[Techevo]

Ok, for the benefit of others who want to fit their own LSD, and for the interest of anyone else, here are a few pics and details of the install of a Wavetrac into the my E91, which has a welded crownwheel as standard.

Firstly, removed the rear underbraces and exhaust heatshield to get access to the diff and propshaft rear bolts;







Unbolt propshaft and halfshafts, marking the position so to bolt back up in the same place (good practice)





Unbolt the 2 front mounts and one rear, then lower diff off the car and onto the bench;





I put the diff in my adjustable vice to allow decent access to strip;



Remove half shafts by tapping out or using a slide hammer attached to the flange;



Remove rear cover to access diff unit;





I then checked the backlash to give me an indication of where it was now in case I wanted to adjust on rebuild. Found to be 0.118mm, within the standard rebuild spec of 0.06mm-0.14mm.



I removed the stubshaft seals and discarded (will fit new ones), then removed the circlip bearing shims and bearings, marked up for correct re-fitment;





Leaving the diff unit with inner races attached;



Removed the diff unit leaving just the pinion in place;



And the diff on the bench next to the new wavetrac unit;



Press off the inner races and mark-up L/R for correct re-install. Also inspect races for any damage (pitting or dents)








I then measured up the new Wavetrac unit and the old standard unit to see how close there were in dimensions, 12 microns difference on one side;





And 1 micron on the other stub, pretty good;





The next measurement to be taken is the most critical, the ‘height’ of the crownwheel. To do this I manufactured a sleeve with ground ends which sat on the face where the inner bearing race sits, as the dimension from this face to the tip of the crownwheel teeth must be the same on the new diff to keep the meshing and backlash the same.

The diff unit with this sleeve attached was then sat on a Grade A granite surface table to enable the height to be referenced and then slip gauges made up to mirror the exact dimension measured. This would then be the reference height when installing the crownwheel onto the Wavetrac.

Measuring the crownwheel tip (a small flat area at the inner most part of the teeth tip) in multiple areas to ensure everything is flat;





Height gauges made up to the exact height measured, now, even if the DTI moves, I have a reference height to use.;



Now that I had the exact original height, the next stage was to machine off the crownwheel;

A carbide tip was used at first to machine away the cast iron housing, then onto a ceramic tip for the welded area and case hardened (around 60HRC) crownwheel;



You can see the transition between the weld and the diff housing on this photo;



Now through the weld;



A video of machining through the weld;

Removed the old crownwheel by pressing off, leaving two parts;





Next was to grind away the machined lip to leave a flat finish to fit to the new wavetrac, and measure the height to work out exactly how much material to remove. Once this was done, a calculation showed 3.35mm needed to be machined off. Most of this removed back on the lathe, then onto the grinder for a precision finish.

Firstly, clocking up the crownwheel on the lathe to make sure it is running true before removing 3mm of material;



Then, back onto the grinder for a small clean-up;



Old and new unit;



Next, set-up the CNC to drill and tap the back of the crownwheel, PCD of 153mm x 10 holes, 12x1.25mm pitch, 14mm deep;









Next, I bolted the crownwheel to the wavetrac, measured the height to enable a final skim to the correct dimension;



Final skimming!;

After this, back to the workshop to re-assemble, pressing on the inner races;



Bolting on the crownwheel (100lbs/ft and high strength Loctite);







Re-fit into the diff housing with the original bearings;







And finally, re-check the backlash, perfect, 0.113mm, just 5 microns difference to original figure;



Next, out with the pneumatic sealant gun and button up the casing;







Lastly, refit the new seals, stub shafts, fill with nice Millers CRX 75w90 NT oil and refit the diff;

[TrAcK TRaP]

wowww! what an amazing work...

[GreekboyD]

Damn Clive. Sick work man!

[2deerwhistlers]

Nice work! Nice write up! Thanks!

[Quasimodem]

I am just going to clear off my garage workbench and get right on it.

[Si-M240i]

That's awesome work and very brave if you to do it. Well done and enjoy your new LSD. I have the quaife and love it

[joe_planet]

you are HUUUUUGEEEE!!!!

[TorqueAddict]

wow!

[WreckerX5d]

This is why I'll pay people like you to do it, lol.

[335D Alpha Pappa]

Originally Posted by Wrecker335d

This is why I'll pay people like you to do it, lol.

+1

Nice to have access to a machine shop

[Techevo]

Originally Posted by N54CherryHill

wowww! what an amazing work...

Thanks.

Originally Posted by GreekboyD

Damn Clive. Sick work man!

Cheers John, all in a day's work!

Originally Posted by 2deerwhistlers

Nice work! Nice write up! Thanks!

No worries, hope it helps others who want to try this mod themselves.

Originally Posted by Quasimodem

I am just going to clear off my garage workbench and get right on it.

why not my man!

Originally Posted by Si-335d

That's awesome work and very brave if you to do it. Well done and enjoy your new LSD. I have the quaife and love it

Not really brave TBH, I'm an engineer by trade and build Hi-spec Evo and R35 GTR transmissions normally. Really loving the E91 after fitting the Wavetrac, the last piece of the puzzle!

Originally Posted by joe_planet

you are HUUUUUGEEEE!!!!

Originally Posted by TorqueAddict

wow!

Cheers!!

Originally Posted by Wrecker335d

This is why I'll pay people like you to do it, lol.

Originally Posted by 335D Alpha Pappa

+1

Nice to have access to a machine shop

Yep, I couldn't have done it without access to my mates shop. I have a small mill and surface grinder in my workshop, but not big enough for this job.

