Purpose of the car, in order:

Spirited street driving, occasional AX, occasional track days.



Here's what i think i know

LSD
- Always locks wheels together under acceleration and deceleration.
- Introduces understeer in slow corners.
- Generally considered the better choice for the big track.

TB
- Only locks wheels under acceleration.
- Acts like a open diff if a driving wheel is off the ground.



So, the question is, what should i get for my 915???

The car will never be a dedicated track car, it's mostly driven on the street.
The TB seems to be easier to drive on the street.
However, the slow corner understeer of a LSD could probably be tuned down with suspension settings.

The TB loses it's magick if one wheel is off the ground. In an AX setting, the suspension would need to be pretty stiff to keep both wheels on the ground at all times, would a LSD be the better choice here?


Anyone compared the two back to back in a 914?
Andy

Only used LSDs....one came in my 915 and it's been good to me. I added a Quaife to my 901 in the Rocket....

TB needs periodic maintenance if I remember....

I have run both and like the LSD better in almost all cases. Most AX'ers I know like the TBD's better because they like to snap the car through AX elements when the TBD goes open on deccel. I've always thought the deccel-oversteer in a turn with a TBD is more acute, but it does make for better slalom snaps. TBD's do one more thing that's easily driven around but it's a little annoying to me.

When I accelerate in a long sweeping turn which of course, we all do, I can feel the bias changing now and then. It doesn't seem to upset the suspension (except that I can feel it) so it's just an itch. Still, it's a little like someone tapping on their glass eye while they're talking to you.

It doesn't really effect you, but it has your attention.

The LSD is smoother and the transition from deccel to accel causes less drama. But the LSD is gonna cost more and the maintenance is higher. The clutches and plates need to be replaced now and then based on your driving style and mileage. Of course, there is something wonderful about the TBD install-it-and-forget-it thing.

There's my 2 cents. They're both good

Good luck

I have run Quaife's in my fwd rabbit, awd audi, and rwd 914 2.7 six.

The torgue biasing takes some learning but I love them. In the rabbit it would
put so much traction to the inside wheel on a corner that you had to limit the throttle
to what you could hold on to (fwd).

The awd Audi was a beast !!! If you got it fish tailing the torque transfer was scary fast.
But when/if you learned it, the beast would hook up and grab !!!
I loved racing anything in the snow See ya !

The rwd 914 is much the same. It puts power down on the wheel that is gripping.
It wants to understeer on the exit of slow corners. But once again the torque transfer side-to side can happen really fast. Can you say tank slapping !!!

That said I prefer the torque biasing.

I forget what the difference is but I have been told by every racer up here that the TB diff is the one you want for AX. It would seem to me that if it didn't work while lifting wheels they would not have said that.

Fordahl's advice for an AX setup for a 914 is no rear sway with 200-250lb rear springs and a TB diff. I did what he suggested and my car does fine

From the Guard website:


"A torque-biasing differential performs like an open diff whenever one of the two drive wheels lifts off the ground. Lock-up and traction are lost until both drive wheels are again planted firmly on the ground."


Andy

So would that mean the power is always on the ground?

Ah, or is it so that you can get both wheels on the ground faster. I don't know. That is why I listen to the pros and do as they tell me too...

No. With an open diff, power goes to the wheel which is up in the air. Hence the wheel spin.
If the TB acts like a open diff when one wheel is in the air, the TB effectively stops working and you get the dreaded wheel spin.

Andy

I guess since all the pictures of my car lifting wheels it is only lifting the front should mean I don't have the dreaded wheel spin but still interesting. Maybe this is why you do NOT want a rear sway with a TB diff.

You can get Guard LSD with 60 accel/ decel40 lock up. Thats what I have on the Boxster and I love it. Very little push in AX and it gives very postive feel with no lightwheel spin. I can kick both rears out

Mine is 60 / 40 as well. And you can build it with other settings without buying any more parts. I just wish it was as easy to get in and out as fast as the 911 R&P's.

It was my understanding that a TB ONLY works under acceleration, even when one wheel has lost grip or in the air... however from the Guard Trans quote you posted, if one wheel is off the ground its an open diff. Interesting, thanks for posting this Andy. I personally would shell out the extra $600 or so for a clutch pack diff and be done with it.

Cheers, Don.

It's also true that TBD's are really stressed bad with wheel-hop.

Torque biasing will divide the power to the wheel that has traction.
IE the one that creats the most torque.

This done by gears so when a wheel lifts the torque is very quickly transfered to the
wheel with grip.

Only way to go for AX. But it does take some learning for rally

The TB does not care if it is acel or decel, it's just gears (no clutches).

Wheel hop always blew my CV's and never a diff.

Track, Limited Slip, no question.
AX, Torque Bias for the simple fact that you can drive the car as you need to in an Autox...with a Limited slip you MUST do burn outs to get around tight corners...

