Rear End Coolers

[billymanfroy]

I was told by my roundy-round engine builder that I absolutely must run a diff cooler or I will smoke my 9" w/ spool and 31 spline axles. He actually laughed at me when I told him we don't run one. I'm running a C6, 35s, and 500hp. Truck weighs about 3500 lbs. I have never noticed a diff cooler on an off-road vehicle. Anyone have any experience with this?

Thanks in advance.

Billy

[johnnyweb]

whats up billy, ive never seen one on any trophy truck or pro truck etc before. how do you pump fluid threw the cooler? the 31 spline axles may become an issue know that you got rid of the chainsaw motor! how is it coming any way? i would procede with getting the truck done and worry about a rearend cooler later. i think a rearend cooler for your suburban would be in order before the race truck. 35's will be a nice addition. we have been cycling our suspension trying to get some bigger tires on our truck. we are pretty muck stuck with 33/10.50 in front without moving the shock mounts. we were able to go to 33/12.5 in the rear. we are also going to run a/t in parker do to bad sand washes. how do the gooryear a/t's work in the sand? were do you guys work on your truck at i would like to come check it out.

[Kritter]

tell him he's smokin some good stuff....you arent a roundy round and you wont be spinning that thing high enough for long enough to need a cooler.

[billymanfroy]

Thanks guys, that's what I thought.

Johnny, here's an example: http://www.manguspumps.com/rear.shtml

http://www.manguspumps.com/images/products/pumprearendbig.jpg

Weaver Bros. and others also make them, but they sure don't seem like a good idea for off-road! I also heard of one that is a pump that gets cycled by the wheel travel (no belts, etc.)

[jeff]

I don't think horsepower has anything to do with rear diff fluid temperature. The faster those gears turn the more heat they generate and in roundy round racing that can be a problem. IThe average off-road dudes and dudettes are lucky to average above 50-mph in the dirt so I don't see how a diff cooler would help you. I'd worry more about snapping a 31-spline axleshaft with the new motor long before I worried about cooked diff fluid in a 9".

The rear diff in my wifes WRX holds less than 1 quart of fluid yet it can handle extended cruising speeds of 110mph+ I say if that little thing can handle it with such a small amount of fluid (right next to the exhaust too) I doubt your rear end will ever have a temp problem.

Aloha

[KitRacer]

At the Leduc swapmeet a few years back Riviera had a diff pump for sale that they had used on their TT. It was like a small shock that conected to the lower link way farther up than the shocks. They said it was not needed on their TT

[Dave_G]

RE:"I don't think horsepower has anything to do with rear diff fluid temperature"

A lot of the heat generated in the rearend comes from the pressure of the tooth loading between the ring and pinion gears. Increase the horsepower and those pressures go up and so does the heat. But dont worry about a cooler in an off road truck. Just make sure you get a good run through a water or mud puddle and splash some cool mud on the diff once in a while and everything will be ok. http://www.race-dezert.com/vb3/attachments/old/images/graemlins/wink.gif

lol

Dave

[UndercoverFab]

very few roundy rounders run diff coolers, we`ve ran 3300 pound dirt modifieds with 800+ horse big blocks over a hundred laps on a mile track and never had any diff problems, unless your taking your truck to talladega i wouldn`t use one http://www.race-dezert.com/vb3/attachments/old/images/graemlins/smirk.gif

[ntsqd]

Billy, Put some Tempilaq paint on the diff housing below the oil level if you're worried about it. Try Pegasus Racing for that. Different colors indicate different temps. Much above 250f and I'd be looking at a cooler.
Tilton makes an electric pump for this. Keeps the thrown belt possible issue of that pic'd pump a non issue.

[TimHayosh]

I used that Tilton pump to cool my class 9 (!!!!) tranny. It works well. It'll suck a few amps, and make some noise (depending on how itt's mounted).

I agree with Thom. Find out how hot the diff is actually getting before following the advice of a left-turn-only type.

[billymanfroy]

Thanks guys. We used to monitor the rear end with an infrared gun, and I don't think it ever got up to even 200.

