Newbie LSD tuning questions

[rudypoochris]

Sorry I am a bit new to anything to do with adjusting the R200 from the 300zxt. Please be patient

 

1. Does the term breakaway torque refer to how much torque it takes to make a wheel spin if both wheels are free in the air? If so, could one measure this simply by putting a torque wrench on one side and a wrench (used to stop slippage) on the other side?

 

2. How does gear oil effect the breakaway torque? How does additive effect it? How does special LSD formulated gear oil effect it? Basically I am wondering if a correct measurement can be had when testing the carrier "dry".

 

3. Can the breakaway be adjusted with out replacing all the shims, disks, or opening the carrier?

 

4. Do the clutches only really wear if the driver abuses them and does heavy launches, or do they often quickly wear down just from normal/light street driving? On a car driven lightly how long might a set give a reasonable amount of torque, say 75-80% of what it was ment to be.

 

Thanks, sorry if any of this is a bit novice.

[johnc]

1. Breakaway torque (BT) is the torque required to spin each wheel independently. Its point where the clutch packs start slipping against each other.

 

2. Not sure how the additive or the lube affects BT but the units I've tested were in the car so the numbers I measured included a lubed up unit.

 

3. Nope.

 

4. The clutches wear, period. The rate of wear is determiend by usage. Dragstrip launches are not a big deal. Tight radius corners with a lot of power application are the big wear producers. Autocross is especially hard on clutch pack LSDs and I rebuilt mine about every 18 months.

 

Most factory installed clutch pack LSDs are worn out by 50,000 miles of street driving. I know the on in my F350 was gone by 40,000 miles and I got Ford to rebuild it under my extended warranty.

[JMortensen]

Sorry I am a bit new to anything to do with adjusting the R200 from the 300zxt. Please be patient

 

1. Does the term breakaway torque refer to how much torque it takes to make a wheel spin if both wheels are free in the air? If so' date=' could one measure this simply by putting a torque wrench on one side and a wrench (used to stop slippage) on the other side?

 

2. How does gear oil effect the breakaway torque? How does additive effect it? How does special LSD formulated gear oil effect it? Basically I am wondering if a correct measurement can be had when testing the carrier "dry".

 

3. Can the breakaway be adjusted with out replacing all the shims, disks, or opening the carrier?

 

4. Do the clutches only really wear if the driver abuses them and does heavy launches, or do they often quickly wear down just from normal/light street driving? On a car driven lightly how long might a set give a reasonable amount of torque, say 75-80% of what it was ment to be.

 

Thanks, sorry if any of this is a bit novice.[/quote']

 

1. No, you can't just put a wrench on a lug nut and find the breakaway torque. BT is hard to measure accurately. You can get an idea of what to do by reading this page: http://www.gordon-glasgow.org/lsd1.asp

 

2. You'll see when you read that page that BT can measure over 200 lbs, but with the clutches oiled, 40. Oil makes a big difference. The additive gets rid of the chatter when they break loose, but I don't believe that it lessens the BT.

 

3. No.

 

4. The clutches are only wearing when the car is cornering. You'll get many years of service out of them if you're just street driving. If you're road racing you'll need to service it more often.

 

Most factory installed clutch pack LSDs are worn out by 50,000 miles of street driving. I know the on in my F350 was gone by 40,000 miles and I got Ford to rebuild it under my extended warranty.

Gotta be careful comparing Ford to Nissan. Most of the Ford and GM diffs and some of the Danas use a spring setup, almost like a Phantom Grip unit. The spring sits in between the side gears and pushes them onto the clutch pack. When the clutches wear, there is less preload, and the preload is the only thing that determines the resistance to slipping. Most of the American LSDs use a lining on the clutch plates that wears off fairly quickly. On this page you can see a pic of the "S" spring which preloads the side gears on the 8.8 Ford diff: http://www.mustang50magazine.com/techarticles/130_0301_slip/

 

Our Nissan LSD's use a Salisbury type LSD which is torque sensitive. The cross pin in the diff works like a cam to spread the pressure rings under load, and the pressure rings push on the clutch stack harder and harder as more torque is applied. So clutch wear and preload isn't as dramatic in its effect on the stack, because when you punch it it isn't JUST the preload that determines how much limiting of the slip you get. Preload matters, but it isn't the only thing in play, like the Ford Traction Lok LSD. Our clutches are all metal. I pulled mine apart and wasn't able to measure the wear on the clutches with a caliper.

