Which Diff / Drivetrain do I have??

[Stephen T]

I thought I was nearing the end of my Triumph apprenticeship …..

I have rear hub bearing problems on my 1978 Spitfire 1500 so am busy swapping over the half shaft for a nice new reconditioned long one. A manageable job I thought.

However I have found my car is fitted with short shafts. Arg. Incidentally the front suspension / brakes have also been modified' by PO's to include early Spitfire vertical links Type 12 calipers (now type 14) and GT6 hubs and stubs which I have been able to successfully sort out - I hope. Looks like I have several generations of Spit / GT6 parts on my car.  

So my rear axle set up looks like I have short shafts on a 5 leaf swing spring - which may explain why the angled radius arms were so horrible to fit; or I may have incorrect radius arms or brackets? The skin has now grown back my hands so I'm ready for another go. The spring also has a strange rubber strip pushed into either side of the pivot box which isn't right so will be coming off whilst I have everything out. 

The Diff looks like it has been rebuilt and is a six hole rear casing (It should be four so is wrong) two of which have been left unplugged. I would rather use underseal than EP90 so suggestions please.  I'm also struggling to find which diff it is as the numbers don't tally with the triumph records I have found. Close examination shows the number HD3999 but looks like it has been over stamped by a reconditioner as I can see an F under the H. The 'D' hasn't been overstamped so originally an FD Diff? Any ideas? It looks like a 'Type D' (Round front pinion flange)The 1500 propshaft flange matches the front input of the Diff. Outputs are square.  

It has the 'correct' 1500 engine which and I've done an O/D conversion (J type).

I'm prepared to leave the Diff in if its got the right ratio ie not 4.11 or 3.27 -  Ideally I think my best bet would be swing spring long shafts (I already have one  side) and a 3.89 or 3.67? diff. Any views would be welcome?   

I bought the car as a partially completed restoration jigsaw - we can all make mistakes .....

[Colin Lindsay]

It looks like all those numbers have been stamped over with a line of 'H'. If it's got the round front pinion it was probably FD originally, there was no HD. It should have bigger bolts round the casing, I think 9/16? 

The four-hole swing spring should be correct; can you see down into the diff casing, (poke a thin screwdriver down into the hole?) or is it just the bottom spring mounting plate that has the extra holes and the diff casing itself isn't perforated? You can screw a short bolt shank into those spare holes, cut the head off one and slot or flare the top so it won't drop down in, but any kind of rubber cap seal or button (even the end caps off biros) will sit there with a dab of sealer.

(Not the writing end cover but the little top-hat on the other end, have used those before!) 

Edited May 20, 2023 by Colin Lindsay

[Josef]

The radius arm brackets for the short driveshaft cars were further outboard than those for the long driveshaft cars. I think your later heelboard should have holes for both though as in the image below. Probably the simplest thing for you to do is make sure you have the early brackets and use the outermost holes. It looks like you are already from your photos though.

  

[trigolf]

To positively identify your diff, visit Canley Classics website. Search for 'Different Differentials'. It tells you how to calculate the diff ratio, by counting driveshaft rotations and also the original part no references. Of course any stamping on casing is now largely meaningless as most have been rebuilt at least once, possibly as a different ratio.

 

 

[DanMi]

FD is Vitesse 2 litre MK1 which makes sense with the 6 holes 3.89 ratio   http://www.wolfitt.com/numbers_and_ratios.htm

 

[DanMi]

so not unlikely that the short shafts came from the Vitesse as well. The long shaft cars have different radius arms and body brackets as well as a different brake hose arrangement. I would guess also a different rear handbrake cable

[Wagger]

Whilst the diff is disconnected from the shafts it is quite easy to check the ratio. With different numbers over stamped you won't be sure unless you do it. With the gearbox in Neutral, mark the drive flanges to each wheel, and the prop shaft connection. Rotate the prop by hand until the two drive shaft flanges complete one turn, counting turns of the prop shaft. The output flanges will both turn together in this state. Just over 3 and a half will be 3.63:1. Just over 3 and three quarters (Almost 4) will be 3.89:1. Just over 4 will be 4.11:1. If you have a 3.27:1  then it will only require 3 and a quarter turns of the prop.

As you have an overdrive, any of them will be suitable. I am told that the 3.63:1 is the toughest one. If you have a 3.27:1, then drive wth care when taking off unless it is a Quaife one.  This is not from experience, just 'Historic' on this and other forums.

[daverclasper]

3 hours ago, Wagger said:

If you have a 3.27:1, then drive wth care when taking off

Is that because it is said that 3.27 is the weaker one?.  Does with care, mean no racing starts?

