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Rear Differential Repaired, Fuel economy up!
http://www.lostjeeps.com/forum/phpBB3/viewtopic.php?f=5&t=35906		 Page 1 of 1
Author:  tulsa [ Sun Sep 14, 2008 9:06 am ]
Post subject:  Rear Differential Repaired, Fuel economy up!
I bought my CRD used in Nov '06 with 14,621 miles. The best fuel economy I have ever gotten was about 27mpg. I had a used tracklok installed at 18.5K and oil was replaced with synthetic 75w/145. I took the Jeep in a couple of weeks ago to have the pinion seal replaced. The tech replaced the pinion seal and an axle seal and reported the differential had water in it I don't think I have driven through water deep enough to get water in the differential. 300 miles later the differential was howling, took it back. Nine days later I got the CRD back with new pinion bearing and seal, axle bearings and seals. The tech first replaced the pinion bearing and right axle bearing, found the diff was still noisy and replaced the left bearing. So the differential oil was changed twice this repair. Yesterday I drove to Leavenworth, KS and back. The reserve light came on at about 560 miles. I will be able to make 600 miles on a tank of fuel for the first time. Could the differential bearings make that much difference in fuel economy?

Lewis
Author:  nursecosmo [ Sun Sep 14, 2008 11:22 am ]
Post subject: 
75w/145 Seem like very a heavy lube if you aren't doing heavy towing, especially for synthetic. Did the mechanic put that same weight back in?
Author:  tjkj2002 [ Sun Sep 14, 2008 11:23 am ]
Post subject: 
Quote:
Could the differential bearings make that much difference in fuel economy?
Yes they can.
Author:  tulsa [ Sun Sep 14, 2008 8:56 pm ]
Post subject: 
nursecosmo wrote:
75w/145 Seem like very a heavy lube if you aren't doing heavy towing, especially for synthetic. Did the mechanic put that same weight back in?


I am sure it is. They used Mopar 4874469. I have towed heavy loads a couple of times, look at my avatar.
Author:  Wobbly [ Sun Sep 14, 2008 10:53 pm ]
Post subject:  Re: Rear Differential Repaired, Fuel economy up!
tulsa wrote:
....... Could the differential bearings make that much difference in fuel economy?

Lewis


Timken claims "up to a two percent gain in vehicle fuel economy" for their "Fuel Efficient Bearings". These bearings don't look like they are replacements that can be slapped into an existing axle or differential.
http://www.timken.com/en-us/products/be ... cient.aspx

2% percent of 27 MPG is a little over 1/2 MPG.
Author:  tulsa [ Mon Sep 15, 2008 8:21 am ]
Post subject: 
I managed to go 605 miles on 19.5 gallons of fuel, about 31 mpg. I would have expected 26-27 mpg based on past history. This makes me wonder if many CRD owners are suffering from parasitic drag somewhere in the drive train. I tend to drive very smoothly and limit brake usage, but could not get good fuel economy till this tank.
Lewis
Author:  dgeist [ Mon Sep 15, 2008 9:06 am ]
Post subject: 
tulsa wrote:
I managed to go 605 miles on 19.5 gallons of fuel, about 31 mpg. I would have expected 26-27 mpg based on past history. This makes me wonder if many CRD owners are suffering from parasitic drag somewhere in the drive train. I tend to drive very smoothly and limit brake usage, but could not get good fuel economy till this tank.
Lewis


I have been having similar experience for about 6 months. Economy is down even though I've been driving like a hypermiling grandma... If you're not hearing any noises, how can one check for parasitic drag, though, unless it's the brakes?
Author:  nursecosmo [ Mon Sep 15, 2008 4:45 pm ]
Post subject: 
If the pinion bearing were causing a 2% fuel economy loss the heat that it generated would be very high. I can put my hand on all parts of my differential after cruising for a while on the hwy and it is barely warm.

dgeist. If you suspect parasitic friction loss from your breaks. put your hands on the center of the wheel after driveing down the Hwy for 5 minutes. If you can keep your hands there the breaks are not dragging.
Author:  tulsa [ Mon Sep 15, 2008 9:08 pm ]
Post subject: 
dgeist wrote:
tulsa wrote:
I managed to go 605 miles on 19.5 gallons of fuel, about 31 mpg. I would have expected 26-27 mpg based on past history. This makes me wonder if many CRD owners are suffering from parasitic drag somewhere in the drive train. I tend to drive very smoothly and limit brake usage, but could not get good fuel economy till this tank.
Lewis


I have been having similar experience for about 6 months. Economy is down even though I've been driving like a hypermiling grandma... If you're not hearing any noises, how can one check for parasitic drag, though, unless it's the brakes?


As nursecomo said there should be heat. Until a couple of weeks ago I had very little noise. That said, if the truck was set on jacks and the transmission and transfer case were put in neutral, torque required to start wheels spinning might give some indication. Or spin axle to a set rpm and time till stop and compare to a good mileage CRD. Anybody have any ideas how to compare?

Lewis
Author:  retmil46 [ Tue Sep 16, 2008 11:29 am ]
Post subject: 
Good bearings and seals, along with proper lubrication, can make a noticeable difference in MPG with an efficient engine such as our diesel.

Month or so ago, based on what I was hearing online and from Ranger1, I replaced the driveshaft u-joints with greaseable Gold Seal units from Tom Woods Custom Driveshafts. So far, on the first full tank since replacing them, fuel mileage in mixed driving looks to be noticeably improved. Also got rid of any clunk and jerk when shifting between reverse and drive, or between drive and neutral at a long stoplight - driveline feels nice and tight.

Synthetic lube and lube weight does make a difference, often not noticeable on an internal combustion vehicle. On an electric pickup I have - an '81 Ford Courier/Mazda B2000 - factory lube in the manual tranny and rear end was 90 weight conventional oil. I switched it over to Redline 75W90 MTF and Redline 75W90 Gear Oil in the rear end. That reduced power consumption from the battery pack by nearly 25% on my work commute. Also, when I first obtained the vehicle, the previous owner had replaced the driveshaft and hadn't bothered to balance it, such that it wouldn't even coast downhill and had a bad vibration over 50 mph. After a proper balance job, it would coast forever and range on a battery pack charge dramatically increased.

In short, yes, some attention to the driveline after the transmission will make a difference.
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