Idea for alternative to front LSD

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Idea for alternative to front LSD

Postby Desifinado » Sun Jan 27, 2013 10:15 pm

Hey guys,

Thought I would throw an idea out there and see if anyone has considered it.

I'm doing a rallyx build, and like everyone else I would love to have a front LSD.

My idea is to implement some sort of electronic diff. It would work by using standard wheel speed sensors and a second pair of calipers in the front. (if you really trust your system you could go with a single caliper and reroute your front brakes through this system)

Basically you would go to a brake-by-wire system for the front calipers which would sense and brake an individual front wheel if it was slipping to transfer power back to the other front wheel. I was thinking you could use something like the Prius brake actuator to just control the fronts.

What do you guys think?
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Re: Idea for alternative to front LSD

Postby Fox 21 Alpha » Mon Jan 28, 2013 5:45 am

I think your effin crazy. Do it. Post pics lol
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Re: Idea for alternative to front LSD

Postby sinerasis » Mon Jan 28, 2013 6:19 am

I do not think this would be a good idea for an alltrac.

My FJ Cruiser has a system that works somewhat similar in theory (A-Trac). Its not designed for speed, and honestly doesn't work very well anytime your going faster than a slow crawl. I would investigate the Land Rover system as they have been doing it longer and may have some interesting info about using it for high speed applications. It does not replace a mechanical traction device (locker/lsd/etc), but does have it's uses.

Plus it would add a ton of complexity and think about what you're saying: put the brakes on. If you're in a situation where you'd use it in an alltrac, you want to be able to keep your speed.
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Re: Idea for alternative to front LSD

Postby CMS-GT4 » Mon Jan 28, 2013 4:46 pm

I think Volvo used to have this system. Supposedly it helped with handling.
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Re: Idea for alternative to front LSD

Postby underscore » Mon Jan 28, 2013 5:50 pm

Wouldn't this burn the crap out of the brakes at speed?
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Re: Idea for alternative to front LSD

Postby Fox 21 Alpha » Mon Jan 28, 2013 7:32 pm

In all honesty I think its possible, but not sure the benefit would be worth it. You'd have to do a decent amount of machine work to get it add in the new calipers, you'd have to add in another master cylinder and piping too and from, plus wiring and the computer to control it all. It'd probably take up a lot of space and add a lot of weight over all. And I think it'd be kinda detrimental to handling at speed, I imagine it'd be somewhat jerky and unpredictable as the caliper actuates on and off, and I'd think you'd want some system that changes the pressure appropriately so your not locking up that wheel or any where near close as that'd throw off the whole dynamics of the turn or whatever your in. I could see it being a plausible system for off road, but for track/race/rally I think the time and money would be less and better spent on an actual front LSD and have way better results.

That being said, if you do go for it, I'm sure it'd be an awesome engineering feat, we'll help from the interwebs best we can :D
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Re: Idea for alternative to front LSD

Postby Desifinado » Tue Jan 29, 2013 2:46 am

So we have a couple months to go in the build before we need to think about getting the driveline sorted, and I have a feeling there won't be any availability of front LSDs by that time. (don't quite have budget for xtrac).

A production unit like the prius actuator should be able to apply brake pressure in pretty fine increments, it would just require some tuning to get right. and I don't think that it would really cook the brakes (shouldn't be in use all that often)
I think the biggest headache would be mounting a second set of calipers. And I'm not sure i trust my programming skills on a long drive at ~80mph. Don't want my brakes locking up randomly.
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Re: Idea for alternative to front LSD

Postby lumbercis » Tue Jan 29, 2013 3:47 am

It sounds like what you're describing is Electronic Stability Control, which is a kind of advanced abs ("electronic diff" seems to most commonly refer to electroncally-actuated mechanical diffs like on landcruisers).

Found this article where a guy retrofitted a modern corvette system to an old hot rod, so it can be done.
http://www.hotrod.com/techarticles/hrdp ... ewall.html

No need for programming or additional brakes or any of that. You just need to find an appropriate modern system that can be retrofit to an alltrac.
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Re: Idea for alternative to front LSD

Postby MWP » Thu Feb 21, 2013 9:31 am

Its a great idea... do it and post the details so we can copy your hard work :rofl:

But seriously, it could be a great solution to our LSD woes.
You'll need a big brake setup though to take the heat from track driving.
All manufacturer setups have brake temp sensors that disable the system when the rotors get too hot.

It might also end up being a great upgrade for our shitty ABS system too.
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Re: Idea for alternative to front LSD

Postby athousandleaves » Sat Apr 27, 2013 8:18 am

In my opinion this would not work with the stock alltrac transmission and would only serve to burn up the VC or explode the center diff.
If you brake both of the front wheels under power the center diff and VC will want to decrease power to the rear at a same amount and if the system brakes hard enough you will stall the engine. You might be able to get away with braking just one of the wheels when turning but for all the work/weight/added complexity its not worth it. Just buy an Audi RS5.

The alltrac system is permanent 4WD where the center diff drives the front and rear diffs, not front diff driving the center and rear like AWD.
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Re: Idea for alternative to front LSD

Postby MWP » Thu Jul 04, 2013 5:19 pm

athousandleaves wrote:If you brake both of the front wheels under power the center diff and VC will want to decrease power to the rear at a same amount and if the system brakes hard enough you will stall the engine.


It only brakes one wheel at a time on each side of the open diff... one front wheel at a time.
All itll do is help tranfer power to the other front wheel, it wont effect how the center diff works at all, and it certainly wont "explode it".
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