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Non-Healey Cruising Rear Possible?

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RAC68 said:
Hi Rick,

I must agree with all you have said and the a 3.54 ring and pinion is most likely what would be best. However, how did you come to know that that rear was in all the cars mentioned? Was it from experience or an informal acquisition of knowledge or from a cross indexed parts list? I expect I know the answer but I can hope.

Thanks Rick and all the best,
Ray(64BJ8P1)
Click to expand...

Ray,

In my wellspent youth, I spent an inordinate amount of time hanging around in what were called "junkyards" and learned more about cars and life than many courses of higher education. Every junkyard had a full complement of Hollander's Interchange Manuals that would magically tell you that a starter from a '54 Studebaker would fit a '67 Plymouth Roadrunner. Somehow the local yard knew a rear axle from a Nash Metropolitan would fit my Bugeye. Hollander is still in business and I was surprised to see they have a foreign version: https://hollanderinterchange.net/ca...id=44&osCsid=045f32df103d1aa96f2e952462881885 . I have no idea whether it covers Healeys. I did know from collected knowledge that some of the larger BMC "saloons" used the same driveline as the Healey and I believe the ones I listed have the same rear end, however I'm not exactly positive and if you were trying to hunt one down you might want to confirm they fit first.
 
I am sure that I have read that the Healey rear end came from a truck. What I believe has been called a lorry. I know the rear end is what is called a semi-floating axle design which is commonly used in heavy applications such as trucks.
 
After all this, it seems to me the $64 question is: would a Jaguar ring-and-pinion interchange into a Healey axle. My reasoning is the Jag is the only reasonably common British car that's faster than a Healey. All the other uses of this axle, such as lorries, saloons, taxis, etc are going to be slower, hence will have a higher numerical ratio. The Jags, being faster, would have a lower numerical ratio, such as a 3.3. So the question is whether this would interchange into a Healey. All other faster cars, such as Aston Martins, Bentleys, Jensen Interceptors - are going to be much rarer, therefore one would expect usable ring-and-pinions to be rarer/more expensive.
 
I believe--but am not certain--that the conversion from the standard 3.9 diff to the 3.5 Lempert diff lowered my 70 mph rpm's from around 4K to 3K. I'll leave it to the mathematicians to figure out but if the commensurate reduction using a 3.09 diff (as discussed) would bring the 70 mph cruise rpm's down to 2000 or thereabouts this would place the revs below the engine's green/go line and would necessitate a downshift of at least one gear in order to have enough torque for a reasonably snappy pass.
 
As said above, Westminsters and their namesakes used the same diff in a couple of different ratios. From memory, the autos used the 3.54 that is desireable nowadays, the manual ones not so much. The Westminster etc engines were about 90% the same as Healey. The later ones used broadly the same gearbox, but with more differences. Im not aware of any other big saloons of the era that used the same components. Jaguar, Rover etc were not part of the group at that time
 
Michael Oritt said:
I believe--but am not certain--that the conversion from the standard 3.9 diff to the 3.5 Lempert diff lowered my 70 mph rpm's from around 4K to 3K. I'll leave it to the mathematicians to figure out
Click to expand...

Michael,

Not a mathematician, but the 3.9 diff has a 43 tooth ring, the 3.55 a 39. Both have an 11 tooth pinion. Arithmetic says that's just about 10%, so your revs would drop by about the same %. That is what I experienced in my Healey and also in my Jag when I went from 3.54 to 3.31.
 
too bad that there are not adaptors for the tremec 5 speed transmission. i have one in my bn6 and cruise at 70 mph at 1800 rpm in fifth gear. i do have an in line six chevrolet motor but the tremec ratios seem perfectly suited to my driving style....
 
maxwedge5281 said:
too bad that there are not adaptors for the tremec 5 speed transmission. i have one in my bn6 and cruise at 70 mph at 1800 rpm in fifth gear. i do have an in line six chevrolet motor but the tremec ratios seem perfectly suited to my driving style....
Click to expand...

Oh, but there is:

screenshot.1736.jpg
 
Hi All,

Per MaxWedge, a 10% RPM reduction from the roughly 4K-RPM @ 70-MPH would produce a cruising RPM or 3600 with a 3.5 rear. Now, doubling that and assuming the same number of pinion teeth, it would seem to yield a ring gear reduced from the 3.9 @ 43-teeth to approx. 35-teeth for a 3.1 rear to cruise at 3100-RPM @ 70-MPH. I appreciate that my numbers are not very accurate but if the logic is correct, going to a 3.09 rear is not that far from ideal.

Now, I appreciate that these numbers are misleading and having had no experience in this area, my knowledge non-existent. So, what would be a good ration to provide a good cruising speed with sufficient pep to run in OD? Although many believe the 3.5 rear is a good choice, is it because of its availability or performance satisfaction?

Bottom line, what would be the ideal rear ration for if any ration was available to choose from?

Just my thoughts,
Ray(64BJ8P1)
 
Well to add a little fodder to the feed or whatever, My BJ7 runs at about 2800 rpms at about 63 to 64 mph with a 3:54 rear and OD. But I don't know what ratio my OD is. As a comparison for a lower numbered rear gear my '70 Vette has a 3:08.1 rear gear and is right on 65 mph at 2500 rpms. the final wheel diameters of both cars is very near the same. I believe the Healey could handle something near the 3:08 number because it has a lot of low torque and the 1st gear is low enough to give it thrust at start off.
 
vette said:
Well to add a little fodder to the feed or whatever, My BJ7 runs at about 2800 rpms at about 63 to 64 mph with a 3:54 rear and OD. But I don't know what ratio my OD is. As a comparison for a lower numbered rear gear my '70 Vette has a 3:08.1 rear gear and is right on 65 mph at 2500 rpms. the final wheel diameters of both cars is very near the same. I believe the Healey could handle something near the 3:08 number because it has a lot of low torque and the 1st gear is low enough to give it thrust at start off.
Click to expand...

Isn't the Vette doing this on a 1.00 4th gear rather than an OD 5th?
22% OD on 3000s; 28% on 100s and 100-6s
 
Yes Steve you have a point. I didn't consider that.
 
Speeds at 3000 rpm. From an online ratio calculator. .82 is 22%OD; .78 is 28%OD.
Formulas: 1-1/.78 = .28 (28%) ; 1-1/.82 = 22%
screenshot.1745.jpg
Stock BJ8
screenshot.1744.jpg
3.54 axle with 28%OD or Supra 5th
screenshot.1743.jpg
3.54 with 22% OD
screenshot.1742.jpg
3.3 axle, 22% OD
screenshot.1741.jpg
3.08 axle, 22% OD
 
Was speaking to a fellow Nasty Boy owner with a Vortec 4200 motor last week. Said he's using a Chevy S10 rear end that he had cut down and axles shortened. Cost him about $650 altogether. Here's a page showing all the axle ratios and what they came in. Probably a good way to pick up a posi rear end in the process: http://www.lsxharness.com/336816530
 
steveg said:
Isn't the Vette doing this on a 1.00 4th gear rather than an OD 5th?
22% OD on 3000s; 28% on 100s and 100-6s
Click to expand...
I have a Toyota 5-speed with a 28% 5th gear ratio and a 3:54 rear end ratio. I specified the 28% 5th gear when I purchased the trans.
 
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