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".

[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.

[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.....

[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?

[Ron Sutton]

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 special. Any recommendations would be great. Is there a fluid that would work the best for this kind of abuse..

I'm probably just wishful thinking ... but any chance you shot the diff with a temp gun to have a number? That would help in our discussion somewhat.

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.....

I agree with what Harley said, as my experience is similar.

A few things I've learned about this topic are:
* Too thick of an oil ... increases the frictional losses ... and makes the oil hotter.
* Too thin of an oil ... reduces lubrication ... and makes the oil hotter.
* Too much oil (too high of an oil level) ... increases the frictional losses ... and makes the oil hotter.
* Having a larger volume of oil … in itself … is a good thing … because a larger volume of oil can handle & dissipate the heat better.
* But when that larger volume of oil is in the diff, we’re making the ring gear run through it. It’s like making you run in sand. Your temp goes up.
* Too little oil (too low of an oil level) ... causes lack of lubrication ... and makes the oil hotter.
* An oil with inadequate lubricity ... regardless of viscosity ... which increases the frictional losses ... and makes the oil hotter.
* An oil with inadequate viscosity stability ... breaks down & thins out ... reducing lubrication ... and makes the oil hotter.

So the viscosity ... the volume (level) ... the lubrication qualities (lubricity) ... and the viscosity stability ... of the gear oil ...all play a role

Plus ...
* How hot the gear oil can get & still be ok ... depends on the oil.
* Once an oil has been overheated & experienced viscosity breakdown ... it needs to be replaced.
* All synthetics are not the same. All mineral based oils are not the same.
* A gear oil utilizing a mineral base stock will usually have a significantly lower failure temp.
* A gear oil utilizing a synthetic base stock will usually have a significantly higher failure temp.
* How high or low for both ... depends on the chemistry mixture from the oil company.

So ...
* The actual lubricity of gear oils ... and all oils for that matter ... varies greatly.
* This means the amount of actual friction ... and heat ... varies with each oil's lubricity qualities.

And then ...
* How hot the rear end assembly & gear oil combination can get ... and the rear end internals still be ok ... depends on the internal components.
* Anything made with inferior grade metals ... fails at lower temps.
* A big problem today is most import R&P's are made with inferior steel alloy & heat treated very hard to make them live in normal conditions.
* When we go run these cars hard on track days & autocross competitions. Not "normal conditions.'
* Regardless of how much the R&P is heat treated ... its ability to withstand heat ... is still based in the grade of metal.
* Same thing with cheap import bearings used on the carrier & pinion. Cheaper grades of metal fail at lower temps.
* But before they fail 100% ... they gall ... and this galling creates rougher surface areas ... increasing the heat further ... creating a snowball affect to the point of melt down.

My motto is “Give me Timken or give me rear end failure.”

Furthermore ...
* The clutch material in most posi-traction units don't work well with some/many synthetic oils.
* If the synthetic oil is too slippery, it causes the plates to slip ... like a clutch in the trans.
* Under autocross or road course track conditions ... where the posi clutches are getting worked hard ... this slippage causes heat build up.
* Some synthetic oil companies put additives in their gear oil to make them work well with posi clutches ... most do not.
* Posi Additives mixed in with the synthetic gear oil can solve this issue.
* Regardless of oil used ... the degree of grip/slip posi clutches have ... changes with heat … so the corner exits change as the rear end heats up.
* This is one of many reasons posi's are not commonly used in racing.
* For all their clunks & pops ... the oil temperature does not affect how Detroit Lockers work ... which is one reason why they are so common in racing.

In addition ... everything inside the rear end that generates friction ... generates heat. This includes ...
* The measured area of the contact surface ... and the smoothness ... of every mating surface in the rear end.
* How much contact patch the ring gear teeth have with the pinion teeth.
* How coarse or smooth that mating surface is.
* What the angle of the teeth meshing is.
* How well the teeth mesh. Do the teeth roll across the surface or scrap?
* How big or small the bearings are. Think roller contact surface area times the number of rollers.

Most things are a trade off. GM 12-bolt ear ends have less tooth contact patch area & less gear mesh angle than a 9" Ford. So the 12-builds less heat. But those same differences are what make the 9" Ford stronger. When we choose to run bigger bearing 3rd members ... we're adding strength ... and more friction area.

In professional racing, the degree we go to reduce friction & heat surprises most people. In my race cars we had the ring & pinion gear surfaces REM micro-polished ... lightened the ring gears ... ran angular contact ball bearings in place of tapered roller bearings ... and ran ceramic bearings everywhere possible. All to reduce friction ... partially to free up parasitic power losses ... and partially to reduce the heat in the rear end & therefore the likelihood of avoiding failure & DNF.

Plus this matters …
* In testing, I see typical “non-trick” 9” Fords have 10-12% frictional losses.
* Friction loss & heat generation are directly related.
* More engine power going through the drivetrain creates more heat.
* 10% of 800 hp generates twice as much heat as 10% of 400hp. Twice as much.
* Strain matters. The heavier the car … like most of our PT cars at 3000-4000# … the harder everything is loaded to get it moving. Load creates heat.

A few final points ...
* So our gear oils have temperature limits ... and if we exceed them they fail.
* We need the gear oil that provides the correct viscosity … not too thick or thin … and the best lubricity possible … with the highest failure temp.
* If we’re running a lot of power … we need to look at ways to cool down that assembly … from oil pumps & coolers to polished or coated surfaces.
* Our internal components have temperature limits ... and if we exceed them they fail.
* They need to be up to the job. Cheap stuff fails at lower temp levels.
* I suggest Timken bearings & US made R&Ps … when you can get them. Cryo treat & REM polish them when you can't.

I’m sure I left stuff out. Hopefully other guys with experience will read this and add stuff I forgot.

[Ron Sutton]

As soon as I posted it I see that I left out successful breather/venting strategies. I'll leave that for someone else to chime in.

[silvermonte]

Ron- where is a good website to look up these Timken bearings that you kept talking about in all your threads. Im due to change out alot of parts on my toys and you have me conviced I need to step up to the safer stuff.

[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.