[BB_cuda]

Firstly, I'm hugely impressed with your work. My father would be right there with you in precision work such as this. He was a journeyman machinist for Bell Helicopter.
I noticed you didn't go back with welding ring (you called it crown wheel) back onto wave track. Any particular reason you did this? I can appreciate the precision of locating the holes for drilling and tapping. Perhaps you didn't have equipment for welding back and most importantly ensuring that the weld doesn't cause a out of parallel interface from improper fixturing during weld.
Good show, mate.

[Crawler]

Awesome work. Knowledge, motivation and patience are more valuable than any tool. You have them all I see.

If you don't mind me asking, why did you choose the Wavetrac over the Quaife unit. I'm paying someone to do mine in the not too distant future and am interested in your thoughts given your engineering background.

Cheers,

J

[BB_cuda]

Another question: I see that you tapped for RH threads (based upon direction i see torque wrench being applied in one of the last photos). I don't claim to know which hand of thread is best for this differential but was the hand of thread researched?

Background is my brother was working on Chrysler 8-3/4" rear end and broke off bolts on the ring gear (as they are left handed) and he was trying to "loosen" them turning counter clockwise. Granted, Chrysler is a little different than everyone else. Before 1970, lug nuts on Mopar was LH on drivers side and RH on passenger side. I know a diff has nothing to do with the lug nuts.

[Techevo]

Originally Posted by BB_cuda

Firstly, I'm hugely impressed with your work. My father would be right there with you in precision work such as this. He was a journeyman machinist for Bell Helicopter.
I noticed you didn't go back with welding ring (you called it crown wheel) back onto wave track. Any particular reason you did this? I can appreciate the precision of locating the holes for drilling and tapping. Perhaps you didn't have equipment for welding back and most importantly ensuring that the weld doesn't cause a out of parallel interface from improper fixturing during weld.
Good show, mate.

Originally Posted by BB_cuda

Another question: I see that you tapped for RH threads (based upon direction i see torque wrench being applied in one of the last photos). I don't claim to know which hand of thread is best for this differential but was the hand of thread researched?

Background is my brother was working on Chrysler 8-3/4" rear end and broke off bolts on the ring gear (as they are left handed) and he was trying to "loosen" them turning counter clockwise. Granted, Chrysler is a little different than everyone else. Before 1970, lug nuts on Mopar was LH on drivers side and RH on passenger side. I know a diff has nothing to do with the lug nuts.

Nice one, I bet I’d get on with your father like a house on fire, I love talking to guys who have had a career in what I’d call ‘proper engineering’ lol. An awesome job IMO, and something that is dying out in this day and age, proper hands on skills and experience.

I didn’t weld the ring onto the LSD as the Wavetrac is specifically designed for a bolt-on item. Welding would damage the material properties of the casing, and also the problem with distortion, as you mentioned. Some of the BMW diffs have bolted rings, some welded, I guess due to the lower costs of welding.

I used normal R/H threaded bolts as I have plenty of these ‘in stock’ from the Mitsubishi Evo transmission builds that I carry out, and I know they can cope with anything I throw at them (over 1000+ bhp in some drag Evo boxes I have built)

As they are fine thread and locked in with loctite, as well as the forces on them being a shear load, not a torque load (on the actual bolt itself) a L or R thread makes no difference. The standard BMW bolted diff also uses R/H threaded bolts, probably more to do with cost than anything.

[Techevo]

Originally Posted by Crawler

Awesome work. Knowledge, motivation and patience are more valuable than any tool. You have them all I see.

If you don't mind me asking, why did you choose the Wavetrac over the Quaife unit. I'm paying someone to do mine in the not too distant future and am interested in your thoughts given your engineering background.

Cheers,

J

I chose the Wavetrac due to it still working in a zero grip environment, ie on ice or snow, and also if one wheel is lifted.

The roads I drive/have driven have caused individual wheels to come off the ground, due to the lower suspension droop with my set-up, Ohlins coilovers and a big rear anti-roll bar.

The Quaife is an excellent diff, but for me, the Wavetrac works in all enviroments and set-ups, where-as the Quaife doesn’t.

I’ve used both pure helical and Wavetrac diffs in many other cars I’ve owned/built/driven on road and track, so made the decision from lots of experience.

[Crawler]

Originally Posted by Techevo

I chose the Wavetrac due to it still working in a zero grip environment, ie on ice or snow, and also if one wheel is lifted.

The roads I drive/have driven have caused individual wheels to come off the ground, due to the lower suspension droop with my set-up, Ohlins coilovers and a big rear anti-roll bar.

The Quaife is an excellent diff, but for me, the Wavetrac works in all enviroments and set-ups, where-as the Quaife doesn’t.

I’ve used both pure helical and Wavetrac diffs in many other cars I’ve owned/built/driven on road and track, so made the decision from lots of experience.

Thank you for your input. Have you noted any sounds produced by the Wavetrac units?

Cheers,

J

[Techevo]

Originally Posted by Crawler

Thank you for your input. Have you noted any sounds produced by the Wavetrac units?

Cheers,

J

No, it's completely quiet, no difference to stock, except loads of extra traction!

I think a lot of people who get noises after LSD fitment are due to poor install, where specs such as backlash are too big on re-assembly.

[Crawler]

Thank you.

I live an hour from Wavetrac and am looking for a SoCal shop to do the work.

J

[Seattlesquash]

Holy shit you are my new hero - wow!!!

So impressive!

[mob17]

Wow Clive amazing work! You finally got the time to do this!

Guys, i have met Clive and he is a wonderful guy and very clever! His workshop at home is amazing.

[Techevo]

Thanks Mo, yes, got some spare time eventually to get it fitted! Car is absolutely spot on now, really great fun to drive. How's yours going?