 

Here is the description of the two types of LSDs from my old workplace, Randy's Ring and Pinion http://www.ringpinion.com/content/technicalhelp/default.asp?pid=128:

Traction-Lock (T/L)

(Also referred to as a Track-Lock, not to be mistaken with the Dana Spicer Trac-Lok) This is the second design limited slip that Ford used in both the 8-" and 9" rearend designs. It is a fairly good design for moderate horsepower applications. This is a clutch type design that uses four plain steel clutches, four fiber lined clutches, and one plate that is steel on one side and has fiber lining on the other side. It uses a two-piece case that looks very similar to the standard open carriers, except the parting line between the two case halves is covered by the left half that "wraps around" the right half. The parting line between the two halves on a standard case is easy to see and is not covered. Traction-Locks are not very aggressive and tend to wear out fairly quickly if used heavily.

 

Newer design Ford rearends such as the 7.5", 8.8", 9.75", 10.25", and 10.5" also can be ordered with Traction-Locks. These differentials use a one-piece case with two spider pinion gears, except for the heavy-duty 10.5" rearend, which uses three spider pinion gears. The 7.5" and 8.8" designs have soft clutches that tend to wear-out quickly and are not aggressive even when new. The 10.25" unit uses composite clutches that holdup fairly well, but it is not aggressive and tends to slip too much when needed off-road. Trac-Lok is a medium-duty limited slip and will hold up without breaking, but will wear out the clutches quickly under heavy-duty use. If the unit wears out it usually can be rebuilt. (factory)

 

Here is the one for the Chrysler Powr-Lock, which is very similar to our Nissan LSD:

Powr-Lok (P/L)

This clutch type limited slip is the strongest and most aggressive limited slip differential available from Dana Spicer. It is a clutch type unit using floating cross shafts that ride up on ramps in the case. When power is applied, the shafts ride up the ramps and load the clutches for a positive engagement. A Powr-Lok will not lock up 100%, but it is a very durable unit that will hold up fairly well with tall tires. It can be rebuilt, and can be set up smooth or aggressive by changing the clutch design or stacking configuration. Powr-Loks are easily identified by their 2-piece case. They are a very strong unit due to the 4 spider gear design that provides twice as many teeth to carry the load as a 2 spider gear unit does. However, the case bolts can stretch or loosen after severe use over time. (4 pin, 4 tab clutches) (factory)

[HeatRaveR]

1. Breakaway torque (BT) is the torque required to spin each wheel independently. Its point where the clutch packs start slipping against each other.

 

So if given a choice, how does one know/calculate what the ideal breakaway torque rating of an LSD should be? Is the ideal BT dependent on engine output?

[bjhines]

well... the cross pin ramp angles are different on the factory and Nismo units which makes a big difference in how the LSD works under load.... regardless of breakaway torque ratings.... any comparisons between the Nismo units and the stock units are incorrect...

[JMortensen]

If it doesn't slip when you're on the power, then it has enough BT. The thread that I had about shimming had a bunch of racers saying 45 lbs was enough, and that I was overdoing it by going with 100. If you're drag racing probably minimal BT would be necessary, because the more torque you put to it the harder it locks up, regardless of the BT.

 

Out of curiousity, what are the different angles on the ramps?

 

EDIT-Nevermind, I saw your pics in your gallery. They are quite a bit more aggressive than the ramps in my diff.

 

Remember John that Gordon Glasgow had a "Nismo" H-190 LSD that was purchased last year and it was internally identical to mine with the one clutch disk and big spacers, so buying Nismo branded LSDs at twice the price doesn't necessarily guarantee you anything AFAIK. If you're just wanting the best, the KAAZ stuff is way better than anything Nissan sells.

[rudypoochris]

Ok ok. I think I may have misunderstood that. So basically even if the clutch disks are worn and the BT is low (say 20lbs) if you are just going in a straight line you probably won't notice because it will lock up anyway? Whats the point of having higher BT then? Is it to give some understeer on a road course and even out the vehicles so it isn't so, for lack of a better word, "dodgy"? Thanks.

[JMortensen]

On a road course you're trying to put the power down to the inside rear tire while you've got lots of weight transfer to the outside tires. So you're much more likely to get the one wheel peel while cornering than a drag racer with sticky tires going straight. There might be a point at which you're putting down SO much power that you really need a lot of lockup in the drag car, but I don't have much experience with that.

[bjhines]

road courses have long high speed sweepers where you are using maintenance throttle to control the arc the car travels in... you don't put a whole lot of power down in the first 2/3rds of the turn... but the unloading of the inside rear tire can allow it to spin with less than full power applied...

 

Having more aggressive ramp angles... and/or (I guess) more BT will allow you to have some LSD action without a lot of torque on the pinion.... part throttle LSD can be important...

 

A drag race launch will apply more than enough torque to lock the diff and launch wothout wheel spin....

 

Too much BT can make the rear end unpredictable in high speed sweepers... hence the 60* ramp angles and low BT ratings on the Nismo road race units...