I'm torn between taking the simple route of using a one piece propshaft and using a split prop on my Firenza, anyone have any useful input to make on this bearing in mind I'm using a live axle and the prop will be 45" overal length?

My concerns are vibration and noise transmission.

I did originally try a one piece prop on my Escort but I swapped it for a split one because I was getting a vibration, this disapeared when the second prop was fitted.

 

so Martin did you swop the single peace prop on your escort for a two peace prop ?if so bollox as i have just copied your prop for my escort ,oh well never mind .



i used to have a single peace prop when it was two wheel drive & it was fine .

 

I have found even company's who specialise in propshafts quite often do not get them balanced well enough causing vibration.

I take it you checked the run out on you're single piece prop before swapping back to the split prop Martin?


I wonder if a perfectly balanced one piece prop should have less vibration than a split prop, Maybe so as the split ones tend to have a rubber bush half way that holds the bearing?

 

Try it and see how you get on, mine only gave issues above 140mph

Yeah I checked runout and had it balanced twice before giving up with it. I've decided on a one piece prop for the Firenza, I'm going to use the original prop that came with the Mustang axle and just have it shortened with a T56 yoke..

 

Tried both in my cortina and the 2 piece was better.

Steve

 

Now you mention it, I do recall a one piece prop fitted to a car that was modded to 4x4 that had a vibration and we could never get to the bottom of.

 

Didn't the one piece prop keep taking out the rear oil seal? or am i thinking of another car

 

my one piece on my 3dr when i went 4wd vibrated like fook over 70mph despite being balanced, when 2wd was fine, it was approx 52" iirc.

 

what would you benefit from fitting a 1 piece over a 2 piece?

obviousley a slight torque loss but less flex ad centrifugal force surely?

converted a mk2 escort to pinto and 1 piece prop and vibe was that bad you couldnt touch the g/knob over 50mph!
everything was off and checked 3/4 times and balanced twice, new prop but never got to the bottom of it.

2 piece prop fitted and car was so much smoother, seemed to accelerate faster over 70mph too, may have all been in the mind but noticable drivability gains.

 

Critical speed is the most important thing you need to consider when deciding 1 or 2 piece ( and overall strength I guess )

A long shaft can only be spun so fast before it reaches it's critical speed and will explode due to resonance.

Just picture trying to spin a flag pole and you'll understand. The vibrations and resonances may not be visible on a prop, but they will be felt ( and when you feel it, it is horrific )

Long shaft = bad
Thin shaft = bad

Alloy or composite shafts will have a higher critical speed for any given length or diameter

2 piece shafts are effectively 2 x short shafts so their critical speed will be much higher.

So you need to determine the shaft length you require, and the maximum shaft speed you will ever see. Then you can decide which is most suitable.

And either way, due to the live axle there will need to be a slip mechanism on the shaft somewhere ( although T56 has this already if you're using it )

 

As a rough guide, see here. 3" is a pretty common shaft size really.

So say a 3" shaft, 46" long will have a critical speed around 8200rpm. You CANNOT run the shaft to this rpm, it must be below it. Mine is an overall length of 57" and when I had a 1 piece I could only do 120mph before horrific vibrations came into the car ( before I knew about critical speed, and shaft supplier never even mentioned the fucking thing when I was ordering, nor when I complained about the vibrations ! ), so as strong as it may have been it was totally and utterly useless.
Custom 2 piece shaft and it's been spun to close to 10krpm smoothly


http://www.markwilliams.com/driveshafttech.aspx

 

harmonic resonance on anything metalic is a fucker, bridges, conrods, propshafts etc

top info as always Stevie

i really dont see the appeal of single peice,
is it rotational weight, overall weight, unsprung weight or loss of torque that may be the issue in this situation?
V8 in a firenza with live axle, cant be weight biased i guess?

p.s i think everyone will get the idea when you use a flagpole as a graphic thaught!

 

A single piece is obviously stronger. Less joints to fail, no centre bearing, no downsize through the bearing etc. It will also be lighter.

Not much bloody use if it can't spin very fast though.

 

exactly, stronget to what point?

same as engine tuning i guess, torque v speed = power!

how to calculate the perfect prop..........

 

Correct

Steve

 

fook am one peace now to

 

Awesome and interesting info from Stevie!

Mart those long cable tie ends are annoying

 

Again it all depends on usage and your requirements.

