Driveshaft Lengthening

[DJThom]

Hello All.

Has any one had any experience trying to lengthen their driveshaft? I've taken it to a shop that does this routinely but was told that mine doesn't have any machining locators identified and thus can't be done.

I'm changing my gearbox to an Alfa Romeo 5-speed, and I need a span of 33 1/16" flange to flange. The Alfa box doesn't have a sliding spline mechanism at the rear. How long is a +2 driveshaft, or the +2S? A MGB GT with OD has a internal sliding spline at 32" which might work with the help of some machined plates on either end.

I am going to post a description of this process once its all done so that the laundry list is available in a single post for anyone interested in following suit.

Thanks as always

Darren

[Higs]

The Plus 2 (4 speed) propshaft is 36 inches from the flange to the start of the sliding spline section (i.e. longer than 36 inches in total).

Richard

[elansprint]

Darren not sure why you are having a problem we have propshafts made with a flange both ends & a 47mm sliding spline incorporated set 1/3 open when you say machining locators do you mean the spigot on the flanges that centre the shaft ?
Ian

[gerrym]

Darren, there's a few issues here you need to think thru but if you could post a sketch of what you are trying to achieve, this will help you to get some advice:-

1/ If the Alfa gearbox has a fixed output flange, you will need some method for providing axial compliance. This is typically external sliding slides within gearbox. Firstly, the tolerances won't be so critical for manufacturing the driveshaft and secondly, the rear axle and engine are resilently mounted and you don't want to connect them rigidly (in an axial sense)

2/If you add in adaptor flanges to a rotating mass, you run the risk of reducing the shaft critical speed such that vibration will be a major problem. Avoid this if you possibly can.

3/ Don't know how you are served near Toronto, but someone like Bailey Morris in the UK have a custom driveshaft service. Generally if you provide them with the critical ends (axle flange and yokes, gearbox matching flange), they will design and manufacture and balance etc. The English axle used in the matching flange is unobtainable new so you will need to canabalise that from your old standard driveshaft.

Regards
Gerry

[bcmc33]

Darren,

Any competent propshaft maker (we have many in the UK and there must be dozens in the US) can make a suitable assembly to your dimensions. From your description you need a propshaft similar to the Lotus 5 speed assembly with a flange at each end and a slip yoke to the g/box flange. The picture is not that good, but does indicate the sort of thing you need.

Gerry makes a very good point - the U/J flange at the diff end is no longer available (in the UK) and you must use the existing one. Assuming the U/J flange to fit the Alfa flange is available, any competent propshaft maker will do the rest to the overall length you specify.

P.S.
Competent propshaft makers have correct level balancing facilities which is essential for vibration free motoring.

[DJThom]

Thanks guys. I will look for a second opinion from another shop. My understanding is that typically at the end of each shaft inside the "U" there is an indicator mark left from the manufacturer that indicates the centre of mass so that any future work can be relocated to that datum. That's what I don't have on mine according to the opinion I got. I'm trying to find someone with a specialty lathe with a passthrough large enough for the shaft. Then I could indicate it by kissing it with a cutting tool in the tailstock.

Also, it was my understanding that cars with fixed differentials do not need any sliding splines. Example: Corvette and XKE, both of which have solid drive shafts without splines for comliance. I was under the impression that the one in the Elan was due to the pre-existing design that was borrowed.

[GrUmPyBoDgEr]

Hi Darren,

I second the very good advice given by Gerry & Brian & I get the impression that the company you are presently talking to just don't want to do the job for you.
As Gerry has pointed out, some form of axial compliance in the prop-shaft is always necessary, if only to compensate for manufacturing tolerances.
The Lotus 5 speed prop-shaft shown in Brian's photo shows what IMHO would be an acceptable method to resolve your problem.
What aroused my interest was your mention of "centre of mass".
I have not been directly involved with the manufacture of prop-shafts but in my experience only much more critical components such as crankshafts are subjected to centre of mass measurement prior to machining in order to reduce the degree of final balancing.
Your idea of putting the part in a lathe & turning a centre will find the geometric centre relative to the feature which locates the part in the lathe.
This could also be the centre of mass on what is technically a finished component, but I doubt it because I doubt if that component was ever subjected to centre of mass definition.
However, if that company wants a "centre" your "turned centre" taken from any pre-turned feature on the component should satisfy them.

Wishing you good luck with what appears to be a company that is not really interested in doing that job for you.
As has been previously mentioned, I'd go elsewhere

Cheers
John

[CBUEB1771]

I second the opinions that you may have just found a shop that does not want the work. In any major city in the north east part of the US you will find at least one good drive line shop that will do the work and I am sure that Toronto is no exception. We have a good shop in the Boston area that primarily works on truck drive trains but they were more than happy to make a new drive shaft for a friend's racing Series 1 Lotus 7 when revisions to the rear axle location required a minor change in drive shaft length. I believe Alfa uses a rotoflex type coupling in the driveshaft to allow some axial motion. Crannyr has done the Alfa conversion in his +2, perhaps he will chime in.

