WTZ, you should watch your mouth. I didnt say that a failure was guaranteed, but mixing 3 mechanical diffs with ABS is not a good idea. Why do you think that mitsubishi only puts a front diff on either the Evo without ABS (the RS) or on the Evo that is computer controlled (the new MR for example). You should do some research before you open your mouth in a chatroom. Getting into ABS pulsation with momentary wheel lockup while turning with the 3 diffs is not good on the center differential. You should also read that I never said anything about the front diff not working with ABS, I mentioned the possibility of diff failure.
Chuntington- I didnt mean a computer controlled front diff, sorry for the confusion. When I said computer controlled I meant ACD. The front diffs are still mechanical.

 

WTZ, as posted here: https://www.evolutionm.net/forums/sh...LSD#post957558

Tell us more about the wet braking. That is my biggest gripe I have about the Evo. I loved the ABS programing in my ITR, but the Evo seems lacking. On the ITR the ABS was later to engage (seemed more so in the dry vs. the wet), but seemed more aggressive when it did (may be a bad choice of words) engage in the wet. Granted we are talking about about an extra 800 lbs. Our cars desperately need a front LSD, but I'm worried that the daily driving aspect may be slightly compromised. I do live in the dumb-*** driver capital of the world you know.

I'm afraid the front LSD will extend wet braking distances...

 

Sorry 2GDSM. Did'nt realize you were so thin-skinned. I am not aware of any mechanical or electronic connection between ACD and ABS. ACD is nothing mre than an ECU controlled pump that varies the lockup time on the VCD. It does not sense ABS pulsation. Now I might agree that a full-on ABS stop is hard on the gears in a helical front differential, but the Torsen design is quite stout. Why not just practice proper threshold braking? It's more effective than getting into the ABS.
You state "STi's computer controlled diffs can work with ABS, Evo mechanical diffs cannot". If this were true, why does my car work? Why would Quaife be bothering to design a front diff for the US car? As far as I know, the reason the RS does not come with ABS is that it cuts cost on an item the rally guys are going to rip out anyway. I'd hate to see a post like yours dissuade someone from a good mod for these cars. If I am wrong, someone else chime in. Until then, I will continue to enjoy the benefits of front LSD.
Zeus, I have not actually measured wet braking distances in ABS mode but my guess is that the front diff would have no effect on this. Mechanical tire grip in the wet would have the biggest effect.
Cheers,

 

The problem with ABS and 3 mechanical LSDs is this... If you have 3 mechanical limited slip differential and your car is jacked up with all 4 tires off the ground, turning one wheel by hand will result in all 4 wheels turning. The opposite is true as well, if all four wheels are turning and you stop one wheels, all 4 will stop. Now if all four tires are spinning while the car is on the ground and in motion, locking one tire will make all the differentials try to lock up all four tires. However, the torque generated by the 3 tires in contact with the ground that are not locking up will be greater than the torque generated by the locked brake on the one wheel that is locked. So something must be going on here, which is one of the differentials in your car is slippping, and chances are it's the center diff.

If you car has a viscous center diff this forced slipping of the differential can overheat the viscous fluid causing it to break down and loose it's lockup charecteristics, something that happens to all VLSDs with age depending on the abuse level they've been subjected to. If you have a clutch type center diff the differential can slip as well, but the holding torque of a CLSD is much higher, causing higher stresses on the differential gearset. The clutches may slip, the gears may break, but "something's gotta give".

However, I would venture to say that of all the diffs in a car equipped with a phantom LSD, the PGLSD is the weakest. It would undoubtedly slip first if a wheel was to lock up under braking. It would still transmit residual torque to the other differentials in the car, something the other differentials probably wouldn't enjoy.

There is also another factor that needs to be considered. ABS doesn't allow a wheel to remail locked up! The wheels pulsated between locked and unlocked. Furthermore... rarely, if ever, do all 4 wheels of the car pulsate at the same time or at the same speed when the ABS kicks in. In most cases it's only one wheel that locks, and if multiple wheels lock they do so at different times and different rates. This rapid lock-unlock causes cyclic loading of the gearsets, which in engineering terms causes the most fatigue on a metal greatly redusing it's life.

ABS in general is hard on a car, especially an AWD car, and very much so on an AWD car equipped with 3 LSDs. As far as an electronically controlled center diff being no help to the ABS situation, that is flat wrong. If the front and rear drivetrains can be sucessfully uncoupled, or their coupling strength greatly reduced while the ABS is pulsating a path for the drivetrain slippage has been created.

