4 replies to this topic

[luvin_the_rings]

Hello, 

 

I am about to purchase a Cusco LSD unit from Mazda Motorsports for the 1.6L VLSD differential.  Does anybody have any resources on doing this conversion?

 

I can't seem to find the thread now, but I've heard there may be some clearance trimming needed, possibly a stub shaft machined?  I am currently using the 1.6 VLSD that has given up.  I have a full 1.6 NA1 drivetrain, including trans, driveshaft, diff housing and 7" ring and pinion set (with the famous unequal length stub axles).  I want to keep the smaller ring gear, so please don't suggest the Torsen, I love it, but are going for that extra little bit of performance with the smaller ring gear.  Also, I already have a full torsen diff and axle set as a spare.  

 

Also, does anybody have a copy of Dave's Advanced Autosport constructor's manual they can sell me? 

 

Help!

 

Thanks, 

 

Z Kuretski #83 Spec Miata. 

[LarryKing]

Advanced Autosport will sell you a copy: https://www.advanced...ta-constructors

 

I let the pros handle diff rebuilds. In the Great Lakes that would be Mark Bennett. He built for me a MazdaComp diff (NA 1.6) in 2017 and it's still going strong. Not sure who the gearbox/differential guru is on the west coast.

[luvin_the_rings]

Hi, thanks for the recommendation, I ordered 2 copies.  

 

I've been asking around for a local guru, but I tend to tackle these things myself.  It's the engineer in me I suppose.  

 

So far, I've found the following information: 

 

1. The Cusco unit requires two of the same "short" stub shafts. So, I've procured a 2nd VLSD diff assembly to use the stub shaft from that one.  
2. Redline oil is recommended, but there are a few weights that could work. 75w100 is mentioned to work with LSD's for consistent operation. 
3. The diff wears quickly, so I understand that the goal is to just set it up with the least amount of lock (~10 ft-lb break away torque), get lower with the friction modifier if you like, but the wear of the diff will wear favorably, so dropping the breakaway torque initially may require another disassembly later on to clean out the friction modifier from the clutches and switch back to regular 75w110 un modified oil.  Might be best to just use basic 75w110 from the start and muscle through the initial wear.  

Any thoughts on the oil? 

 

Additionally, regarding the rebuild and setup, there are a few places it could go wrong.   My goal is to try and replicate the performance of the VLSD as much as possible.  

1. Turning down the initial torque through clutch combinations.  My plan is to set it up at the 60% torque setting. This can be seen in the Cusco brochure. 
2. Setting the cage to 1 way lock instead of 2, in the brochure as well.  Anybody know if Mazda sells the diff in this setup already? 
3. Gear Lash, I understand that the Mazda lash spec can result in damage? is this true? I saw this in the major Differential thread on this Forum.   My idea was to just check the gear engagement with paint marker and take measurements of lash before I disassemble, then measure and aim for that same lash and engagement when I reassemble.  Keeping in mind that the Ring and Pinion we have now is working fine. Also, I see its still possible to order shims from Mazda for the Pinion if needed. 

Anybody have tips on the diff setup or rebuild?  Or a source of a rebuild manual? 

[mdavis]

I think #3 is a reasonable approach.  I set up one like that years ago but also confirmed with a dial indicator.  It lasted at least one season before I sold the car if that means anything.

[luvin_the_rings]

Thanks Matt!

 

I was able to find the Mazda FSM for the VLSD 1.6 Diff.   So, there is a proper rebuild procedure that I will follow in there.  There are 3 tricky parts of this rebuild.  

 

1.  Checking the diff carrier bearings are square to the input pinion axis.  This is done by putting a dial indicator on a "dummy" pinion shaft making sure the diff carrier bearing housing is still perpendicular to the pinion shaft axis.  

2. Since I will be replacing the VLSD diff with the Cusco unit, ring gear location may change, so gear lash must be measured. I'M STILL WORRIED ABOUT RUMORS THAT THE FSM PINION LASH SPEC IS INCORRECT.  Can anybody chime in on this?

3. Replacing crush sleeve requires assembly and disassembly of the pinion shaft twice.  Since the ring gear position may change, that will change the pinion gear shim stack, and therefore probably need changing of the pinion crush sleeve.  Is this a correct assumption? 

 

Z