Whats the final on synthetic in the differentials?

Messages
1,513
Location
Peterborough
Hi guys, Whats the final word on synthetic in the differentials? I'm running Lucas 75w90 in my front and rear diff and the guys on the Jeep forum say, conventional is better for the diffs. they say it pulls heat away from the gears better. I'm running the lower viscosity of the two options, and though synthetic would be the best seeing how we see cold winter as well. Any thoughts? The havoline 80w90 is much cheaper than the lucas, Id be happy running it, and just changing it yearly if it was better. The Lucas feels so smooth though, just weather or not it'd run cooler with dino. any thoughts?
 
Messages
446
Location
NV
I like running synthetic in the diffs and everyone I know with my truck thinks the same. I think it came from the factory that way.
 
Messages
1,335
Location
Arizona
If that was true about dino gear oils thats what the racing community would be using. They aren't. Enough said. Any high end synthetic gear oil will give excellent results.
 
Messages
3,338
Location
Kansas, USA
My 00 f150 had synthetic from the factory my 06 ranger did not. Had it manual if I remember correctly. I drained the f150 at 65-70k and it looked better than the ranger's at 5k.
 
Messages
528
Location
Jupiter, florida
 Originally Posted By: ryan2022
Hon the Jeep forum say, conventional is better for the diffs. they say it pulls heat away from the gears better.
No offense to the "jeep crowd" but they spew more incorrect information than any other 4x4 crowd. p.s. I'm part of the land rover crowd and run synthetic in my transfer case and diffs.
 
Messages
14,715
Location
Santa Barbara, CA
 Originally Posted By: firemachine69
 Originally Posted By: Billy007
All F150s coming for the factory are running synthetic in the diffs.
Source?
pretty much all ford's come with synthetic fluid in the rear axles from the factory.
 
Messages
1,010
Location
South East Asia
 Originally Posted By: ryan2022
Hi guys, Whats the final word on synthetic in the differentials? I'm running Lucas 75w90 in my front and rear diff and the guys on the Jeep forum say, conventional is better for the diffs. they say it pulls heat away from the gears better. I'm running the lower viscosity of the two options, and though synthetic would be the best seeing how we see cold winter as well. Any thoughts? The havoline 80w90 is much cheaper than the lucas, Id be happy running it, and just changing it yearly if it was better. The Lucas feels so smooth though, just weather or not it'd run cooler with dino. any thoughts?
The differential running better on synthetic, but personally for this type of application I feel petroleum based synthetic is better than ester-based synthetic due to the stronger chemical bond with the metal and moderate operating temperature.
 
Messages
3,023
Location
USA-Michigan
Here is a quote from a GM Technical Bulletin dated 1999...
 Quote:
Info - Rear Axle Lubricant Compatibility and Usage #99-04-20-001 - (06/18/1999) Rear Axle Lubricant Compatibility and Usage 1988-99 Chevrolet and GMC C/K, G Van and P1-3 Series Models 1999 Cadillac Escalade Built after the VIN Breakpoints (C/K) listed below: This bulletin is being revised to add the 1999 Model Year, VIN Breakpoint information, and additional text. Please discard Corporate Bulletin Number 86-42-04 (Section 4 - Driveline/Axle). gapped....model info This bulletin is being issued to inform dealers about the compatibility and usage of the new Fuel Efficient SAE 75W-90 Synthetic Axle Lubricant, GM P/N 12378261 (In Canada use P/N 10953455), with current axles, and with the non-synthetic axle lubricant, GM P/N 1052271 (In Canada use P/N 10950849), for the rear axles on the above light-duty trucks. Testing has shown that the new synthetic lubricant will chemically attack the Room Temperature Vulcanizing (RTV) sealant. Use only the non-synthetic lubricant, P/N 1052271, in axles using RTV sealant (See 9.5 and 10.5 information below). American Axle and Manufacturing (A.A.M.) has approved the use of the new Fuel Efficient SAE 75W-90 synthetic axle lubricant for rear axles with the following restrictions: All 8.6 inch axles are compatible as originally built. 9.5 inch axles on vehicles built prior to mid-February 1998 are NOT compatible because RTV sealant is used on the cover pans. On vehicles built after mid-February 1998 and equipped with 9.5 inch rear axles, synthetic lubricant, P/N 12378261, can be used because the RTV was replaced with a gasket. Other mid-February changes to the 9.5 inch rear axles include a new cover pan and cover pan fasteners common to other axles. Important The new cover pan is not retro-fittable to the housing of 9.5 inch axles on vehicles built prior to mid-February 1998. A new retrofit kit is available that will enable the use of synthetic lubricant for vehicles built after mid-February, 1998. All 10.5 inch axles prior to March 3, 1999 are compatible if the axle shaft hub seal (RTV) is replaced with P/N 327739 gasket when changing to synthetic lubricant. As a product improvement, this new lubricant has been released into 1999 current production C/K vehicles built after the above VIN breakpoints (Except HD3500 models which use 75W-140 synthetic lubricant, P/N 12346140). It is recommended that synthetic lubricant be used when changing rear axle lubricant for the following reasons: Potential fuel economy Lower operating temperature under severe usage conditions Important You do not need to wash/rinse any non-synthetic lubricant from the axle cavity when changing over to a synthetic lubricant. However, you should remove debris from the magnet and the bottom of the axle cavity whenever the axle fluid is changed. On light-duty trucks equipped with locking differentials, do NOT use a limited-slip additive.
 

ryan2022

Thread starter
Messages
1,513
Location
Peterborough
Too many posts I agree with to quote all of them. You guys are right. I love the Jeep forum, a lot of decent guys, but they are sometimes missinformed. Same can be said for anywhere I guess, BUT even after a LONg drive on the highway yesterday, I could reach down and rest my hand on the rear diff, and it still felt cool. I was really surprised. Thats not scientific I know, I just couldnt see how synthetic could be a bad thing in any metal on metal lubrication. I'm going to stick with synthetic. the LSD operates well, and the Jeep just feels smoother with less effort off the line. My wife noticed, and she didnt even know Id changed the fluids! Thanks again. Ryan
 
Messages
1,992
Location
Windsor,Ontario
 Originally Posted By: peterdes
 Originally Posted By: ryan2022
Hon the Jeep forum say, conventional is better for the diffs. they say it pulls heat away from the gears better.
No offense to the "jeep crowd" but they spew more incorrect information than any other 4x4 crowd. p.s. I'm part of the land rover crowd and run synthetic in my transfer case and diffs.
We also eat our young
 
Messages
528
Location
Jupiter, florida
I off-road with a lot of jeeps and the local 4x4/jeep club. My close friend has a rubicon. As I said earlier, A lot of incorrect information gets passed around in that crowd. No offense or anything. I love jeeps. If only they made the 4 door JK with a bigger engine or a diesel, I would be all over it.
 
Messages
6,917
Location
NH
I always swap my vehicles over to synthetic in the diff's. Never any problems. I don't buy into conventional oil being better for gears than synthetic.
 
Messages
1,992
Location
Windsor,Ontario
Alot of wheeling in water ,then regular fluid is most cost effective ,due to the fact changing it regular is a must.Mostly on highway /daily driver synthetic is better.
 

ryan2022

Thread starter
Messages
1,513
Location
Peterborough
Right on, thanks guys. Its a bit of everything, but no water crossings. Just the nature of a gear oil, I couldnt see why a dino would be better. If there was ever a perfect application for syn, this would be it.
 
Top