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I need to replace some items on my totally standard Spitfire Mk3... so I am thinking of replacing them with below:

> 3 rail J type OD box from MkIV

> 3.89 or 4.11 diff - large flange (possibly a 3.63 off my old 1500 - not sure how it would "pull" though)

> Propshaft for above - (according to the Canley Classics website my old non-OD 1500 prop should fit? (38", 0.97m))

>1500 rear halfshalfts/radius arm/uprights (virtually new from my old 1500)

>1500 rear spring (virtually new from my old 1500)

Can anyone see any immediate problems with above? Speedo cable is the only thing I can figure out at the moment...

James

James,

If you have the 3rail J type box then fit it, if not you may have trouble finding one, they are hardly common.
Surely you don't want to fit a 4.11 diff? 3.89 OK but the 3.63 would be nicer for cruising and not too much for the car to pull at all.
The driveshafts and spring should make a nice difference, no problems there.

On the subject of diff ratios, I sold a Dolly 1500 engine and box and a 3.27 diff to a chap locally whos wife runs a 13/60.
He popped round after the conversion was done, I had expressed concern that I thought the diff would be too tall for the 1500 to pull in a Herald.
Well that little Herald tore past my unit like nothing else, I've never seen one in such unmodified trim move so quick! I regret selling that diff too as the one in my V8 is howling despite a full rebuild.
Anyone got one?

Tim

Willow Triumph

James,

Not wanting to contradict Tim's advice here but if you are going to switch to a swing spring you absolutely MUST make sure that your diff only hase four mounting stud holes. If it has six you will have to dowel the two centre stud holes otherwise you will very quickly lose all the oil in the diff and end up with a crown wheel and pinion like my GT6 did a few weeks ago.

You will also have to be sure that all the flanges on the diff are the correct sizes - Input and Output.

When you were following me up to Stoneleigh I know you were saying your car was noisey but I was hitting 3500-4000 rpm and cruising. Why not work out what kind of revs you'd like to cruise at and work you final drive ratio out from that. Of course just 'dropping' the O/d onto your existing ratio will simply give you a 'fifth gear' and change nothing else.

Dropping in the 3.89 would give you longer gears and better cruising, but the longer you go the heavier your fuel bills will become around town - it's all a trade off.

In conclusion... decide what rpm you want to cruise at on the motorway and work it out from there.

Can't help thinking that if you are going to switch the rear suspension to 'swing spring' then it is pretty important to fit the later, bigger front anti-roll bar. On the other hand, if the bits you plan to fit are from an early mk IV then then I think they should all just bolt together. But equally, there's no advantage in fitting them over what you already have.

Having all sorts of trouble with the message board today, so if this appears twice, I can only apologise.

Just re-read your message and notice you are talking about 1500 parts. If you use any diff other than a 1500 one, you will need to blank off two holes. The 1500 swing spring works in a different way from earlier springs so if fitting this you must: fit the 1500 mounting box (complete with rubber pad), the longer (by one inch) 1500 half shafts, and the thicker 1500 front anti-roll bar. Otherwise you will have real handling problems.

You should pick the diff that most suits your needs, but an awful lot can be achieved simply by playing around with tyre sizes.

The MKIV spring is the same as the 1500 one and the MKIV diff (3.89) also only has four mounting studs. These 'swing' springs work with either the short shafts or the long ones - it doesn't really matter as the MKIV had both (pre and post '72).

Anti-roll bar preference is entirely up to the driver. A heavier bar will induce more understeer, but if James still has the one from his 1500 then he can try both.

Yikes... a load of messages to reply to...

In some sort of order...

Tim W: Well I am told its a J type - Im not too fussy anyway... as long as its an overdrive and works it's fine by me...

Im thinking that perhaps a 3.63 would be good now... because I have my old 1500 one - which is of known origin, as it was fitted to the car just before I got it - and so its free

) So I can fit it - and if I dont like it (and can be bothered to) I can always change it...

NiG: I know all about dowelling those two center holes... if you remember, the reason my first diff went bang was because for some reason the DPO didnt use the proper 6 hole spring box - using a later one - so all the oil flew out the top... when I put in the diff I got off you I had to put some studs in it to block it off - which actually does beg the question - does my rear spring work properly if its using a later spring box? hmmmm...

Regarding flange sizes - as far as I know there are only 2 different types? small and large? but I shall double check them all before I go and try putting them on the car...

Im not quite sure what I want - its one of those trade offs - 4.11 diff for the acceleration - or 3.63 for relaxed motorway cruising... then again I plan on rebuilding my engine at some point... and it'll be a corker...

so I guess it'll get back some of that va va voom (not suggesting at all that my car is some nasty french thing...) Plus - my old 1500 went like something off a shovel with a 3.63 diff... so I shall have to see if the Mk3 engine has enough torque to pull it off...

Tim E: No advantage over what I have now? Swing spring? wider track rear end? longer diff for cruising? I wouldnt be doing this if there wasnt an advantage...

plus my diff and a UJ needs doing anyway...

NiG (again): Annoyingly the 1500s anti-roll bar was one of the last bits planned to remove... it was a case of... darn those nuts are siezed... "oh hello mr scrapman, you're early"... grrrr...

James

69 Signal Red Spit

James, regarding that item you were asking about - I had a look tonight after getting in from work and I can confirm it is!! (This'll get the rest of the buggers guessing!!

)

Regards

James,

You seem a little unsure about your proposed course of action, and you a Triumph junky, glued to this message board, surely all the relevant expertise has entered your system through osmosis has it not?

Diff casings are all the same dimensions so different springs will work, you just need to make sure you have the correct number of studs / type of flange for the application, as per factory spec.
You aren't doing anything wild and risky, just updating to later spec.

In short it will all work if you use your nut and do it sensibly.

Tim

Willow Triumph

Look, I don't want to get into an argument here but some facts are being a bit glossed over. The late Mk1V and 1500 swing-spring set up works in a very different way from earlier versions. It deliberately allows the rear of the car to roll much more. It was matched with longer half shafts to give a very different camber angle at the rear. The additional roll induced in the rear of the car was counterbalanced by a stiffer front anti-roll bar. I'm not an engineer, but the guys at Triumph who came up with this solution to rear wheel 'tuck under' were. And given cost constraints, if they did not think it was absolutely necessary to change something then I'm sure they wouldn't have. IMHO if you are going to mix and match swing-spring and non swing-spring components then you do so at your own peril.

> Im not quite sure what I want - its one of those trade offs - 4.11 diff for the acceleration - or 3.63 for relaxed motorway cruising...

Compromise with a 3.89?

That's exactly what I was thinking Mark...

However - as I have a very nice spare diff that came out of my old 1500 - I'll use that and find out what a 3.63 is like in a Mk3... if it's too long then I can put in a 3.89...

Top speed of 120mph @ 5500rpm with a 3.63...

(not that I would be stupid enough to go that fast! 90 is scary enough in a Spit)

If I was to have to buy one though - I would have probably bought a 3.89 though...

James

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