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MG MGA - Speedo for MGA

OK, my try at rebuilding the little gears in my speedo didn't work (epoxy too soft to remake the teeth.)
How can I find out if this speedo: http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=014&sspagename=STRK%3AMEWA%3AIT&viewitem=&item=330146006390&rd=1,1
will be correct for an MGA?
The numbers on the face of my Jaeger are: SN6161/06 1440
Thanks!
Steven B

Steve, go over to the TF TD board and scroll down to the TF instrument repair. I just did this repair on My TF speedo. The key will be to get the correct number of teeth on the gear. There is an excellent site in the posting on speedometer repair.

LaVerne
LaVerne

I don't know for sure, but doubt that ebay speedo would have the correct ratio for your MGA.

Mine was only missing a few teeth on the fiber gear, and I was able to fill with JB Weld. JB Weld is a harder epoxy and so far has held up well. I filed a groove where the old teeth were to give more area for the epoxy to adhere to and filled it in with the JB Weld. Before it was totally cured I pressed the brass gear into it to shaped the new teeth, then cleaned up with a needle file when it had hardened completely. On mine, only the main odometer gear was bad. When I reassembled, I put the repaired gear on the trip odometer because there is less stress than on the main odometer.


Jeff Schultz

I would contact MOMA in New Mexico. How muck is your time worth and then figure out the cost to have it done right.
JEFF BECKER

Jaeger speedos for MGA are 1050 or 1040 turns per mile, depending on tire size. This eBay Smiths early MGB Speedo is 1040 turns per mile. Aside from saying "Smiths" on the face, it will work for the MGA. Speed and distance output will be 1% excess with the smaller tires.
Barney Gaylord

Barney,
I thought the MGA's were 1440 or 1450 turns per mile. Mine says 1450. The Smith's on ebay say 1040 which would be greatly different.

Jeff
Jeff Schultz

Steven, I have a working Jaeger speedo (SN6161/06 1440) that I was thinking of selling. It was removed from my car last month in favour of one that had been recalibrated for my 5 speed. Email me (bounsalla at taske dot com) if you're in the market. Alternately, maybe Nisonger or MOMA would sell you just the part that you need to fix yours.
Andy Bounsall

Yeah, Jeff, you're right. Scratch the one on eBay, no good for MGA. My dyslexic eyes thought it was marked 1440.
Barney Gaylord

But the one on ebay should be good with a B differential, right?
dominic clancy

I think it is more than just the differential. The normal MGA diff is 4.3 and the normal MGB is 3.9, only about 10% difference. That wouldn't account for the difference between 1440 turns per mile and 1040 turns per mile which is nearly 40%. Don't know for sure, but would imagine the speedo drive gear is different in the MGB gearbox.
Jeff Schultz

15" wheels on an MGA vesus 14" wheels on an MGB. That also accounts for part of the difference.
Andy Bounsall

Thats a part of it, but only about a 7% difference in circumference between the stock tires.
Jeff Schultz

The missing part of the formula is the speedometer gear ratio in the transmission. i.e. how many turns the driveshaft turns per speedo cable rotation( or vice versa). I'm either too lazy or ..... to try to find the data but I'll bet this is the major difference.

Chuck
Chuck Schaefer

I believe that an early B box has identical innards to an A box, so I don't think that the difference lies in the gearbox.
dominic clancy

This thread was discussed between 13/07/2007 and 15/07/2007

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