Im giving up. Broke another 6 speed last weekend.

going to try a Quaife wide and swap rear end ratios a lot.

4.778 for autocross

3.909 for track.

 

Props for continuously sharing experiences/stats.

 

Josh, stay in touch with me when you decide on a different trans. Since an adapter plate is needed for the K24 anyway, there's no reason we can't design one to work with another trans, with a matching flywheel. We simply went with the stock Miata trans due to cost, and to keep things OEM and simple as possible (PPF, driveshaft, VSS, etc).

There would have to be enough interest from other customers, but its something we're open to exploring.

 

Buy mine. You can buy my giken too and swap from 4.3 to a different R/P. ;-)

 

Just received a call from the shop that took my box apart. Apparently one of the gears is missing a tooth. I'm heading there this afternoon to take a look and I'll post pictures once I have them.

 

I lost all clutch fluid the other day heading home, had to power shift and found it wasn't that bad really. I think I'm ready for a dog box, Emilio.

Bob: Why not a turboII transmission? Classing?

 

Read the thread, TII boxes have atrociously bad gearing

 

**** gearing.

 

I might. your price is too high though.

Several places list the gearsets in stock from england shipped new ~$2600. I have like 8 core 5 speeds and I can build a transmission myself.

4.778 ring and pinion from mazda comp is $475 in stock.

Other issue is I am currently totaly wiped out for racing budget cash.

 

You can get that same exact 4.778 ring gear and pinion from the kia dealer for $380, it just has to ship from the warehouse.

 

I paid ~$310 shipped for mine BNIB from an online Kia parts place.

 

Yeah, but you still need to pay ~800$ for all of the parts from mazdacomp to do a full rebuild (your cores are worn out), so you're at a little over parity with my box. Totally fair though, if you value your time to do work at 0$. I value mine higher than that.

 

Also, if you do it yourself, make sure to figure out what machining you need to do on the case. You need to clearance some spots inside the housing, and I don't know what they are. Advanced Autosports might tell you what needs doing (they've done it several times), but they might not.

 

Sorry to hear that, but I was afraid that would be the outcome given the sounds you described.

 

None of those online retailers have them in stock either. They will have to get it shipped from the UK. Assuming Quaife actually has the gearset ready to ship today it will still be a while before you get it. I paid for mine in middle January and the first event I ran with it was the Wilmington Pro Solo in July.

And David is right. You need to order several hundred dollars worth of parts from MazdaComp($860) AND you will need to have the case Machined. On mine, buy the time I bought the gears, paid for shipping, ordered everything from MazdaComp and paid someone who is experienced installing Quaife gears in Miata gear boxes to do the machine work and install($560)...the total bill was $4,393.96

The Quaife install is not a "drop in" and IMHO it would be pretty stupid to put used shift forks which wear out VERY quickly, used syncro rings which wear and crack, used syncro springs which snap and used bearings out of a gear box which suffered a catastrophic failure like most all of yours have into a transmission you are building to last for several years.

I wouldn't let mine go for what David is asking for his....supply and demand..... I would be willing to bet David's is the only complete gear box WITH verifiable records as to the quality of the install....for sale in the US right now.

 

Very good point, which is why I bought it from him last night. Serendipitous, to be sure.

For those interested, here are pictures of the aftermath:

Stripped and ready to confirm the bad news:



Missing tooth:



The tooth was broken off fairly cleanly:



How does tooth wear look, in general? If the broken gear is replaced, can the box be reused, do you think?




None of the long bolts had broken in the month or so since the clutch job, but apparently one was loose. There is also a crack starting to propagate near the shifter:




I thought long and hard about replacing it with another Quaife gearset. In the end, I decided that there are no solutions in the short-term and I don't want to be stranded come next spring. I think I'll turn the boost down for track days and look at the possibility of adding a cooler. Does anybody have any thoughts about how to reinforce the case, as it's obvious that it's a flexy-flier.

 

From those pictures, it looks to me like if you were to replace that specific gear you would have a good to do gearbox.

 

IMO, if the case is flexing/cracking that much then stronger gears will not be a huge leap forward towards a solution.

I'm wondering about a few things:

1) Case to case, is the six speed case itself any more resistant to flex than the five speed case?

2) Is any of the tailhousing area cracking shown above related to forces from the differential being transmitted through the PPF? If so, would isolation of the diff contribute any benefits?

3) If case flex is a possible contributing factor to gear failure in either the five or six speeds, would a case girdle or brace help to prevent gear failures? I ask because I have seen them previously on other makes of vehicles and they are an easier solution than a custom case or certain other remedies.

 

I believe there is more ribbing on the 6 spd case. I would imagine they flex less because of that. My question is can you TIG on some extra ribs onto either?

 

Most of what can be seen in your pics is the coasting side of the teeth. The arrow I've added points to the drive side, and it looks pretty rough, at least in this glimpse. If the teeth on it look like this all the way around, and across, then that gear is iffy. It's a surface roughness that is making the gear engagement grabby as opposed to slippery, which is adding to the stress on the teeth. Do all of the gears look like that on he drive side? It is possible that only 4th looks like that, which helped lead to it failing.

Look for pitting as well. It will appear near the root of the tooth, and if there's more than a spot or two it will appear as a broken line of pits/dots across the width of the tooth.

I'd probably run the gearbox even if all the gears look a little smeared like that, but replace 4th as a set, not just the single one on the layshaft. And turn the power down a little, since you've already found the limit

Edit: What does your builder think about it? He's got a better feel for it than anyone else since it's on his bench.