Testing LSD
03-13-06 | 07:29 PM
#3
Old [Sch|F]ool
Joined: May 2001
Posts: 12,635
Likes: 464
From: Cleveland, Ohio, USA
Okay, here we go... 
You need a torque wrench, a click type or a beam type will do, both have their drawbacks but also both have their advantages.
Jack up one (1) rear tire with a floor jack under the axle
Block the other three tires
Handbrake OFF, transmission in NEUTRAL
Can you turn the wheel easily with light finger pressure? Yes? Diff is worn, or is an open diff.
Good amount of resistance? Okay, let's quantify. The measure of a clutch type limited slip is the breakaway torque - how much force it takes to initially make the tire turn. I have never seen an actual spec for this, but 40lb-ft of torque is a nice figure. A *goood* diff will be up around 90-120lb-ft but those are a real pain to drive on the street, you're pretty much driving a spool at that point.
So how do we measure the breakaway torque? Take your click type torque wrench and set it to 20lb-ft and put it on one of the lug nuts. You kinda want to make a right angle between the torque wrench, lug nut, and axle centerline, to try and get a semi-accurate torque reading. Does the tire move before the wrench clicks? Diff's done, although it may still lock up well enough under power. Wrench click before the tire turns? Set it up higher, say to 30lb, and try again.
If you have a beam type torque wrench, you just have to watch the torque reading just before the tire starts to turn.
Either way, you have to apply a smooth even load on the torque wrench. NOTE: After the diff "breaks away" the torque to turn the tire goes down a LOT. This is normal.
You need a torque wrench, a click type or a beam type will do, both have their drawbacks but also both have their advantages.
Jack up one (1) rear tire with a floor jack under the axle
Block the other three tires
Handbrake OFF, transmission in NEUTRAL
Can you turn the wheel easily with light finger pressure? Yes? Diff is worn, or is an open diff.
Good amount of resistance? Okay, let's quantify. The measure of a clutch type limited slip is the breakaway torque - how much force it takes to initially make the tire turn. I have never seen an actual spec for this, but 40lb-ft of torque is a nice figure. A *goood* diff will be up around 90-120lb-ft but those are a real pain to drive on the street, you're pretty much driving a spool at that point.
So how do we measure the breakaway torque? Take your click type torque wrench and set it to 20lb-ft and put it on one of the lug nuts. You kinda want to make a right angle between the torque wrench, lug nut, and axle centerline, to try and get a semi-accurate torque reading. Does the tire move before the wrench clicks? Diff's done, although it may still lock up well enough under power. Wrench click before the tire turns? Set it up higher, say to 30lb, and try again.
If you have a beam type torque wrench, you just have to watch the torque reading just before the tire starts to turn.
Either way, you have to apply a smooth even load on the torque wrench. NOTE: After the diff "breaks away" the torque to turn the tire goes down a LOT. This is normal.
03-13-06 | 07:34 PM
#6
Originally Posted by peejay
Okay, here we go...
You need a torque wrench, a click type or a beam type will do, both have their drawbacks but also both have their advantages.
Jack up one (1) rear tire with a floor jack under the axle
Block the other three tires
Handbrake OFF, transmission in NEUTRAL
Can you turn the wheel easily with light finger pressure? Yes? Diff is worn, or is an open diff.
Good amount of resistance? Okay, let's quantify. The measure of a clutch type limited slip is the breakaway torque - how much force it takes to initially make the tire turn. I have never seen an actual spec for this, but 40lb-ft of torque is a nice figure. A *goood* diff will be up around 90-120lb-ft but those are a real pain to drive on the street, you're pretty much driving a spool at that point.
So how do we measure the breakaway torque? Take your click type torque wrench and set it to 20lb-ft and put it on one of the lug nuts. You kinda want to make a right angle between the torque wrench, lug nut, and axle centerline, to try and get a semi-accurate torque reading. Does the tire move before the wrench clicks? Diff's done, although it may still lock up well enough under power. Wrench click before the tire turns? Set it up higher, say to 30lb, and try again.
