Rear diff backlash adjust question

[jemsoccer]

I'm in the middle of adding the EVO diff in my 2g housing. My issue is I have about .009" backlash (book says .004"-.006"). So obviously the answer is that I need to reshim.

I see in Mitsu ASA that the shim kit I need is MB241903. What shims come with this kit? I can't seem to find the info of what all is included.

Is there a rule of thumb of how much shim is needed to take out X thousandths of backlash? Or is it pretty much trial and error?

Should I tighten up the OEM tolerance specs more if I plan to run 500+ hp?

 

[twicks69]

Well, there are about a dozen shims in the set ranging from around 0.099" - 0.127" so you can adjust the position of the differential. The MB185350 shim set is to raise or lower the height of the pinion gear if you run out of movement in each direction to center the gear mesh while getting your backlash measurement, while the MB185360 shim set is for adjusting the preload on the bearings for the pinion shaft.

Normally if I am using a used ring and pinion in excellent condition I still have to use a shim on the diff thinner than 0.099", typically closer to 0.096" or 0.094", which I do by using a magnetic base surface grinder and grinding down one of the shims from the MB241903 shim sets that aren't normally used during the setup process. Especially since you can get those shim sets for like $12.00 a set whereas the other sets are closer to $40 a set.

To a portion, it is trial and error, but typically, let's say you have 0.009" backlash, I would start with a shim about 0.005" thinner on the diff housing side, and a 0.005" thicker shim on the diff cover side. You also need to take into consideration the bearing preload on the tapered roller bearings for the differential.

As well, the Evo cast iron diff cover is extremely thin and likes to deflect under load. Personally, I recommend using the "Ninja" side cover from TRE with the proper bearing to fit the new side cover; MD710663 is that bearing for the TRE side cover. You would use longer machine screws as well for assembly. The factory side cover likes to deflect and damage the bearing bore and push the ring gear away from the pinion shaft. This is more prevalent on higher power cars but it is always a risk you will have to take at the 500hp level.

I would also try to get your backlash closer to like 0.002"-0.004" with a centered gear mesh. It might take installing a shim on the pinion shaft under the inner tapered roller bearing (closest to the pinion gear teeth under the bearing) to space the shaft out enough to utilize the factory shim set.

If you are going that far though, then replace the tailshaft seal as you will smoke it during the disassembly and reinstallations which should be done with a press.

 

[jemsoccer]

Thank you for the very detailed reply Tim. I am going to try to shim with the MB241903 kit. I am hoping this will not require the need to mess with the pinion shims. In the off chance it does, how do you remove the pinion? Is it a press fit and I would just push it out w/ the press?

 

[twicks69]

You would support the housing and press the pinion shaft through after you remove the shaft nut and driveshaft yoke. During the removal process, the outer bearing will seperate and the inner bearing would still be on the shaft. The inner bearing is the one you would need to gently remove with an OTC1123 splitter.

 

[jemsoccer]

Since I HATE when I finally find someone who had the exact same issue as me in a forum, but they never post back how the issue was resolved, I figured I'd go ahead and make my update.

I received the shim kit (MB241903) and they range from .102" to .126" as seen in the picture. I definitely need a shim less than .102", so I will have about 4 surface ground to give me a good selection to choose from, probably shooting for .092, .094, .096, .098. Hopefully one of those will work without messing with my mesh pattern.

Will update once this thing is finally together!

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[TimIacobucci]

Tim, do you have any opinions or input on the setup of the actual lsd internals of the evo diff? I just did this all myself recently and I'm wondering if you shim the clutch pack at all or measure or modify break away torque? Many other rwd based platforms discuss the setup of the salisbury in more detail than I have been able to find on this particular lsd aside from restacking the usdm clutch setup correctly or the weir upgrades. Do you have any opinion on the weir setup btw?

The evo fsm lists LSD differential torque with old clutches to be between 2-19 Nm, ~ 1.5 - 14 ft lbs. I have not tested mine yet to see how a decent used setup stacked correctly will compare to factory specs but I will. Even at that though 14 ft lbs is not allot. Most aftermarket salisbury clutch style lsds are in the 50 - 80 ft lbs range. Offroad and drift setups more in the 100 - 200 ft lbs range.

I've also never done more than a hand spin test on the dsm viscous lsd but is there any kind of spec for break away on those? Most I've had were toast but even the good ones I'd doubt were even as stiff as the factory evo one I just setup.

 

[twicks69]

I have done alot of Evo clutch type rear diffs; there isn't a shim per say for the clutch packs; Mitsubishi has a plus-sized 1.75mm friction disk available (the factory standard size is 1.65mm); the reaction plates and spring plate are only one size. Typically, for most customers, I use the 1.65mm disks. You can get preload up more if you want but it is quite noisy otherwise, even with using a 75w140 plus LSD additive. In mine I run standard flipped plates with the additional plates instead of the spring plate (maxlock), and run 75w140NS; its extremely loud on slow corning and totally fine for higher speeds.

