Stick axle, spool or lsd?

[Guest Jim Cambon]

Hi everyone,

I bought Mr. Mustang's yellow Birkin a couple of years ago. It's an early S3. Made some changes to make it more track worthy.

I'm way into the light weight thing, but that's another story. Been having a great time with it, driving on the street and track, though it's primarily my track car.

 

There are a couple turns at Colorado's High Plains Raceway, where I get a lot of wheel spin. The open diff rear end in my car is allegedly from a Toyota pickup not imported to the US. It looks like it weighs about 5 tons.

 

I'm considering a limited slip or spool. Previously I've found a lsd to be worth 2-3 seconds per lap. I don't have any experience with a locked rear end, but my friends say they work well at the track. The great thing, they say, is they are light, consistent and cheap.

I'm not concerned about accelerated tire wear, but I am concerned about massive understeer. Since the rear end in my car is kind of unknown, I don't know if I can get a suitable lsd, but I'm pretty sure I can get a spool.

 

My question is: Spool or LSD? IF LSD, Quaife or ? added to existing axle or possibly some other LSD axle from another car (RX7 or ?)

Can I add a lsd or spool to my axle without removing it from the car? Or is that a bad idea?

Any guidance would be most appreciated, thanks!

 

Jim Cambon

[rzempel]

I converted my car to Quaife and would never go back or even think of any other solution. It now feels impossible to break a rear wheel free. I dunno how you'd get a Quaife now, though, unless someone had one laying around. Quaife won't do runs of less than ten, and we barely made the group purchase a few years ago.

 

I believe Dick Brink at Texas Motorworks has a conventional LSD that fits in the Birkin.

 

Randall

[Davemk1]

I owned a live-axle Birkin years ago and autox'd it a lot. It had an open diff and spun the inside wheel all the time. I put a quaife in it and it worked perfectly. No wheel spin and no understeer. After the first few solo runs I forgot about it.

 

I've driven, but never owned, a few cars with welded diffs and they just flat out sucked. Unpredictable rear end behavior but totally predictable front end push during acceleration.

 

It sounds like Quaife doesn't offer their LSD anymore? Is that right? That would be a bummer. I'd search long and hard for one.

 

 

dave

[w650gb500]

Toyota rear axles, ring & pinions, brakes and differentials are normally used in numerous of their other vehicles. Even though it may be from a vehicle that was never offered in the US, there is a good chance that an LSD from a different Toyota vehicle will work. By pulling the rear "chunk" out and doing a bit of research, I would bet you can find something that fits.

 

Good Luck and let the search begin.

[slomove]

I have that Quaiffe LSD installed on my Birkin and IIRC there were folks on the Birkinowners list who researched an alternative for long time consulting with diff specialists and no alternative was found. Not to say there is none but apparently not so easy to find.

 

As for the usability, I appreciated the LSD a lot for track days on dry pavement and obviously it would be great for autocross where wheel spin becomes an issue. But if it was for public highway driving I would not bother.

 

Besides the improvement in acceleration I noticed a serious downside on wet and slippery curvy roads which may not be intuitive. It happened to me once at the Infineon track (or whatever the name is nowadays) and once locally on Mulholland Highway where I lost traction at one rear wheel on wet pavement due to a mud patch while driving fast but not spectacularly so. The sudden torque doubling on the remaining rear wheel that still had traction broke that one loose as well. At least that is my theory for a spin out of nowhere and without warning. I guess without LSD the spinning wheel would rather relieve the torque on the other side and keep that wheel able to keep up with the lateral forces.

[Croc]

I often used spool diffs in non-seven track cars on certain circuits to improve traction. But it took a change in driving style to get the car to rotate since the car will be induced to push/understeer with a spool. Its great for traction out of a corner with a high hp car but seems at odds with the corner carving abilities allowing a seven to carry higher speeds through a corner with relatively low hp. For that reason an LSD seems to be the better way to me.

 

Dan's suggestion of seeing if you can do a Toyota parts swap would be the easiest. If that is not an option then the common LSD replacement options for Caterhams are AP Suretrac and Quaife. Of these Quaife are the higher end option and I have seen these used in Birkins before.

[m wirth]

Hello, I am currently using a viscous LSD but have recently purchased another open diff and am saving up for a Cusco unit, I have heard some good things about them and they are available for many applications and are offered by several shops in my area.

http://www.cusco.co.jp/en/catalog/limited_slip_differential_-_hy.html

 

mike

[Warren Nethercote]

I had a locker diff on a street vehicle (OK, a 2WD pickup, but a street vehicle) and would not do it again. Maybe OK for track, but as noted by Slowmove, handling can be scary in low-grip conditions - you think you have lots of grip until it disappears all at once and you swap ends. You typically only do it once, after which you are wiser, but you never again take full advantage of the extra traction. My pirouette happened in lonesome splendor and did nothing but put a hole in the snowbank, but it might have been otherwise ...

[w650gb500]

If you have the ambition, skills and tool required to swap in a different rear axle tube, there are several other Toyota units that you can use or as you mentioned, the 1st Generation RX-7 GSL. There are many different r&p ratio's available as well as clutch and Torsen diffs for the RX-7 as they use the same as the Miata.

 

Toyota info: http://www.legendsracer.com/index.php?action=printpage;topic=113.0

Edited December 5, 2016 by w650gb500

[Guest Jim Cambon]

Thanks very much for all your responses, i really value your insights. I'll start calling tomorrow and report back if/when I find a solution.

 

Jim

[Guest Jim Cambon]

Here's what I found out on the LSD question.

 

The stick axle used in the Birkin is a Borg Warner M68, mine has 11/43 gears (3.90:1) but there are several other ratios as well.

 

Quaife has made an automatic torque biasing lsd for this axle for many years.

It's called the QDH1L, you can download a very good drawing with all relevant dimensions and read all about it here

 

 

https://shop.quaife.co.uk/birkin-s3-roadster-quaife-atb-helical-lsd-differential

 

 

I emailed Ben (ben@quaife.co.uk) a few times for more info, found him very friendly and helpful. I could have bought direct, but then I'd have to handle shipping and customs. He directed me to Brian at their US distributor, VAC Motorsports (great guys!).

 

 

brian@vacmotorsports.com 1-866-714-2002

 

 

My QDH1L, the last one in stock, has been shipped to me, I expect to receive it in a week or two. I ordered through VAC, the cost was a little less than ordering direct and so much easier.

 

Ben at Quaife indicated 12-16 weeks after an order for the next batch. They might start with an order for just one, but I don't know for sure. Check with Brian at VAC.

 

Please note: I have not yet received this item, everything indicates it will fit and work, but I won't know for sure till it's installed. I have no financial interest in selling limited slip diffs, I am just reporting the results of my research.

 

 

Also, in my research I happened upon this excellent article on the different types of differentials, their relative merits and suspension tuning for each one.

http://www.taylor-race.com/pdf/understanding_differentials.pdf

 

From this article I found out that Eaton also makes an ATB limited slip, called Truetrac. If they have one for the M68, I didn't find it. If so inclined, you could start your search here:

http://www.eaton.com/Eaton/ProductsServices/Vehicle/markets/performance-aftermarket/Differentials/detroit-truetrac/index.htm#tabs-2

 

best wishes,

 

Jim Cambon

 

 

[Guest Jim Cambon]

Finally got the Quaife installed, not difficult to do. Not noticeable on the street, ride quality not degraded despite additional 8 pounds of unsprung weight. Huge improvement on track. Wheel spin virtually eliminated, no significant increase in understeer, 2-3 second reduction in lap times.

Edited August 16, 2017 by Jim Cambon
unintended duplicate and further info