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Thread: Installing MFactory helical differential in a RS5F32V

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2015-03-25 01:05:05
Installing MFactory helical differential in a RS5F32V
Installing MFactory Helical Limited Slip Differential in a RS5F32V

1. Introduction
First of all, don't trust me to be any sort of authority figure on transmission work. I just did a little homework, then jumped in. I have been in the FWD SR20 world since 1998, and never on any relevant forum (SE-R List, SR20Forum, SR20-Forum, etc.) did anyone detail what happens when you try to install an aftermarket differential in a RS5F32V. I thought I would share. The victim is my 1992 Sentra SE-R, which is a left-hand-drive model for our international readers.

Secondly, this assumes you have the minimum aptitude and tools to perform a clutch replacement. If you aren't able to get the transmission off the car and onto your workbench, a do-it-yourself differential install may not be your thing. Otherwise, it's not dramatically more difficult than replacing fifth gear pop-out. It just takes a few more tools and a little more time.

The MFactory Helical differential
As of this post, MFactory makes the only readily available differential for the RS5F32V and friends (aka the factory VLSD SR20DE cars). I bought their helical differential, which is a torque biasing unit not unlike a Torsen or Quaife brand. A helical shouldn't require any maintenance in our application because it's bathed in the same transmission fluid as the rest of the gearbox, and has no friction plates to wear out like the out-of-production clutch-type Nismo differential. That's a major plus with a FWD transmission that has to be pulled entirely off the car to access the differential. Clutch plate differentials have their merits, but the MFactory helical is available now and hits a nice cost-benefit point.

Rather than replace the entire differential unit, the MFactory differential only replaces the half of the factory differential with the side/spider gears. The factory viscous coupler is retained and bolts to the MFactory helical half, combining both types of limited slip.

Normally, the main drawback of a helical is that it's really just a torque multiplier (not a "locker"), thus putting one wheel in the air or on sheet ice will render it near-useless. Some helical designs like the Wavetrack or Torsen T2R have a preload mechanism to help in extremely low traction, but those aren't made for our cars. In theory, retaining the VLSD half should help with that issue. The factory VLSD is a sealed unit filled with a fluid that increases viscosity in shear and causes a certain amount of lockup when there's a speed differential between the front wheels.

Mandatory Additional Parts
  • Transmission axle seals - the ones where the CV shafts mate with the transmission case
  • Passenger/right differential bearing - this is commonly available as Timken 32010X in the United States
Good Idea Parts
  • Nissan 3140831X08 BEARING - driver/left differential bearing
  • Nissan 38431D2100 WASHER - metal speedometer gear ring
  • Nissan 3270170E00 GEAR - plastic speedometer gear
(Note: I had to wait weeks to get these three items from Japan via Amayama Trading. If you are really careful and your original parts are in good shape, there is a way to reuse these.)

Tools and materials
  • Typical clutch change tools - breaker bar, ratchets, sockets, etc.
  • Bench vise - you will want something to hold the differential in place while working on it. I suggest at least a 4" vise, and using/making/buying jaw pads so you don't scratch things up.
  • Seal puller - helps remove the axle seals from the case.
  • Snap ring pliers - removing the case from the transmission requires a snap ring to be removed.
  • Two-jaw puller, straight puller, and/or bearing spreader - you'll need some tools to coax the old bearings off the differential if you want replace them, as well as remove the outer races from the transmission case.
  • Step plate adapter or similar - metal disc that your gear puller (or press) can push against. I used OTC part number 8061.
  • Press - I have a 12-ton Harbor Freight hydraulic press. They are not expensive, and the box fits in the trunk of a B13 Sentra with the rear seat back removed.
  • Rubber mallet - may be necessary for coaxing stubborn pieces.
  • Torque wrench - probably a good idea to use a 3/8" drive or (even better) 1/4" drive torque wrench for all the little 10mm and 12mm bolts that get torqued in the 5 to 20 lb-ft range.
  • Dial indicator and base/clamp - used to measure differential end play and determine preload. Harbor Freight sells an inexpensive dial indicator combo with locking pliers and flexy arm that works fine.
  • Machinist caliper or digital caliper - great for measuring shim thickness and other little measuring tasks. A roughly $30 or less digital caliper from Harbor Freight or similar is good enough.
  • Feeler gauges - not mandatory, but might come in handy for double-checking your preload and various clearances.
  • Gasket scraper - the transmission case is soft aluminum, so be careful when you scrape off the old RTV on the case parts during disassembly.
  • Threadlocker liquid - Loctite 243 is a good oil-resistant formula. You'll want to use it on the bolts that hold the final drive gear to the differential.
  • Gasket maker - grey RTV or equivalent for sealing case when you're all done.

