Not mine I'm afraid, found it when Googling to help people visualize the problem.

From here:

http://www.mmmiata.com/catalogsite/suspension01.php

The thing is mark, that some find it offensive. I just find it intensively stressing, when all i was trying to do was makesure no one makes the same mistake as me. My heatbeat rises everytime i look on the forum to see what im being flamed for next. I now understand what andy was going through, as i feel pretty sick aswell now with the stress, i think i may be in a pretty dark place at the moment, so for now im going to stay away from the forum as i feel that a small percentage of people have turned it a bit nasty. Everybody i know used top post regular updates on their builds, but now i speak to builders who dont want to incase they get a load of bad critisism. Everyone needs a bit of a boost/ positive encouragement now and again, and sadly i think that has all but dissapeared from the forum. Im a pretty hard f@cker, so its a bad day when a grown up bloke starts welling up sat infront of a computer on an internet forum

Im sorry if im putting more of a downer on things, but i just want to get how i feel out in the open. Ive tried to make an effort with certain people, yourself included. I try and treat people how i would like to be treated, iv never said anything that i wouldnt say in person.

Yes the saturn mx5 isnt perfect, (and neither a voodous for that matter) but then again andrew made the plans as a guide for free download. Its up to individual builders to decide wether they want to follow the guide or modify it to suit their requirements. At the end of the day its just a guide. Ive given my car an extreme thrashing trying to break it and it hasnt broke, I drove it over a curb at forty miles an hour the other day in reverse for gods sake so im confident that the chassis is strong enough.

Anyway, ive said what i had to say.

Well wishes to all, im out of here

Nathan

I have to agree I don't post as much on my build thread or on the forum at all for that matter as I don't want to receive overly critical demotivating posts.:rolleyes:

From what I can see its always the same person being negative towards the roadster. Just ignore him. I've heard it all from the same person : the roadster understeers, its huge, its heavy now going on about the design of diff carriers, what next ?. If I thought a car was that shit I wouldn't frequent around the forum designed for enthusiasts who are building the car.

MarkB only comes on here to stir things up, he's not a builder or a problem solver. he snipes from the sidelines at other peoples builds and in my opinion has nothing useful to contribute.
He seems to have failed to understand the problem Nathan had with the diff failure and has tried to use that as a way to attack the basic chassis design which has already been proven. (Are the Sierra based chassis's failing - NO)
He tried to use an example to highlight his point but the builders of that car are having EXACTLY the same diff problems!
His argument is as flawed as his engineering knowledge. Waster

Sorry AshG - I accept a wrap over the knuckles for such strong statements but we don't need this guy poisoning the forum.

BV:)

Hi all,
Having not been on this forum for too long I'm not sure of the history of certain members...
In my opinion Andy of SSC and Nathan of NTS have done an outstanding job. The amount of times I have asked them questions about the build and recieved a swift answer is second to none...
Without them there would be many ppl out there scratching their heads..
Nathan delivered a bodykit personally on a Sunday to us in Norfolk. How can anybody complain about the devotion this guy is willing to give towards many peoples hobby/dream.

I for one can only take my hat off to him for the job he has undertaken.

Where would many builders be if he hadn't take on what Andy Hugil started.
I can only guess....:(

I personally started this as a hobby and looked forward to visiting the forum to look at other ppls ideas and hopefully things I have done may have helped some ppl I don't know.
One thing I do ask regulary when I do post something is "if you see a problem with what I have done please let me know". If somebody points out a problem I'm only too happy to take their advice, but some of the posts ppl write are not constructive in any shape or form.:(

Everybody has a right to say something but if you have nothing good to say then say "NOTHING"

Johno

Don't let the Troll win mate
 

Hi Nathan,

Please don't let the verbal garbage of just one sad sorry individual drive you away from the forum. :(

You have a great deal of respect from the genuine forum members on here.
These are members who are actually building a Roadster & look towards the suppliers for help, parts & moral inspiration.

