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Topic: Pre-load springs in differential

in Forum: C3 Driveline Components


Pre-load springs in differential

Posted: 6/14/05 10:16am Message 1 of 9
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Virginia City, NV - USA
Joined: 1/19/2005
Posts: 314
Vette(s): 1979 Coupe, white in color

Here are some thoughts regarding the springs in a differential. The springs are there to preload the axle gears so under certain conditions, both axles will rotate. The intention of a limited slip was to provide traction in poor conditions.  It doesn't always work well, since you can have one tire spinning and the other one still. The method to lock the axles is to lightly apply the parking brake. The springs, even the heaviest ones, don't apply a lot of preload. A little bit of biased axle torque will overcome the pre-load. The reason you hold the ebrake is to allow the spider gears to apply torque to the side gears. The way the spider gears work in any differential is when they rotate they apply outward pressure on the axle gears. If you have a clutch type differential, the outward pressure compressed the clutch pack between the axle gears and the differential case. So the lock up comes from the input torque from the spider assembly, not the pre-load springs. The more torque applied, the tighter the clutch pack can compress. What the springs do in most cases is make the rear snap and pop  when cornering under light throttle pressure. There's not enough torque to lock the axles. one axle needs to turn faster than the other. The springs are the reason the additive is required so the clutch packs don't bind. If you remove the springs, the rear can behave like an open rear under light throttle and perform to its intended capacity as a limited slip when you put the hammer down. It's more benificial to run without the springs as long as a lot of snow and ice driving isn't done. This is almost a verbatem post from an other site. (call me a plagerist if you will-lol) The reason I'm posting it is to see what our fellow members have views about this. The person who posted it on the other site appears to have his stuff together in all his posts. Seems to make sense to me. I purchased heavier than stock springs for my differential overhaul, and I can see that the amount of torque that even a tired L82 can produce would easily over come the spring pre-load. So, come on all you gearhead, weigh in on this one!

Pumps38517.4297337963


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Pre-load springs in differential

Posted: 6/14/05 8:01pm Message 2 of 9
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Duncanville, TX - USA
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
Pre-Load.There is a reason its called that! The springs put enough tension on the axle gears/clutch packs to keep them engaged all the time. While it is true that the more torque you feed it, the harder it clamps,(to a point) taking the spring assy. out will do nothing but make it a regular open diff., and wear the clutches out really quick. It will also create more clearance in the axle gear-to-carrier, which will create a 'clunk' on accell & decell.
btw....who uses the parking brake to do a burn-out, or get out of being stuck in mud, ice, or snow? Adams' Apple38517.8358333333


Joel Adams
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Pre-load springs in differential

Posted: 6/15/05 9:42am Message 3 of 9
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CUYAHOGA FALLS, OH - USA
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The idea of the parking  brake is to create drag at a spinning wheel to cause torque to be be applied to a non-spinning wheel.  This works to a limited point, and is worthless with a properly functioning posi diff.  It's also very tricky.  To little application and it won't help enough to do anything.  Too much and the car won't move due to brake application.  You can't judge one situation to another, due to varing traction conditions.  It's a bit of a crap shoot.  Granted you can make slight variations, and may have some success, but it's limited.

A road race car usually has a open diff.  This cuts drag on corners and allows the car to corner faster, and more stable.  But it will not have as much traction on acelleration or slipperly surfaces.  But that is not the condition where most of the operation of a road racer is driven.  Typically they are dry, and at speed.

The posi can double the amount of torque applied to the ground on launch.  If a tire spins, you lose torque.  With a posi, you must apply almost twice as much torque to break twice as much rubber loose.   Spinning tires may look cool, but they don't make the car go forward.

Posi supples more traction in almost any situation.  Almost.  In a hard corner the posi can grab with hard acelleration, and cause BOTH wheels to spin.  This means there is NO traction at the rear of the car, and it can slide sideways uncontrolled.   With an open diff, only one tire will spin, and the other will supply traction to prevent the sideways slide, so it's easier to control for the untrained or unexperienced driver.  This does not mean you can't slide an open diff sidesways, it's just harder.