Given your motor, you can use either one. Torque Bias has little to no maintenance where a Limited Slip has a clutch pack that needs to be changed and maintained...which in the case of a 915 tranny is not a simple nor a cheap thing to do...you may end up having to reset the pinion depth but I dont know how the unit is designed (like can you swap out the clutch pack from just one side???)

I would go with whatever Guards recommends...he has alot more knowledge than most people about these things...and he sells both units.

Rich

As someone who has rebuilt a lot of clutch type LSDs I can tell you for certain that they need service - really depends on how hard you drive the car. When one wheel is up in the air the only thing transferring power on a clutch type LSD is the spring pack. The stronger the spring pack is the more the 'evil' characteristics come out - like major over-steer on lift throttle corner entry - they also want to go in a straight line on power. Real racing diffs are a different story with the different ramp angles but we don't usually have that luxury in a street car. I have built LSDs with enough pre-load on the spring pack to snap axles in drag cars so they can certainly do the job.
I also drove a car for many years that had a true 'locking diff - a Detroit Locker' and would not wish that POS on anyone. In my car I am going with a helical diff - it will be used for nearly all street and some open track events. Smooth, doesn't wear out or need special oil - just works.

On the street I would use a torque bias for sure. Just smooth power and doesn't remind you it's there all the time except when you need it.

I used the TB diff in my AXer If you lift the inside rear, it does act like an open diff....I hear....never done it. The TB diff transfers the power to the wheel with the most grip ( even if the inside rear is just lightly loaded) and you can feel it happen.....the car tucks tighter into a corner. If you're lifting the inside rear your suspension settings are not even close to right and you should fix that before you think about an LSD. The TB was recommended to me for AX by Fordahl, Burfield, & Guard amongst others. Nobody recommended a clutch type.
I have a TB (stock) in my MR2 turbo also. It is seamless on the street and has no problems with AX.....all stock suspension with no inside rear wheel lift....even with a rear anti roll bar.....of course AAR set that car up for Toyoda so it figures.

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Andy,

your going to want the TB for a street car

I had an interesting conversation with Paul once.
he admitted to me that in a mid engine car with low power the TB might actually be better on the big track too....

I pushed him on this issue because AJRS ran back to back testing with a TB at 205rear wheel HP and found the TB faster than and LSD in a mid engine 914. Paul verified this could be the case theoretically

guess what I went with in my track box with F, J, S, O, V and a 2ltr

the locker and LSD are much better under braking
but slower in some situations over all
much too much understeer in autox and tight stuff.

fun, because you have to play "dukes of hazard" in tight stuff.... but still slower.

the TB does turn off and on.. and does take some getting used too. you can feel it, and it takes some mental re-learning.
on a big sweeper at 80mph... you have to floor it just when your not sure your going to make the corner. This causes the car to "tuck" and make the corner.

brant

Guard specifically recommended 60/40 LSD to me for AX car application given my HP profile.

I would recommend talking with Matt at Guard tell him about HP and application etc. Its not as simple as AX or not AX car as some might believe.

You have a lot more power than any of the people posting suggestions here. I dont have any push in my AX car with 60/40 LSD. No burnouts required. Ask all the people have driven the car.

Funny, Bill C wrote it pushed badly in the tight stuff.....that musta been a tire problem, eh?

I'm running a low-geared 3.6L motor also and I'd write nothing different. Matt at Guard is very helpful. He and I just talked at length about LSD gear oils and Porsche synchronizers a couple of weeks ago.

Good Luck

instant classic thread!

JP, Youre absolutely right! Andy should definitely go with TB.


..and who's 60/40 LSD based car spanked your very well setup TB car by almost 4 seconds last Autocross event? Oh thats right youre superior power plant had dirty carbs. LOL!

Andy....915? I can't believe it!

Before you start you should drive my car to see what you like or don't like. It is regeared, WEVO, has a Guard TB and a shifter. I really like the TB

You will have to do a little work inside to run a 915 like machining the bolt heads of the ring gear, clearancing the case, installing the mag pickup for the speedo etc.

I'm glad to help out, it's a worthy mod and I never regretted spending the money.

Give me a call....

Yes, Brit got beat. It's happened before. Yes, even you wrote the shitbox was running foul.....but Brit still beat you on 4 or 5 clys.

You gonna bring that Boxturd out again for a rematch or sit back & crow about your one hit wonder?

I've had two 911's, one with LSD, and the one I drive now with TB. The diff is definitely open when the wheels are off the ground on the TB. In Montana I couldn't even back the car out of my garage on the packed snow or ice. The TB worked as a tire polisher. LOL. \
The LSD I drove in the ice and snow.

My .02c.

