Truck axles

[deeretails]

I recently purchased a 1986 Ford L9000 with a 6V92 and an Allison HT740. The truck when completed will be used for toting tractors and related items to and from shows. My question is this, the rear axle is rated at 23,000# and has a Rockwell R170 differential with 4.11 gearing and a Detroit Locker. The tire size is 24.5 and the top speed is about 64-65 mph. I'd like get the top speed to the low 70's, mainly so the engine isn't against the governor when cruising. So I'm looking for a rear end ratio of about 3.70, and I'd like a locking differential. Are there other differentials that will fit this axle housing? I've worked around trucks all my life but never paid much attention to this aspect of trucks. I realize axle spline count and possibly axle length are another variable.

Thanks for your response.

 

[Janicholson]

I recently purchased a 1986 Ford L9000 with a 6V92 and an Allison HT740. The truck when completed will be used for toting tractors and related items to and from shows. My question is this, the rear axle is rated at 23,000# and has a Rockwell R170 differential with 4.11 gearing and a Detroit Locker. The tire size is 24.5 and the top speed is about 64-65 mph. I'd like get the top speed to the low 70's, mainly so the engine isn't against the governor when cruising. So I'm looking for a rear end ratio of about 3.70, and I'd like a locking differential. Are there other differentials that will fit this axle housing? I've worked around trucks all my life but never paid much attention to this aspect of trucks. I realize axle spline count and possibly axle length are another variable.

Thanks for your response.

The Rockwell R170 differential has come in a variety of ratios, including 3.42, 3.55, 3.70, 4.11, 4.33, and 5.86. So changing out the internal gears or searching for that same model Axle is the best/easiest solution. Changing the ring and pinion (at a real truck repair facility would be my first choice. Jim

 

[Vito]

Too bad it's an automatic transmission. Those engines can sign if shifted correctly.

Vito

 

[used red MN]

Too bad it's an automatic transmission. Those engines can sign if shifted correctly.

Vito

That’s the operators that have to “sign” because they went deaf from all the racket. My best guess is that you intended to place “sing” in there for your verb.
To dt, Probably easiest to find a salvage third member with the correct ratio and bolt it in.

 

[caterpillar guy]

First that engine is not designed to run only wide open when traveling. Idling will kill that engine. Tall 24.5's will add about 3mph versus low pro 24.5's What is the over drive ration in the transmission. I can gear to pull the world with a big enough lever or stall it just letting in the clutch in low. With Tall 24's in 3.55 Gear and an .73 over drive will leave you at about 75MPH at 1500 RPM and at 60 around 1150-1200 RPM which is to low for a Deriot engine. They have no lugging ability the reason for the wide open down the raod we didn't call then hill sniffers for nothing. The 71's and 92's both the same. When you get into the Penske engines(60 series) the\n you can set the engine and gearing different more like a Cat or Cummapart set up. That engine needs to run around 1800-2100 to keep going or it will fall on it's face if you come to a mole hill. I have drove plenty of those old hill sniffers over the years before I owned my own. Hauled a 4 axle dump with Sugar beets and that 350 would sing in lower gears but struggle with higher ones and with changing road conditions traffic and stops it never saw only about 11th out of 13 in it. Would also warm up a bit when loaded. Ran about 100,000 or just under loaded and 43,000 with the dirt coming back. Hauled a 3or 4 axle with an old 6inline 71 on a 15 speed would not cross the Z bridge at over about 25MPH starting at the bottom at 50MPH would get to my exit in Bay City at 60MPH no speed demond. The auto is your saving grace in one way and nemesis in the other.
Rockwell axles have weird ratios like 4.11or 3.73 Eaton will have the 3.70 or 3.55. If you have the rockwell axle you will have to stay with rockwell differential gears. The spline is a factor but if you look at the end of the pinion shaft clean the dirt/grease off and look at the numbers on there it will tell you what ration you actually have . Being your truck is close to 40 years old they could have been changed in that time. The numbers will be the tooth count on the Ring and pinion gears. Something like 10and 41 or 10 and 40 not sure the exact tooth count but those are close for what you would have in it for a 4.11. IF you have in fact the 4.11 with tall 24's then you could go to an over drive transmission or if you go to a 3.56 then you would probably need to drop back to short 24's to keep your engine speed up. I took a 9 speed with an R over drive one time and went to tall 24's then changed to a 15spd with the .73 over drive and the engine would struggle to pull right at 60 in 15th the engine on a 350 Cat was in the 1300-1400 range and would struggle if I was loaded. Empty it was fine. So I had to run in 14th loaded with tall 24's. That was just a .80 to a .73 overdrive difference. This is the reason I say you are set right now and maybe able to jump to tall 24's if not there now or with the taller gears drop back to short 24's and be fine.