[bcmc33]

Thanks guys. I will look for a second opinion from another shop. My understanding is that typically at the end of each shaft inside the "U" there is an indicator mark left from the manufacturer that indicates the centre of mass so that any future work can be relocated to that datum. That's what I don't have on mine according to the opinion I got. I'm trying to find someone with a specialty lathe with a passthrough large enough for the shaft. Then I could indicate it by kissing it with a cutting tool in the tailstock.

Also, it was my understanding that cars with fixed differentials do not need any sliding splines. Example: Corvette and XKE, both of which have solid drive shafts without splines for comliance. I was under the impression that the one in the Elan was due to the pre-existing design that was borrowed.

My advice is simple - don't let anyone apart from a propshaft specialist anywhere near your parts. The company you've been talking to are clearly not fit for your purpose.

The slip yoke arrangement on our cars is only to allow for any variation in length between the g/box and diff. When you know the distance between the diff and g/box flanges, deduct 20mm (or 3/4"), and that will be the minimum length you tell the propshaft maker. The chances are that you will need to have the g/box fitted to the engine in order to be sure of the length dimension

[GrUmPyBoDgEr]

Thanks guys. I will look for a second opinion from another shop. My understanding is that typically at the end of each shaft inside the "U" there is an indicator mark left from the manufacturer that indicates the centre of mass so that any future work can be relocated to that datum. That's what I don't have on mine according to the opinion I got. I'm trying to find someone with a specialty lathe with a passthrough large enough for the shaft. Then I could indicate it by kissing it with a cutting tool in the tailstock.

Also, it was my understanding that cars with fixed differentials do not need any sliding splines. Example: Corvette and XKE, both of which have solid drive shafts without splines for comliance. I was under the impression that the one in the Elan was due to the pre-existing design that was borrowed.

My advice is simple - don't let anyone apart from a propshaft specialist anywhere near your parts. The company you've been talking to are clearly not fit for your purpose.

The slip yoke arrangement on our cars is only to allow for any variation in length between the g/box and diff. When you know the distance between the diff and g/box flanges, deduct 20mm (or 3/4"), and that will be the minimum length you tell the propshaft maker. The chances are that you will need to have the g/box fitted to the engine in order to be sure of the length dimension

That's a bit tough Brian; after all if they're asking for centre of mass markings they appear to have a fundamental understanding of the elements of component balancing.
Nevertheless in this case they may be accused of "Gilding the Lily" in order to lose a job they really don't want.

Nix f?r ungut
Cheers
John

[bcmc33]

That's a bit tough Brian; after all if they're asking for centre of mass markings they appear to have a fundamental understanding of the elements of component balancing.

John,
When I saw this comment I just smiled , and said to myself "what a load of b@ll@cks".
I didn't get all my grey hair without a long history of recognising bullsh1t when I see/hear it.

[gerrym]

My limited experience with propshaft lengthening is that you don't. Basically what is required is a NEW propshaft of the required length re-using the old prop shaft ends if necessary.

Keep in mind that any balance in the shop will only be as good as the centre location on the matching rear axle inlet flange and gearbox output. So working to a different centre in the "shop" would be a waste of time. By the way, the bolts don't achieve the centering, there should be a spigot.

It's illustrative to do the ISO 1940 calc, feed in the rev range and the numbers drop out pretty simply as to the effect of a shift in the rotational centre.

Regards
Gerry

[bcmc33]

My limited experience with propshaft lengthening is that you don't. Basically what is required is a NEW propshaft of the required length re-using the old prop shaft ends if necessary.

Keep in mind that any balance in the shop will only be as good as the centre location on the matching rear axle inlet flange and gearbox output. So working to a different centre in the "shop" would be a waste of time. By the way, the bolts don't achieve the centering, there should be a spigot.

It's illustrative to do the ISO 1940 calc, feed in the rev range and the numbers drop out pretty simply as to the effect of a shift in the rotational centre.

Regards
Gerry

I have never seen a flange that did not have what you nicely called a centering spigot. Then again, I don't think I've seen an Alfa propshaft - but I'm sure it is what we expect to see.
A good propshaft maker will use the two end flanges and everything else will be new.

[crannyr]

DArren,

I did an Alpha 5 speed conversion for my Plus 2 about 3 years ago and have no regrets. The gear box worked out very well with little or no problens after some 3000 miles. As to the drive shaft I took a spare elan shaft and had a splined end grafted on at the tranny end. The local driveshaft shop had little problem doing the work other than finding the universal joints which I ended up providing. I do not recall where I got the splided part (it too may have been an Alpha unit) but with a flat steel adapter plate welded on the tranny output everything bolted in place. I will attempt to attach some recent photos. If you wish to chat about the process drop me an email.

Rick

[DJThom]

Thanks all for your notes and advice. I actually have the tranny and engine and differential in the car in their proper place and was able to take an actual measurement. I didn't trust myself to do it properly mocked up on the floor.

I went to another driveshaft guy today and he can do it. He says they hardly see any British stuff and that it always requires extra machining just because its not what they're used to and set up for. Typically he has guys coming in with Range Rovers that have busted something, so he has done them before and has the proper ballancing equipment.

So I'm one step closer.