won't be handling much more than about 75 or 100 bhp

Prior consensus would seem that they are made of chocolate...

Not a good reputation. Spitfire diffs only had to cope with 75bhp max and were unreliable.
GT6 or Vitesse diffs had about 100 bhp put through them and were also unreliable. Diff numbers for Vitesse and GT6 start with KC, KD, FD or HC. Spitfire diffs FR, FH or FC should be left in the scrapyard.

not in the scrapyard in the garage have one in the a wheel barrow with a load of other spit bits and the other is still in a partly striped car

is it the planet gear is weak, the crown wheel or something else? or is the whole thing just weak

The spits had swing axle independent at the back didn't they: I'd have thought that could be made to work OK with proper spring/dampers & limited travel. Dunno about the diff but I reckon if they just coped in a spit they'd be well on top of the job in a locost.
Bob

I dont think the Spit diff should cause a problem with a low HP motor. After all, the Ital axles in the Caterhams seemed to stand up to some abuse and they're almost the same unit as the Spitfire (albeit a live axle rather than the mickey mouse IRS).

I was thinking about using one in my current build, but i came to the conclusion that it would be too difficult to properly design and build an IRS set up, not to mention being a bit pricier. So i'm using an MG Midget axle.

~Rod

i dont plan on useing the spit irs setup as i think its pretty poor since its only got the one uj at the inside and this causes for to much camber, i plan on using audi drive shafts (like the sierra) with a plate to adapt from the uj flange to the blot-on cv thats at the rear and then at the front i might just use the housing and crown wheel but replace the planet gear with whatever i use the front drive shafts out of

Hi Goodall,

I've been reading with interest, and can't help asking:

Are you going 4x4? if not, why the interest in Audi driveshafts & diff internals? I assume you will be 4x4, because an Audi 5 pot probably puts out about 2x(75 to 100BHP).

If you will only be RWD, I would think a Spit/GT6 diff would be OK with 100BHP.

I'm not entirely sure, but I think the GT6 (non-overdrive) diff @ 3.27:1 might be weaker than the 1500 Spit 3.63:1 diff, as the crown wheel is thinner. Don't take my word for it, do a bit more digging.
GT6s kicked out (a staggering!!) 95 (early) or 105 (late) BHP.
1500 Spit was 72/73BHP.
1300 was about 63BHP and had a 3.89:1 diff.
Also, many GT6s (and Spits) received the 2.5PI transplant (150BHP) in later life. I'm not suggesting that the diffs lasted for ever, but they clearly had a bit of excess capacity built in.

(I hope all you zetec/K-series users don't get too jealous of Triumph power!!!).

Triumph diffs may not be up to handling high BHPs of modern twin cam EFI stuff, but they ain't made of chocolate!

If camber angle is your main objection to using Spitfire rear suspension, you could always mount the diff with some degree of height adjustment. That way, once the car was finished (i.e. back end at its final kerb weight), you could adjust the height of the diff to get the camber you are looking for.

You've already got a wheelbarrow full of Spitfire back end, so why not dare to be different, and use what you've already got, in true LOCOST spirit.

At the risk of upsetting 99% of Locosters, life doesn't begin and end with Ford.

Just my 2p worth.

EDIT.

Iv'e just re-read your post properly and you clearly are going 4x4. However, I think most of my comments are still valid.

[Edited on 21/1/07 by TL]

[Edited on 21/1/07 by TL]

yep its going to have all 4 wheels driven, the reason for the audi driveshafts is i already have them and i dont like the spit irs set up just to difficult to work with because your top link has to bolt to the diff housing either it be a A-arm or a leaf spring which would meaning designing it to be shimmed to be archive the desired angle, but it could be the route i will end up taking at the back drive system and use the CV's up front

my engine wont ever give me much more than 170bhp and thats if i do some work at it, as standard its meant to give 136bhp divide that by two and you have 68bhp per axle, which is a wee bit more than the spit give out at the least so shan't be to much bother then

as for ford parts we had a granada which my father got rid of over the summer before i wanted to build a car other wise it would have been just plain old rwd but since i have these spit parts i want to use them and what better why than by splitting the power so they can cope

Just curious as to what your choice of transverse drivetrain is for the engine/box/centre diff? Only it could be argued it's very important for (at least) the centre diff to be limited slip in an awd tranny. Without one you could spin the front axle off the line like a fwd and then spin the rear axle cornering like a rwd. I.e. all the drawbacks of fwd and rwd in one car. A 4wd tranny with three open diffs can in theory spin all it's power away through any one wheel that may have low grip - arguably worse than a 2wd which requires one of the two driven wheels to loose grip. I'd say centre lsd is a minimum and ideally the rear should be too, or it's a lot of work to end up with something that may not even have traction of a normal 2wd.

Liam

its looking like an GM 5 speed transalxe, with an open diff. yes having an open diff will mean that if one wheel breaks grip that your stuck, but its only 1/4 of the turning force going to each wheel therefore its not a major concern because i will definitely at some point if this is successful replace the diffs with torsen or lsd diff centers.
i don't plan on diving on poor surfaces much anyway so it wont concern me that much its just a way to put the power to the road in a smoother and more refined (i hope) manner, also if i stay with drums at the back and discs at the front i can if front wheels break traction gently press the brakes or if the rear wheels break traction gently pull the handbrake, this only works at low speed and once your moving these ideas arnt reliable for gaining control, so you just drive her the way that she is behaving ie if shes oversteering drive like rwd or if she understeering drive like fwd

its purely just a bit of an experiment at the moment and if it works out ok then it will get a few pounds spent on it to make it become a proper car

[Edited on 22/1/07 by goodall]

Fair enough. Good luck to you. So what engine and box you using? This gonna be custom chassis/body locost style, or you modding a production car? Obviously this tranny layout can just as easily be front or mid engined - what you going for? Sounds interesting...

Liam

its going to a pretty much by the book chassis with a few mods like irs and space for the front diff

the engine will be a vaxhual 1.6 soc for the first while (when its still a test dummy) and once all the bugs are sorted out there is going to be a 2.1 audi 5 fited from an audi 100 cs, the engine is similar to that fited to the first quattro ur's

and for a second car build in the furture a RS200 look a like might be done if this system is anygood

Sptifre had a (badly designed) swing axle not IRS.

Late Mks of GT6 models had a crude IRS

I think swing axle fulfils the defining criterion to be called IRS... yeah the TR6 had a more wishboney thing in its 'rotoflex' variant
cheers
Bob
PS that would mean if you fit an antiroll bar it's not IRS any more..... Actually I think anything without a beam axle can be called IRS...

Triumph took a lot of stick from the motoring press in the 1960s for calling a very badly designed swing axle IRS.

Although full IRS the late GT6 suspension wasn't anything like the TR4A/TR5/TR6 rear end.

The TR suspension was semi-trailing arms with standard hardy-spicer joints on the drive shafts which had sliding splines..

The MK3 GT6 suspensions was the original Herald type but with the addition of an additional lower link to in effect create a wishbone, while the outer end of the drive shaft gained a rotoflex coupling borrowed from the fwd 1300 and 1500 Triumph parts bin. At the top the tranverse leaf spring remained forming the top wishbone and this resulted in rather odd geometry.

quote:

---

Originally posted by Bob C
I think swing axle fulfils the defining criterion to be called IRS... yeah the TR6 had a more wishboney thing in its 'rotoflex' variant
cheers
Bob
PS that would mean if you fit an antiroll bar it's not IRS any more..... Actually I think anything without a beam axle can be called IRS...

---

Movement of one wheel has no effect on the other. So it's independent. Thats what the I in IRS stands for... ;^)
Bob