 

[joeysmith]

First that engine is not designed to run only wide open when traveling. Idling will kill that engine. Tall 24.5's will add about 3mph versus low pro 24.5's What is the over drive ration in the transmission. I can gear to pull the world with a big enough lever or stall it just letting in the clutch in low. With Tall 24's in 3.55 Gear and an .73 over drive will leave you at about 75MPH at 1500 RPM and at 60 around 1150-1200 RPM which is to low for a Deriot engine. They have no lugging ability the reason for the wide open down the raod we didn't call then hill sniffers for nothing. The 71's and 92's both the same. When you get into the Penske engines(60 series) the\n you can set the engine and gearing different more like a Cat or Cummapart set up. That engine needs to run around 1800-2100 to keep going or it will fall on it's face if you come to a mole hill. I have drove plenty of those old hill sniffers over the years before I owned my own. Hauled a 4 axle dump with Sugar beets and that 350 would sing in lower gears but struggle with higher ones and with changing road conditions traffic and stops it never saw only about 11th out of 13 in it. Would also warm up a bit when loaded. Ran about 100,000 or just under loaded and 43,000 with the dirt coming back. Hauled a 3or 4 axle with an old 6inline 71 on a 15 speed would not cross the Z bridge at over about 25MPH starting at the bottom at 50MPH would get to my exit in Bay City at 60MPH no speed demond. The auto is your saving grace in one way and nemesis in the other.
Rockwell axles have weird ratios like 4.11or 3.73 Eaton will have the 3.70 or 3.55. If you have the rockwell axle you will have to stay with rockwell differential gears. The spline is a factor but if you look at the end of the pinion shaft clean the dirt/grease off and look at the numbers on there it will tell you what ration you actually have . Being your truck is close to 40 years old they could have been changed in that time. The numbers will be the tooth count on the Ring and pinion gears. Something like 10and 41 or 10 and 40 not sure the exact tooth count but those are close for what you would have in it for a 4.11. IF you have in fact the 4.11 with tall 24's then you could go to an over drive transmission or if you go to a 3.56 then you would probably need to drop back to short 24's to keep your engine speed up. I took a 9 speed with an R over drive one time and went to tall 24's then changed to a 15spd with the .73 over drive and the engine would struggle to pull right at 60 in 15th the engine on a 350 Cat was in the 1300-1400 range and would struggle if I was loaded. Empty it was fine. So I had to run in 14th loaded with tall 24's. That was just a .80 to a .73 overdrive difference. This is the reason I say you are set right now and maybe able to jump to tall 24's if not there now or with the taller gears drop back to short 24's and be fine.

X2 on don't pull at low rpm with them
Will soot up the liner holes
Seen it many times

 

[caterpillar guy]

Excessive idling will plug them up also. That's the reason they always told driver to drive like they were mad it it. Or to shut their hand in the door first then get in. USed red you funny. Sign because they went deaf.

