mx5 diff problems

[PorkChop]

This is my point.

The mounting options have been done to death. The Miata has been the donor of choice for a number of years Stateside, Keith Tanner has a blog which runs into hundreds of entries. They've already gone through this, we're not breaking new ground here.

[CTWV50]

Originally Posted by PorkChop

This is my point.

The mounting options have been done to death. The Miata has been the donor of choice for a number of years Stateside, Keith Tanner has a blog which runs into hundreds of entries. They've already gone through this, we're not breaking new ground here.

Can you provide a link so we can all have a read? Cheers.

[Numplumb]

I have removed the bushes and bought Flow-Flex poly bushes which arrived today, they are like Stot's solid. Ones I was thinking of placing a large washer at the bottom so that they would be like solid mounted but with the poly bush giving a small amount of movement, I am thinking of mounting the nose of the diff with rosé joint type eyelets with poly inserts if that makes any sense.
Regards Mick.

[TSM Locost]

Keith Tanner http://www.cheapsportscar.net/diary....ate=1980-01-01

[jason 82]

After a visit to gbs ( great British sportscars & kit spares - same company ), I had a conversation with a chap called Richard. They cut the arms off their mx5 diffs & use a bracket system, curing the problem. The mx5 diff brackets are available from kit spares/gbs.

[Short]

have you got a link to the bracket?

[jason 82]

No mate sorry. It's not in the catalogue on the web site either. If you ring GBS on 01623 860990. It's not an item that they usually sell, but if you ask them specifically for it, they will supply one. Obviously you will have to adjust your rear cage to suit, but Richard guarantees that this will completely eliminate the problem. I have ordered my one to pick up early next week.

[Short]

Can you post a picky when you've got it? And how much are they?

[Talonmotorsport]

I've sat on my hands for long enough now and I've to get this out so I can sleep at night.
The chassis designs:
First off the in the beginning there was the standard Sierra diff mounting as per the book, any body remember what that looked like? Yes mounted to a pair of SB4's and a pair of 5mm thick chassis plates mounted in the middle of the chassis. There are no known brakages of this design to date even with some of your more suspect welding.
The mount sits in the middle of the chassis surrounded by that material that makes up the seat back and the diff cage,thats not going to twist unless you smack a curb side ways at speed at which point a broken diff is the least of your worries. It's solid mounted does not move and if you can feel any vibration from it after you've fitted your car with 350 and 250lbs springs your up there with the princess and the pea.

The Saturn design...
It's been no great secret amongst those that I have talked to that I am not a fan of this design as it assumes to many things in the way of peoples ability to make it, the design also over looks some very basic engineering understanding or should that be lack of it.
The design of the lower wishbones that uses the M20 adjusters is fine for the top rear Sierra set up as it just holds the upright in place, the Saturn design puts these under greater loading by putting these on the bottom. Your thinking so what theres 2 of them, at this point I'd like to point out that there is now 2 high stress points acting on 2.5mm thick tubing that may have been MIG welded by a less than proficient person.
Top rear wishbones:
What a great idea to put the end of the damper in the middle of the wishbone, it means you need a spring so hard that the car will knock your teeth out and tend to bounce over the bumps rather than absorb them. To my knowledge no one has as yet to have a Roadster corner weighted and had a set of coilovers valved to the correct requirements of the suspension. If your using cheap single adjustable bump and rebound coilovers then getting your suspension to react quick enough is going to be a problem.

The MX5 diff and it's cover...
In the Mazda shell the diff is mounted to the sub frame which could be argued does not move or twist, at the other end it's bolted to the ali spine which in the grand scheme of things only moves by 1-2 mm ever. Mazda have designed a car which smooths out the vibration of road noise to give a better ride,thats not why you are building a Roadster.
People have got caught up that the diff is rubber mounted on the arms and decided that the nose should be too, if you can move your choice of rubber mount with your fingers it's too soft, if you can move it with 2 pairs of mole grips it's too soft, if it has a metal plate bonded top and bottom it's too soft. By the time you have found the right grade of rubber mount you will have run out of cast ali diff covers.
The nose of the diff needs to be held in place top and bottom with a one piece bracket made from 5-6mm plate that is bolted to 5mm chassis plates and SB4 with M12 bolts. This will stop the nose from nodding under load and stop the arms of the diff from breaking.

GBS design:
If any body is looking at that and thinking ah they have cracked it just bolt through the ali casting at the top.... DON'T! The top of the casting is not flat at any point, there will only be the edge of the nut sat against the casting causing a stress point. All you will have is another broken casting in a different place.

Talon's diff cover...
Many said it was not needed and this may be true but consider this...
it fits the standard Roadster chassis although you have to move SB4 abit, it gives 4 large areas in which to put 4 M12 bolts, it's made of 2mm steel so you can weld extra mounting lugs to it, I doubt that any body will ever manage to brake the 6mm main plate, it has no in built fail point (well not intentionally any way), it will fit the Saturn design the same as it fits the standard chassis.
I will be publishing the drawings for the extra tubes and mounts when I have fully tested the design by trying to break it... by vigorously driving around the rough farm track and taking it drifting.

[TheArf]

Like you Phil I will only bite my tongue so long, I am sorry for the pressure you are under in your personal life and your business, but that does not give you the right to rubbish other peoples efforts, maybe not everyones welding is top notch, but they do have a go.
I wonder how you would fare if you were to try the jobs that some of the others on here have, I am qualified to make comment on their work but wont as I know the effort that these guys put in and good for them, each time they do something on their build they are learning something new OK

my rant in now over

Arfon