Im sure those Avons had nothing to do with it either

It should be noted that the reason you hear the comparisons of LS vs TB is that when you stand on the throttle on a TB it locks harder and less when you are off throttle and why it's called TB because its the amount of torque applied that determines it's lock amount. This is great for AX for tight turns when you are off the throttle and don't want the rear wheels pushing you straight and also good for the street. When you want to apply a 3.6 to the ground in a straight line it's hard to beat. However, as others noted both wheels have to be on the ground to get the benefits. TB is maintenance free

The LS on the other hand works on a percentage of lock that is determined by the assembly and clutch pack and isn't variable when you are on and off the throttle but keeps you driving even if one tire is loose. A clear benefit. The same benefit can be a drawback on the tight corners of an AX where the outside tire is turning much faster than the inside tire and the lock of the LS wants to turn them at the same speed.....The car wants to go straight but suspension setup can reduce that. LS requires clutch pack replacement once in awhile but not so frequently that I would not buy one because of it.

They each have pros and cons for sure and your car setup, tire size and stickiness should be considered. For me it is a no brainer to go TB since I don't race and just do spirited street driving and need to get 3.6 power to the ground and nothing more.

Also, I think it's inappropriate to "directly" compare a 911's response to these vs a 914. They handle completely different.

Snow.....LSD will get you moving but will also want to drive you straight. It's a double edged sword. Something to be at least aware of.

Hopefully this info helps out.

On the subject of "lifting". I AXed a 914 with a rear AR bar for a couple passes. I think I took it places where the owner hadn't gone. We were making fun around a sweeper feeling good when the inside rear lifted.....acceleration ceased (open diff)
and the cars well behaved attitude went to hell....then got worse when that inside rear sat back down....I really can't describe the move except to say that it got ugly trying to catch up with it. I can't help but feel that a clutch type LSD wouldn't have made it any better than the open diff action of the TB.

*Fix the suspension first* if you're "lifting". At one point the shitbox went thru a "smoke the inside rear" around a corner with an open diff (no rear AR bar).
I kept jacking up the rear spring rate & adjusting the front AR bar to suit untill it quit that action.

I really don't give a damn which LSD anyone else uses. The data is in this thread. Pick your poison.

A pic...note the single circular black line on the left behind the car.

Hey SirAndy,

I believe it is well established that an LSD is the choice for a pure track-car with the advantage of "locking" the wheels for braking. This design also induces a good bit of understeer.

For the street and AX, I would choose the TORSEN (torque sense or ATB) design with it's ability to turn tight corners happier and less induced understeer.

However, NO ONE has mentioned the issue of COST and WORK to maintain an LSD. I ran an LSD when I was running SCCA in a Datsun 510 and after a season,
the clutch plates had worn to the point that the Diff had to be pulled and worked on. The Stock Porsche LSDs use carbon clutch plates (I've been told) and wear fairly rapidly. While Guard has better material replacement clutch plates, they are very expensive! Are you up for this burden?

With the TORSEN there is NO maintenance, other than making sure it has oil. I did quite a bit of emailing with the Quaif guys in England and they swear I could run their diff with ATF or 5 wt oil! I took the whole Diff apart before installing and it is amazingly simple: just worm gears and drive gears: nothing to wear.
I tried cleaning up some rough edges in the carrier with my carbide air tool and found that the material on all the parts was EXTREMELY hard! So I understand why Quaife is so confident about the reliability.

For this reason, I bought a Quaife for my 914 V8 which I run at Willow Springs. It DID cause a bit of understeer, but with the addition of a rear swaybar, it came right. The diff works GREAT and changed the car from SMOKING the inside wheel off corners and 1/2 way up the straights(in an expensive cloud) to just putting the power down.

I'm willing to live without the rear axle "lock-up" under braking as I never had it before...so I have to be a more precise driver.

The Diff in the 915 is the SAME as that in my 930 box, so I have personal experience with the model you would use. It was also pretty easy to set it up myself....All is GOOD!

I hope this helps....it's your decision.

Terry

From what I recall from the last factory LSD rebuild I did recently, the parts may be prohibitively expensive, but the labor definitely adds. If you go LSD vs TB I would recommend learning how to replace the worn bits yourself. It is not too bad. Here are some ball park prices (as I recall them) for the parts I needed:
- 6 plates ~ $40 ea
- 4 disks ~ $85 ea
- 2 belleville washers ~ $85 ea
- 6 bolt plates ~$11 ea

Without labor the parts total is about $800-850.

If you want to learn how to deal with understeer on accelleration, go AX a front-drive car for a season or two. Not for nothing did I do two seasons in the ur-GTI -- I wanted to learn race tires and I wanted to be able to drive through understeer on power.

Part of it is suspension setup, and part of it is technique.

I knew then I wanted to be able to drive with a LSD on the track and decided front-drive would be a good way to learn the technique.

