Thunderbird Diff Ratio


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By LON - 14 Years Ago
Removed the diff centre from Lynnes 57 Thunderbird last weekend to track down a clunking noise .Found the problem of  a missing tooth on a sun gear .I thought that Automatic Thunderbirds had a diff ratio of around 3.1 or 3.2 ??? This one has a 3.7 ???? No wonder it is quick on the take offs ???? Case has WAA 4025- A  cast on it .. Tried to decode ,but can't find a prefix of WAA ???Any ideas ?
By glrbird - 14 Years Ago
Lon

Does it have the extra rib on the carrier running from top to bottom? I think those were from 57-59. I am sure John will know, He knows everything!

By joey - 14 Years Ago
According to The Book of the Ford Thunderbird by Brian Long, Ford in 1957 adopted a 3.10:1 final drive rear axle which went with the Ford-O-Matic as a $215 option. That year, a 3.56:1 rear axle ratio accompanied the 3-speed manual tranny. For $146 extra you could opt for an 0.70:1 overdrive with "a revised 3.70:1 back axle gear", which was changed in '57 from the 3.92 that went with the overdrive the previous two years.

According to the book, T-Birds in '55 and '56 came stock with ratios of 3.73:1 with the manual shift, 3.92:1 with the manual-plus-overdrive, and 3.31:1 on the automatic.

By marvh - 14 Years Ago
I am not sure for the T birds however the cars have the ratio stamped in the differential housings. It is stamped horizontal on the forward side of the passenger side axle tube (driver side for Aussies) it is just about 4" to the left of the carrier unit as you are facing the pinion shaft. The numbers are stamped laying 90 degrees to the axle housing or longitudinal along the axle housing .



You will see something like 3.10 if it is 3-10 ratio rear end. This would tell you what was originally installed in the car. Maybe someone has changed out an OD trans for an automatic during its lifetime.



The WAA cases were the first Ford 9 inch.

Here is link to a page about them.



http://ultrastang.com/Page.asp?PageID=11













marv
By RTCLASSICS - 14 Years Ago
WOW! Great site. Thanks very much.
By LON - 14 Years Ago
Thanks Guys ,

Maybe someone swapped out the diff centre at some time . I plan to keep it at 3.70 just for fun . The diff guy is installing new crown & pinion ,4 pin hemishere ,new bearings, etc. After having the car tuned ,and a new MSD dizzy fitted a couple of weeks ago ,I had to take it for a test drive .Planted it flat to the floor ,kicked back to first ( as it should ) and spun those tyres like there was no tomorrow .Spun them again when it changed into second gear .The kickdown is adjusted  perfect .I just hope Lynne doesn't discover how hard it goes ??? I will not have a chance to catch her in the Victoria ??

Lon

By Y block Billy - 14 Years Ago
Doesn't she read this too Lon? so now she knows!
By Ted - 14 Years Ago
LON (2/2/2011)
.......I just hope Lynne doesn't discover how hard it goes ??? I will not have a chance to catch her in the Victoria ??
Lon.  You are indeed your own worst enemy.  I wouldn’t be worried about Lynne reading this as much as Rob seeing it.  Can’t wait for Rob to get hold of that comment and put a global twist to it.