 

[DWF]

I have several hundred thousand miles, (maybe 5 or 600,000 on an 8-71 back in the late 70's and 80's. No AC then, so summer was at least driver window down. Still have pretty good hearing at 75 years old. Bought a 2021 Western Star dump truck, with a Detroit engine, a very modern 6-71. Very quiet engine.
DWF

 

[Frankmn]

I have several hundred thousand miles, (maybe 5 or 600,000 on an 8-71 back in the late 70's and 80's. No AC then, so summer was at least driver window down. Still have pretty good hearing at 75 years old. Bought a 2021 Western Star dump truck, with a Detroit engine, a very modern 6-71. Very quiet engine.
DWF

Barron County Wisconsin.
My daughter and her husband own Mixed up Staples lake in Comstock. I guess its actually on he Polk county side of the road.

 

[Bob Bancroft]

I recently purchased a 1986 Ford L9000 with a 6V92 and an Allison HT740. The truck when completed will be used for toting tractors and related items to and from shows. My question is this, the rear axle is rated at 23,000# and has a Rockwell R170 differential with 4.11 gearing and a Detroit Locker. The tire size is 24.5 and the top speed is about 64-65 mph. I'd like get the top speed to the low 70's, mainly so the engine isn't against the governor when cruising. So I'm looking for a rear end ratio of about 3.70, and I'd like a locking differential. Are there other differentials that will fit this axle housing? I've worked around trucks all my life but never paid much attention to this aspect of trucks. I realize axle spline count and possibly axle length are another variable.

Thanks for your response.

My truck has a 3.55 ratio on 11r22.5 tires. High gear is direct, and it will do 70 MPH easily. So I'm guessing your figures are in order.

 

[Fritz Maurer]

X2 on don't pull at low rpm with them
Will soot up the liner holes
Seen it many times

How does soot get in the liner holes? By time the piston uncovers the 'holes' , the combustion pressure is zero and the fresh air is rushing in.

 

[Destroked 450]

That truck was geared to cruise 55-60 mph which was the speed limit when the truck was built, 3.70/3.73 will help but you’ll be down to 1600 rpm on secondary roads doing 55 mph, 3.55 will have it running secondary roads in 3 rd gear to stay in the power band of that engine
Locking differentials for those rears are rare and pricy, you’d be best to have the gears swapped in your carrier

 

[used red MN]

Bought a 2021 Western Star dump truck, with a Detroit engine, a very modern 6-71. Very quiet engine.

In actuality, DD-13 or DD-15 shouldn’t be put in the same paragraph as 6-71.

 

[caterpillar guy]

Fritz just let one set and idle all night then go to take off with it and it is loaded up such it will smoke and stumble for a bit till it cleans out some of it. Those ports will fill in . I've seen where they had some in them when changing sleeves on an old 671 inline we had apart one time to change the rotation of the engine so it would go from one truck to another that needed the exhaust on the opposite side . Yes if you have a service book on those engines they were pretty changeable for rotation and the block could be turned end for end in them or another words you could swap ends of the crank in the block. there were a lot of things to do to accomplish that like removing oil galley plugs put the oil pump on the opposite corner of the block and turn oil pan around for the sump in it. Cam on opposite side and end for end. All lots of fun for a young guy at the time. Don't know what the engine came out of now. It went into a 2070 or some such number IH truck so the exhaust had to be on the right side and intake on the left I believe it was. This was all 30-40 years ago now. As for the DD13&15 those around here have a problem with rotting the wires off at the ECM on the engine . I've been in shops when they had to rewire them. they will not pull with the Cat engine either I've driven both engines in same make and model trucks both 379 Pete's. And both up through VA and WV on I-77 probably the most crooked mountainous interstate east of the Mississippi. I would suppose the oil going by the rings and unburned fuel all aid in the plugging as it slowly collects in the port surface then turns to carbon. Those Deriots were the most forgiving engines and the least durable while the Cat was the least forgiving and the most durable. If hired done changing a set of rear end gears will probably cost in the 2-3000 range now days with labor and if changed in his carrier and not set up right will not last long.

