this past weekend i had a rear end failure due to 5 of the pinion gear teeth failing. this is not at all an uncommon problem with this differential (currently the only legal one), just this weekend 3 of us had failures, and another had a problem that was caught before it became catostrophic.

there are other problems with the LSD unit itself, but specifically referring to the ring and pinion gear, i'm looking for a way to keep this stuff from breaking, as it's just too expensive to replace on a regular basis.

i was thinking of sending them off to be cryo treated and REM'd. cryo would hopefully harden the material, and a REM on them would hopefully reduce friction and thus oil temps, allowing the oil to work as it was intended. although i don't think oil breakdown is our problem (mine was certainly not cooked when it gave up the ghost).

i'm looking at you engineers and materials experts as to if this is a legitmate solution to a rather significant problem.


this probably applies to you racerbowie if you have a 1.6 mazdacomp diff.


Modified by tnord at 8:47 PM 10/11/2005

 

I think the first question is to ask if these processes are legal in SM? I've spoken about the cryo treatment with a metalurgist at work and he agrees that the process really does have good effects on metal. The big IF he cautioned about is that the process must be done correctly. The time to bring the parts down to min temp must be very well controlled and the dwell time at the min temp is also very important. I could not get a clear idea from him how much it really does help, just that it does.

The coating should reduce temps, but is that part of the failure mechanism? Could the issue be flexing of the diff case or housing? In general, even if the fluid is not overheated/burned, a reduction in the temp of the fluid and parts will help lifespan. Is there any sign of the oil film breaking down between the teeth of the ring and pinion gears?

More info on the specific failure mode could help in trying to figure out a cure. Are the teeth coming off whole or breaking apart? Is the hard wear surface coming off the teeth first? Are there wear signs on the non-broken parts of the gears?

I assume the cryo treatment is legal but would want clarification on any coating before doing it. I know the 1.8"s have a bigger diff, do they also have these issues?

 

At this point, anyone who protests a cryo-treated ring or pinion or both in a 1.6 Spec Miata will have his tires slashed after the race. This is getting rediculous, and while I've been lucky, too many people haven't.

 

Im not really familiar with miata rear end but do you guys run any kind of diff housing reinforcement like comptechs offering for the s2000 ?



One of the local racers started cryo treating various drivetrain compenants and said he's getting 3x the life from his transmission, I guess the hill climbs he does are hard on them. He uses another builders in house set up but I guess it's a comercially available unit

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mohudsolo &raquo;</TD></TR><TR><TD CLASS="quote">I think the first question is to ask if these processes are legal in SM?
</TD></TR></TABLE>

no, it's not legal per the letter of the rules. but frankly, i really don't give a ****. for one, there wouldn't be any way to tell if it was done, so even if you know i did it, you can't prove it in the tech shed, and thus it becomes legal in a roundabout way. for two, the problems with these diffs are so widespread that as rich alluded to, nobody is going to protest unless they want to be banished from the unusually high levels of comrodary (sp?) we have in this group.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
I've spoken about the cryo treatment with a metalurgist at work and he agrees that the process really does have good effects on metal. The big IF he cautioned about is that the process must be done correctly. The time to bring the parts down to min temp must be very well controlled and the dwell time at the min temp is also very important. I could not get a clear idea from him how much it really does help, just that it does.

The coating should reduce temps, but is that part of the failure mechanism? Could the issue be flexing of the diff case or housing? In general, even if the fluid is not overheated/burned, a reduction in the temp of the fluid and parts will help lifespan. Is there any sign of the oil film breaking down between the teeth of the ring and pinion gears?
</TD></TR></TABLE>
i don't know, what should i be looking for? i still have the failed parts and can find out if you tell me what to look for.
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
More info on the specific failure mode could help in trying to figure out a cure. Are the teeth coming off whole or breaking apart? Is the hard wear surface coming off the teeth first? Are there wear signs on the non-broken parts of the gears?
</TD></TR></TABLE>
all 5 of my teeth that broke failed consecutively approximately 1/2 way up the tooth toward the diff. in other words, there wasn't 1 good tooth, then 2 broken ones, then 1 good one, then 3 broken ones, it was all 5 in a row. and all 5 of them broke at approximately the halfway point between the pinion and the ring gear itself. once again, i don't know what to look for in the way of wear signs on the non-broken parts, so if you tell me, i will go look.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">
I assume the cryo treatment is legal but would want clarification on any coating before doing it. I know the 1.8"s have a bigger diff, do they also have these issues?</TD></TR></TABLE>

again, it's not technically legal, but i would not make it a secret in the paddock that i had done it, and if it worked, would actually enthusiastically inform other 1.6l miata drivers about it to try and help them. 1.8's have a bigger ring a pinion, along with a completely different type of diff. theirs is a torsen, vs ours is a clutch type. the 1.8 diff's have never ever failed. it is possible to put a 1.8 diff in a 1.6 car, but it would be definitely illegal, whereas the cry and rem treated 1.6 diff would be illegal, but undetectible. it is also a somewhat involved conversion, with changing the axles, driveshaft, and final drive to make a legitimate conversion.

and no, we are not allowed any reinforcement of the diff carrier or anything else. but if upgrading the unit by using different materials for certain components would resolve the issue, i would certainly be open to the idea.