Go read 'The Unfair Advantage' to get some insights on understeer, 'The Friction Circle,' and driving with a spool. OTOH, I suspect none of the cars he was really good in would AX worth a damn...

My experience with the Quaife TB diff has been that it is great on the AX course. I hardly know it's there. It puts down the power and I love it, for AX. On the street it is fine until you start doing some tight radius stuff like tight turns into a parking space. Then it feels like a locked diff!! The tires grab and slip. There may be something wrong with mine, I'm not sure. That stuff about it acting like an open diff when you lift a wheel, not true. Last fall I broke a CV joint and so you would think it would not transmit power because that is about the same as lifting a wheel. Well, I was able to drive it. It put down power to one wheel. Pretty dangerous as the car would jerk one way when I hit the throttle and jerk back when I lifted. But I was still able to drive it and get it home. I find the low speed stuff to be very irritating and think it may have contributed to the broken CV. As my car is pretty much AX only with very little street driving I live with it. I wouldn't like it for a daily driver running errands and stuff. You may remember I was at the Doc's tranny clinic at McMarks talking about it and checking out Rob's tranny trying to see if mine felt different from his. I would recommend that you drive Rob's car sometime a see for yourself.
My $.02

I have no experience with a Quaife TB. My Guard does not act like that at all. No weird locking, no noise, no locking or jerking in turns and I never know it's there. Are you sure it's a TB and not a LS? Also, I don't know the differences in design between the two brands but it sure sounds like something is wrong....I have had LS's act like that and sometimes a fluid change helps

Hello Guys,

It's been a while since I logged in. I just happened to be looking for some information today and came across this fine thread on my other search.

Andy,

I am going to side with the guys who are telling you to go with a torque biasing differential. For all but a dedicated track car I really feel that it's the best option for a 914. It's what I personally run in my own 914. I think it's the way to go for the vast majority of us 914 owners, whether it's got a bone stock 1.7 Type IV or a monster 3.6 swap. It's just very well suited to the chassis dynamics of the car.

Part of why so many 911 owners swear by a true LSD is because of the rear engine design. With all that weight out on the rear end, there's that infamous 911 tailwag under hard braking. Because an LSD locks under braking it helps to make the car much more stable as you bring it down from speed. The midengine design of the 914 makes it inherently more stable under those same conditions. That stability isn't needed in the same way with the 914.

Aside from adding those comments, I don't really see much of anything that I will disagree with in the conversation going on here. Though there is one thing that I do want to mention, and that's regarding the service life of our LSDs. Every time this topic comes up there's a lot of discussion about the cost of rebuilding the LSD and the fact that it does need service over time. This is a practical reality of LSD ownership but it's not something that is a deal breaker for most people. The service life of the internals for our LSDs are about the same as the service life of the clutch or synchros. This isn't something that you're going to be ripping out every year or two and rebuilding, even if the car is a dedicated track car. People get years and years of use out of these things between rebuilds.

Just a couple of examples from recent experience. Last month I rebuilt an early GT LSD. This LSD was so old it still had a welded cap and wasn't CNC billet. The owner had purchased it new from Paul and it was well over a decade old. It was from a 911sc running a hot rod 3.2 engine on carbs that was mostly street driven with a couple of DE/track days a year. The owner said he drives about 5000 miles a year. This was the first rebuild on it. Or, there's Pat Williams' personal 400whp 930. He's been running the GT LSD for 4 seasons of dedicated PCA club racing now. He checked his before he put the car on the track this year and said that he wasn't even close to needing it rebuilt. So, there's a couple real world examples from different applications and levels of abuse. The short version is they hold up and stay together a good long time between services.

I'll try to come aroud more. This used to be one of my favorite P-car boards and work just kind of drew me away. Maybe we should even look at becoming a site sponsor. We've got some new products coming out that are appropriate for the 914 and you would be a good group of people to offer them to.

Regards,

Matt Monson
Guard Transmission LLC

Would you be the Matt from Carquip? If yes, glad you are here!

Thank you Sir!


And welcome back ...
Andy

PS: Now all i need is the side-shifter conversion for my 915 ...

I think the LSD is still overkill for a purely street 914... I'll be running the Orange Smasher 901 in Dad's car to make sure it works, and then deal it...

New stuff do tell more

Hello Paul,
That's me. You might recall that we spoke last summer shortly after I bought Guard.

Regards,

Matt

Let me talk to management around here before I go too deep down that path. I don't know how you guys are around here with the vending thing, but I don't want to step on any toes. Regardless, I personally am not fond of the very commercial approach a lot of guys take and prefer to participate on a more informational level.

But I'll give you a hint. It starts with 901 and ends with ears...

I'm listening. I had a Guard TB in the car I just sold and the difference was big. I know the next car I build will have one in it.

hmmm...
actual testing of 914's verify this...
hmmm...