Diff Ratio's

[Steve28]

Hi all, I've got an overdrive gearbox for my 1500 and was wondering if there is a certain diff to go with it or keep the standard one or would an auto one be an improvement.
Also how many and what are all the Diff ratio's throughout the dolomite range ,Sprint ,1850,1500 1300, 1500tc and toledo manual and auto.

thanks in advance Steve

[xvivalve]

Steve, the diff ratio doesn’t change with the 1500 whether with or without overdrive, or automatic.

The only automatic to have it’s own diff ratio is the 1850 at 1:3.27

Manual 1850 and 1500 were 1:3.89 or 1:3.63 respectively, though some very late 1500s were fitted with the 3.89 diff.

1300 were 1:4.11

Sprints were 1:3.45

[Steve28]

Steve, the diff ratio doesn’t change with the 1500 whether with or without overdrive, or automatic.

The only automatic to have it’s own diff ratio is the 1850 at 1:3.27

Manual 1850 and 1500 were 1:3.89 or 1:3.63 respectively, though some very late 1500s were fitted with the 3.89 diff.

1300 were 1:4.11

Sprints were 1:3.45

Cheers for the quick reply Alun, so would my sons 1300 toledo be better off staying standard or fit a 1500 one ?

[SprintV8]

Just to expand on this.
What diffs ratios are available for the Sprint.
Guessing 3:45.1 may be a bit tall for the 13B Sprint.
RX8 is 4:4.1 standard.

[Richard the old one]

If you are going to fit an Overdrive to your 1500 make certain you get the correct one for the rear axle you have got fitted or your speedo will not read the correct speed.

[Carledo]

Just to expand on this.
What diffs ratios are available for the Sprint.
Guessing 3:45.1 may be a bit tall for the 13B Sprint.
RX8 is 4:4.1 standard.

There is more to it than just gearing! You have to figure in wheel size as well, the RX8 probably runs on 17 or 18" wheels not the 13" Triumph rims. And whilst the 13b revs MUCH higher than any Triumph motor can, how much torque goes with it?

There IS only one diff for Sprint, that is the 3.45 and it's the only Dolomite axle that can handle more than 120 or so horses. (250+ for a Sprint axle in good order)

Which is a bit limiting, HOWEVER the Sprint diff is related quite closely to that in the Stag, TR4-6 and the big saloons (2000/2500/2.5Pi) Sufficiently so, that a CW/P assembly from one of those could be persuaded into a Sprint case by someone who knows what they are doing. Besides the stock Sprint 3.45, the other choices offer 3.7 and 4.11 and at least one other I can't remember. (note, The TR8s 3.08 WON'T fit, but you don't want to go in that direction anyway!)

My advice is to bung in the 3.45 and see how it goes! If it turns out too tall, have a word with Mike Papworth about getting a custom axle built with a different ratio. Better still, look at a Gripper or similar LSD!

Steve

[xvivalve]

Well, now you have me; I’m not actually certain about Toledo ratios, I was quoting Dolomite models...

[Carledo]

Stock Toledo diff for all 1300cc UK models is 4.11.

I would advise nothing taller than the 3.89 from a 1500 unless you're also considering a sustantial horsepower hike.

Steve

[gmsclassics]

Sorry, two discussions going on in one thread, but this is in answer to putting a 13B in a Sprint:

The alternative ratios for the Sprint axle are 4.1:1 (41/10) from the Triumph 2000 manual and the 3.7:1 (37/10) from the auto cars (2000, PI, 2500TC and 2500S), all the rest and some late autos had 3.45:1 (38/11). However, that was original fitment and because of the predominance of later manual cars, the 3.45:1 ratio has often used as a replacement for a worn out original 4.1 or 3.7, so each diff head will need to be checked regardless of the car model. I did use a 4.1 crownwheel and pinion in my racecar Sprint axle early on. Finding someone who understands how to setup a Sprint diff / live axle correctly wasn’t easy.
With increased horsepower and torque using a tuned Sprint engine or a more powerful transplant the weaknesses of the Sprint axle start to become apparent. This especially with circuit use with wider and stickier rubber. Standard half shafts will bend and can then let oil out past the hub seal and into the rear brake. They will also break! Thicker half shafts were used along with a support bearing with works racers ‘in the day’, but recent discuss here has failed to find any secondhand, let alone a current supplier of those thicker axles.
There was someone on the forum who put a Cosworth motor in his Sprint and used a Hilux rear axle (similar width and LSD as standard) and for racing I moved to a Ford Capri 3L English axle to which we welded on Sprint mountings. There is a wide range of diff ratios available along with manufacturers of LSDs and uprated half shafts for the Ford English axle (Quaiffe and 3J Driveline for example).
All depends on what horsepower / torque you want to use and whether it is for road or track.
Hope this is of help
Geoff

[SprintV8]

The idea is to try the standard diff ratio to start with 3:45.1.
It was purely to see if there was any other options.
I don’t think it’s gonna be that far out.

13B renesis engine will have a few tweeks
Aiming for 240/250Bhp which is realistic

She already has a LSD and running Stag Wheels 185 60 14”
RX8 is on 18s.

That Cosworth powered Sprint is Darrens ALG1K over 700bhp if I remember correctly.

[xvivalve]

Hi-lux axle is five stud...