I read something once that said any increase in HP at the crank means you get roughly 1/3 the horspower to the ground, 1/3 to the exhaust & radiator, and the last 1/3 gets lost in friction in the tranny and rear end. Thier point was that even if everything else stays the same, a small increase in HP will heat up everything a lot more and sometimes cause problems you never had before. An abundance of horsepower is something we've never tried so I'm a little lost! lol

We're pretty much expecting the rear end to explode (at least the axles and/or the 7.50 gear) but I'm spending our money now on just geting it running again. I'll pave that bridge with $100 bills when I come to it.

Billy

[Kritter]

Why run 7.50s which have a low life when you have all that HP? You should be able to get away with something in the 4's if you have a lot of HP. My ranger was fast enough with 4.56s and 160 HP!

[billymanfroy]

You have to remember we were also doing short course, and I don't need a 225 mph top speed for that. Even with the 7.50s we got creamed off the standing oklahoma land rush start. a 200hp 4cyl with a C4 is frustratingly slow below 3,000 rpm. people with 4 cyls closer to stock and a stick could beat us, and any mildly done V6 with an auto or stick would also get us off the line. They're all getting a face full of rocks next time!!!

We are probably going to around 6.00 with the gear and 35s for the desert to keep the revs down below 7200 in top gear at 120 mph (on paper). Our new motor supposedly can go over 9,000 rpm all day long, but why torture it if you don't have to? With a taller gear, we'd be going 60 mph in first, and that's no good either.


Oh, and they're never fast enough! lol

Billy

[R_TAYLOR]

my brother is trying to talk me into this cooler for the diff. Theres a guy down here that ran a fast stock car and he swears by it. Im afraid its one more part thats going to fail especially in our conditions. Swebco is a good lube

[hoeker]

run good oil and deal with the heat! remember thick oils cost HP!

[ntsqd]

I'd be REAL cautious about that 9k all day claim. I doubt you've spent that kind of money (Starts in mid 5 digits).

SwepCo; South West Petroleum Company. Pretty good dino oil, don't know if they've now got a synthetic. Since Redline is literally in your backyard......

[NicksTrix]

you can now run a internal pump in a 9" gear. adds quite a bit more expense than the external pump set up.
the internal pump is a pretty slick set up. if i recall it's about an extra 1100 bucks per gear.
for what you do, run a good gear lube, set the gear up right, monitor your temps and you should be fine.

[FABRICATOR]

There have been quite a few coolers on IRS cars. The reason is extra heat and easy plumbing. A transaxle gets extra heat from the engine. It also does not get much free flowing air because it is usually buried in the car and sits above a skid plate. A solid axle for off-road does not need a cooler because it gets lots of air and the duty cycle is not high enough. In a TT, there is plenty of power to create plenty of heat but the off throttle time is enough to allow cooling. Eventually coolers could be a necessity if we keep going faster and keep using ring and pinions for the final drive. Reliable plumbing is not easy for a solid axle and any leak would be disastrous. BTW, Ford rears are stronger and run noticeably hotter than other gear designs because of their lower positioned pinion gear. This increases tooth contact area, but also friction and heat.

[ntsqd]

Food for thot:
The man who repairs nearly every Keith Black block after it's been windowed on the dragstrip has a dual Paxtoned big block Dodge in his LSR's old tow rig. That thing used to EAT Dana 80 axles. Lotsa HP + lotsa weight = muy feo parts. He made a new inspection cover that holds an additional ~2 gallons of oil (unsprung is not an issue). This cover also has vertical tubes running thru it like those auto trans pans, only bigger. He has turned the inspection cover into an oil cooler. Not a hugely efficient cooler, but might be the difference. No reason a 9" housing couldn't have a similar mod if it proved needed. Could even use flexy hose to duct scooped or blown air thru the tubes.

[billymanfroy]

We actually talked about ducting some fresh air over it last night. That would be simple, cheap and probably enough insurance judging from everyone's responses here. We're thinking the bracing for the 4-link might be a bit of a heat sink, too. I appreciate your help, guys.

Billy