 

What type of LSD do you run in the car?

EDIT: what brand...


Modified by jisu009 at 2:22 AM 10/12/2005

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jisu009 &raquo;</TD></TR><TR><TD CLASS="quote">What type of LSD do you run in the car?</TD></TR></TABLE>
<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tnord &raquo;</TD></TR><TR><TD CLASS="quote">

, vs ours is a clutch type. </TD></TR></TABLE>

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by jisu009 &raquo;</TD></TR><TR><TD CLASS="quote">What type of LSD do you run in the car?

EDIT: what brand...


Modified by jisu009 at 2:22 AM 10/12/2005</TD></TR></TABLE>

it's a competition part from Mazda.

 

Cryo treatment is specifically ALLOWED unless the class rules specifically disallows it.

A search thru the GCR show the word cryo is not in any class rules.

 

you've got it backwards,

"no modifications that in any way may improve performance are not permitted unless explicitly allowed."

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by tnord &raquo;</TD></TR><TR><TD CLASS="quote">you've got it backwards,

"no modifications that in any way may improve performance are not permitted unless explicitly allowed."</TD></TR></TABLE>

but does it [cryo on the ring and pinion] really improve performance; I would like to think it improves reliability, not necessarily performance.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by chrisw85 &raquo;</TD></TR><TR><TD CLASS="quote">

but does it [cryo on the ring and pinion] really improve performance; I would like to think it improves reliability, not necessarily performance.</TD></TR></TABLE>

that's not the issue at hand.

cryo and REM treatments are illegal in SM, the question is will it help keep these parts from failing.

 

I know it's not the issue....but....there are some builders who will make the claim that REM treating the gears is legal, based on (drumroll, please.....):

The factory service manual says you should clean the parts before reassembly.

In their eyes, because REM treating is essentially ultrasonic cleaning, they ARE cleaning the piece, per the manual. (There's no spec on HOW it should be cleaned.)

Back to the topic: I do believe the solution is upsizing the pieces. If only we could find a suitable manufacturer......

Jarrod

 

If the main failure issue was from heat, the gears should look burnt with discoloring of the wear surface along with small chuncks of the hard surface coating missing. From your description, it sounds like something in the diff is simply mechanically overloaded. I'm not sure how to tell if the issue is simply lack of strength in the gears or flexing of the case or housing. It sounds more like a lack of strength in the gears themselves similar to what I've seen in assorted front drive VW transmissions. Am I correct in remembering that the 1.6 Miatas use a rather short diff ratio? That makes the base diameter of the pinion gear very small, particularly with the small ring gear diameter.

Using the above logic, the increase in fatigue life attributed to cryo treatment is exactly what you are looking for and would be a good experiment. What is the mean time between failures on the diffs in your experience? You would get much more meaningful results faster by having more people try it than just you. Is there something about the tracks you run that give a shock loading to the diff? Is there one specific track that is hard on them? Can I assume you are using new parts each time and that they are being set up by someone who knows how to best set up a ring and pinion? There are a ton of people in my region running SM so I'll ask about it at the next meeting and see if I can get it posted on our local board. I don't recall hearing about diff failures and I think the 1.6's are more common in my region.

 

over the curbs under power is what causes it in other cars I know

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by e9 &raquo;</TD></TR><TR><TD CLASS="quote">over the curbs under power is what causes it in other cars I know</TD></TR></TABLE>

Well miatas dont have any power, so thats ruled out

 

Is "performance" and "reliability" the same thing. Cryo makes the gears last longer, not perform better. They achieve the same level of performance over a longer time. And since cryo is specifically allowed for ALL classes, and cyro is specifically not disallowed in SS or SM, my vote is legal.

On seperate point, if cryo is illegal, it it a rule that cannot be enforced. There is no way that I know of to detect a cryo treated component.