Take some time out to chill mate.
With a little luck you'll take some heart in knowing others feel the same way about our " Resident, forum troll " ;)

Speaking from personal experience, I have been daft enough in the past to let this, sad sorry individual get me down ( Leading to some very public & childish outbursts on my part ) :o
It got to the point that I have now decided to take a back seat on the forum, worse still, I have completely lost all interest in completing my own Roadster build & this has now sadly fallen by the wayside.

Good news is, I have now bought a road registered 7 in need of a full refurbishment.
Fortunately the majority of the Roadster parts can be re used :)

As I am no longer building a Roadster I don't see much of a future for me on this forum as I will no longer have anything in common with all of the good folk on here.
That said, I do still read most posts as I am genuinely interested in each & every build in progress.

Take care Nathan, don't be away too long.

the way I see it is... if anyone decides to boycott the forum because of those who intimidate via these threads, then they have won, so the best thing to do is just simply ignore and carry on posting...... the wealth of knowledge that is and can be found on this forum is way to valuable to be lost, so I would implore both Nathan and Andy to come back and talk to those who would benefit from their input as they have done in the past and recent present. The vast majority of members on here including myself NEED the likes of you around to further the roadsters life cycle....howay lads git yersels back on ere

Never made a car in my life or so much as looked at a tub of resin so quite why I comment on things is beyond me.


Think triangles and all will become clear

Sarcasm and abstract sentences. Wow!

I don't think anybody is doubting your knowledge or technical ability its your ATITUDE . You have helped me in the past and for this I'm greatful but why do you seem to be constantly digging at people with cryptic comments that don't help anybody ?

There it is in a nutshell mate !! :p :D

You honestly believe that you are the only one who has ever opened a tin of resin or allegedly built a kit car.
Again, I think you honestly believe that you are the only one who knows how to grow Onions ( As you put it )

Sorry to be the bearer of bad news, some of the local boat builders down here also know their Onions, that's how they manage to stay in business.
If I were feeling in a spitefull mood, I might say that they could make your work look like apprentice pieces but I won't :D
Same can be said of some of the kit car manufacturers, again, they manage to stay in business just fine.

Lot more technicaly minded folk out there, a good few on this forum ;)

Get over yourself mate & move on with whatever floats your particular boat.

Now here's a theory, given that this problem isn't solely confined to Locosts but exsists in MX5's too, maybe it's not the mounting of the diff that causes the problem (OK, if it's allowed to move around too easily then it may highlight the weakness) but MX5's that have broken the diff have pretty much the same thing in common.

They have been involved in an accident.

The diff has a cast sacrificial point in it designed to break to prevent the PFF puncturing the tank. Now given that most of the kit cars using the MX5 as a donor are built from wrecked MX5's maybe we are inheriting the fault without noticing it.

As i said, just a theory :rolleyes: :D

TK

Your correct it does appear they've made a point at which they want it too fail so actually what we need to do assuming we don't have a crash damaged diff is to protect the diff from violent movement which makes sense.

It is true some of the donors used may have been involved in accidents but by no means all of those being used have been in accidents - many are now cheap enough (mot failures etc) to be used as donors without any accident history.
Not aware of MX5's suffering diff carrier failures. Anything likely to compromise the diff will like as not cause it to fail though there's always the 'exception that proves the rule'
Usually in a front or rear impact the power plant frame bends downward twisting the nose of the diff down to the road to avoid pushing through and puncturing the tank, this action usually fails the diff carrier so few would have made it on to other cars for further use or be available for sale as salvage.
The diff failure, as happened to Nathan, is something I've seen before and on diff carriers that were known not to be compromised, though I get the point we should all be vigilant and inspect all used parts in the build for signs of damage/fatigue.

http://www.mx5oc.co.uk/forum/forums/t/34429.aspx

This thread lists a few examples and shows the diff in the MX5 subframe.

TK

This is accident damage or the result of, and cracked diff that may have been missed by the repair shop if they wern't looking for it. I accept there might be the odd rogue part that has cracked but not completely failed at the time of the acceident and that could get onto another car as a salvage part - as I said we should all be vigilant in checking the condition of our used parts.

