mx5 diff problems

[Not Anumber]

A while back i'd read this problem could be solved in a single stroke by throwing out the MX5 diff casing and housing the diff in a simpler box that would mount up the same as a Sierra diff would.

Has that idea gone out of the window ?

[Stot]

Originally Posted by Not Anumber

A while back i'd read this problem could be solved in a single stroke by throwing out the MX5 diff casing and housing the diff in a simpler box that would mount up the same as a Sierra diff would.

Has that idea gone out of the window ?

Phil has posted this up before with the extra chassis parts required but he removed it so I guess its not available yet.

Other problem is that many of us already have saturn based chassis so need a solution for that.

Cheers
Stot

[Short]

Not out the window, but people who already have the MX5 diff cage cant simply install that box. It requires a whole new diffcage and changing the transmission tunnel. - Not an option for some.

[Short]

beat me to it Stot..........

[PorkChop]

Originally Posted by Short

1 comment on that - the bolts are in shear. eventually, it will snap them if there not tough enough.

As for solid mounts all round, you need to allow SOME movement due to chassis twist. No matter how braced it is, the chassis will twist in corners and over bumps. the mild steel diff cage will twist, but the cast diff wont. To be honest, I think a stiff mounted diff is more likely to fail than a bushed diff. Think how much damage a car would get with no suspension at all?

One common mod on MX5s is to stiffen the diff rubbers, because tired mounts can give a reduction in gear change quality due to excessive movement (if I remember what I read correctly, it was some time ago and I can't find the bookmark). The mounts could be stiffen by filling with shoe goo, fitting diff void fillers or stiffer mounts (which I think Mazdaspeed did along with uprated engine mounts).

The Sierra diff is solid mounted in these cars. AFAIK there have been no issues with diff mounting failures.

There are several kit car manufacturers using solid mounts on their MX-5 based builds; GBS and Roadrunner Racing are two certainties because I have seen their cars IRL. Well, GBS cut off the arms and solid mount the centre part of the diff upper.

[Davidbolam]

Can someone not maufacture a brace to go over the existing arms. Both of the breaks have occurred on the right hand arm where it has had a notch taken out. The original mounts etc could then be used

David

[CTWV50]

Originally Posted by Short

1 comment on that - the bolts are in shear. eventually, it will snap them if there not tough enough.

Maybe, they are engine big end bolts, but as I say I'll be interested to see how it fails.

[Short]

Originally Posted by PorkChop

The Sierra diff is solid mounted in these cars. AFAIK there have been no issues with diff mounting failures.

Agreed - but the Sierra diff is mounted at the nose, not on thin arms 300mm away from the application of torque. The mazda diffs are designed to fail. that's why the O/S arm has 2 notches taken out the arm.

Please don't think im shooting you all down - im certainly no expert!

heres a few shots of a simpe idea:

Viewed from rear



viewed from below/rear



viewed from above


Its simply 25x25x1.2 (but I will use 40x20x3) tube. I will of course use bolts to secure it, and weld it into the chassis with stiffener plates.

Can anyone see any issues?

[PorkChop]

I know, this subject has been done to near death. The arm is designed to fail to prevent the PPF from acting like a battering ram in an accident.

My point is that the Sierra diff is solid mounted (the MX-5 diff has a nose mounting as well) and doesn't suffer from chassis flex related breakages.

[Short]

I think its safe to say we all know that the MX5 diff needs to be mounted at the nose, but its a case of 1) how to fix it to the chassis, 2) to bush mount, solid mount or a combination of the 2.

Were all in agreement that the Sierra diff is a superior mount, but that doesn't resolve the owners/builders with a Saturn design rear cage who are nervous about how to mount there diff.