Removing the springs can make it act like an open diff at low torque.  But it will also require more traction to make it lock up, if it ever does. On dry pavement with hard acelleration, it will lock.  But this does limit it's operation.  No springs will create a lot more traction loss at accelleration under that point, including mud and snow.  In slick conditions, snow, ice, mud, wet, the torque required to lock the diff is far less than required to break one tire loose.  Once a tire spins, torque is lost, and the posi won't lock at all with out the springs.  This means you are stuck and going nowhere.  With the spring in place, both tires grab, and you go.  This puts the very tricky, very poor parking brake method to shame.

Some people without the understanding of how thier car handles perhaps should NOT have a posi.  This is only providing the car has enough power to break the tires loose with the posi.  For almost anyone here this is not true.  We have enough sense to let off the gas a bit if the car goes sideways on a turn. Some people don't.   Most of them don't own cars with posi, so it works out.

Why disable or restrict something that with a bit of common sense will almost always help you, only to use an inferior method to attempt to do the same thing?  Oh and by the way, create more wear in the process.

With the correct lube, the clutches will not crack or pop on turns.   Who would buy a new car doing that?  There are many cars with production posi.  Some are performance, some are not.  Many of the old rear drive station wagons had posi to help when towing the family camper, boat, or just the extra load the wagon would hold.  Many people had them and never knew it.

I personally would prefer to have a properly working posi in every rear drive car I drive.  Granted, that's not for everyone.

So what do I think?  I think the guy who removes the springs has too much time on his hands, and sits around thinking up odd stuff.  It is not sound logic when considering all aspects.  It may work for very limited applications, but your maintance is bound to go up.  And once the wear is there, the popping and cracking is back, or you have lost the posi effect completely.  Overall, it's a bad idea.




Pre-load springs in differential

Posted: 6/15/05 9:55am Message 4 of 9
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Virginia City, NV - USA
Joined: 1/19/2005
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Vette(s): 1979 Coupe, white in color
Good reply Ken. I was waiting for you to weigh in on the subject. I have the springs in mine, but was pondering what he said. This fellow does some nice work, as evidenced by the pictures he posts and comments on his work by other forum members who by parts and units from him. I read in one of my many mags that Auburn has a new style diff that works better that the clutch dics type posi, but to my knowlage they don't have one for our cars. I'm still hunting for that issue to check it out again.


Pre-load springs in differential

Posted: 6/28/05 8:32pm Message 5 of 9
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CUYAHOGA FALLS, OH - USA
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There are several different types, but what we have does work very well.  The others operate basicly the same way, but with different design.  They also work well.  Chrysler uses a cone type that works well.  But again, if all work about equally well, why change?


Pre-load springs in differential

Posted: 7/21/05 8:40am Message 6 of 9
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Clearwater, FL - USA
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The Auburn units are stronger than the Eaton units and they do not have clutch packs in them. They are also non-rebuildable posi units. A downfall to the Auburns. They use the cone style as well but when they wear they wear into the case of the posi unit, hense why they are not rebuildable. They do make them for the 63-79 vettes.


Pre-load springs in differential

Posted: 7/22/05 9:25pm Message 7 of 9
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CUYAHOGA FALLS, OH - USA
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Vette(s): 1975 C3 Red, T-Tops, Black Interior. All I need is time and money! Getting there!

Then it would seem if you want max strength, go with the Auburn unit.  If you want a cruiser, and are going to keep it on the road for years and rebuild it in the future, the standard posi would be the way to go.

I was not familiar with the Auburn unit. But it sounds a lot like the Chrysler.  Can someone send me a web site?

kstyer38555.8933912037


Pre-load springs in differential

Posted: 7/23/05 8:39pm Message 8 of 9
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Duncanville, TX - USA
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Vette(s): #1-1974 L-48 4spd Cp Med Red Metallic/Black deluxe int w/AC/tilt/tele./p/w-p/b/ Am-Fm/map light National/Regional/Chapter NCRS "Top Flight" #2-1985 Bright Red/Carmine Cp.L-98/auto Member: NCRS, NCRS Texas, Corvette Legends of Texas
Ax and ye shall recieve!

Auburn Gear web-site

Adams' Apple38556.8655902778


Joel Adams
C3VR Lifetime Member #56    

My Link


(click for Texas-sized view!)
             NCRS

"Money can't buy happiness -- but somehow it's more comforting to cry in a CORVETTE than in a Kia"

Pre-load springs in differential

Posted: 8/6/05 12:10pm Message 9 of 9
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CUYAHOGA FALLS, OH - USA
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Thank you.  I will check that out.


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