• Hi Guest!
    If you appreciate British Car Forum and our 25 years of supporting British car enthusiasts with technical and anicdotal information, collected from our thousands of great members, please support us with a low-cost subscription. You can become a supporting member for less than the dues of most car clubs.
    There are some perks with a member upgrade!
    **Upgrade Now**
    (PS: Subscribers don't see this gawd-aweful banner
Tips
Tips

Substitute for OD

Share this page

ArtQ

ArtQ

Member
Offline
I have a 62 BT7 that was delivered without overdrive. My goal has been to restore the car to original as it was built. I have been told that I can substitute a different rear end (a 341 or 354 not sure which), get the same rpm reduction at freeway speeds as if I had overdrive without any "visible" changes to the car (easy pumpkin swap). I was also told that the only problem I might run into was a mostly useless first gear (which I never use anyway).

Any insight or help?

thanks

Art
 
Mike Lempert makes the parts for this modification, I don't have his contact info, but someone on the forum probably does, I think he runs them off in sets, so not sure if he always has them available, also can get them from boneyards (junkyards) but I don't think they are to easy to find.

Greg
 
Hi Art,
I believe that your BT7 originally came with a 3.9 axle ratio if it had overdrive or a 3.55 axle ratio for non overdrive. You may already have the 3.55 ratio. Even so, the 3.9 ratio with 22% OD would have a final drive ratio of about 3.2. This is still quite a bit more rpm reduction than the 3.55 ratio axle without OD.

Greg,
I have a 3.54 differential in my BN2. As you say, they're getting pretty scarce. They were originally fitted to the Austin A99-A110, Wolseley 6/99-6/110 with Automatic Transmission. Mine came from a kind soul in Canada.
D
 
ArtQ said:
I was also told that the only problem I might run into was a mostly useless first gear (which I never use anyway).
Art
Click to expand...

Who ever said that was thinking back to front!

If you put a taller diff (eg 3.9 replaced by 3.5) first will become MORE useful/necessary. It would only become useless if you put a shorter (eg 3.9 replaced by 4.2) one in.
 
Art, On the top side of the aluminum gear housing there is a flat spot that has a number stamped in it. for a 354 gear the number will be 39/11 this is number of teeth on ring and pinion gears
39 divided by 11 = 3.54 Bob
 
Actually, if you hav a 3.54 rearend and the tranny is stuck in OD 1st gear is nice - you can get to 7 mph instead of 3 mph. /bcforum/images/%%GRAEMLIN_URL%%/smile.gif I had to drive the last 400 miles to Conclave that way. A big hammer got it out of OD and the 3.54 made the 1600 mile drive home bearable. Actually the car seemed to like 3000 -3500 rpm much better than I did.
Problem has been resolved with a Supra 5 speed - nice.
 
BlueRidge2 said:
Art, On the top side of the aluminum gear housing there is a flat spot that has a number stamped in it. for a 354 gear the number will be 39/11 this is number of teeth on ring and pinion gears
39 divided by 11 = 3.54 Bob
Click to expand...
The marking can be hard to find. Usually under dirt or paint. Here is a pic of a housing that is stamped 10/41, or 4.11 ratio. On a flat spot near the top & slightly to the outboard side. Other housings may look slightly different.
D
 

Attachments

  • 6651.jpg
    6651.jpg
    154.7 KB · Views: 125
If you can't locate the numbers you could set the car on jack stands and mark the rear wheels and the drive shaft with chaulk. Turn the drive shaft 3.5 times and see if you get 1 complete turn on the rear wheel. if so it a 3.54 If it takes a tick over 4 you most likely around 4.10 or a tick under 4 probably a 3.90. I haven't tried this but I think it should work???
 
Back
Top