Drive train upgrades

[Calvin]

Hi everyone and all the best for the season. 

I have an Equipe Gt4s with a modded 1500 engine, a Mk 3 spit O/D gearbox running through a 4:11 Herald diff and standard Bond driveshafts. 

I want to uprate to the 3:63 diff to make the most of the extra power and raise the top whack a bit.  

So I need to know a couple of things...

1) Is that the best diff or should I go to 3:89?

2) Do I need to change the flanges on the driveshaft/propshaft? 

3) Where are the best/best value ones available?

Many thanks,

Calvin.

 

[Steve P]

Cant help with where to get one,other than speaking to Mike Papworth.(details in the courier).

I have a modded 1500 in a Herald 13/60,with a single rail box with O/D, i think i used a Vitesse non O/D prop from memory.Definitely dumped the strap prop that was on there.

I fitted a 3.63 as well, i find it a really good setup for decent acceleration and relaxed cruising.

Steve

[NonMember]

The 3.63 is probably the best ratio for that engine.

The flanges on a 3.63 (Spitfire 1500) diff will all be the larger type. The easiest option for the nose flange is to change the propshaft's rear flange to the large type. You can also do that with driveshafts but it's also possible to swap the Herald diff's stub shafts into the 3.63 one, assuming it's one of the later ones

[Clive]

I have had through y hands several later type diffs (eg 3.63) where the diff front flange has been drilled to accept the earlier type prop flange. Should not be difficult to do, as long as the drill is centred correctly (there is a seating ring, so the prop will always sit perfectly concentric) Changing a flange, or even a UJ can put a prop out of balance, not much, but irritating.

And as Rob ays, you can swap te 1/4 shafts from the later 4.11 diff into the 3.63 but not the erlier 4.11 type

Pln B is to change the driveshaft flanges, no balance issues. 

Don't worrt about using 5/16 bolts not being able to cope. My Subaru diff came from a 300bhp car, mine is about 180bhp, and that uses 8mm bolts. They don't break. And I really have tried.

[Josef]

Just note with a 3.89 diff you should be able to fit an earlier Spitfire MkIV speedo (1184 TPM) and have it be accurate (your current one should be a Spit MkIII type at 1248 TPM?), and match the Bond's other instruments. With the 3.63 something custom would be needed afaik, or at least a later Spitfire one wouldn't 'just work' as Triumph switched to modifying the gearbox output ratios leaving all speedos calibrated to 1000 TPM. There's not much variety in speedo drive pinions available for the D-type overdrive.

[Pete Lewis]

D type you can get 15T and 16T  should a ratio change be needed 

https://www.overdrive-repairs.co.uk/buy-spares.php?cat=D Type Spare Parts List

and for non Od all small chassis 3 rails   only use one pinion  119100   i dont recall any 1000tpm  speedos from our range 

always been a variety of speedos to match the drive line not a variety of pinions to standardise the Tpm  as far as i recall ??

pete

 

[Josef]

35 minutes ago, Pete Lewis said:

D type you can get 15T and 16T  should a ratio change be needed 

https://www.overdrive-repairs.co.uk/buy-spares.php?cat=D Type Spare Parts List

and for non Od all small chassis 3 rails   only use one pinion  119100   i dont recall any 1000tpm  speedos from our range 

always been a variety of speedos to match the drive line not a variety of pinions to standardise the Tpm  as far as i recall ??

pete

 

I thought the Spit 1500s finally used 1000 TPM? But regardless I was meaning that the single rail / J type setups were different from the three rail / D type, and that Calvin’s current three rail with a change to use a 3.63 diff probably wouldn’t match any factory small-chassis drivetrain configuration. So some thought might be needed on the speedo choice / calibration. 

[Pete Lewis]

Aha wasnt thinking single rail   being a later design thats possible   Triumph were never that good at standardisation 

so 4 diffs  /1 gearbox  tend to have  4 speedos to suit the Tpm.

 

on trucks with wild variations in drive lines we had many pinions and a rotating eccentric to mesh the worm to get the right Tpm

then electronics solved that headache 

Pete