2. Disassembly
Transmission removal
Start with the transmission off the car, sitting on your work surface. Consult a clutch swap thread or factory service manual (FSM) to get to this point. Marking the location of all the bolts and harness plugs that you disconnect will help later. The transmission should be drained of fluid and cleaned of any loose debris or gunk that could get into the innards. Remove the passenger side axle seal so that the transmission can lie flat on the work bench.

Digging into the Guts
There are some how-to guides on fifth gear pop-out and disassembly (for example) that walk you through the basics of dissecting this transmission, so I won't detail it too much. Remove all the 12mm bolts on the case and the 10mm bolts on the end cap. Make note of where all the little accessory tabs mount on the case. Clean all the old gasket gunk off the bolt threads, too. Remove the top cap, and remove the snap ring. Carefully pry on the case to separate it. Tilting it at an angle is the official way to shimmy the case up and over the gear stack.

Pull up to remove the short rod holding the reverse idler gear, and remove the gear and washer, noting their orientation. Then remove the longer rod holding the shift forks, and remove the top two forks from the gear stack. Note where they go, and how the little fork caps key into the shift selectors. Unbolt the shift selector control unit (three 10mm bolts) and pull it out along with the bottom shift fork. Now unbolt the triangular mount on the output shaft (three 12mm bolts), and the entire gear stack should lift right out. Toward the bottom of the case are a couple of little springs (one with a sleeve and ball bearing). Pull them out with a magnet or tweezers and store them somewhere safe.

Breaking Down the Differential
With the gear stack out of the way, the differential will lift right out as a whole. I secured the unit in a vise, protecting it using vise pads (strips of an old leather belt may also work). The first step is removing the 14mm bolts holding the final drive gear ring to the differential. The factory used threadlocker, so they can be a little stubborn. A 1/2" drive breaker bar helped get them started. If the differential wants to squirm in your vise, a small deep socket (6mm or so) fits in the hole on the differential and helps prevent it from spinning around while you try to loosen the bolts.

If the gear seems stuck to the differential after the bolts are removed, a few taps from a rubber mallet should free it. Remember which side of the final gear faces which direction.

With the final drive gear removed, take out the two Phillips head screws still holding the two sides of the differential together.

The halves may be stubbornly stuck together, so try a few taps of a rubber mallet. Or maybe twist one side with a rubber oil filter wrench or similar. They come apart, I promise.

Removing the Bearings and Races
Since the viscous half of the factory differential will be retained, replacing the driver/left side differential bearing is not mandatory. However, most of our cars have seen a lot of miles. Is it worth the hassle of tracking down a new OEM part? Your call. I went ahead and replaced it. At the time, I had to order it from Amayama and wait for it to get sent from Japan. As a bonus, the old removed bearing came in handy as a drift for the new bearing and race. I pulled the old bearing off the differential with a small two-jaw puller and step plate. Large pullers may have jaws too thick to fit in the gap between the bearing and housing, so a grinder may help you there.

If you prefer, you don't have to touch the passenger/right side of the differential if you have all new parts. That half of the differential will not be reused at all, unless you want to go through the trouble of saving the old speedometer gear and ring. I took apart the bearing on that side just to see how it all comes apart. The factory service manual says standard procedure is to cut off the plastic speedometer gear and throw it away. However, I think you could save the gear and ring by first carefully cutting off the roller bearing cage, then using a bearing separator puller on the top lip of the inner race.