I am not sure if there is a break-away spec for a viscous diff; either way, you can't do anything about it other than note that the viscous coupler is junk.

Even in stock form the Evo diff is considerably better. Yes, you can still crack the pinion gears, but that normally happens from a ton of power, or wrong axles being used. The weakest link to the stock clutch type differential is the side cover of the diff. It will deflect and elongate the bearing bore causing failure of the bearing or deflection of the ring gear causing gear failure. Jon @ TRE makes a better side cover for this differential and it can be used with the Frontline Fabrication billet rear diff cover if clearancing is done, or if you have the side cover machined to clear the diff housing cover.

As for the Weir kit, I have installed only two over the years, and they were harsher lockup than the MaxLOCK or flipped friction disk setups.

 

[TimIacobucci]

Thanks allot for the response, you've always been a terrific source of good tech info. I know maybe allot of people would rather just pay to have the work done that requires the level of knowledge and detail you just described but for those who can and do use this information on their behalf I will say it is greatly appreciated. I know you don't need to share this hard earned knowledge and most choose not to.

I do still have a few more follow up questions if you are game.

So there are 5 friction plates and 1 spring on each side from the factory, are you saying you use a 6th oem friction plate in place of the spring? No special aftermarket fictions? If so do you still aim for the oem 0.06 - 0.25 mm clearance?

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From looking at posted pictures of the old 12 plate weir kit, they use 6 thinner plates and still use a spring, I am not certain how the newer 14 or 16 plate kit is arranged.

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Pictures are from this thread on evom, http://www.evolutionm.net/forums/evo-how-tos-installations/564095-how-assemble-rear-diff.html

Which weir kit were you referring to that you have installed that has harsher lockup?

Are you saying the total lock seems about the same but the weir kit just locks more quickly/harshly?

Is it just a matter of noise and civility or do you feel the greater preload wanting to understeer more into corners?

Are you saying the 6 oem plate is the same maxlock setup TRE does? I did look at the TRE ninja and cusco cover. You think 500 hp ish is the breakpoint for that? My stock cover seemed perfect thus far. What is your opinion on the HD pinion spacer? Any recommended power level for that as well?

When I said shim, I know there really is none from the factory I meant simply to fabricate something to preload the spring plate a bit more. Without the spring plate in your setup is there any preload at all? I can see how this would be usefull for less understeer and still lock harder and quicker under acceleration when the clutches engage.

The reason I am asking is for winter snow/ice use. When one tire is on ice basically all you have is the preload to transfer torque to the grip wheel, the whole salisbury lsd function with the cam ramp against the cross shaft only engages the clutches using resistance from the tires to react against engine torque.

Anyone whos had their awd car spinning one back and one front tire because of an open front diff and a pos worn out rear viscous (or a plain open rear on those cars without a rear lsd, aka my colt) can attest to the usefulness of a real rear lsd with good preload.

 

[TimIacobucci]

I just went and looked at the new billet frontline diff cover, I only ever saw his plate steel ones before. How much help do you feel the load bolts are?

I have solid mounted the rear mustache brace before on my 1g, colt is very similar. I was contemplating just welding the mustache brace into a custom plate steel rear diff cover. I've already cut a 1/4" flange for the housing I'm just debating if it's worth the work. Adding load bolts to that shouldn't be too difficult if they are worthwhile though. Also any opinions on solid mounting the rear diff cover to the chassis? Aside from nice harmonics from the chattering evo lsd broadcasting through the floorboard?

The billet is pretty I guess

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I still like his old school beast welded 1/4" plate steel better though. I also like making stuff myself better than that though.

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[twicks69]

For high power cars the load bolts are extremely useful, especially on conjunction with the billet bearing caps. The biggest liability to the Evo diff is the side cover, so I would strongly suggest getting the TRE ninja cover for it, and the proper MD710663 side cover bearing.

Regarding the set up of the WEIR diff plates, its been a few years since I did one, so it was an old version for sure; they were a 12-plate kit if I recall on both diffs.

With the Evo clutch pack, the MAXLock is simply using properly sized friction disks, removing the spring plate, and adding another friction disk. As for the HD pinion spacer, I have not seen his product for that yet; I have only worked with the billet Ninja side cover.

Just keep in mind, the more aggressive the lockup, the more load on the spider gears; something that are well known to crack under very harsh conditions. For most people the flipped frictions are plenty with a no-slip gear oil like Redline 75W140NS.