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PostPosted: Mon Apr 30, 2018 9:23 am 
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I chewed up a 4.88 ring and pinion a while back, finally getting around to replacing it.

Through a series of conversations and internet wanderings, I came across these solid pinion spacer kits from Weir Performance: http://www.weirperformance.com/solidpin ... rkits.html

The reasoning for going to a solid spacer instead of a crush sleeve seems sound to me, but before I spend more money on parts that may or may not be useful, I thought I'd ask here.. The goal here is to improve reliability of the ring & pinion. Mazda diffs are well known to eat R&Ps from what I understand to be shock loading and movement/deformation of the R&P clearances during said shock loading, which eventually causes the teeth to eat each other. usually the shock loading is caused by offs, curbs, etc and is generally to be avoided, but we all know sometimes s*** happens.

Per the description in this sales blurb, this might help to improve reliability/longevity by replacing the crush sleeve with stronger steel sleeve and shims for clearance. If this will improve reliability, it surely seems worth the price over a $800 R&P replacement.

Thoughts? worth the money, or snake oil?

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Matt Blehm
Houston Region
EP 1st Gen RX7
STU Nissan 240SX


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PostPosted: Mon Apr 30, 2018 11:50 am 
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Matt, being you said a 4:88 I presume it was a Torsen which has a 7 inch ring/pinion compared to 90/93 which has a 6 inch ring and pinion. It's my understand that the crush sleeve shortens and clearance increases and crunch goes the teeth. The SM beat the living $hit out of the torsen without blowing up the ring and pinion. The 6 inch not so good. I get the differences of torque and HP. Search miataboxs.com for a bunch of videos of Miata trans, diffs and other stuff by Mark Bennett of Ohio. Talk with Jesse Prather.

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David Dewhurst
CenDiv Milwaukee Region
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PostPosted: Mon Apr 30, 2018 12:22 pm 
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I am assembling a 4.78 Mazda R&P right now and I bought the solid spacer kit from weir. I bought it for piece of mind as I remember people suggesting that the crush spacer was a problem on the 6" miata diff. I'm also curious if its necessary for the bigger r&P


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PostPosted: Mon Apr 30, 2018 2:17 pm 
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Not sure how you could possibly know that the spacer was exactly the proper height for your R&P and case combo.

Snake oil to me; let's see what Jesse says...


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PostPosted: Mon Apr 30, 2018 2:38 pm 
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David Dewhurst wrote:
Matt, being you said a 4:88 I presume it was a Torsen which has a 7 inch ring/pinion compared to 90/93 which has a 6 inch ring and pinion. It's my understand that the crush sleeve shortens and clearance increases and crunch goes the teeth. The SM beat the living $hit out of the torsen without blowing up the ring and pinion. The 6 inch not so good. I get the differences of torque and HP. Search miataboxs.com for a bunch of videos of Miata trans, diffs and other stuff by Mark Bennett of Ohio. Talk with Jesse Prather.


David, it is the 7", but not a Torsen. it's got a clutch type diff in it, although I'm not sure the source (maybe later model RX7?) since I still not that familiar with the 35+ years of Mazda history and parts.

SM drivers have learned not to bounce the car off curbs and when they go off, DO NOT nail the throttle until both rear tires are fully back on the racing surface. one good 'off' and spinning the tires on re-entry can destroy a diff. I've unfortunately

Compound that known issue with the fact my RX7 makes approx 200whp whereas an SM makes 125ish (no idea on torques since it's never been dynod), but you get the point that there's considerably more oomph at the wheels than in an SM, which means more stress on the spinny parts.

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Matt Blehm
Houston Region
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STU Nissan 240SX


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PostPosted: Mon Apr 30, 2018 3:25 pm 
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blamkin86 wrote:
Not sure how you could possibly know that the spacer was exactly the proper height for your R&P and case combo.

Snake oil to me; let's see what Jesse says...


There is a solid spacer and stack of shims. You assemble with all the shims and then check end play. Remove shims until endplay is correct. Then you do a post check of drag on the bearings like the fsm states. In my opinion i think it should feel and act exactly like a crush sleeve in 99% of usage.


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PostPosted: Mon Apr 30, 2018 4:03 pm 
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Location: SE NM
I'm following along closely, a rebuild of mine is up next to change out ratios.

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PostPosted: Mon Apr 30, 2018 9:19 pm 
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Crush sleeve sets the distance between the tapered bearing sets. A solid spacer will never keep you from killing a pinion. Both directions of thrust load act against a tapered bearing. It takes almost twice the torque setting for the pinion nut to crush the sleeve on initial install. After that you back off and it becomes a solid sleeve. The solid kit works fine if you know what you are doing, if not you will kill some bearings real quick. Have fun.


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PostPosted: Tue May 01, 2018 4:15 am 
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Ok, ok.

The 1.6 Miata ring and pinions are much smaller than the later model 1.8 Miata ring and pinions which are the same as Matt's first gen RX7. I have a process that crushes the crush sleeve properly and then keeps the nut in place. I've run rear ends with crush sleeves for years and years. The solid spacer kit will have some extra shims to get the preload on the pinion bearings just right. As Steve said, this is critical. Personally, I'm not sure it's worth it if you do the crush sleeve correctly however done right it should stay in adjustment longer. This will have nothing to do with the longevity of the pinion and ring gear assembly, just pinion bearing life and wear. FWIW, the crush sleeves take about 150 ft/lbs to get started to crush. They are very heavy duty and work very well.

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PostPosted: Tue May 01, 2018 4:46 am 
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Thanks, Jesse. If there's no tangible improvements in R&P life, then I won't worry about it and just stick with the crush sleeve. I trust that measurements and crush sleeve will be installed right, as I'm having Greg Lucas do the diff and build up another rear axle for my car at the same time. (going to take a little camber out and see if I can get better bearing life out of it.)

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Matt Blehm
Houston Region
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STU Nissan 240SX


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