Jason's 1987 SAS'd truck gets Nitro 529 gears/Harrop in a Marlin HP Diff Housing
(72 BIG pics loading)
AUGUST 19 2018

Jason's lives up in Oregon where they have a lot of the white stuff in the winter time.

It was time to upgrade the front to a bare High pinion 8" from Marlincrawler.com and install a set of Nitro 529 gears and Harrop electric locker.

Empty Marlin housing on the left...the Nitro V6 master kit.....the Harrop Elocker....529 Nitro gears and the solid collar/dual drilled flange.

They chamferred the circumference of the V6 wheel adjusters which was much needed.

Parts are unpacked and layed out. All looks to be here.

The big inner pinion race is tapped in.....360 degree support, of course.

Same with the small outer race.

Will start with a .076" pinion shim.

The pinion loading station.

Tighten the pinion nut til the estimated preload is somewheres in the neighborhood of 10~20 ft/lb.
This is only a pattern check so it's not critical.

Now onto the other end. A quick check of the coil resistance of the electro-magnet.
Measuring about 4 ohms.

Surfaces were checked with a file and all was just fine.

75 ft/lb and blue loctite.

The new Koyo carrier bearings were a very nice tight fit onto the journals.

The top bearing cap has to slide on horizontally first and then the 2 long bolts go in.

Line the threads up...tighten the 2 bolts....and then thread the large wheel adjuster in.
Then dial in some bearing preload and backlash.

First paint check and way too deep. This is the drive side.

Coast side.

Teardown and now trying a much thinner .034"

Drive.....much better but over-shot just a little. This is slightly shallow now.

Coast....can't complain.

I did notice that the 529 ring gear was so thick that the teeth were almost hitting the tunnel groove
so did some clearancing with the flapper wheel.

Took about 20 seconds.....


A final look at the pinion paint shows that the comet tail is too deep into the root and that means to add more pinion shim.


So now to increase the thickness by .004" Now trying .038".

Repaint.....Drive side....beautiful.

Coast....very nice indeed.

Final confirmation....pinion tooth....comet tail is starting to feather out to the center. That means to leave it alone and button it up :)



Now to set the solid collar in place....took about 7 tries on this Hi-pinion to get it right.

3 adjustments on pinion depth......

7 on the solid collar.

The 27 spline fanblade slinger will fit with a slight enlargement of the center hole.
A Makita 1/4" die grinder and 3 minutes did the trick.

Grease on the garter spring prevents the spring from popping off during the install process.

The Yukon brand seal appears to be a quality seal.



The new flange is next.

Anti-seize on the flat surface...not shown but also applied to the pinion threads.

All that anti-seize really helps in dialing in the pinion preload.

This side goes together like usual.

This side requires a little order of assembly as mentioned earlier.

The 2 long bolts are tightened and the wheel adjuster freely threads in.
A quick final check of the locktab freeplay shows 1 mm.

The wheel adjuster threads in smoothly.

Now the 4 bolts are torqued to the 70 ft/lb spec.

Bearing preload is set/measured at 6 in/lb (as measured from the pinion flange end).
Backlash is recorded on every other tooth for 20 measurements.

A small amount of rtv is applied to the rubber grommet.

The rubber grommet now pushes thru about 3 times easier ;)


10 inch/pounds with Loctite

3.9 ohms of resistance. There is no Harrop spec on this but it seems to be a very common number.
Ohms Law says that with 16 volts and 4 ohms that the amperage will be 4 amps.
So, the reality is, the Harrop only draws about 3.5 amps on a good day.

This is my Sealed Lead Acid battery that has served me well for a number of years.

12 volts is applied to the 2 wires....no particular polarity.

The locker is not "active" until the 3 pins start to recess into the holes....the driveshaft has to turn a small amount.

The ring gear has to turn a small amount..... causing the pins to recess in as shown.

Locker fully engaged.

Additional turning of the ring gear causes the grey ramp ring to move with the pin.

Now remove the 12 volts.............

...and the ramp ring snaps back into place due to the strong internal spring on the other side of the pin.
Locker is now unlocked.

Basic specs are inscribed.


This is the harness.

The recorded notes.

Sure is a pretty High pinion 529 Harrop 3rd