JXB C7/D4 Front Mechanical Limited Slip Differential

[Alabama]

JXB advertises this product for the C7 Audi. It looks very slick but not trivial to install. Has anyone installed a front LSD and if so, please share your experience.

[brad281]

JXB advertises this product for the C7 Audi. It looks very slick but not trivial to install. Has anyone installed a front LSD and if so, please share your experience.

From what I've read, you have to remove the whole front LSD and ship it to JXB for them to install and they ship it back.

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[gk1]

What would be an advantage of the front LSD over the current open one with EDL? Serious question... as I don't know.
Does it offer more traction like for Stage3+ or something since I feel like traction limitations aren't such an issue?
Is it better in the corners, ie acceleration out of corners?
I sorta get it on a FWD car or even a haldex with FWD bias, but the advantage is not as apparent to me on Longitudinal models with more traditional or RWD bias quattro.

[brad281]

What would be an advantage of the front LSD over the current open one with EDL? Serious question... as I don't know.
Does it offer more traction like for Stage3+ or something since I feel like traction limitations aren't such an issue?
Is it better in the corners, ie acceleration out of corners?
I sorta get it on a FWD car or even a haldex with FWD bias, but the advantage is not as apparent to me on Longitudinal models with more traditional or RWD bias quattro.

https://www.jxbperformance.com/produ...mechanical-lsd

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[gk1]

https://www.jxbperformance.com/produ...mechanical-lsd

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Thanks.
Interesting, I can see the benefit on a fully built race car like in the video but get the feeling it's not for 99% of people. Still cool this kind of development exists though for sure.
Going from 1.6 to 1.5 60ft is great on a race car but from my readings many users report in the 1.7-1.8 range so they still have some work to do on stock setup before thinking about getting that extra tenth. Even I snapped of a 1.6 back in the day on lowly Stage I.
Also would the new diff now find the limits of the front axles since I know people have already found the limits of the rear axles?

[brad281]

Thanks.
Interesting, I can see the benefit on a fully built race car like in the video but get the feeling it's not for 99% of people. Still cool this kind of development exists though for sure.
Going from 1.6 to 1.5 60ft is great on a race car but from my readings many users report in the 1.7-1.8 range so they still have some work to do on stock setup before thinking about getting that extra tenth. Even I snapped of a 1.6 back in the day on lowly Stage I.
Also would the new diff now find the limits of the front axles since I know people have already found the limits of the rear axles?

Since the upgraded front LSD moves more of the torque to the front wheels, it distributes the engines power more evenly, reducing stress on the rear parts. The front drive axles are the same as the rear, if I remember correctly, so there less chance of failures overall.

I haven't done the upgrade, but I think it has benefit for anyone pushing the limits of their car on the track or the street.

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[gk1]

Since the upgraded front LSD moves more of the torque to the front wheels, it distributes the engines power more evenly, reducing stress on the rear parts. The front drive axles are the same as the rear, if I remember correctly, so there less chance of failures overall.

I haven't done the upgrade, but I think it has benefit for anyone pushing the limits of their car on the track or the street.

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Good point. Perhaps...
I don't know enough about the front vs. rear axles to know if there is a structural difference. They are different part numbers for sure because of the different lengths, but I don't have specs on shaft diameter or joint size and hollow vs. solid to know if one is beefier than the other.

[ericw.]

If you regularly (winter) drive on icy or snowy roads, open front diff is the safest.

4x4 stuff and things... locking your front diff on an slick turn sometimes will pull you right off the road.

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[Alabama]

If you regularly (winter) drive on icy or snowy roads, open front diff is the safest.

4x4 stuff and things... locking your front diff on an slick turn sometimes will pull you right off the road.

So one needs a design that does not lock? How about on wet? Do you have personal experience? I'm confused as Quaife seems to sell a lot of LSDs for front-wheel drive. From their website: "On front wheel drive cars the Quaife ATB limited slip differential also delivers significant performance benefits during heavy braking. In this situation the Quaife differential’s inherent torque transfer characteristics work in reverse to transfer torque away from the locking wheel. This enhances deceleration, delaying the intrusion of electronic ABS systems and allowing drivers to brake later and deeper with the Quaife ATB limited slip differential than is possible with a standard ‘open’ differential unit."

[ericw.]