The speedometer gear and ring are just sandwiched between the differential housing and inner race of the bearing. If you sacrifice the bearing (which can be bought stateside no problem), you could probably reuse your harder-to-find speedometer gear and ring. It's tricky, but possible.

The outer races for the bearings on each side are stuck in the transmission case. They are press fit, but you can pound them out. Remember that the aluminum case is soft. The driver/left side race sits on top of the shims (thin metal rings) that set the overall preload for the differential assembly. Even if you reuse the left/driver side bearing and race, you still have to remove the race from the transmission case to get the shims out. There are no shims on the passenger/right side bearing. To pull the races, I used a straight puller turned backwards, and hammered on the puller screw from the outside of the case.

The outer races are tight, but not obscenely tight. Your own tools and technique may make this task easier. A slide hammer with some sort of pulling jaw attachment would likely also work. Just don't try to pry them out like a gorilla and gouge the case.

3. Assembly
Assembling the differential
You probably noticed the thin metal washer that sat between the VLSD half and the differential housing half that contained the spider gears. I'm not sure that it matters if you install it or not. MFactory said you might as well. I figured it was used to set the preload for the spider gears, which aren't reused in this installation.

Put the VLSD half and MFactory half together, and install the Phillips head screws. You'll see how the bolt holes line up. Slide on the final drive gear with the correct side facing up. I hand-tightened a few of the final drive bolts to make sure the gear is lined up and seated on the differential. Apply thread locking liquid to each bolt and tighten in a crossing pattern. Torque to 54-65 ft-lbs. If the differential wants to spin in your vise, that small deep socket (6mm or so) inserted into the differential housing can help.

Place the speedometer gear and ring on the right/passenger side of the differential. The tabs on the gear and ring will match indentations on the differential housing.

Press on the right/passenger side bearing. The old bearing inner race can be used as a drift.

Next, press the outer races into the transmission case halves. No shims on the left/driver side this time around. I used a variety of odds and ends as drifts for these races.

The left/driver half of the case is oddly shaped, so I cut a length of aluminum pipe to keep it propped up from underneath.

If you are replacing the driver/left bearing, go ahead and press it onto the VLSD housing. The old bearing can be used as a drift.

Prepare to Check Clearances
To check preload, everything has to be put back together. As previously mentioned, you will have to install the driver/left side bearing race into the transmission case with no shims. Make sure it goes in straight and fully seats. I confirmed that it was fully seated in the bore with my feeler gauges.

Lower the differential assembly into the race and confirm that it freely spins while applying a little downward pressure. I had one of the early production MFactory differentials with a housing that was a touch too large. A machinist friend lathed a little bit of material from the shoulder of the differential.

I also very carefully ground and sanded small increments of material from the rub points on the inside of the transmission case (covering everything up to prevent aluminum dust contamination). Read more in this post from MFactory: http://www.sr20-forum.com/mfactory-competition-products/68865-pre-purchase-32v-sr16ve-helical-lsd-10.html#post1015202

Install the little springs and ball-bearing, gear stacks, shift selector control assembly, and shift forks. First, wiggle the gear stacks into place, and torque the 12mm bolts on the triangular output shaft retainer to 12-15 ft-lbs. The bottom shift fork and shift selector are easiest to wiggle into place at the same time. Make sure the selector arms are horizontal so that the tab on the shift rod matches the orientation of the shift selector indentations. Torque the 10mm shift selector bolts to 4.6-6.1 ft-lbs. To install the reverse idler gear cog, hold it in place and and slide the reverse gear rod down notched side first into the bore. The washer goes on top.

Then put the other two shift forks into place, with the little caps properly positioned on selector rods.

Now slide the main shift rod down the bore of the shift forks.

Install the outer half of the transmission case, starting at an angle and coming down until it sits flush on the other half of the transmission. No RTV gasket this time, just a dry run. If the two case halves don't sit flush together, make sure the differential housing doesn't rub the case and that the gear stacks are correctly seated. Install all the 12mm case bolts and torque to 20-22 ft-lbs.

