Rear Diff Cooler

[phantomjock]

Well, AS long as I'm, at it... (C-3/'78 major mod)

I looked at my newly rebuilt 4.11 (VanSteel and Toms) and the parts to assemble the rear suspension, and thought - well, isn't this the time to add a rear diff cooler. DOOH - shoulda added that to my list earlier! :suicide:
Yep do it now and avoiid a rebuild/mod later.

So, I have a few questiond guys:
1. Can I use the "drain" plug for one of the lines? - Like the feed line to the pump and cooler?
2. Where in the rear cover should the return line go? Above the midway point?
3. Temp in the case - low point I suppose.
4. Electric pump on a thermostat/relay like radiators?
5. How big a pump GPH - any recommendations?
6. How big a cooler? 13 row/15 row?
7. FAN? CFM recommendations (A puller? Shroud?)
8. Thinking at least AN-8 or maybe -10 - ideas?


Any help or advice on any of these is MUCH appreciated!

Thanks, and
Cheers - Jim

FWIW - NO SPARE since 1981! Double mount rear 'glass Spring, electric fuel pomp/surge tank and filter all complicate the mounting. Considering Boom Tubes not rear exhaust.

 

[mrvette]

I have only ONE comment, that being about MY Muncie running cooler and much easier to shift from doing 30 W synthetic engine oil.....maybe 15? years ago for a few years....

now, I have heard that the same oil with GM additives will run much cooler, as was with my Muncie...not so much energy spent whipping heavy oils around ....

NOW, combined with that in FWD vehicles, they seem to take the diffy lube into the same as the ATF now that's still a standard diffy, and so why NOT, what is the difference between front and rear drive on the ring/pinion/spider/side gears???

about POSI, I dunno....but they say friction additives are in ATF...

well, isn't that waht the GM posi additive is all about???

:twitch::smash:

 

[redvetracr]

have you priced a pump capable of moving gear lube?

 

[mrvette]

have you priced a pump capable of moving gear lube?

Dunno what you mean, but I am tempted to run a street test using 30W engine oil and posi additive in my diffy, fore ***** and giggles....

trick is, I don't race, just drive quickly in FLORIDA traffic....

thing is, I not prepared to take a science ANALysis of wear on the unit for the test....

but I BET I could do ATF back there and be fine....

:smash::smash::twitch:

 

[turtlevette]

have you priced a pump capable of moving gear lube?

use a fuel pump. 40 bucks

 

[big2bird]

have you priced a pump capable of moving gear lube?

Dunno what you mean, but I am tempted to run a street test using 30W engine oil and posi additive in my diffy, fore ***** and giggles....

trick is, I don't race, just drive quickly in FLORIDA traffic....

thing is, I not prepared to take a science ANALysis of wear on the unit for the test....

but I BET I could do ATF back there and be fine....

:smash::smash::twitch:

Don't do it. The old Jags used engine oil in the stick trannys. Burned em up. They use 90W on the rebuilds.
The old Chevy constant 4wd used ATF. Burned em up.

 

[big2bird]

have you priced a pump capable of moving gear lube?

use a fuel pump. 40 bucks

"I don't think so Tim."

 

[turtlevette]

have you priced a pump capable of moving gear lube?

use a fuel pump. 40 bucks

"I don't think so Tim."

I could respect your answer a lot more if you gave me a technical reason other than it says "gas" and not "oil" on the label. Remember it doesn't have to pressurize anything, just move the oil slowly say a few quarts or a gallon a minute. That would be enough to exchange all the oil in the diff in a minute. Consider that nobody on this forum will ever get a diff hot enough to require cooling anyway. It's just a cool looking mod.

I kinda like what Roger is doing over on CF. Mythbusting.

 

[Twin_Turbo]

A fuel pump stays running cool from the fuel, now try to run hot oil through it that is much thicker too. I think it won't last or even work. A mocal oil pump or a mech driven single stage scavenge section pump will work reliably. Add a filter and you will need to overcome a restriction. We have a cooler setup w/ gauge and thermo switched pump on the 77. When blasting down the autobahn it does kick in.

As for setup, you need to pull it from somewhere down the fluid level do you have to drill & tap the lid.



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[phantomjock]

Thanks - Great Help

TT -
That's the ticket. :thumbs:
Looks like AN-8 lines on about 1/2inch in/out on the pump. And unless I miss-counted - about a 15 row cooler too. I don't see any fans - just the Ram Air Shroud. BUT the additional fitting left of the lower sump line? Drain at lowest point? Good plan!

VERY HELPFUL picture.

But, now compromises and adjustments - the crossmembers - fuel pump and filter on the forward - and surge tank on the one below the fuel tank.
Ahh - sweet adjustments!