So one needs a design that does not lock? How about on wet? Do you have personal experience? I'm confused as Quaife seems to sell a lot of LSDs for front-wheel drive. From their website: "On front wheel drive cars the Quaife ATB limited slip differential also delivers significant performance benefits during heavy braking. In this situation the Quaife differential’s inherent torque transfer characteristics work in reverse to transfer torque away from the locking wheel. This enhances deceleration, delaying the intrusion of electronic ABS systems and allowing drivers to brake later and deeper with the Quaife ATB limited slip differential than is possible with a standard ‘open’ differential unit."

That design is called an open diff and it's what you have from the factory.

A limited slip diff allows the wheels to turn independently to an extent but once a wheel slips too much (over a certain ratio), it locks the diff so both wheels will move at the same time. So on ice, your 1 spinning wheel can turn into 2 spinning wheels on the same axle (front) = no steering.

It's good for getting traction on dry surfaces, racing in cars that spin tires will see an improvement but there's just some added risk on slick surfaces if it kicks in when you didn't expect it.

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[Alabama]

That design is called an open diff and it's what you have from the factory.

A limited slip diff allows the wheels to turn independently to an extent but once a wheel slips too much (over a certain ratio), it locks the diff so both wheels will move at the same time. So on ice, your 1 spinning wheel can turn into 2 spinning wheels on the same axle (front) = no steering.

It's good for getting traction on dry surfaces, racing in cars that spin tires will see an improvement but there's just some added risk on slick surfaces if it kicks in when you didn't expect it.

I'll take your word for it, but that doesn't seem like how Mona Lisa Vito explained it in My Cousin Vinny. "The '64 Skylark had a regular differential, which, anyone who's been stuck in the mud in Alabama knows, you step on the gas, one tire spins, the other tire does nothing." I thought a properly designed LSD gradually tries to transfer torque away from the wheel without traction to the wheel with traction. If neither has traction then neither has traction.

[ericw.]

I'll take your word for it, but that doesn't seem like how Mona Lisa Vito explained it in My Cousin Vinny. "The '64 Skylark had a regular differential, which, anyone who's been stuck in the mud in Alabama knows, you step on the gas, one tire spins, the other tire does nothing." I thought a properly designed LSD gradually tries to transfer torque away from the wheel without traction to the wheel with traction. If neither has traction then neither has traction.

That's a totally different situation... I'm not referring to being stuck in mud and getting moving.

I'm talking about moving/turning on a slick road and losing traction. Hollywood movies were never a good source for information. haha, if you lived nearby I'd let you try driving my jeep with locked axles on gravel. On any sort of loose or slick surface, with the locked front differential, it doesn't want to turn. It pushes through your turn, similar to understeer. Sure it'll get you moving, just maybe not in the direction you want to go unless you can get enough traction on the front wheels.

This is why it was universally decided that open diffs are safer for the masses than LSD or locked diffs so you get an open diff in every car that you buy off the lot... except for a few specific designs intended for offroad.

[Jay@JXB]

Hey, Jay from JXB here. Stumbled upon this and wanted to help shed some light.

Install. Your trans has to come down. The front diff pops out of the side of it in about 5 mins after that. Typically, you need to send your diff in to have the ring gear adapted over to the new diff; however we do try to carry cores in to avoid this. If you send it in, it's a 2 week turnaround. A 3-day rush option is available too (plus transit times of course).

Benefits. I can't begin to name them all. It's not just a track guy's mod. Of course the biggest thing you'll feel is mind-boggling grip out of the corners. I've talked to many of my customers about their experiences (none of which are track guys so far), and they're all blown away by the effects. You'll go faster off the line. The steering wheel will feel tighter and more connected (less slop in the steering). Braking is more stable. It's a pretty big improvement in overall driving experience.

It does take more strain off the expensive rear end.

Low-traction scenarios...I wanted to go into depth on that. A helical diff is actually open in the absence of substantial traction. It actually needs a large torque differential in order to lock the gears up inside. The best way to explain this is by giving examples.
- You can turn the axles by hand in opposite directions once it's installed
- When you turn a corner with no wheel-spin, it does not lock (just like an OEM open diff)
- When you turn a corner and get wheel-spin, it does lock, as long as there is a reasonable amount of traction on the spinning wheel (i.e. it's not lifted in the air, and not on ice, in mud, etc.)
- When you turn a corner and get wheel-spin, it does not lock if there is low traction on the spinning wheel (in the air, on a low-traction surface as mentioned above)

I think the situation ericw gave is not reasonable for this type of diff. A helical is not an on/off switch. It acts like an open diff under most driving conditions, and smoothly starts to lock as traction varies. The type of diff in off-road front-ends is generally one that locks 100%, forcing both front wheels to go exactly the same speed. This is needed because off-road vehicles lift wheels all the time and need to still deliver power to the tire on the ground. A helical differential like mine wouldn't work in that situation (at all). Also, often times people run things like "lunchbox lockers" that are open until they immediately lock under a bit of throttle. Those are inherently dangerous, especially in the rear end, as they go from normal to burnout in a split second.

