Practically Classics Forum

Perhaps someone familiar with the Austin A55 Mk 2 could help solve a technical problem--I installed a 4 "on the floor" transmission from an A55 Mk 2 in my Nash Metropolitan--an easy "drop-in"--the rear transmission mounts fit perfectly.
I did some "deductive reasoning" as to why this is--but that would require a new topic. The Metro has the original
4:22 differential, and the original speedometer. The speedo reads slow (I think!) The "rev" number on the front of the speedo is 1220---It would seem to me that the speedo only looks at the differential--it doesn't care (in 4th gear) where the cable drive comes from. Will I have to get the speedo recalibrated? Is there something I'm missing here?

If the difference is all in the speedo's TPM figure, then that's easily sorted. In some cases, simply lengthening the hairspring (to reduce the reading for a given number of TPM) or shortening the hairspring (to increase the reading) is enough.

However, there's every chance that the drive pinion at the end of the cable (the square locates inside it when you screw the outer cable to the gearbox end) has a different number of teeth and if that's the case, you might not need to do anything beyond removing one pinion and fitting the one from the original gearbox in its place.
That worked for me when I had a Reliant Rebel with Rialto internals in the original casing of the gearbox and wanted to use the original, 940tpm speedo head.

hmmm--very interesting--I am/was under the impression that the pinion had to match the speedo drive gear. So the pinion from my original Metro 3 speed tranny wouldn't fit unless I changed the speedo drive gear also --is this right?

Unless the drive gear is straight cut, then no, I see no reason why it wouldn't work like that and all the ones I've met have been worms.

thanks John--I talked to my tranny man, and he is going to look for the Metro tranny that he took when he delivered the Mk 2 tranny to me after checking it over--he will remove the pinion and post it on--I think I will be okay--

JPB wrote:If the difference is all in the speedo's TPM figure, then that's easily sorted. In some cases, simply lengthening the hairspring (to reduce the reading for a given number of TPM) or shortening the hairspring (to increase the reading) is enough.

That would still leave the mileage reading incorrect though.

Thanks for all the information--after over 50 years of owning British cars-I'm still learning things!!! I'm sure I can sort this out after I get together with my tranny man--

I wish you'd stop calling him a "Tranny man" - that brings to mind some pretty bizarre and unpleasant mental images!

Nice Motor Always fancied a Metropolitan
On the speedo, thought my speedo overreading probs on the MGB were speedo cal so bought a recon speedo - same - then thought it was the tyres but with correct size replacements - same.
Have now "calibrated" the dial aginst my TomTom and noted it is 7 mph fast at 30 - red chinagraph line on Speedo at 37mph is my final solution
No worries about 70MPH as as my better half always screams in terror if we go over 60

Since I'm on a roll here--I might as well add my "Wallace and Gromit" 1967
A35 Van--I have a pic of my 1953 Morris Minor Series 2 somewhere in my computer--