Thanks guys -
Cheers - Jim

 

[shipy59]

when i was a dumb kid i was at a road race event where a well known canadian driver (allan moffat) had an unusual setup under his ford in that he was using another shocky as the pump to move the diff oil through a cooler.I thought it was very clever in that the harder they cornered or the roughfer the track the more it pumped. just a thought,no wires,simple,compact.

 

[big2bird]

have you priced a pump capable of moving gear lube?

use a fuel pump. 40 bucks

"I don't think so Tim."

Remember it doesn't have to pressurize anything, just move the oil slowly say a few quarts or a gallon a minute. That would be enough to exchange all the oil in the diff in a minute. Consider that nobody on this forum will ever get a diff hot enough to require cooling anyway.

Then why not just tap the top inline with the ring gear, install a slim cooler behind it, even with the top and bottom, and run the return to the drain plug. Let the splash of the ring gear pump it out, with gravity return.
Model T's do this, and when the line breaks, the 4 qts are gone in seconds.
No special added pump required.

 

[Twin_Turbo]

when i was a dumb kid i was at a road race event where a well known canadian driver (allan moffat) had an unusual setup under his ford in that he was using another shocky as the pump to move the diff oil through a cooler.I thought it was very clever in that the harder they cornered or the roughfer the track the more it pumped. just a thought,no wires,simple,compact.

Yes, a stewart shock pump, I have a couple of those and will use them in one of my current projects just to see how it goes.

Phantom,

The setup uses brake cooling hose to supply cold under car air to the cooler:

 

[69427]

when i was a dumb kid i was at a road race event where a well known canadian driver (allan moffat) had an unusual setup under his ford in that he was using another shocky as the pump to move the diff oil through a cooler.I thought it was very clever in that the harder they cornered or the roughfer the track the more it pumped. just a thought,no wires,simple,compact.

I like that idea. I've been kicking around trying to come up with a setup that doesn't require a pump. My diff case has a drain plug on the bottom (in addition to the fill plug in the batwing), and I've been trying to figure out a system with a cooler/extra sump and a check valve/ball in one of the lines to allow accel/decel forces to pump the oil into and out of the cooler. I'm still working out the bugs on it.
Right now I'm just relying on the limited track session lengths (generally 20 minutes) and the aluminum batwing construction to conduct out heat better than the original cast iron and steel setup.

 

[big2bird]

I like that idea. I've been kicking around trying to come up with a setup that doesn't require a pump. My diff case has a drain plug on the bottom (in addition to the fill plug in the batwing), and I've been trying to figure out a system with a cooler/extra sump and a check valve/ball in one of the lines to allow accel/decel forces to pump the oil into and out of the cooler.

See post #12. I tell you Mike, the force of the ring gear flinging the oil around would be enough. Just imagine driving around with the filler plug gone.:twitch:

 

[turtlevette]

A fuel pump stays running cool from the fuel, now try to run hot oil through it that is much thicker too. I think it won't last or even work. A mocal oil pump or a mech driven single stage scavenge section pump will work reliably. Add a filter and you will need to overcome a restriction. We have a cooler setup w/ gauge and thermo switched pump on the 77. When blasting down the autobahn it does kick in.

As for setup, you need to pull it from somewhere down the fluid level do you have to drill & tap the lid.

I looked up your mocal pump. I agree there is no need to take a chance using a fuel pump if the mocal is only $180. I might experiment though.

What temp is your t-stat set at and how fast and long did you have to drive to kick it in?

My 456 spins at 5000 on the highway on long trips and it smells hot when i stop.

I wonder if you should put a filter on the suction side of that pump. Mine always has a LOT of metal in it sitting in the bottom and you are sucking the oil right off the floor.

 

[Twin_Turbo]

The filter is on the pressure side, otherwise the pump won't be able to pump the fluid. Just a mesh prefilter before the pump so no trash goes through and a magnet near the pickup in the cover

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[phantomjock]

REAR END Oil Pressure -- What is it?

Got a bunch of work done on the rear cover this weekend.
Got the pickup and returns all drilled and tapped and the temp switch for the pump and a temp sensor for a gauge monitor.

As I was reassembling - mounting the the rear cover to the diff, I got to thinking, If I knew what the approximate pressure of the diff fluid is supposed to be - I could do a "leakdown check" before I remount to the carrier and continue on with the 6link assembly.

Naturally if I mount it all up - and continue with the build - and it leaks -- re dissamble and reseal -- ARGHH! [I suppose the vent will leak some pressure too - but can't I bypass that - finger/tape?]

So the Question of the Hour is:
"What is the oil pressure (aproximately) in the differential?"

 

[big2bird]

Pressure? Aren't you just looking for flow? The vent is to keep from blowing past the seals.

