to low the same way and some folks do the same thing in some different gears.
Cheers
It was not the pattern on the dash ( which said 7 speed ) but you could start in LL behind R, shift top center, straight back, preselect and shift straight forward, then straight back, horse shoe back to the bottom right. The preselect and go back to the top center, shift straight back, another horse shoe and then shift straight forward.
Some of those 8 LL's will shift out of deep reduction to low the same way and some folks do the same thing in some different gears.
Cheers
cuttin edge
Senior Member
Pretty well all our tandems have 8LLs except for some automatics. A couple converted tractors have 18s. All the tractors have 18s except for one international pornstar with a 9 speed. They buy new tandem Freight shakers like crazy, but continue to buy used tractors
cfherrman
Senior Member
I never really shifted out of deep reduction while moving, but thought you weren't supposed to preselect it
For what we do seems like it has more then enough down low. It started life as a county truck in Kansas.