Not aware of any in service failures of cars that have not been in some sort of accident so I don't believe this is an inherant failure of the MX5 dif when used in an MX5.
As I've said elsewhere in this post its only designed to resist rotational forces about the propshaft axis. When used in isolation and without proper constraint the diff can and will rotate about the driveshaft axis or indeed any fore aft movement as you have pointed out will cause the diff to fail as it did on Nathan.
As I have previously stated Nathan would do well to implement a better way of contraining the the diff movement as the method he has used hasn't worked. I can fully understand why he did what he did and he's not the first to have tried something like that nor is he the first to have had such a diff failutre.
As I have said all along the key to this is understanding the forces involved and engineering a solution to constrain them. Some good suggestions as to how that could be done have already been presented.
Did the diff Nathan originally use come from an accident damaged car? I thought not if it was the one Saturn started out with.

This particular failure was due to Nathan forgetting to fit the two big washers that restrict the rotational movement of the diff.

It still remains to be seen whether the design as intended works or not.

Agreed, and i did state this fact in my post, the point i'm trying to make is that people are assuming that the failures of the diff when used in LSIS kits is because of poor location when it would seem that as it does not affect every kit made but just a small percentage, rather than the builder just being lucky there is some other reason.

It would be interesting to find out from those who have suffered diff failure in an MX5 LSIS how many of them used cars that were insurance write offs. I bet there would be a high percentage.

TK

Not every kit has poor location of the MX5 diff, a study would need to be carried out to determine who's kit did or did not break the diff. From what I have seen all those experiencing trouble do not have the diff properly constrained! a point I have been making through out this thread.
Failures of the MX5/RX7 diff when used in isolation are due to poor mounting design with insuffiecient constraint of movement. This is a known problem and there are plenty who have come across this problem - just google search and you will find.
Poor location will cause diff failure as I have tried to explain, Nathan failed to fit the diff washes and that contributed to unconstrained diff movement. A compromised diff could also cause failure but I am aware of people building westfield miata's amongst others including the MNR who are also having failures where the diff has not come from an accident damaged car.
Whilst I get the point you are making RE: the need to be vigilant in checking the parts we use for building cars don't assume that the failure was neccessarily because it must have previously been in an accident and blindly go on believeing the inadequate mount arangement will be alright. Nathan forgetting the washers for the rear isolaters may well have played a part in this.

BV:)

Good point well made - hhmm where did I miss that vital bit of evidence:o
The rotational movement they are designed to restrict though, is about the propshaft axis not the driveshaft axis. The type of failure Nathan has experienced exibits all the hallmarks of a failure about the driveshaft axis, the cause of which has been encountered by others as poor diff mounting and constraint of movement of the diff nose.
This failure is due to poor diff constraint but perhaps due to technician error rather than design.
BV:)

I think big vern is right, the nose of that diff needs to be well and truly controlled. When you think that a few thousand rpm and a dropped clutch that pinion is trying to climb that crownwheel, that beam across the back is only there to hang the diff unit in place the rest of the forces go to the front mount. i had a quick look round the mx5 fourms and there are dozens of failures with a thousand reasons why, I dont know if I would want something as hit and miss as that an inch from my spine. You could also fabricate a steel brace to run the whole length of the thing and bolt it through the ali bit. It could crack then but at least it would all stay in there.

Bob

Edit: An extract from another forum


Join Date: Jun 2005
Location: Arizona
Posts: 2,007

They do break there very easily.

I also think the alloy or casting method somehow makes them excessively brittle too.

I had an diff assembly accidentally roll off a floor jack close to the floor and produced the exact same break off with a really minor impact. The exposed cross section's inside looked like classic metal fatigue.

Thank you Bob, at least there are a few of you who can see the problem.
Using an the old mx5 engine mount as the front diff mount ain't gonna work. Engine mount is not designed to work in tension!
1.8 mx5 puts out 149N.m torque/5000rpm at the flywheel.
=183N.m/4070rpm to the propshaft in 5th gear (0.814:1)
Diff ratio= 4.3:1
=787N.m/946rpm at the driveshaft. Thats whats trying to twist the diff out of the chassis:eek:
There's no way the tired old engine mount can handle anything like that tension - the rubber will tear away from the steel backing - just try lifting an engine out of the car without undoing an engine and you'll easily see its not up to the job.

