NTS MX5 Build

[robo]

Well all I can say is something needs doing, the yanks have dealt with the problems with the braces. In normal hairdressers mode the car probably has no issues but these things are going to get a spanking and as the mx5 fails so will the roadster version. Needs looking at.

bob

[costlow7]

I have just noticed something, I dont know if it is that important but if you look at the saturns/nts mx5 build guide revision 3 page 30 you will see the diff in the car. If you look closely you will see two very small cut outs notches top and bottom on the right hand side of the ally casting, if you look at nathans post you will see that the diff broke at this point. I know it broke because of other reasons and this has probably nothing to do with it, apart from this being a bit weaker. I have not checked my diff yet for these marks, just thought I would mention it.

[robo]

http://forum.miata.net/vb/showthread.php?t=349293


http://t0.gstatic.com/images?q=tbn:A...pnBhU7U06neswg

There is a mod. worth reading. A frame that bolts the diff to the gearbox. What I dont understand is that if mazda fitted this as standard on some cars called a ppf <and they break> how come they have they have been omitted in the roadster builds.

Bob

[PorkChop]

Originally Posted by robo

http://forum.miata.net/vb/showthread.php?t=349293


http://t0.gstatic.com/images?q=tbn:A...pnBhU7U06neswg

There is a mod. worth reading. A frame that bolts the diff to the gearbox. What I dont understand is that if mazda fitted this as standard on some cars called a ppf <and they break> how come they have they have been omitted in the roadster builds.

Bob

Bob

The PPF frame is standard to all mark 1/2/2.5 MX-5s (not 100% sure about the mark 3, but I would be surprised if it's different).

It's essentially an ali C section beam (about 5mm material thickness) that is hard mounted to the diff nose via 2 x 8" bolts. The beam runs alongside the prop (and covers the O/S side of the prop) and is hard mounted to the gearbox tail, again with 2 x 8" bolts. It's worth noting that the PPF is the only mounting on the front of the diff. The only compressible mountings (AFAIK) are the diff ear rubbers and the engine mounts on the front subframe. Therefore, any rotational movement about the driveshaft axis will be affected by the moment of the engine/gearbox.

As an aside, I read on miata.net that Mazda say that if the rear upper top hat washers are removed, they render the PPF scrap.

It might also be worth seeing what sort of upgrades Flyin Miata or Performance 5 do for the rear diff area (FM have built a 800+bhp Miata and offer lots of tuning bits).

[robo]

If thats the case then the sooner someone knocks up a torque control arm that replicates the job of the mx5 jobby the better. Me thinks.

bob

[Johno]

Hi,
I know this subject has been a sore point for many but there are quite a few MX5 builders now on the forum and Iv'e been looking at Keith Tanners build of the Locost with MX5 donor, quite interesting.
I guess many of you have already viewed it (1439 entries,,,pheww ) but I found it very interesting.
Originally he had a rubber mounted bracket from the front top of the diff to the chassis rail on the transmission tunnel. This after some time failed,


Here's the failure



He then decided to make a small frame bolted to the front of the diff top and bottom and solidly mount it to a plate welded in the tranny tunnel,





It was bolted to the thick plate towards the rear of the tunnel with three bolts with captive nuts welded to the diff bracket.
He used the car for track days and after a few years decided to change the diff.

This is what he said,

"August 1, 2008: Since it's out, here's a shot of my PPF substitute."



"I don't think I ever took a good picture of it before. This bolts on to the front of the diff, and then three bolts are run through the side of the transmission tunnel. Everything was still nice and tight when I removed it and it's undergone a fair bit of abuse in the last few years - so I think it's fair to call this little bracket a success.

Less successful was the fact that I managed to pull the driveshaft out of the transmission while removing the diff. I'm not sure I have access to that without pulling the interior transmission panels - I hope I don't have to do that!"

Hope this may be of some help to some people.

Johno

[trick-kit]

Originally Posted by costlow7

I have just noticed something, I dont know if it is that important but if you look at the saturns/nts mx5 build guide revision 3 page 30 you will see the diff in the car. If you look closely you will see two very small cut outs notches top and bottom on the right hand side of the ally casting, if you look at nathans post you will see that the diff broke at this point. I know it broke because of other reasons and this has probably nothing to do with it, apart from this being a bit weaker. I have not checked my diff yet for these marks, just thought I would mention it.

Yep, that's the Mazda designed in safety point, designed to break at this point in an accident so the PPF doesn't pierce the fuel tank. It is a built in weak point.

TK