Fabric Joint Propshaft Lengths

[AustinWood]

I'm not sure that the axles affect this greatly. More likely chassis and gearbox.
4-speed box needs a shorter shaft and long wheelbase needs longer. Several permutations possible.

[JonE]

Jim - I think Douglas has already comprehensively outlined that there are 3 variants factory listed just for the short chassis.

One variant is linked to gearbox, which leaves the other two linked to axle/torque tube length, once that gearbox change occurred.

[AustinWood]

I have never seen the propshaft driven speedo arrangement. However it must have had a longer shaft because the gearbox doesn't have the speedo drive on the back.

[Douglas Alderson]

I have never seen the propshaft driven speedo arrangement. However it must have had a longer shaft because the gearbox doesn't have the speedo drive on the back.[/quote]

Hi Austin

The prop for the cars with a speedo driven on the prop are 20” when the speedo moved to the gear box the prop became 19.5” long. The following impact on the lenght of the prop the chassis, gearbox and back axle.  Have a look on this link.

http://www.da7c.co.uk/technical_torque_a...ngths.html

Extract below
   

[DavidK]

Finally I have managed to get out a couple of propshafts and measure them.

   
The bottom one closest to the ruler is BP93 from mid-1931 swb chassis type 3 axle
   
The one immediately above it is BP73 from a 1928 chassis with type 1 axle
   
As you can see they are exactly the same length 19.5ins to centre of pin.

[JonE]

Thanks David. My apologies to Jim... the fact these are known as linked to Type 1 AND Type 3 axles means that the Type 2 must also require the same length.

So what explanation comes about for the part number change? Could it be the factory initially monitoring the replacements from later vehicles and needing to differentiate?

[JonE]

was just re-reading the Austin part number notes from earlier in the thread. This still comes back to the plain fact that the annotated notes between BP73 and BP93 note unequivocally "increased length" for propshaft... and yet the parts we find are the same length! Can anyone come up with a rationale?

[Douglas Alderson]

Hi Jon

Looking at the fabric propshaft lengths I would concur with you that the BP93 is longer than BP73 19.5” and probably shorter than BP118 26”, mainly as the index card records it as longer, but difficult to prove with out finding one and as they generally do not have a part number on them difficult to check.  But looking at the part numbers and chassis numbers they are not as rare as I though unless I have my numbers wrong and putting aside that Austin probably used up old stock and what was available, also excludes sports and specials.

BP30 up to April 1923 only 2,994nr used (index cards list BP1 from chassis 2,995)
BP1 and BP28 20” 42,022nr used, difficult to be exact but BP73 starts at chassis 45,016
BP73 19.5” 72,485nr used starts from chassis 45,016 to 118,501
BP93 ?” 24,142nr used, chassis 118,501 to 142,643 (guess at first long chassis Oct 1931)
BP118 26” 34,044nr used chassis 142,643 to 176,687 (interchangeable with BP125)
BP125 114,313nr used chassis 176,687 to 291,000
But depending on the tolerance and ware on components it possible to fit a 20” propshaft in a car which should have a 19.5.” propshaft, not recommended.  The BP93 may only be fractions of an inch longer.

[DavidK]

To add a little more information to my previous post:

The propshafts that I believe are BP73 & BP93 are not just random spare parts.

The BP73 comes from chassis 642nn a mid 1928 and was still connected to a rear axle of mid-1928.
I have only owned it for a few years and know little of it's history.

The BP93 comes from my 1931 RM saloon which I have owned for 53 years, it came with the original engine and rear axle. Chassis 1379nn mid-1931. Cannot prove it is the original but the car was remarkably unaltered when I bought it.

The two propshafts are the same length but not identical in manufacture, slight differences. I need to thoroughly clean both and try to specify the minor differences. Does anyone know if they have part numbers on, if so where?

I will also try in due course to measure from the back of the gearbox to the carden block on each chassis, my guess is they will be the same, unless the mounting holes are different on each chassis.

Does anyone else have any thoughts?   Ian Williams has an orginal RM in NZ any info?

[Douglas Alderson]

I have seen one prop with the part number from memory it was cast raised at the spider end.  I’ll see if I can take a photo of it.

Do those with large number of spares know the answer?