 

[Fritz Maurer]

Fritz just let one set and idle all night then go to take off with it and it is loaded up such it will smoke and stumble for a bit till it cleans out some of it. Those ports will fill in . I've seen where they had some in them when changing sleeves on an old 671 inline we had apart one time to change the rotation of the engine so it would go from one truck to another that needed the exhaust on the opposite side . Yes if you have a service book on those engines they were pretty changeable for rotation and the block could be turned end for end in them or another words you could swap ends of the crank in the block. there were a lot of things to do to accomplish that like removing oil galley plugs put the oil pump on the opposite corner of the block and turn oil pan around for the sump in it. Cam on opposite side and end for end. All lots of fun for a young guy at the time. Don't know what the engine came out of now. It went into a 2070 or some such number IH truck so the exhaust had to be on the right side and intake on the left I believe it was. This was all 30-40 years ago now. As for the DD13&15 those around here have a problem with rotting the wires off at the ECM on the engine . I've been in shops when they had to rewire them. they will not pull with the Cat engine either I've driven both engines in same make and model trucks both 379 Pete's. And both up through VA and WV on I-77 probably the most crooked mountainous interstate east of the Mississippi. I would suppose the oil going by the rings and unburned fuel all aid in the plugging as it slowly collects in the port surface then turns to carbon. Those Deriots were the most forgiving engines and the least durable while the Cat was the least forgiving and the most durable. If hired done changing a set of rear end gears will probably cost in the 2-3000 range now days with labor and if changed in his carrier and not set up right will not last long.

Sure it will smoke after idling all night , any engine with mechanical injection will. But that doesn't explain the claim of the ports plugging up.... after all that idling , the engine is, or on the verge of, wet stacking. I say again, no exhaust whatsoever passes through these ports! The only explanation I can offer for what you have seen is running the engine without an air cleaner... if the lower oil control rings are weak, there will be a film of oil in the vicinity of the ports and the dirt will stick to the oil as the air is blown into the cylinder. It's not soot. Soot is incompletely burned fuel ... wet stacking is unburned fuel... neither of which passes through the ports at any time.

As far as all that work you guys did to that motor .... just to make the exhaust fit? A custom-built exhaust from the manifold to the rain cap would have been a fraction of what was spent taking that motor apart. I'm guessing the part about changing rotation was a typing mistake, unless they wanted 13 speeds in reverse.

 

[farmersamm]

My ol' LN will top out at 58mph. Singin' a song...........

Hauling hay out of Texas during The Big Drought of 2011.

I grew up on these things, and small horsepower Cummins motors. Guess it makes me an old guy(sigh)

 

[Cash4Toys]

There is one other option for you to pickup speed/decrease rpm. Find yourself a Spicer 8341 4sp auxiliary. Pretty simple install if you could find one in a truck yet, then you would have the shift linkage and all. 8331 would work, but 41's were way more plentiful. That would give you, depending on which one, D or E, F maybe, but they were made with either .83, .80, .77 and I think one was even .65 , all 4th gear Over drive. I've been around a lot auxiliary, they really work good, 425hp cats and 434hp detroits with auto's and the bigger 1241D behind them.
Detroit's (2stroke) will slobber if idling, or if not worked hard. They draw so much air that don't warm very well. All detroits leak a little oil, the standing joke was, " I hung a picture of Detroit on my wall, had to take it down cause there was oil running down the wall"

 

[Fritz Maurer]

My ol' LN will top out at 58mph. Singin' a song...........

Hauling hay out of Texas during The Big Drought of 2011.

I grew up on these things, and small horsepower Cummins motors. Guess it makes me an old guy(sigh)

Is this you??? I watch that video so much that I got an automatic bookmark on you tube suggestions.

 

[Fritz Maurer]

That truck was geared to cruise 55-60 mph which was the speed limit when the truck was built, 3.70/3.73 will help but you’ll be down to 1600 rpm on secondary roads doing 55 mph, 3.55 will have it running secondary roads in 3 rd gear to stay in the power band of that engine
Locking differentials for those rears are rare and pricy, you’d be best to have the gears swapped in your carrier

Where does this power band start and where does it end?

 

[Destroked 450]

Where does this power band start and where does it end?

1800 and up till it hits the governor which is usually 2100, but I’ve seen some that would go to 2400