With a helical, as long as you're not on throttle, it will never lock. In the dangerous situation of slipping off the road, the helical acts like a factory diff because you are on the brakes or coasting and it has no torque differential to lock-up. If for some reason you were accelerating while trying to stay on the road, if you were doing it so slightly as to not induce wheelspin, the diff would remain like the factory diff. If you were accelerating to the point that you were inducing wheelspin, the helical diff would lock at least partially (keep in mind low traction/torque may not be enough to lock it entirely) and keep both tires delivering power, which would result in more effective turning. Typically, when a car is skidding off the road on ice, you're not lighting up the tires with the gas pedal, so your helical diff is the same as OEM. Take a look at rally cars. They all have limited slip differentials. When you're hammering on it and trying to turn, both front wheels spinning is better than just one.

A helical basically acts like an OEM diff until you need it, then it makes everything better. There really are no downsides compared to an open diff. ericw's point is valid for vehicles with locking front ends (trucks/Jeeps/etc), but that's just not how a helical acts.

[ericw.]

Hey, Jay from JXB here. Stumbled upon this and wanted to help shed some light.

Install. Your trans has to come down. The front diff pops out of the side of it in about 5 mins after that. Typically, you need to send your diff in to have the ring gear adapted over to the new diff; however we do try to carry cores in to avoid this. If you send it in, it's a 2 week turnaround. A 3-day rush option is available too (plus transit times of course).

Benefits. I can't begin to name them all. It's not just a track guy's mod. Of course the biggest thing you'll feel is mind-boggling grip out of the corners. I've talked to many of my customers about their experiences (none of which are track guys so far), and they're all blown away by the effects. You'll go faster off the line. The steering wheel will feel tighter and more connected (less slop in the steering). Braking is more stable. It's a pretty big improvement in overall driving experience.

It does take more strain off the expensive rear end.

Low-traction scenarios...I wanted to go into depth on that. A helical diff is actually open in the absence of substantial traction. It actually needs a large torque differential in order to lock the gears up inside. The best way to explain this is by giving examples.
- You can turn the axles by hand in opposite directions once it's installed
- When you turn a corner with no wheel-spin, it does not lock (just like an OEM open diff)
- When you turn a corner and get wheel-spin, it does lock, as long as there is a reasonable amount of traction on the spinning wheel (i.e. it's not lifted in the air, and not on ice, in mud, etc.)
- When you turn a corner and get wheel-spin, it does not lock if there is low traction on the spinning wheel (in the air, on a low-traction surface as mentioned above)

I think the situation ericw gave is not reasonable for this type of diff. A helical is not an on/off switch. It acts like an open diff under most driving conditions, and smoothly starts to lock as traction varies. The type of diff in off-road front-ends is generally one that locks 100%, forcing both front wheels to go exactly the same speed. This is needed because off-road vehicles lift wheels all the time and need to still deliver power to the tire on the ground. A helical differential like mine wouldn't work in that situation (at all). Also, often times people run things like "lunchbox lockers" that are open until they immediately lock under a bit of throttle. Those are inherently dangerous, especially in the rear end, as they go from normal to burnout in a split second.

With a helical, as long as you're not on throttle, it will never lock. In the dangerous situation of slipping off the road, the helical acts like a factory diff because you are on the brakes or coasting and it has no torque differential to lock-up. If for some reason you were accelerating while trying to stay on the road, if you were doing it so slightly as to not induce wheelspin, the diff would remain like the factory diff. If you were accelerating to the point that you were inducing wheelspin, the helical diff would lock at least partially (keep in mind low traction/torque may not be enough to lock it entirely) and keep both tires delivering power, which would result in more effective turning. Typically, when a car is skidding off the road on ice, you're not lighting up the tires with the gas pedal, so your helical diff is the same as OEM. Take a look at rally cars. They all have limited slip differentials. When you're hammering on it and trying to turn, both front wheels spinning is better than just one.

A helical basically acts like an OEM diff until you need it, then it makes everything better. There really are no downsides compared to an open diff. ericw's point is valid for vehicles with locking front ends (trucks/Jeeps/etc), but that's just not how a helical acts.

