#41 Sebring Alpine Rear Ends

[jdoclogan]

When I got the #41 Sebring Alpine it came with an installed rear end with an unknown configuration. In addition I received a separate Limited Slip (LS) pumpkin and a race prepared housing (with baffles welded in the axle housing). I disassembled the installed rear end and compared it's pumpkin to the LS (this is also what came with my Promotional Harrington Le Mans). Here is what I found.

Standard Pumpkin Limited Slip Pumpkin


The ratio appears to be 3.89 for the standard (pinion tooth count = 9 ring gear tooth count = 35).
The ratio appears to be 4.44 for the LS (pinion tooth count = 9 ring gear tooth count = 40).

The standard has a 17 spline axle and the LS has a 10 spline axle. Also here is a photo of the baffled rear end housing.




All very interesting. Now I'm looking for comments on what I should install back into the #41 if I personally don't plan on racing. Consider #41 also comes with an Overdrive.

 

[GlennB]

The 3.55:1 will give you ultra long legged cruising - good for long journeys, and especially with overdrive - but you may never get out of 3rd gear around town. It will theoretically raise your maximum speed but I doubt if you will have enough power to exploit that. Still, if you won't be needing to blast away off the grid when the flag drops why not go for a comfortable easy cruising configuration? Less gear changing. You will probably use OD with 3rd gear more often. My diff has the ratio stamped on the rim of the crown wheel (9x35=3.89). I put this 3.89:1 in my HLM in place of a 4.22:1. Amusingly it corrected the speedometer indicated speed to absolutely correct as per my GPS so I didn't need to recalibrate it.

 

[sunbeam74]

I'd guess Ted Block added the LSD when he acquired the Alpine. Based on some letters from John Panks I am fairly certain the 62' Alpines did not run with limited slip.

The Axles should be the competition axles but you'd need to check the PN to verify. I think the competition axle PN is in the Alpine tuning guide.

You should opt for the open differential and choose a ratio which makes sense with the OD. (then make a small wood crate for the pumpkin, LSD, and axles to keep all the parts together)

 

[jdoclogan]

Looks like I'm putting the LSD away. Do either of you know if the factory used the 3.50:1 rear end on the Sebring Alpines. Or any racing Alpines?

 

[Barry]

FWIW, a 10-35 pinion-ring gear is a 3.50:1 ratio, not a 3.55:1.

 

[alpine_64]

Iirc the LeMans alpines in 63 were hitting 132mph down the mulsane straight ( in its pre chicane days) they ran 13" wheels and the taller dunlop racing tyres so gearing was a bit taller via rolling radius. They had OD but i always wondered what diff they ran. The cars had an aluminium undertray and the kamn tails with shaved gutyers on the hardtops so they were more silppery. I assumed they ran a 3.89 diff but a 3.5 if avaialble would make sense for both top speed and the longevity of the motors over 24hrs

 

[RootesRacer]

I would love to see the photos of the outside of the pumpkin to see if its a stock pumpkin. We know its got a dana 23 powr-lok LSD unit but since Rootes never sold a 3.5 crownwheel set, what crownwheel set was it from? Perhaps someone figured out how to mount a dana 23 pinion into the rootes case?

 

[jdoclogan]

Dick, here is a photo of the two casings. Understand the LSD is a 40 tooth ring gear. Did Rootes sell a 3.55 crownwheel set?
Standard and LSD


Also any input on the Rear end casing number WAL 146 35 would be of interest.

 

[jdoclogan]

The Axles should be the competition axles but you'd need to check the PN to verify. I think the competition axle PN is in the Alpine tuning guide.

Steve, where do I find the PN on the axle?

 

[RootesRooter]

Are you sure its a 10-tooth ring gear? Except for the Arrow Range 3.7 (10 X 37), I think Series Alpines all ran 9-tooth ring gears. If so, that would make yours a 4.44 (9 X 40), a ratio I've read was used in racing, tho probably just on shorter courses. Even with OD, I don't think this would have been used on the Mulsanne. That would be about 8 grand. Boom!!

 

[alpine_64]

I think Series Alpines all ran 9-tooth ring gears. If so, that would make yours a 4.44 (9 X 40), a ratio I've read was used in racing, tho probably just on shorter courses. Even with OD, I don't think this would have been used on the Mulsanne. That would be about 8 grand. Boom!!

No way you'd run 4.44 at LeMans... 3.89 at least. Sebring had quite a few tight 90deg corners but i think 4.22 with od would be as short as you'd try.. And even then probably not ideal for sebring.

 

[Barry]

Based on the gear ratio and MPH/1,000 RPM information in the WSM, the factory tires had an aspect ratio of about 83% and a diameter of about 23". If the "taller dunlop racing tyres" were 24" in diameter (a 90% aspect ratio), OD and a 4.22:1 rear axle would have been about 6,440 RPM at 132 MPH and a 3.89:1 rear axle would have been about 5,950 RPM at 132 MPH. With racing engines, top vehicle speed is typically achieved at several hundred RPM above peak HP RPM, so 6,400+ RPM at top speed is not out of the question. Repeatedly turning almost 6,500 RPM for 24 hours is a completely different question.