 

[redvetracr]

the older Chevy power books have a small section on cooling a Corvette diff, the GM engineers recommend you drill the rear cover in two places behind the ring gear.

 

[phantomjock]

Right - Flow - But I was thinking if I could just put a "wee bit of pressure" inside the diff - I could spray soapy solution on my seal to check it. But of course there is the vent to contend with. Suppose I could cap it somehow. Definately low pressure - 1 -2 psi minimum, so as not to blow any seals out - just pre check for potential leaks.

I think I've got the plan sorted out. Thanks for all the help.

Cheers - Jim

 

[phantomjock]

Here's the general "scheme of things."
My diagram below shows -12AN, but I went with -10AN. Availability of something to size down to the pump. MOCAL and Tiltons have 3/8" ports and finding a -12AN to 3/8" NPT was proving too much.



BTW - Hope the original owner of the basic image doesn't mind me using it as a "planning tool." Note: the finished bits are a "little different"-- the nature of planning!

Cheers - Jim

 

[Twin_Turbo]

those pumps are good at pumping, not at sucking put it in line irst, before the filter and the cooler but with a small mesh trash filter. Barnes and Peterson have small cone shaped pre filters normally used on dry sump systems, they are perfect for the job.

 

[phantomjock]

TT -
Copy all and Thanks. What say you regarding the pump's vertical location?
Should it be below the pick up point? "On plane" with the pick up - or could I settle for mounting it above the entire rig?
My plan with the check valve is to provide sort of precharge the line - by filling the system and then mounting the pump - so it is always "full"and doesn't require any priming - as they are not self priming. I'm going looking for the Barnes & Peterson filters now. THX!
Cheers - Jim

BTW this is what I have - can't find the Barnes & Peterson:

 

[turtlevette]

I'm going to be curious if you will ever be able to get that 200 degree switch to kick in. I don't think a typical 20 minute track session will do it.

It's all gonna look super cool though.

 

[phantomjock]

turtlevette -
That's a good point - I have no idea what temp it will hit and will be hoping the temp gauge actually gets to read too! A bit of a compromise on it's placement - it's pretty close to max height of the fluid.
Beside any super cool looks - its an important insurance policy on my rear end.

Cheers - Jim

 

[mfain]

As just another data point, I run both a differential (C-3) cooler and a trans (Tremec TKO 600) cooler. The big advantage of the diff. cooler is a significant increase in fluid volume, which in itself helps cooling. I run the pick-up line off of the bottem of the case in the low trough below the pinion (drilled and taped for a fitting), and I spray the return oil on the ring gear AFTER it makes contact with the pinion. Some experts say if you spray the lube between the pinion and ring gears, that it will cause the gears to push apart on contact. I run a pre-screen, a Tilton pump, an 18-row cooler, and no filter. The diff. vent runs to a catch/fill can mounted above the rear end. The Tilton pump is a low volume/low pressure pump designed to move hot, thick fluids. The top of the cooler is just above the top of the diff., and it has a 10 inch Spal fan (pull). Air is ducted from side scoops through two 3 inch hoses to a receiver duct in the trunk. Exit air is ducted through a nozzle that exits through a screened area where the license plate goes. The trans. cooler uses a Tilton pump, a pre-screen, an 8-row cooler (no fan), and lots of -10 line. The cooler is also mounted and ducted out the rear of the car.

 

[phantomjock]

Great tips there

mfain -
CATCH CAN - yep! gotta add to the projo-now. Did you just slip a tube over the vent - or replace the vent and use the catch can as the new vent? That seems like the best approach.
Was thinking the same idea - air exit through the License plate - but hinging the plate at the top -- sort of 007-style That exit is well shown in your pics in the gallery - but nothing on the low mounted pickup. Considered that - but ruled out for ground clearence.
Again Thanks - more work to do.

Cheers - Jim

BTW - which ftrs when & where? - me phantoms - LUF/BIT/RMS/HST/OSN/HST/GSB...

 

[mfain]

Jim,

I over-drilled and tapped the old vent tube hole and installed an AN fitting for the line to the filler/catch can (it is a Peterson part). It is mounted directly above the third member and is accessible from the trunk. I had to use a 30 degree fitting to clear the crossmember, but it worked okay. The third member in my older photos is a 4:11 "place-holder" -- I haven't installed the Tom's unit (3:08), but I will drag it out and take pictures of the cooler in/out fittings. By using a 90 degree fitting on the lower port, ground clearance wasn't a real issue.

 

[mfain]

Jim,

Missed your last question -- I flew F15s (1985-1997 @ Eglin, Nellis, Bitburg, Mt. Home), F-5s (1979-1985 @ Nellis), and F4s (1974-1979 @ Eglin, Kunsan) and after I retired, A4Ns for a civilian contractor. Also 02s at DaNang.