I'm referring to the characteristics of any differential that has the potential to lock at any point. Generally a limited slip diff will act as a locked diff when one wheel has a rotation ratio of 3-4:1 (aka 3-4 rotations on one wheel per 1 rotation of the other). It begins turning both wheels on the same axle. Ideal for being stuck and getting moving, preventing the "1 tire fire" but not ideal for snow driving where you might already be traveling at speeds on icy roads when you have 1 tire start to lose traction. You need that shift of power to remove power from the wheel that has traction, so to prevent it from also spinning.

The negatives of this on a front axle IMO, far outweigh the benefits. Go for it on the rear, that's a lot of fun.

[Alabama]

The negatives of this on a front axle IMO, far outweigh the benefits. Go for it on the rear, that's a lot of fun.

Great discussion, thanks! I've known folk with rear-wheel drive cars with OEM open diffs who switched to LSD with great happiness as ericw. writes. I'm less familiar with doing the same to front wheel drive cars since steering becomes involved, so my question about the JXB product. However, I find that the Honda Civic Type R comes standard with a front wheel LSD, and apparently so do others. Another web site mentions ericw.'s caution about ice driving but apparently is independent of axle. I was taught to minimize acceleration when losing traction on snow and ice anyway. I'd still like to hear from someone who has actually done this to an S6.

[mpk1996]

Hey, Jay from JXB here. Stumbled upon this and wanted to help shed some light.

Install. Your trans has to come down. The front diff pops out of the side of it in about 5 mins after that. Typically, you need to send your diff in to have the ring gear adapted over to the new diff; however we do try to carry cores in to avoid this. If you send it in, it's a 2 week turnaround. A 3-day rush option is available too (plus transit times of course).

Benefits. I can't begin to name them all. It's not just a track guy's mod. Of course the biggest thing you'll feel is mind-boggling grip out of the corners. I've talked to many of my customers about their experiences (none of which are track guys so far), and they're all blown away by the effects. You'll go faster off the line. The steering wheel will feel tighter and more connected (less slop in the steering). Braking is more stable. It's a pretty big improvement in overall driving experience.

It does take more strain off the expensive rear end.

Low-traction scenarios...I wanted to go into depth on that. A helical diff is actually open in the absence of substantial traction. It actually needs a large torque differential in order to lock the gears up inside. The best way to explain this is by giving examples.
- You can turn the axles by hand in opposite directions once it's installed
- When you turn a corner with no wheel-spin, it does not lock (just like an OEM open diff)
- When you turn a corner and get wheel-spin, it does lock, as long as there is a reasonable amount of traction on the spinning wheel (i.e. it's not lifted in the air, and not on ice, in mud, etc.)
- When you turn a corner and get wheel-spin, it does not lock if there is low traction on the spinning wheel (in the air, on a low-traction surface as mentioned above)

I think the situation ericw gave is not reasonable for this type of diff. A helical is not an on/off switch. It acts like an open diff under most driving conditions, and smoothly starts to lock as traction varies. The type of diff in off-road front-ends is generally one that locks 100%, forcing both front wheels to go exactly the same speed. This is needed because off-road vehicles lift wheels all the time and need to still deliver power to the tire on the ground. A helical differential like mine wouldn't work in that situation (at all). Also, often times people run things like "lunchbox lockers" that are open until they immediately lock under a bit of throttle. Those are inherently dangerous, especially in the rear end, as they go from normal to burnout in a split second.

With a helical, as long as you're not on throttle, it will never lock. In the dangerous situation of slipping off the road, the helical acts like a factory diff because you are on the brakes or coasting and it has no torque differential to lock-up. If for some reason you were accelerating while trying to stay on the road, if you were doing it so slightly as to not induce wheelspin, the diff would remain like the factory diff. If you were accelerating to the point that you were inducing wheelspin, the helical diff would lock at least partially (keep in mind low traction/torque may not be enough to lock it entirely) and keep both tires delivering power, which would result in more effective turning. Typically, when a car is skidding off the road on ice, you're not lighting up the tires with the gas pedal, so your helical diff is the same as OEM. Take a look at rally cars. They all have limited slip differentials. When you're hammering on it and trying to turn, both front wheels spinning is better than just one.

A helical basically acts like an OEM diff until you need it, then it makes everything better. There really are no downsides compared to an open diff. ericw's point is valid for vehicles with locking front ends (trucks/Jeeps/etc), but that's just not how a helical acts.

That looks like it will make the car real fun!! need to start another piggy bank

is there a power point where this becomes more necessary than another on say an RS7?