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Matching speedo with gearbox

Hi all
I've posted before on this subject and thought I'd solved my issue when I got a reversing box so that the speedo drive from the gearbox was converted into going the right way for my speedo.... So, went for a drive on Sunday and find that I need to be doing about 45mph before the speedo moves and the when I'm flat out it only registers about 10mph..

So, can anyone tell me what the correct speedo is for a 4Speed 2Syn gearbox? My current speedo is a smiths PA 0-60mph model.. As my car is a Rod Yates Ulster special I'd like to keep the look right being the 4"? Speedo in a bezel'd case but at the end of the day I need something that works....

Any guidance much appreciated
Cheers
Robbie

Location: Horsham, West Sussex

Re: Matching speedo with gearbox

Dave Armstrong's old Speedex site is the best source of information on this...

http://myweb.tiscali.co.uk/speedex/index_files/Page1138.htm

If you don't get to the gearbox axle ratios etc page from the link above, a swift Google search on Speedex 750 should bring up a tiscali site and it is on the special builders guide page.

Good luck with the maths!

The 4 speed 3 syncro box in my ORT spins something like 1000 turns per mile.

Location: not in the garage :(

Re: Matching speedo with gearbox

As Nick says, the speedo required is one suited to 1040 revs per mile. Your, not originally Austin 7 one, appears to be designed for a drive providing something around 4000 revs per mile.

This list contains some info that may be helpful. http://www.austinsevenfriends.com/Bruce/Speedo%20Summary%20Sheet.htm

Ian Mc.

Location: Shropshire