If 88 gross HP was good for 100 MPH, it would take about 155 gross HP to go 132 MPH. Getting 155 gross HP from 1,592 cc would be a stretch considering the rat p*** gasoline the French supplied back in the day, but never say never. The Mk-II Tiger with 200 gross HP (@ 4,400 RPM) was only reported as having a top speed of about 125 MPH (5,450 RPM in 4th gear), but maybe the power was down to something like 140 HP at that RPM.

A long time ago (young and ignorant), I discovered that a Tiger got VERY light in the front end at 120 MPH. Don't even want to think about a Series Alpine at 132 MPH.

 

[spmdr]

My Alpine book collection is weak but I went a looking.

The highest MPH I found is 123 MPH in 1963 at Le Mans.

I'm more inclined to believe that over 132.

Maybe just a transposed number deal?

BTW, you NEED to be able to PULL a gear, just changing a gear will not mean the car WILL go faster.

DW

 

[puff4]

Don't even want to think about a Series Alpine at 132 MPH.

I've had mine to 115 or so, and you're right, it's a scary ride - front starts getting light around 95 and it gets really squirrely shortly after that.

 

[jdoclogan]

Thanks racing fans for all your input.

Wow, my first college degree was in Mathematics and I still can't properly count to ten. Dick you are right - pinion tooth count is 9 for both rear ends. Making the standard rear end 3.89:1. Following Michael's assumption about Rootes Competition Le Mans Sunbeams I suspect this is the original rear end. The LSD actually had 39 teeth on the ring gear making it a 4.33:1.
So I will put the original Rootes Competition configuration 3.89 with OD back in #41. If #41 were to be used for auto cross racing then maybe swap in the 4.33 LSD? Mmmm maybe I could actually compete with you Dick. At least in my dreams.

 

[jdoclogan]

I've had my HLM up to around 95. I don't know if that is correct since I have the LSD with OD installed. No front end lift, but, the HLM is a bit heavier.

 

[Barry]

My Alpine book collection is weak but I went a looking.

The highest MPH I found is 123 MPH in 1963 at Le Mans.

I'm more inclined to believe that over 132.

Maybe just a transposed number deal?

BTW, you NEED to be able to PULL a gear, just changing a gear will not mean the car WILL go faster.

DW

I agree that 123 MPH seems much more realistic than 132 MPH. Based on 88 gross HP for 100 MPH, 123 MPH would require about 133 HP which is feasible for a 1,592 cc engine in racing tune.

With 24" tires, OD and a 3.89:1 rear end, 123 MPH would be about 5,540 RPM. With 24" tires, OD and a 4.33:1 rear end, 123 MPH would be about 6,150 RPM. IMO, 6,150 RPM at maximum speed seems more likely than 5,540 RPM for a "racing engine."

 

[alpine_64]

As Dan suggested it might have been an error in the typing given the switched numbers. 132mph v 123mph.

The LM alpines had a fair bit of rudimentary aero work to help them pull the gearing. As a side note 3000RW with the faired in headlights, fastback and underside tray was no faster than the kamn tailed alpines with undertray.

As stated before I would think 3.89 + OD as the setup... But if they had taller gears available given that top speed on mulsane was king back in the day they would long gear as much as possible.

Intially the cars ran the factory UK licence plate and bracket initially which acted as a splitter and apparently added a fee MPH to top speed and stability but the scruitneers forced them to remove them on safety grounds......

The 63 cars were the most powerful factory cars, they were the only year that ran 2x40dcoes and also had a hybrid S3 spec.. The S3 adjustable steering column, telescopic shocks and S3 style non seperate header tank cooling system.

They also had the kamn tails, alloy bonnet boot amd doors with shaved hardtop. Thr cars bith suffered engine failure. Later in 63 they ran in that spec at the Tour de France.

 

[jdoclogan]

Great info Michael! I put twin Webers on my HLM and have always enjoyed the sound. It would be a lot easier to install Webers on #41 because of the right hand drive configuration. Desire for originality may have me rebuilding the Zenith 150s matched with original intake.

Barry, nice work on the math calculations. Although, I'm not certain about the inclusion of 24" tires.

 

[spmdr]

Just for the record, the Rootes ratios are likely 3.89 and 4.22

The 4.33 is likely a Dana/Spicer gear set, with a Dana 23 or 27 LSD/Powerloc.

For racing, 4.22 or 4.55 are better gears, than a 3.89, in general.

Steve Alcala's old Green Alpine was faster than his current Sebring car, because he ran Webers and a 4.55 gear in the old car.

We have been running Zenith Carbs on Alcala's Sebring, the Love Bug and Weekend Racer Alpines. A change order has been put in...

The Love Bug Alpine has a 4.09 Dana 44 rear.

The Weekend Racer has a 3.89.

I think Larry Young's Alpine ran a 4.27 Dana 44 rear.

I think I want a 4.27 or lower number in the Weekend Racer.