SSSOOOOOOO! I was told the other day,,,

That I shouldn't run synthetic oil in a 9" rearend...?? He said they hold too much heat?? Anyone else know of this, or running synthetic without issue?

i've had it in a 8.8 for almost 20yr's,so i'm call'n b/s

this on your truck?

now that i think about it i have it in my race car too...9".

what im getting at is in a drag application you need a heater pad on the housing........ unless you drive it there its not gonna ever generate any heat in a 1/8th-1/4 mile run..... I run motorcraft syn 75-140 in mine beacuse its free......ford uses it in about every diff anymore, Go put a heat gun on the diff in your towvrig after you getbto the track you be amazed at how hot it is.......

richter69 wrote:what im getting at is in a drag application you need a heater pad on the housing........ unless you drive it there its not gonna ever generate any heat in a 1/8th-1/4 mile run..... I run motorcraft syn 75-140 in mine beacuse its free......ford uses it in about every diff anymore, Go put a heat gun on the diff in your towvrig after you getbto the track you be amazed at how hot it is.......

i noticed my 9" in the car was pritty hot when i loaded it at the track back in june.

richter69 wrote:this on your truck?

Yep... The guy told me not that it doesn't get warm enough, but that the 9" rearends can't get rid of heat fast enough and that the fluid will lose its viscocity and doesn't stick to the gears like a conventional fluid... I was under the impression that's why people run synthetics...?

s think the guy that told you that is full of s_it bcause the heat you can get rid of with minimal lubrication is optimum. Actually water is the best but has poor load bearing capabilities. I've always ran 30wt engine oil in a ford 9" rear application. Thinks about it, it gets around 10 sec under heavy load and the rest is idling around in the pit ??

FWIW Mark

ThndrChkn wrote:

richter69 wrote:this on your truck?

Yep... The guy told me not that it doesn't get warm enough, but that the 9" rearends can't get rid of heat fast enough and that the fluid will lose its viscocity and doesn't stick to the gears like a conventional fluid... I was under the impression that's why people run synthetics...?

ask him what rearend gets rid of heat faster than a 9" or is it a 9" gets a rearend hot
nothing wrong with a HOT rearend .

IMO synthetic lubricants are a bonus! If your in a hunt for consistency (drag race), the synthetic lubricants may offer a bit of consistency considering they are not affected by temperature change as petroleum based lubricants. In a drag race rear axle application, make sure the lubricant you choose has good shear properties. I have tried different types of oil in drag race rear axles, a few not intended for this service and have had more than one ring gear assembly fail.

As Mr.richter69 posted, it's amazing how high oil temperatures (rear axle) can get during long duration towing, although a drag race application should not be hampered by high rear axle lubricant temperatures.

Just another two cents,
Dave.

LivermoreDave wrote:IMO synthetic lubricants are a bonus! If your in a hunt for consistency (drag race), the synthetic lubricants may offer a bit of consistency considering they are not affected by temperature change as petroleum based lubricants. In a drag race rear axle application, make sure the lubricant you choose has good shear properties. I have tried different types of oil in drag race rear axles, a few not intended for this service and have had more than one ring gear assembly fail.

As Mr.richter69 posted, it's amazing how high oil temperatures (rear axle) can get during long duration towing, although a drag race application should not be hampered by high rear axle lubricant temperatures.

Just another two cents,
Dave.

These are my thoughts exactly... A drag race rearend, shouldn't get hot. If it's getting hot, there's probably not "enough" fluid in it. IMPO, I think the hard part is getting it warm enough with conventional fluid, hence the need for synthetics.

richter69 wrote:sorry in advance Doug..........

.........Harold, was the hot rearend you saw on a dude or a chic?

Harold doesn't care. I run a syn blend in my 9" with no problems.

Actually, it was a 56 chevy, with the spiders welded, they forgot to refill the housing.

ThndrChkn wrote:That I shouldn't run synthetic oil in a 9" rearend...?? He said they hold too much heat?? Anyone else know of this, or running synthetic without issue?

Well, we ran two cars at the 12 hour Sebring race; neither was a Ford 9" rear but, this seems to be about the gear lube.

Mobil 1 was the sponsor so you can guess where our gear lube came from. I don't really know about HOLDING more heat but, it can sure WITHSTAND higher heat before breaking down, (as normal petroleum based lubes would).
One rear, (the car without a rear end cooler) developed a pinion leak as it got hot enough to melt & distort the front seal. The gears held-up just fine. It was a Tru-Track so, there are a lot of gears.

cool40 wrote:

richter69 wrote:what im getting at is in a drag application you need a heater pad on the housing........ unless you drive it there its not gonna ever generate any heat in a 1/8th-1/4 mile run..... I run motorcraft syn 75-140 in mine beacuse its free......ford uses it in about every diff anymore, Go put a heat gun on the diff in your towvrig after you getbto the track you be amazed at how hot it is.......

i noticed my 9" in the car was pritty hot when i loaded it at the track back in june.

EVERYTHING was HOT that weekend.

The guy that used to build my rearends suggested not to use synthetic unless I was gonna take the time to warm the rearend in the pits before racing. His reasoning was that the synthetic does not get its full shear strength until at operating temperature.

I have been running plain ole Mobil 80-90 in mine last few years and the gears looked perfect when I pulled the cover to inspect them (I started building my own to save money so I wanted to check the wear patterns).