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MG MGB GT V8 Factory Originals Technical - MGB speedo w/ mustang T5-accurate?

i have 93 mustang 5.0 & T5 trans fitted to my 1978 MGB, my B speedo has 1000 on the face at the lower right side. i have the correct drive and driven gear for mustang speedo. the diff is 3.31, 8.8" ford. does the MGB and Mustang expect the same revs per mile? can anyone share their experience with their conversions and accuracy. any advise or suggestions will be considered.
kelly stevenson

Most modern speedometers are 1000 tpm, so the later MGB speedos should work fine.

Out of curiosity, what number of drive and driven teeth gears are you using? I calibrated mine (GM T5) with an Excel spreadsheet I made, it works great for GM transmissions, my speedo is spot on, so I don't see why it wouldnt work with the ford gears unless they offered different tooth counts. If you want to see it, check my website on the gauges page under the MGB V8 link.

I am using a modern Electronic speedo and getting signal from the stock mustang VSS sensor...

The problem we will usually have is rear end ratio and tire size skewing our speedo reeading. Htat is where the electeronic's are so usefull as you program yourself for your actual set-up and you can reprogram at anytime you change something..
Larry Embrey

thanks for info, the gears for trans were determined using the speedo utility on: site. enter tire size or dia and the r/e ratio and it provides the needed info. with the 93 T5 mustang, i changed the drive gear from 8T to 7T and used the pink 19 T.driven gear as indicated. these will be connected with a hybrid cable made for the ford trans end (VSS) and the mgb speedo head end. i changed the tach from 4 to 8 cyl and wanted to keep the dash looking OEM. NEVERMIND the 5.0 EFI drivetrain. the 1000 revs or turns per mile helps me very much, i was concerned the speedo would be off too much.
kelly stevenson

To add my two cents worth, I just removed my Olds/T5(GM) in favour of a 302/T5(Ford). The drive and driven speedo gears that I had calculated using the attached link for the Olds were within 1% speedo error - I have since worked out the drive/driven gears for the Ford conversion and expect them to be within 1.29% (although I'll have to wait 'til spring to verify).
For the record, with 225/50-15 tires, 3.27 rear axle ratio and a 1120tpm speedo (MGC gauge), I use an 8 tooth drive and 20 tooth driven gear.
There are a few sites available to run the calculation – attached link is the one that I used and it works very well.
Look under “MGB V8” and then “misc”
Also, D&D Fabrications
will make up a made to measure speedo cable for the Ford T5/MG speedo.
Graham Creswick

I am using a Ford T5 and the original MGB speedo hooked up with one of Dan LaGRou's cables using a grey gear and yellow internal gear. My rear ratio is 3.08.I also have an electronic speedo hooked up to the rear wheel by a magnetic pickup which is dead accurate.The MG speedo reads about 5 to 7 MPH high.
Gil Price

This thread was discussed between 30/11/2004 and 01/12/2004

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