My Peugeot GT10 › Transmission guide · GT10 and 103 SP
Transmission guide · GT10 and 103 SP
Easy to set up but not optimised out of the box: here is, step by step, how I made the Doppler ER3 use its full range on my 1972 Peugeot GT10.
The starting point
Before the Doppler, I ran a Malossi Variotop long-range variator. I never managed to get it to use its whole range. The Doppler ER3 is much easier to set up, but it is not optimised out of the box: at rest the belt does not sit low enough, and at full throttle it does not climb all the way to the top.
This guide goes through, in order, what I did on my 1972 GT10 to use the full range. The GT10 shares its engine and transmission with the Peugeot 103 SP, so the method also applies to a 103 or a similar setup.
A little throwback: I had already tried fitting an ER3 back in 2011. The belt was floating, because it is a long-range variator, and I had to cut the engine mount again. This time, every millimetre is dialled in.
Current transmission
In the order I did them
I add a 2 mm washer on the sleeve and open up the bore of the pulley face. At rest, the belt now sits as close to the sleeve as possible, without touching it.
That is what gives the best take-off: you start on the smallest possible diameter.
Out of the box, the belt does not reach the top of the faces at full throttle. A light sanding of the bore fixes that.
I work in small passes and check often: better to remove too little than too much.
On my GT10, I had to shift the engine 4 mm to the left for the belt to be perfectly in line with the clutch pulley.
I check it with a tape measure along the belt: poor alignment wears the belt and costs you range.
With 10-inch wheels, the GT10 revs out quickly. I swapped an 11-tooth Doppler ER2 clutch for an Omega Revo clutch pulley that takes a 13-tooth sprocket: the gearing goes from 11x38 to 13x38.
When it arrived, a machinist cut the pulley to 32° to take the 15 mm Malossi belt (ref. 617233, 15x8x853).
To stop the engine from revving too high, I replaced the stock Doppler ER3 weights with better-quality CBE ones, at the heaviest weight available.
I am testing the red or the yellow Doppler spring depending on the trial. It bears directly on the centre stand pivot thanks to a part I designed and 3D-printed in PETG: no welding and no extra bolt on that side.
It is still a prototype, but every test so far has been conclusive.
Set-up validated off load
16 s
Oct. 2026Doppler ER3 test: the full rangeSet-up validated off load: the belt climbs right to the top of the variator.Watch on YouTube ↗
The test, engine running and nobody on the moped: the belt climbs right to the top of the variator. The set-up is validated off load.
What remains is to confirm it on the road, with tests under load.
And what comes next