Prop Shaft Lengthening/Shortening
 

Hi guys,

Anybody here have any experience of lengthening or shortening a propshaft?

Im planning to lengthen a chassis to increase the wheelbase, which of course will involve lengthening the prop too.

Anybody hady good or bad experiences with this? If anybody has link to a site where I can see the process in more detail Id sure appreciate it. The prop in question is for a mercedes 16 tonne truck.

Many thanks,

Dave The Hat

Try ...propshaft services in Feltham Middx, I used them years ago for a UJ. good service. Propshaft Services - Propshaft Manufacturing Specialists

Many thanks Dave, they might just be the boys to do the job. Absolutely critical to get the lengthening done properly and then balanced or my whole project could be buggered later down the line.

Thanks for the link!

Another recommendation for Prop-saft services. In the past I have had them shorten, lengthen and make hybrid shafts for me (half escort, half LJ80) They did one for an SJ410 while I waited.

Hi BYT,

If lengthening, I understand the shaft is cut and a new piece of tube is welded in.

My concern is the strength of the weld.....if for instance seriously bogged and trying to power out of the mud, all that torque and twisting going through the shaft may start to open up the weld over time.

How have your shafts performed over the years (sorry if that sounds a bit kinky!)

Cheers.

worth dropping the propshaft clinic a mail to, they may be able to help. They could probably knock you up 1 from scratch, saves you worrying to :thumbup1:

G

I wouldn't worry about the weld strength, it will be at least as good as the original. There are issues with very long shafts twisting/bending due to torque. If you look at very long drive-trains (on HGVs for instance) there will be a bearing carrier and another set of UJs midway.

What vehicle are we talking about ??

It's for a Mercedes 1617 truck. Already has a carrier bearing mid way. As you stated, there will be a recommended length you cant go over before torque/twisting becomes a real issue, so you must add a second carrier bearing. I dont really want to do that. Sooooo......

Im talking about lengthening the prop by approx 70cms as this is what I am increasing the chassis length by. As this is quite substantial, Im going to buy a prop that has come off a longer wheel based scrap truck, then will only have to lengthen it marginally (or might have to shorten it, depenmds on the length). Think this would be the safest option. Or if cheaper, as you say, get one made from scratch.

If your existing prop has a high milage the UJs will have settled in to their 'comfort zones' - by lengthening you will presumably change the angles with the carrier and rear diff, just as you would if you raised the suspension - not such a problem if messing about offroad but for an overland truck a potential source of vibration. I would get the UJs checked while lengthening to be safe.
Also take note of the phasing on the shaft and make sure it is put back the same, do you have a sliding joint too?

Yes, has a sliding joint. Im amazed at how far this joint can extend before the splines show, quite alot of extra length hidden away in there.

Part of the lengthening process involves balancing the prop for you (so Im told).....yes, 100% with you, balancing the prop is essential or the vibrations will affect the diff and gearbox. Ive seen them attach weights to the prop in different areas which seems to solve any balancing issues.

Thanks for everybodys advice.

Be aware of not using the sliding joint to add length too far, for the obvious reason that there then ends up being a possible situation where the suspension is at full travel (like going a bit too quick over a bump and all the weight comes off the axle when it bounces down as the body goes up) and the propshaft extends - then the splined part shoots out of the other bit, drops to the road, you then catapult yourself arse over tit.

Just lengthened the chassis, now just about to get the prop sorted.

I have a Mercedes booklet which goes through the process of extending or shorthening a wheel base. They touch on the subject of the prop shaft. They say that you can go upto certain lengths without a carrier bearing (ie unsupported), and these lengths vary according to the thickness of the tube on the shaft.

I have a 90mm thick shaft, and they say you can go upto 1700mm long without a carrier bearing.

If you have a 140mm shaft, they say you can go upto 2300mm long without a carrier bearing.

Question that I have is the following:

Can you have a 90mm thick shaft from the gearbox to the carrier bearing, and then have a 140mm thick shaft from the other side of the carrier bearing to the diff? Or do you have to have both parts of the shaft at the same thickness?

Might sound a bit far fetched, but several mechancis I know said this is possible.

If so, then I may be okay, as I can keep my front section of prop as it is, then swap my rear section for a bigger shaft and pay some extra for it.

I don't see any problem with what you suggest.

Will depend on the availability of UJs that can match 90mm prop shaft off the back of the gearbox to a 140mm prop shaft connected to the diff, thats a big size hop - I dont know what Merc have available - its generally not a good idea to have mismatched or custom made parts when you might need spare parts support that will rely upon your VIN to get the correct part to you.

Thanks guys that's reassuring.

I looked at a Mercedes Atego today that has been altered, and this had a different thickness shaft at front compared to the back so I guess it is possible, providing balancing is done correctly.

Spare UJs wont be a problem they're readily available for both sizes of prop shaft, and I intend to take spares with me on the journey Im planning.

Am going to speak to the prop specialists this week, so appreciate the heads up regarding what is and is not possible.

Cheers.