Preload Specifications
The factory service manual calls for measuring the gap between the driver/left side of the differential and the transmission case. Remember, no shims should be in there right now. This gap plus a small amount of preload (~0.010 inch) is what the FSM specifies to determine the shim thickness to install later. There is a table of shim thicknesses and part numbers in the related section of the FSM. In my case, the measured gap was 0.032 inches. Add 0.010 inches of preload, and in theory I should install 0.042 inches' worth of shim(s) behind the outer race. My transmission came with a couple of shims from the factory, and the thickest one measured 0.0375 inches with my digital caliper. Rather than wait on new shim(s), I decided that the single 0.0375 inch shim was close enough for me.

If you're following along at home, that meant the MFactory differential installed fairly closely in dimensions to the factory differential assembly. Perhaps even 0.020 inches thicker in my transmission. I read stories of cheap OBX differentials for other cars requiring a lot of additional shimming to fit correctly. Hopefully you also have good luck with MFactory.

Taking the Measurement
I set up my dial indicator against the face of the differential on the driver/left side. You may need to remove the axle seal for this step. Take your time to position and zero everything for an accurate measurement.

When you lift up on the differential from the bottom, the dial plunger will move the needle. I carefully positioned only the passenger/right axle bore of my transmission to hang over the side of the workbench, just enough to maneuver the passenger axle into the differential. Don't let the transmission fall on you. Pushing up with the passenger axle shaft lets you get enough leverage to push the differential up as much as it will go. The maximum reading on the dial is your starting point.

Add 0.010 inches of preload to that amount, and you have your ideal shim thickness per the service manual.

Buttoning up
When you are satisfied with your measurements, take the case apart again. Pull the driver/left race from the transmission case. Install the appropriate shim(s) in the bore of the race, then reinstall the race on top. Confirm that the race is fully seated. Assemble the transmission as before, this time adding a modest bead of RTV gasket around the mating surfaces of the transmission case halves and the top cap.

Before you install your axle seals, the FSM also specifies measuring turning torque: how many in-lbs it takes to move the differential from rest. In theory, this should tell you if your differential is shimmed too tightly or loosely. Is this step mandatory? If your preload gap was shimmed correctly, maybe not. The FSM specifies 26-61 inch-pounds. I did not want to find or make an adapter to mate the differential to my beam torque wrench, so I skipped it.

The rest of the installation is the same as the back end of a clutch swap. Good luck.
Last edited by JimR on 2015-08-28 at 18-09-49.
2015-03-25 02:04:33
Thank you very much for the photos and write-up @JimR.

The parts list alone is exactly what i was looking for.
2015-03-25 03:27:35
nice write-up @ jimR, thank you sir
2015-03-25 09:19:42
Excellent write up
2015-03-25 18:53:35
Concur, excellent write-up!
2015-03-25 19:05:49
Great info! You going to do a review also? Thanks for the solid contribution.
2015-03-25 23:21:13
My SE-R only gets driven a few hundred miles per year, and mostly in an unpaved RallyCross setting. So far my limited impressions are favorable. Earlier to throttle, a subtle neutrality. On dirt, I can keep the pedal matted to the floor in many parts of the course, and adjust the attitude of the car with left foot braking. I'll be taking my car all the way up the ladder to RallyCross Nationals in August, so I'll keep building impressions.

Autocross, track lappers, and street guys will probably enjoy this. I co-campaigned a '99 Neon FSP autocross car with a Quaife (similar design), and it was a hustler. A torque biasing differential will try to spin up the outside tire in cornering, which is great for neutralizing power-on push epidemic to FWD cars. The fact that a helical doesn't need revolving maintenance will be a plus for weekend warriors, too. Ice racers and road racing curb hoppers may want a clutch type, though.
2015-03-26 13:35:10
I ordered some timken bearings. working on the three OEM ones now. Thanks a bunch, @JimR
2015-04-15 13:23:09
Got these suckers in yesterday.

Also got the Timken bearing in almost immediately after this thread went live.

Thank you @JimR
Last edited by Kyle on 2015-04-15 at 13-24-32. Reason: added thanks
2015-04-15 19:47:10
their logo has a little anorexic horse!
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