02Pilot
02Pilot SuperDork
9/4/18 8:19 p.m.

This thing claims to convert an open diff to a limited-slip and doesn't require selling an organ to buy it. Their youtube videos show how it works. Problems are 1) I'm skeptical to say the least, and 2) I don't know enough about diffs to evaluate the design. So, naturally, I turn to the hive. Go to it.

https://www.ebay.com/itm/Bmw-2002ti-168mm-Progressive-Limited-Slip-Differential-conversion-set-LSD/263565725719?hash=item3d5dbdd017:g:m9UAAOSwF2xbWwYd

 

84FSP
84FSP SuperDork
9/4/18 8:31 p.m.

So this is a modern detroit locker setup.  Effectively two hardened metal blcoks with aprings forcing the locking behavior desired in the spider gears for more two wheel traction.  Phantom Grip sold them for many import and euro cars over the years.  They are 70% of a real lsd like a quaiffe or wavetrack for 25% of the price. 

I ran one in my fwd mkiii gti with pretty good results.  At the time it was a $175 solutions vs the $700-900 real lsd's. 

I'm wondering if there aren't better bmw parts bin options from later years that would give results for similar coin.  I'd check out bimmerforums or some of the bmw cca sites to see what others are doing.  I always error on the side oem+ mods where possible over aftermarket.

Pro's - cheap and functional

Con's - they generally require hand griding of the spider gears to create the mating surface needed to fit.  They also wear out in ~70k miles or so.

ProDarwin
ProDarwin PowerDork
9/4/18 8:45 p.m.

Search for feedback on "Phantom Grip".  Used to be the big brand selling this type of thing.

02Pilot
02Pilot SuperDork
9/4/18 8:48 p.m.

So it's a time-tested design - that's good to know. The question comes down to execution, which is an unknown at this point. As far as grinding the spider gears - is this just to provide the proper surface, or is it a clearance issue?

As far as BMW options, well, the one I linked to is for my 2002; small case LSDs have skyrocketed in price, just like almost every part for 2002s it seems. The same company produces units for a lot of different models, including my 128i. In that case, it's a few hundred bucks vs. over a thousand. It's the cheapest option I've seen for either car by a considerable margin.

mikeatrpi
mikeatrpi HalfDork
9/4/18 9:08 p.m.

Item location: Belgrade, Serbia, Serbia

Looks like its got a long way to travel to you!

Donebrokeit
Donebrokeit SuperDork
9/4/18 10:13 p.m.

Back on the day the Shelby Dodge people tried them and found the life cycle was measured in oil changes. They seemed to work, just very short life span.

 

 

Paul B

Stefan
Stefan MegaDork
9/4/18 11:02 p.m.
Donebrokeit said:

Back on the day the Shelby Dodge people tried them and found the life cycle was measured in oil changes. They seemed to work, just very short life span.

 

 

Paul B

Yep, we had one in a Turbo Shadow for a ChumpCar race and it lasted maybe half the race before it was open all the time.  Very annoying on a turbocharged FWD car with hard tires in the rain and cold. 

ProDarwin
ProDarwin PowerDork
9/5/18 7:27 a.m.

What was causing it to go open?  Wear?  Heat/spring fatigue?

 

93gsxturbo
93gsxturbo SuperDork
9/5/18 7:38 a.m.

Generally wear - they work by jamming the pinion gears against the differential case using die springs.  Not an ideal situation, not really like a Detroit Locker since they dont really lock anything.  Probably fine for a budget 1/4 mile car, not really for street duty.  Also that rig is way overpriced, they used to be sub $200 BITD.

Ransom
Ransom PowerDork
9/5/18 7:45 a.m.
84FSP said:

So this is a modern detroit locker setup.  Effectively two hardened metal blcoks with aprings forcing the locking behavior desired in the spider gears for more two wheel traction.  Phantom Grip sold them for many import and euro cars over the years.  They are 70% of a real lsd like a quaiffe or wavetrack for 25% of the price. 

I can't speak to the veracity of the claim, but they go to lengths in the ad to distinguish themselves from Phantom Grip, noting that the Phantom Grip stuff was only LS via spring preload, while this claims to also use a conventional ramp arrangement to increase clutch load with accel/decel.

flatlander937
flatlander937 HalfDork
9/5/18 9:00 a.m.

The problem is the clutch still relies on pressing against the side gears. It'll wear stuff out.

In a real LSD setup the clutches are splined to the side gears(on the backsides) with steel plates that spline to the case between the clutches. You need surface area for the friction to occur or you'll just turn everything into metal shavings... Ramps or not.

 

Also to set the record straight since someone mentioned it... The Detroit Locker is anything but similar to a clutch type limited slip. They work by not allowing the axle shafts to spin slower than the ring gear. Result is they send power to the inside wheel only... Until it exceeds traction, and the ring gear matches the outside wheel speed... Meaning now you are sending power to the outside wheel, with the inside tire spinning. 

 

Skip to 2:10 for the technical explanation.

https://youtu.be/ekgBnktLw8k

Stefan
Stefan MegaDork
9/5/18 11:38 a.m.
ProDarwin said:

What was causing it to go open?  Wear?  Heat/spring fatigue?

 

I suspect heat.  If you think about the load that has to try and control (that spinning wheel/tire, hub, rotor, axle, CV joints, etc.) and how little contact patch there is for it to grab inside the differential you'd see that it wasn't really going to work by rubbing steel against hardened steel with oil being splashed about without using spring pressures so high that it would effectively be welded.

I've seen some variations on the PG units where they add friction plates to help keep spring pressures reasonable and get more grab, they seemed to work better, but not all of them would work within the confines of the typical open FWD differential.  Some people tried machining their side gears to add friction material, etc. and resulted in weakening the gears and eventually causing a failure there.

It isn't an easy or cheap answer to get around, which is why there are still people welding diffs.  It works, provided you adjust the car's handling and the driver's style to compensate (basically make the care wildly loose in the rear and use point a shoot driving style)

trucke
trucke SuperDork
9/5/18 12:07 p.m.

I have a similar design in my FX16.  However, this one has a proprietary plate material, all the gears were machined to be flat, parallel, perpendicular and the proper surface finish.  You can see the tight tolerances on all the mating surfaces.  The springs were selected based on my cars power output.  This baby hooks up every time!  Been in the car since beginning of 2010, still going strong!

I would be very skeptical of buying the one posted.

 

02Pilot
02Pilot SuperDork
9/5/18 1:38 p.m.

So if I'm understanding this correctly, this design is better suited to track use than street. Further, even though the basic design is sound, problems of materials and limited friction surface, not to mention a lack of precision fitting without significant machine work in most cases, suggest that results are likely to be less than optimal, especially over time.

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