Rear end Getting Pretty Hot. Need Help

[rsss2nvy]

I just ran the USCA event in Fontana. It was pretty hot there outside and after running the road course, my ford 9" was super hot. It was puking oil out the vent on top of the rear end. I'm using a heavy duty rear end fluid but nothing speacial. Any recommendations would be great. Is there a fluid that would work the best for this kind of abuse..

[j-c-c]

What power level, track speeds, and differential are you running?

[CTSV]

Mine gets scorching hot as well 389 strange nodular tru trac. I drive my car in the 3-5k rpm range and hard. Looking into a diff cooler now im sure this heat will break down the diff fluid cause failure over time

[raustinss]

What is the ideal temperature for a rear end...or gear oil as I should say.

[68sixspeed]

You might also consider running inboard axel seals to keep the oil from going down the tubes. But only do this if you have sealed bearings on the axels. I was getting a lot of oil puking out the vent even with a hose running to the frame/body before doing the inboard seals. The vent needs to be relocated to the center area as well when doing this.

Sometimes straight axel cars rear ends run hot just from being low on oil in the corners. Also 9" fords are famous for puking out the vent, most people end up relocating the vent higher or using a catch can.

[bryant]

a diff will run at temps close to engine temp under heavy use. this is normal. you can put a hose and a catch can on vent.

[CTSV]

Mine never puked oil i have about 2.25 quarts of 85-140 oil in mine but was pretty surprised at the heat of the housing under there.

Does anyone know what heat range gear oil can withstand before breaking down and becoming ineffective?

[j-c-c]

Reg oils I thought 300F is top end of the range, syns are obviously higher. To the OP, any aero mods restricting air flow, or nearby exhaust issues? I suspect with the typical total powertrain loss (20%?), that lost in the rear end, 400hp?x<20%x 745watts/hp makes the rear end, a pretty decent size heater. I have an electric pump/cooler on my mopar 8.75", which has slightly higher efficiency of the lower effiency ranking 9".

[Ron Sutton]

Mine never puked oil i have about 2.25 quarts of 85-140 oil in mine but was pretty surprised at the heat of the housing under there.

Does anyone know what heat range gear oil can withstand before breaking down and becoming ineffective?

Most mineral based gear oils are good to 240°. Most Synthetic gear oils are good to 280°-300°. But many times the internal components (gears, bearings, etc) fail at temperatures below these numbers if they are made from inferior metals.

When Harley mentioned rear ends running close to 300° & surviving racing conditions, those rear ends have the best components to the nth degree. We ran ours to 280° often with no failures, but we didn't buy crap from the cheapest vendor & throw it together. There is a LOT of care that goes into those rear ends from deburring every edge on the R&P, REM polishing the gears & bearing races, making sure the bearing preload is EXACT, etc. That's on top of buying the every best quality gears, bearings, etc.

I think for most of the ProTouring world, commonly available imported rear end internals will fail somewhere in the low to mid 200's. I do not have personal hands on experience running the cheap-gear-brand-of-the-week in tough conditions, so I can't say at what temp they will fail. So my "low to mid 200's" guesstimate is just that.

[CTSV]

im gonna borrow my friends IR thermometer this week get a decent reading of my axle housing and the oil after a an aggressive drive. I might consider switching to synthetic Royal Purple or Redline.

[shmoov69]

At Putnam Park mine was puking out after about 7 laps. It was so hot that after about 10 minutes of cool down and jacking the car up and all it would still sizzle the brake cleaner I was spraying on it to clean the oil off. I'd say that is pretty freakin hot! LoL!
I was running Royal Purple diff gear oil in a 9" with 3.00 gear and a locker, with the turbo engine set at about 550 at the wheels. For a quick fix, I zip tied a power steering bottle to the vent tube. Worked fine for the rest of the weekend. Now I vented the rear into the roll bar/cage tube, may be a bad idea but it'll allow the oil to expand in it and then run back into the rear after.

[CTSV]

i spoke to Strange Eng today they advised not to run any synthetic oils in their tru trac and eaton systems.

i mentioned about the heat the tech said he has never heard of such a thing which i call BS.

he advised me to try different weight oil from Mobile 1 or Vavoline. I am currently using Lucas 85-140

i will also test the temp when my buddy brings over his IR thermometer this week.

[CTSV]

ok i took a 7 mile hard drive and the rear end housing was 134F the exhaust pipes around the rear were 112F

that was with 2.5 quarts of 85-140 oil Lucas non synthetic

waited 3 hours to cool

i drained the oil and then put 80W90 Lucas non synthetic

went for the exact same drive and the rear end temp went up to 152F


Should i really be concerned or these temps aren't out of the ordinary for a 9 inch?

[shmoov69]

Measure it after beating on it on a road course like before. That is the problem, not the street driving.

[bryant]

150 degrees is normal for diff temps. in my experience, ive seen many premature gear wear from synthetic gear oil. gear sets starting to make noise in under 15k miles. in my shop we use straight schaeffer's 209a 140 wt oil. its really sticky and we have never had a gear oil failure. lucas oil is what we will recommend if schaeffers is not available.

the puking out the vent us usually from the turns pushing all the oil into the tube. ive had some road race guys put vents in each tube then run hoses to the catch cans.

[AMSOILGUY]

150 degrees is normal for diff temps. in my experience, ive seen many premature gear wear from synthetic gear oil. gear sets starting to make noise in under 15k miles. in my shop we use straight schaeffer's 209a 140 wt oil. its really sticky and we have never had a gear oil failure. lucas oil is what we will recommend if schaeffers is not available.

the puking out the vent us usually from the turns pushing all the oil into the tube. ive had some road race guys put vents in each tube then run hoses to the catch cans.

Was the fluid tested to determine it was the culprit in your past experiences?

[bryant]

no testing, but its pattern failures seen mostly in ford f150s and explorers. i first started see f150s that were making gear noise in under 15000 miles around 97 when ford went to synthetic oil. now i do realize that all company's oils are not the same. a few aftermarket limited slip manufactures even say not to use synthetic oil. i have seen amsoil used is diffs from other builders and see no problems with it. we have used schaeffers and had no oil related failures. it a bit over kill but thats what is needed to stand by our work.

[CTSV]

Where can i buy some Schaeferrs moly gear oil to try out?

[AMSOILGUY]

Where can i buy some Schaeferrs moly gear oil to try out?

You'll have to find a distributor in your area I believe. I would think that they would have a locator online.

If you have any interest in running AMSOIL here's a link to our gear lubes. AMSOIL Severe Gear Lube

[HarleyR]

I wouldn't worry about 150 degrees...I would absolutely install inner seals..... And put a baffle near the vent hole in the housing....I rarely have any venting
Problems while running a mine inch for the last
14 seasons.... When run our splitter nearly completely sealed off at places like Michigan and Kansas and gear temps run close to 300 with a cooler.....