If you have a beam type torque wrench, you just have to watch the torque reading just before the tire starts to turn.
Either way, you have to apply a smooth even load on the torque wrench. NOTE: After the diff "breaks away" the torque to turn the tire goes down a LOT. This is normal.
You need a torque wrench, a click type or a beam type will do, both have their drawbacks but also both have their advantages.
Jack up one (1) rear tire with a floor jack under the axle
Block the other three tires
Handbrake OFF, transmission in NEUTRAL
Can you turn the wheel easily with light finger pressure? Yes? Diff is worn, or is an open diff.
Good amount of resistance? Okay, let's quantify. The measure of a clutch type limited slip is the breakaway torque - how much force it takes to initially make the tire turn. I have never seen an actual spec for this, but 40lb-ft of torque is a nice figure. A *goood* diff will be up around 90-120lb-ft but those are a real pain to drive on the street, you're pretty much driving a spool at that point.
So how do we measure the breakaway torque? Take your click type torque wrench and set it to 20lb-ft and put it on one of the lug nuts. You kinda want to make a right angle between the torque wrench, lug nut, and axle centerline, to try and get a semi-accurate torque reading. Does the tire move before the wrench clicks? Diff's done, although it may still lock up well enough under power. Wrench click before the tire turns? Set it up higher, say to 30lb, and try again.
If you have a beam type torque wrench, you just have to watch the torque reading just before the tire starts to turn.
Either way, you have to apply a smooth even load on the torque wrench. NOTE: After the diff "breaks away" the torque to turn the tire goes down a LOT. This is normal.
03-13-06 | 07:41 PM
#7
Rotary Freak
Joined: Sep 2004
Posts: 1,901
Likes: 0
From: Kitchener, Ont. Canada
how about an easy check
what i did to test mine, was simply jacked up the rear. then i turned one of the wheels, and the other one turned too. then i had a buddy hold one of the wheels while i turned the other, and it too quite a bit of muscle to make it turn. i figured that was a good easy way to check...obviously not precise, but still i know its at least ok....
what i did to test mine, was simply jacked up the rear. then i turned one of the wheels, and the other one turned too. then i had a buddy hold one of the wheels while i turned the other, and it too quite a bit of muscle to make it turn. i figured that was a good easy way to check...obviously not precise, but still i know its at least ok....
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03-13-06 | 08:14 PM
#9
Originally Posted by 31rx7
I must be old. When I read the thread title "Testing LSD", I thought it was something else entirely.
thats some funny ****
anyone know how to make lsd lol
then i could contribute for the old fella
03-13-06 | 08:59 PM
#12
FB+FC=F-ME
Joined: Jul 2004
Posts: 3,353
Likes: 5
From: Rohnert Park CA
Even if your breakaway torque is low,the LSD can still function.
Granted,its probably worn and likely has some miles on it,but even if the plates are thin and the springs soft,the standing resistance of the LSD is only that,no-loaded,standing resistance.When you drive,and apply torque into the LSD,the spider pins will push the torque plates out under force,clamping the LSD discs together and making the diff "one",so to speak.The more torque you apply,the tighter it grips.
This of course is influenced to a degree, by the condition of the friction discs,oil used,temp and engine output,but dont necessarily write off an LSD rear that has little/no breakaway resistance.My SE rearend has been feeling like a one legger for years when I jack it up,but I can still pitch it sideways and spin donuts with ease under power.
Granted,its probably worn and likely has some miles on it,but even if the plates are thin and the springs soft,the standing resistance of the LSD is only that,no-loaded,standing resistance.When you drive,and apply torque into the LSD,the spider pins will push the torque plates out under force,clamping the LSD discs together and making the diff "one",so to speak.The more torque you apply,the tighter it grips.
This of course is influenced to a degree, by the condition of the friction discs,oil used,temp and engine output,but dont necessarily write off an LSD rear that has little/no breakaway resistance.My SE rearend has been feeling like a one legger for years when I jack it up,but I can still pitch it sideways and spin donuts with ease under power.
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