I could go on talking about this, but I won't.... As far as putting a PGLSD in the front of my car? I'm going to have to think about it for a while before I decide whether or not to. TT is very correct when they said that wheel hop causes much more stress on the driveline than ABS braking with the PGLSD would, so if I were a serious drag racer. Yea, I'd buy it. But for how little time my car sees the dragstrip, I don't think the accelerated differential wear is a tradeoff I'm willing to make.

- Steve

 

Sorry to have taken that the wrong way. I was not trying to dissuade anyone from not purchasing a Front LSD, I was simply trying to warn them of the side effects in doing so. Mitsu did avoid ABS on the RS to save some money, but they also did it to avoid conflicts with the 3 mechanical diffs. A center electronically controlled diff can work with ABS, but as I stated, a center mechanical diff with front and rear mechanicals is very hard on the drivetrain during ABS pulsation.

 

Does ACD decouple the front and rear drivetrains when ABS pulsates? I know that AYC disengages when the handbrake is pulled on, but that's a little bit different.
Cheers,

 

The ACD is suppose to disconnect the front from the rear. Not sure why AYC would disengage since both rear wheels are locked and not spinning.
Non-spinning or rear is what causes problems to non-electronic center diff which locks up because it thinks more toque is needed to the front (slipping) and then stress is applied to it.
As for the previous discussion for ABS, the reason why they don't put one in the RS is not cost cutting but it does absolutely no good when driving in dirt or to experienced race car driver. To those that never went nuts in the wet or on the uneven road surfaces ABS tends to kick in when you least want it and your car just goes strait (and doesn't stop or brake the way you wanted).

I'm not sure if ABS was a reason why they didn't put it in the US Evo, I think that was cost cutting. There wouldn't be much different between the current setup in regards to drivetrain stress.

 

About the Torsen and ABS...A torsen diff will act like an open differential when not under load. View definition below:

Torsen: invented by American firm Gleason Corp. Stands for TORque SENsing differential. Mechanical device of worm gears and a worm wheel that will split torque 50/50 in a no-slip situation. When one axle slips, the gears will send more torque to the axle with most grip, thus working in the opposite way of a conventional diff. Locking is instantaneous because it's a fully mechanical device. The gears work by sensing differences in torque instead of differences in rotation. This means it will prevent wheelspin instead of reacting and curing it. Also, it won't inadvertently lock under braking, as it will only lock under power. So torsen had all the advantages of the VC but none of its disadvantages. Not only used as a center or rear differential, but also as a "trick" LSD for a sporting FWD car such as the Honda Integra Type-R.

Basically, when you're not spinning the wheels (i.e., on the brakes), the Torsen acts as an open differential.

 

Good point... I'd forgot about that. Sounds like a front and center Torsen upgrade would be a good choice for those cars that spend 90% of their time as daily drivers.

 

Thanks 4G63,
I was just going to make that point about the Torsen being open under braking. So, no problem in the US Evo.
Cheers,

 

Well, I don't know about a center Torsen diff. The way that the engine's mounted in the Evo makes retrofitting a Torsen that would work (never offered in any factory Evo before) looks to be expensive at best. I don't even know if it's worth it, to be honest.

I do want an ACD 6 speed, though.

 

Hey, when there is a will, there is a way... look at wtz, and his fitted front LSD (be it already an OE part). However, you're right in that the expense, and how extensive the work would be, would probably make the endeavor unreasonable.

 

supposedly the 05 evo's will have ACD and a front lsd. of course they're going to add them on to the current evo production, instead of bringing in a totally new model (kinda like how there's the test version of the MR, a 03 evo modified with all MR parts).

assuming the msrp will go up somewhat, isnt mitsubishi losing money for these additional features, since people are speculating it to be ridiculously expensive to install both on the 03/04?

 

bump

 

The short answer is no. MSRP will probably go up, but you can't use the retrofit costs on an 03 as a reference. For one thing, when you retrofit ACD onto a USDM Evo (if it is even possible) you are throwing away many thousands of dollars in parts that you paid for when you bought the car originally, and replacing them with slightly more expensive parts.

The US transfer case is unique to our market, so there are some savings in standardizing ACD across all the worldwide Evo lines and eliminating production of the US only parts. So yes, the ACD components are undoubtedly more expensive, but you're not paying for installation labor or for the original parts you're replacing, so the marginal increase is probably not going to be that high.