 

jarrod:

i assume you mean upsizing the ring and pinion, and if my assumption is correct, how would we go about doing that without changing the whole thing? i mean, could we just take the ring and pinion out of the torsen and put it in the 1.6 unit? if that somehow works, i'd say that it's very real solution. although if the ring and pinion were bigger, i don't see how the ring gear would bolt up to our existing LSD unit, and i would think that it would change your gear ratio's also based on my very crude understanding of how things work in there.

mohudsolo:

i will inspect the ring and pinion gears today for signs of overheating. i don't think that happened, because my gear oil certainly didn't smell when we split it open (well, what was left of the gear oil). we do have somewhat soft mounts on the diff housing, is there any reason to think that these rubber inserts could be becoming too soft and the diff is twisting a bit to put extra stress on the ring and pinion? what would burning those bushings out and replacing them with metal inserts do? jarrod may have to answer your question on the short diff ratio, as i'm really don't know.

it really hasn't been just 1 track where these things have been giving up, it's every track and every car at every speed level from every builder. that's what's so frustrating, is we can't figure out just what's going on, except for our assumption that they are weenie parts.

Grumpy:

i completely agree that since these procedures are undetectable, in turn they become legal, but per the letter of the rules, they are not allowed.

SCCA GCR SMCS-1
A. Purpose and Intent
Unless specifically mentioned or approved in these rules, no additional modifications may be made.

C. The following items represent the only mnodifications and safety items permitted and/or required on Spec Miata automobiles beyond those of the SSCS. No permitted component/modification shall additionally perform a prohibited function.

3. b. 1990 to 1993 Miatas may use the stock, unmodified viscous limited slip differential or the MAZDASPEED Motorsports Development limited slip differential, part number #QN1064-A00.

it is up to you (or the tech inspector) whether or not you/they consider cryo/REM treatments modifications. Although as we have agreed, you can't tell, so it really doesn't matter.

 

Bigger everything is my solution. You're right that it won't fit in the case, Travis....but it just so happens that the 1.8 has a bigger case, plus everything else.

Our ratio is 4.3:1, so it's nothing insane that is torquing the innards wierd. (And we all know the engine itself can't....)

Jarrod

 

I remember reading that Miata diffs were extremely sensitive to the angle of the driveshaft being relative to the diff. GRM's locost that they built with a 1.6 drivetrain failed in almost the exact way you describe after about a day of driving around because they didn't line up the drive shaft at the same angle as it was when it was in a Miata.
If your engine, transmission, or diff mounts provide that much flex, and it was augmented with slamming curbs and the stress of a racing environment, then perhaps it is just the same issue?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Grumpy &raquo;</TD></TR><TR><TD CLASS="quote">Is "performance" and "reliability" the same thing. </TD></TR></TABLE>

Yes. With an intact diff, he finishes the race in a higher position than without.

 

My memory is that the diff in the GRM Locost broke the housing not the gears inside and that was due to not using the brace between the diff and trans.

One thought is that if the diff mounts are in fact soft, that means the diff can move around a bunch. If it moves enough to get out of line with the trans, I could see uneven speed in the driveshaft. Basically the universal joints will "whip" as the driveshaft rotates. That could add some uneven torque loading that comes out in the weak point, namely the pinion gear.

Do the gears break on cars using the wimpy viscous original diff? I suspect that the breakage is a combination of not very strong parts combined with the lockup of the competition clutch style LSD. Within the existing ruleset as I understand it, there is not that much to be done. Playing with metalurgy by trying cryo treatment can help. Shotpeening can also help if it can be done without damaging the gear surfaces. A higher grade of steel could be used if custom gears were possible. From a using stock Mazda parts point of view, the 1.8 diff is the best bet and most likely to get past the ruleset but would add significant cost to setting up a 1.6 car. Is the 1.8 diff available with the same 4.30:1 gears that the 1.6 uses?

Has this issue been brought up with national level SM people and if so what did they have to say about it? I would guess that if you can document a real need that it can be addressed. The coming of a national level ruleset may make SCCA national more responsive. You need to be able to document the failure issues as well as possible to get anywhere.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Mohudsolo &raquo;</TD></TR><TR><TD CLASS="quote">\One thought is that if the diff mounts are in fact soft, that means the diff can move around a bunch. If it moves enough to get out of line with the trans, I could see uneven speed in the driveshaft. </TD></TR></TABLE>

How is the diff going to get out of line with the trans with that big *** powerplant frame that bolts the two together?

 

I agree: shotpeen the R/P. In another race circle, I know of folks who have put an end to broken gears with shotpeening + cryo. Could you get away with one but not the other? Dunno. But when your diff is puking its guts every other weekend, a belt-and-suspenders approach is cheap insurance.

 

Good point on the PPF. It should keep the diff from moving in an up down plane. I'm thinking it is fairly flat so it might allow some movent sideways or through a vertical axis? It does keep sounding like the parts are simply undersized. Any info on the failure rate with/without Mazda Comp diff?