Nathan,
I'm trying to pee on your bonfire, far from it, If only I lived closer I'd come round to see for my self and help out with a solution. There are a few good ideas already coming on here.
Do you have a dxf of the chassis in that area I might be able to look at possible solutions a bit easier.

BV:)

http://www.solomiata.com/images/RX7pinion.jpg

How about an upgrade to an rx7 diff. No problem with these they have beefed up the whole thing but the prop would be short, the diff mount would end up in the tunnel.

Just thoughts

Bob

That is what spud originally started out using as an alternative donor. However stopped and went for the mx5 instead

They also need to be properly constrained - They'll still break the diff hangers if they're allow to rotate about the driveshaft axis - The RX7/8 and the MX5's all use the powerplant assembly principle so a strong front mounting system is still essential.
BV:)

Mazda beam
 

I have been thinking about mounting the diff in a better way and have read all the posts. I am thinking of mounting it the same way as mazda did with a light weight aluminium beam, using the same bolts spacers etc. Can anyone find a problem with this? I reallise the beam with have to be strong but it will be a little shorter and therefore stronger, with a little thought to the design I think this can be done. the mazda beam was only aluminum anyway.

As for the people who post nothing but unhelpful comments, these people are very shallow minded and are easy to root out. I just look at there previous posts and if most of there comments are unhelpful, I just ignore them. And there posts are usally short.

I think that something along these lines is a no brainer as its basically reducing the amount of strength needed at the mounting point and acting as a torque control arm. It is reproducing the long snouted rx7 concept with a simple bracked. It would not be hard to mount within the gear tunnel and could be done on rubber bushes rather than an engine mount. The longer the better, mind if it was behind me in a car I would still like to see some steel bolted to the cast arms.

On the subject of input from certain members I think there are enough intelligent people on here to sift through some of the crap and make their own logical decisions. As far as this diff problem goes its in the interests of the forum members to iron out any bugs to keep things safe. No one wants to go down the road with a diff banging around behind them and a broken prop flailing around a gear tunnel. The mx5 concept is reasonably new and will have the odd issues but nothing insurmountable we have to just keep bouncing ideas about to find that eurika moment.

Interesting juxtaposition. 149 Nm with acting on a lever arm of ~30 cm results in 500 N force pulling on one of the engine mounts (minus half the weight of the engine, which I guess is about the same). On any engine with a bit more torque than standard the engine mount works in tension!

Hi guys,
I know this is getting a bit of a concern but this is what I have came up with.
I decided to make a brace between the top of the diif mountings to tie the two together as if it were a chassis. I've fitted two rubber mounts off the back seat rail one in compression and one in tension at all times (tight bugger to fit)....LOL but seems rigid enough.





Sorry no triangulation just old plain engineering....LOL



Also fitted lower diff washers as per photo...




Well if that's not good enough I'm going to get a sore backside as well, because that's what I'm fitting to my car...

Have a good weekend Johno..

Ok then whats the verdict,
What do we have to do to make this safe?
I don't think it's possible to make a frame to go along the transmission tunnel as per the MX5 unless you widen the tunnel. My son is going to be the first passenger so i need to get it right.

Johno

Simple, 6 bolts 2 brackets and a ford diff :D

I spent some time looking at this and noticed that all the broken beams I have looked at on the net <dozens of them>are broken on our nearside . That I reckon it is due to the diff being mounted on the offside and when the diff is loaded its putting the beam on the nearside under a lot more pressure. A bit like a tripod with unevenly spaced legs. That brace gadget thing I saw spreads the diff loadings at the nose of the diff evenly. Just a theory I will keep eating the toblerone

Bob

I don't think you have anything to worry about Johno, if you are worried still use steel for the tub back and make sure you have and inch of play at the gearbox end of the propshaft. That's what I'm doing anyway! And test first without child. :D

Robo they are design to fail on that side.

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

Mx5 diff
 

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.

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

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

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).