141 replies to this topic

[davew]

When I have a box of rocks for a transmission, I don't analize the rocks !!!!!! Most failures seem to occur coming out of a corner, following a downshift.

 

Just take the shift knob off. That bare stick gets really uncomfortable after a few laps.

 

When you have to fix it yourself, mechanical sympathy becomes natural.

 

Dave

[davew]

Talk about co-inke-dinks

 

I went in back to take a trans apart. This trans ran at the Runoffs and one session at NOLA. Other than that, I do not know the history as it is not one of my customers. Maybe the car owner will tell us.

 

No parts on the drain plug. Took the tail housing off and thought I would see something, but it all looked normal until I turned the output shaft and 5th gear fell off !!!!!

[davew]

Sorry, forgot the pic

Attached Files

•  dots 099.jpg   23.66KB   6 downloads

[FTodaro]

wow Dave I have never seen anything like that. so just a broken shaft, any broke teeth on the gear.

[davew]

Teeth look fine, nut was tight. Other than the broken shaft it looks beautiful.

 

I have had about 200 of these transmissions apart, and I have never seen this.

 

Dave

[HoneyBadger - BrianW]

dots 099.jpgTalk about co-inke-dinks

 

I went in back to take a trans apart. This trans ran at the Runoffs and one session at NOLA. Other than that, I do not know the history as it is not one of my customers. Maybe the car owner will tell us.

 

No parts on the drain plug. Took the tail housing off and thought I would see something, but it all looked normal until I turned the output shaft and 5th gear fell off !!!!!

Is this the trans that came out of Bickhams car? If so, it was in a pretty decent wreck at the runoffs, which could explain the damage.

[SaulSpeedwell]

Sorry, forgot the pic

 

OK, Drago forwarded me your email me on this but I am just now catching up on here for the context.

 

Dare I ask, was this a 99+ trans?

 

I have ZERO hard proof, but some suspicion/correlation (not causation, I know, I know, I know) that the 99+ countershaft is "softer".   Also, it seems like the modern "crate" transmissions (no VIN plate) fail sooner than anything else.  I only know enough to be dangerous about gear processing and treatment, but I know that the surface has to be hard and the middle and root has to be "tough". 

 

I agree that driving habits can fix every problem noted in this thread, but I do still get some satisfaction out of analysing failed parts (I have a metallurgist friend that works for beer and compliments, and all of our SM problems are more interesting than his day job!)

 

If anyone sends me failed gears, failed shafts, failed anything, I will test them if I can and post whatever I have learned (or think I have learned) here.  If you want the results to be "confidential" as to what driver or builder last touched the parts, I'm happy to honor that.

[davew]

Saul, I just sent you an email. I have broken parts in stock.

 

The trans in the pix does appear to be a NB crate unit. No Vin tag. But, some one was in there. There is sloppy silicone everywhere including on the front gasket.

 

I have never used a crate trans, but the anecdotal info I have heard is that they break faster than rebuilt units. My theory is the gears have been work hardened over their 15-25 years as street cars. But I know less than you about metalurgy. Heck, I can't even spel it!!

 

Dave

[davew]

Yes, this is the box from Bickhams car.

[davew]

I am sending a box of parts to Saul. Once he inspects them, we will report to the masses

 

Dave

[Johnny D]

I am sending a box of parts to Saul. Once he inspects them, we will report to the masses

 

Dave

 

https://www.youtube....h?v=aB2yqeD0Nus

J~

[SaulSpeedwell]

I am sending a box of parts to Saul. Once he inspects them, we will report to the masses

 

Dave

 

Thanks to Wheeler and Drago, I have a desk full of parts that I'm hoping will help all racers and rebuilders understand more about the weak spots in the Miata trans.

 

So - I got all the failed parts this week, and I WILL section the parts (especially the 3rd gears and countershafts that are causing repeat failures for some drivers at some tracks) and check hardness in hopes of determining if the countershaft and gear hardness/toughness is any different across years. 

 

A big thanks to Jim and Dave for shipping the parts for failure analysis.  I've known both of these guys for 12+ years now, and I truly believe these "failures" are not the result of any rebuilder's workmanship, but a simple reality of overstressing a transmission that was designed to be driven on the street with 185/60-14 tires with a sprung organic-face clutch. 

[SaulSpeedwell]

Catching up on YouTube uploads, here is a video of 57K street mile, no race time, "original" 1999 synchro springs ...

 

Edit:  (Version 2 improved spring vid removed at supplier's request, see below ...)

 

[Ron Alan]

SS...did you purposely use different pliers in those tests and grab the springs in a different locations? 

[SaulSpeedwell]

Ron - the answer is "Yes and No".   (And you already saw the much longer answer ...)

 

Edit:  Removed big long discussion of springs and test and processing methods at request of the supplier.  I'll be using square pliers test only, for any future "demonstrations" ... sorry for the edit. 

[Jim Drago]

I'm glad you asked the question, I'm not being curt or combative, I'm just typing fast. 

 
Typed fast .... sorry if it is disjointed or has typo/grammar probs ...

If you ever saw him type.. You would know what he is talking about He is a very ANGRY typer

[SaulSpeedwell]

If you ever saw him type.. You would know what he is talking about He is a very ANGRY typer

 

Bridget just said that ... "You are typing angry!"... haha you know me too well ...

 

P.S.  You stick your chin out 2" when you text  ....

[Ron Alan]

Thanks Mark for the write up! And I'm glad you took my post as it was intended...opportunity to clarify. True professionals are happy to do this when questioned...whether the question is justified or not

When you, Mike C, Jim D(both),Dave W and a few others speak...I stand up and listen. So appreciate the knowledge you guys are willing to share to benefit us all....on my little soap box clapping here!

BTW...if typos and misused words were and issue on this site...Drago would have been forced to ban himself a long time ago

[SaulSpeedwell]

 

Public Service Announcement:  3-4 Shift Forks

 

https://picasaweb.go...feat=directlink

 

Some of you may have noticed a change in appearance and processing to Mazda's 3-4 Shift Forks ever since the "D" revision of that part came out.  (Pic link above, but it may take me some time after I post this to get it working and displaying just right - and I now realize I have some pics to add later)

 

As one of the most frequently operated/worn out/ and replaced components in the transmission, I have been meaning to get around to testing and measuring these parts versus the "C" Revision that we have used for most of the time the SM class has been around. 

 

Results:

"C" Revision: 

Base Material hardness:  15 HRc

Pad Hardness at wear surface:  19 HRc

Pad thickness:  0.271"

 

"D" Revision:

Base Material hardness: 24 HRc

Pad Hardness at wear surface: 28 HRc

Pad thickness: 0.278"

 

Conclusion:  Although arguably "uglier" than the old "C" revision forks, the newer "D" revision forks are significantly "harder" and 0.008" thicker at the unmachined pad surface.  The unmachined surface will "polish down" rapidly during break-in.

 

Bottom line:   Compared to a machined "C" revision, these forks are expected to last longer, but with increased chance of wearing the mating hardened hub sleeve (~ 57 HRc at the wear surface).

 

-MB

 

 

Well, the 3-4 forks are coming in machined again ("E" Revision?), but still way too soft if you ask me ....

 

"E" Revision:

Base Material hardness:  ~15 HRc

Pad Hardness at wear surface:  ~23 HRc

Pad thickness:  0.270"

 

http://youtu.be/zUMlpO-JNOE

[38bfast]

The hulk will still tear them up.