Hot Rear-end
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Senior User
Joined: Aug 2004
Posts: 350
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From: central MN
Hot Rear-end
What's to hot for a rear-end in a 06 6.0L pulling 6000lbs? I have been getting an hot oil smell when I get out of the truck after pulling. Today I crawled under her to investigate and I couldn't even hold my hand on it. The truck has 41000 mi on it and i'm not sure if this is normal. Any info would be greatly appreciated.
thanks,
jason
thanks,
jason
Fleet Mechanic
Joined: Jul 2005
Posts: 1,470
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From: Staten Island, NY
There was a question on one of the forums a few months back about this so I did a little checking. I ran my 350 on the interstate for an hour or so and then checked the rear end temperature with an infrared non contact thermometer. The outside air temp at the time was in the high 30's and the rear end was 140. Hauling a load or lower gearing (I have 3.73's) would raise the temperature somewhat. It will also be hotter in greater ambient temperatures. Most differential temperature gauges go up to 220 to 250. I would think anything up to about 200 would be OK. Synthetic lube is usually good to 250+.
Just remember, for most people anything over 150 is too hot to keep your hand on. You really need to measure the temperature immediately after stopping with a good thermometer.
Just remember, for most people anything over 150 is too hot to keep your hand on. You really need to measure the temperature immediately after stopping with a good thermometer.
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Senior User
Joined: Aug 2004
Posts: 350
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From: central MN
Thank you for the info. It makes me feel alot better about the temp. I did check the level yesterday and it was a 1/4" below the fill port, which should be good. I might have to do some more investigating on the smell, maybe the transfer case. I also have guages so I know the tranny is ok, besides a harsh down shift when in tow haul.I braught it to the dealer for that but they could not duplicate. The tranny slams really hard at about 28 mph when towing and coming to a stop, but not all the time. Any ideas?
Again, thanks for all the info. This site awsome.
Jason
Again, thanks for all the info. This site awsome.
Jason
Fleet Mechanic
Joined: Jul 2005
Posts: 1,470
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From: Staten Island, NY
Tow haul does firm up the gear changes and also raises the rpm at which they take place. In addition, it keeps the torque converter locked which provides more compression braking while decelerating. Usually you can barely hear and feel the downshifts when coming to a stop. In tow haul they are a LOT firmer with a bunch of compression braking behind them. It sounds like everything is pretty much normal.
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Senior User
Joined: Aug 2004
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From: central MN
The down shift that I am feeling is more like getting rear-ended. When it does it really hard I can feel the anti-lock brakes activating and the brake pedel goes further to the floor. Is there something ford can put on the truck while I'm driving it to record what is happening since it only does it with a trailer on it, in tow-haul, and not all the time.
Fleet Mechanic
Joined: Jul 2005
Posts: 1,470
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From: Staten Island, NY
Maybe you are being rear ended. Are you using a fifth wheel? Is everything tight? Most importantly, are your trailer brakes and the brake controller working properly? If the trailer brakes or controller are intermittent, you're being rear ended by 6,000 pounds.
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Posting Guru
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From: Monroe, MI
That was sure a dirty trick to play on us! But also a good way to grab our attention. All that talk about a hot rear end 
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Joined: Sep 2006
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From: Santee, CA
Mine does this also, I think is normal. The trans has some steep gears at that speed, is being forced to downshift, and the torque converter is being held locked up - all with a significant weight pushing. The first time or two that it happened, my wife even asked What was that?? I had to explain to her, then got the deer in the headlight look.
The other thing that comes into play in the Tow/Haul mode is that if you are off the throttle, and tap the brake, the controller interperates that as needing to slow the truck so forces a down shift. Try this sometimes, on a long highway downgrade in Tow/Haul mode if you are off the throttle and especially if you are gaining speed, tap the brake and it should downshift automatically. Really helps control downhills pretty well. The bow-tie Allison does this also and is one of its selling points. Don't know why Ford has not stressed all the advantages built into the TorqueShift.
The other thing that comes into play in the Tow/Haul mode is that if you are off the throttle, and tap the brake, the controller interperates that as needing to slow the truck so forces a down shift. Try this sometimes, on a long highway downgrade in Tow/Haul mode if you are off the throttle and especially if you are gaining speed, tap the brake and it should downshift automatically. Really helps control downhills pretty well. The bow-tie Allison does this also and is one of its selling points. Don't know why Ford has not stressed all the advantages built into the TorqueShift.
Senior User
Joined: Sep 2006
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From: Santee, CA
The rear end temp has also been a worry of mine, because of the load and work we put these truck through. While I have not yet done it (did on a previous truck), I will be adding a Trans temp guage. I will also add the same sender to the rear end and wire both senders to a small switch next to the gauge. That way I can actually monitor both temps (though not at the same time). This is a cheap and easy way without adding a second gauge. You may also want to consider this.
Post Fiend
Joined: Jun 2004
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From: Parker, CO
Originally Posted by wiingnut
That was sure a dirty trick to play on us! But also a good way to grab our attention. All that talk about a hot rear end
Hotshot
Joined: Dec 2006
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From: Melbourne, Ky
For differentials to get hot enough that you can't touch them is not uncommon, especially after a long trip or working it by hauling something or towing. If you can't touck it, that shouldn't be a concern. If it will boil water, or is smoking, then you most likely have a problem somewhere.
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Joined: Sep 2006
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From: Santee, CA
The issue with the filler hole is that it is by design above the fluid level (fluid at the bottom of the hole. I used the drain plug for the sender location. It was actually the same type/size, just made more sense to have the sender completely in the oil rather than just at the surface.