Differential - Installing a Mini Spool
What a Mini Spool does:[edit]
A Mini Spool simply locks the diff... i.e. The wheels can NOT spin independantly. It replaces all the spider gears inside the diff centre with a solid chunk of metal. It will have the same effect as welding the diff. The advantage is that it is a lot stronger than welding and if necessary, reversible.
This is a Minispool for a BorgWarner 78 - 28spline diff: (apologies for the poor quality phone camera pics)
NOTE: Locked diffs are not street legal.
Installing:[edit]
1. First of all, you'll need to remove the diff centre from the car. That has been described in another article so I won't go into it. When you get the back cover off the diff housing, that's the best time to crack the crown gear (the really big cog) bolts. The diff is the only part of an R31 that has imperial sizing. The crown gear bolts need a 5/8" socket or spanner. They are extremely tight so put the car in gear, get a really big breaker bar and push down hard. NOTE: They are LEFT HAND THREAD!!!! They have a large "L" on the top to indicate this. Once they are all loose, continue to remove the diff centre from the car.
File:Minispool crown bolts.JPG
2. With the diff centre out, remove all the crown gear bolts. The actual crown gear will stay put as it is tightly pressed onto the centre. You will need to remove it so continually tap around its outer edge with a hammer.
File:Minispool removecrown.JPG
3. Find a suitable punch in order to remove the long thin pins holding the bigger pins in.
File:Minispool pinlocation.jpg
Just place the punch on top and smack it with a hammer. They can be very tight so just keep whacking them.
4. The diff centre spits into two halves, one half has all the gears inside it and the other is basically just a cap piece. Grab a flat headed screwdriver or similar wedge and hit it between the two halves until the come apart.
Once apart it'll look like this:
File:Minispool spidergears.JPG
They are the spider gears, the heart of an open wheeler diff.
5. Find a much larger punch, approximately 1cm in diameter, to punch out the large pins holding the spider gears in. Pop out all 3.
6. Remove everything inside the diff centre, including the small, thin shims behind each spider gear.
7. Drop the Mini Spool inside the diff centre, making sure to line up the holes for the large pins.
8. Using the large punch, smack the large pins back through the Mini Spool, making sure to line up the small hole at the top of each pin the the small hole that the small pins came out of. The small pins actually secure the larger pins.
The large pins should be flush with the outer edge of the diff centre remember that the crown gear has to go over the top of the pins.
9. Place the top half of the diff centre back on. line up the pin holes and push the pins back in. This is when you'll find out if everything is lined up.
10. Place the crown gear back on, making sure to line up the bolt holes. Slowly tap the crown gear in place with a hammer until it is seated.
11. Replace the crown gear bolts, remembering that they are left hand thread. Install complete diff centre back into the car. Use a large breaker bar again to fully tighten the crown gear bolts.
12. DRIVE!
Note that a locked diff will be a little strange to drive at first, especially when turning at full (or close to) lock. The inside wheel will have no choice but to spin at the same speed as the outside wheel, making it spin on the spot.
Locked diffs have the advantage of NEVER open-wheeling. This is a great, cheap solution for drifting. It will also allow greater traction on launch due to both wheel driving all the time and improved corner exit speeds as the inside wheel will not be able to spin by itself.
Compiled by
Decs
Thanks to Naife and evosR31 for their help and expertise with my install.