[Wagger]

1 hour ago, daverclasper said:

Is that because it is said that 3.27 is the weaker one?.  Does with care, mean no racing starts?

That is abou right. The carrier is weak.

[Pete Lewis]

many forget that the higher the ratio the more torque has to be transmitted to power at the wheels 

the 3..27 has a bigger diam pinion thinner crown wheel/  bevel gear carrier 

apply too much torque and curbang goes the castings 

3.63 is far better option of them all  

 

[Steve P]

I have a 3:27 in my 2.5L Vitesse, putting 170ish Bhp through it, no breakages yet, it does have a stronger carrier in it (TR7?).

Steve

[Wagger]

1 hour ago, Steve P said:

I have a 3:27 in my 2.5L Vitesse, putting 170ish Bhp through it, no breakages yet, it does have a stronger carrier in it (TR7?).

Steve

Well, there is your answer. However, I would not 'Dump the Clutch' with any car, especially a classic.

[Steve P]

2 hours ago, Wagger said:

Well, there is your answer. However, I would not 'Dump the Clutch' with any car, especially a classic.

Me either, snapped a driveshaft once though, now got CV shafts.

 

Just to add for the original poster, I also have a Herald with a 1500 engine and J type O/D gearbox with a 3:63 diff and it`s a great combo.

Steve 

Edited May 23, 2023 by Steve P

[Wagger]

1 hour ago, Steve P said:

Me either, snapped a driveshaft once though, now got CV shafts.

 

Just to add for the original poster, I also have a Herald with a 1500 engine and J type O/D gearbox with a 3:63 diff and it`s a great combo.

Steve 

Presumably your car has the Mk2 rear suspension set up. I wish the Mk1 could have CV's without major work.

[Steve P]

It is a MK 1,all you need is wishbone brackets welded on and to move the tie bar mountings inboard,not too bad.

Steve

[thescrapman]

On spitfires, rear radius arms always mount in same place, arms and brackets change for longer shafts.

inner holes are for rotoflex on GT6, just panels are common.

You will want a 3.63 with a 1500, 3.89 is too low, I have one in my Spitfire.

 

[thescrapman]

On 21/05/2023 at 09:28, DanMi said:

FD is Vitesse 2 litre MK1 which makes sense with the 6 holes 3.89 ratio   http://www.wolfitt.com/numbers_and_ratios.htm

 

FD is Mk3 Spitfire. 

🙂

[johny]

There seems to be some confusion over this but John Kipping noted FD diff as coming from Vit mk1 and FC in mk3 Spit. I think thats correct as the latter car used a 4.11 ratio and if that was fitted to a 2L Vitesse it would be manic😁

[Pete Lewis]

thought all Vit6/mk1mk2  were HB HC prefixed 

pete

[johny]

JK says GT6 had KD in non OD cars 3.89 ratio and the equivalent in mk1 Vit was FD while the mk2 went to HC😳

[68vitesse]

From JK catalogue.

[DanMi]

7 hours ago, thescrapman said:

FD is Mk3 Spitfire.

Oddly FD is mk3 spit for engine and gearbox but diff remained FC and all spitfire chassis are FC as well

[Josef]

The US models got a bit mixed up too. See more info from John Kipping.

[Stephen T]

Thanks for the advice so far  - sorry about the delay in getting back - not much rebuild time this week.

Using the Canley method the Diff is definitely a 3.89 and FD therefore looking did indeed originate from a Mk 1 Vitesse (and possibly driveshafts as well) 

On the positive side it has been rebuilt at some point and doesn't leak (open threaded holes will be plugged!). Input and output flanges match the Spitfire half shaft / prop. 

As pointed out by Scrapman its the wrong ratio for UK cars so should be 3.63. From Mintylamb this looks like it equates to about 230rpm in OD top rev range. 

A quick look indicated 3.63 diffs are hard to get and expensive. Any views / experiences / suppliers? I can bolt the big lumps on / off but I don't have the skills to build recon one myself.

Radius arms look like they have angled ends with 12 3/4 inch centres and the brackets are angled too see photo of drivers side set out on the floor. Is this correct for a 1500?  - I only have 1 set of body tub mounting holes for the brackets. 

The bolt holes in the brackets are worn and will now be replaced. Thinking of going to adjustable radius arms to save time on set up. Polybush types seems expensive but get excellent reviews - presume blue for road use? Spring is also suspect and will be coming off soon.

[Paul H]

Spitfire Graveyard on EBay is a reliable source . Last week he was offering a 3.63 spitfire mk4 with little backlash for £265 deld and it was sold within 1 hr 

Paul