I struggled to get anywhere to make me a 2 piece when I told them what I was doing with it. Making it wasnt difficult, but most places didnt want any risk attached to their names if it was to break.

Hell, even halfshafts, one huge company in the US making supposedly strong shafts refused to sell them to me in case they broke because they were drag specific shafts and should not be used on the road. I think because the driving flanges were pure shite and couldnt take side loadings. Like WTF ???

Either they make a proper product or they dont, clearly they dont despite all their website bullshit.

My first 2 piece shaft was made by South Carolina Driveline in the US, was very good and also very cheap.
I then discovered a larger centre bearing from another company and they made me a new shaft, slightly different and with the larger joint.
Inland Empire Driveline Service made my my current shaft, not much different but was quite a bit more expensive.

No idea if anywhere in the UK can make the same. Dont see why not, as the parts are just readily available parts from shaft/UJ suppliers etc.

 

Cheers Stevie and everyone else thats given input. The reason I was considering a single piece prop was mainly because my car doesn't have a centre mount in the a new tunnel and thats all painted any tidy

Anyhow after reading of the experiences of those that posted and that coupled with the issues I had with my Escort has convinced me that a split prop is the only way forward. I did make a bolt in bracket for the centre mount on my Escort and maybe that will work on the Firenza too.



I've decided that a Sierra Cos 2wd will do the job if I change the gearbox yoke and change the diff flange to Mustang 8.8 and then shorten the rear section at the front to the required length (cant shorten at the rear as its a tube in a tube with rubber insulation inbetween). It's at the prop place now so hopefully I will get it back by this weekend.

 

Rear can easily be shortened, just replace the tube. Any local prop place can do that and wouldnt cost that much extra compared to shortening/welding/rebalancing anyway

Are you using the 8.8" in the car ?

A 1 piece shaft could be viable as long as you wont see shaft speeds in the chart, or stepped up diameter, or went to alloy or composite.

That will depend on wheel/tyre combo, diff ratio and road speeds you may see. And of course if you have room for the 1 piece with the axle motion up/down before it hits the bodywork.

But retaining 2 piece and altering a shaft you have can make most sense, as less parts to buy.

 

You can only shorten the rear part by a certain amount as it has an inner tube sandwiched in rubber, I want to retain that rather than just fitting a new piece of plain tube.

Yes I'm using the 8.8" with 3.54 gears and 245/35 x 17 tyres..

 

Think that's roughly what I had at the start, albeit with 16" wheels. Could barely turn 5500rpm shaft speed before the vibrations near took the car apart( 1 piece ), although my overall length was about 57"

When I first fitted the axle to the car I used a modified Toyota Supra shaft as was using a Supra gearbox at the time. It was 2 piece and much larger diameter/joints than my original Ford item.

Although not sure how it would compare to a Cossie shaft.

If you put your tyre size etc into a gear ratio calculator. Critical speed of a 3" shaft 46" long as per table above would work out at roughly 160mph road speed.

A smaller diameter 1 piece would be lower. So no way will a 1 piece be an option IMO.

 

Does that mean I now have to do more than 160 to warrant having a split prop??

 

It means you have to get a 2 piece and test it to find it's maximum

 

How did you narrow the 8.8 axle to suit? New shafts from America?

 

I narrowed the axle tubes and had the shafts re-splined at Wisbech engineering back in 1993, I have never used it yet but I'd bet their guarantee is up now If I get problems I will buy new shafts.

 

New shafts really arent expensive.

Moser will make you anything you need for around Ł3-400 a pair ( was cheaper when I bought a few years ago, so assuming they are dearer now )

Hauser or Andy Robinson Race cars can supply.

Moser offer a lifetime guarantee....not much use when it would cost more to send them back to the US for replacements lol

 

I ran my car with a split prop
When i changed to a single
I had massive vibration
Had it re balanced no change
went back to the split all ok
Im using a split prop on the new build.

 

Original shafts are pretty bullet proof from what I hear. Are they 28 spline or 31 spline shafts? I only ask as I have an 8.8 that I've had narrowed for my Cortina but no one (including Wisbech) will touch the 31 spline shafts I have!

About to order a new set from Moser this week.

 

You can get them in both.

I think actual cost for the Mosers is about US$350

There are also different bearing sizes at the end if using their c-clip elims ( which tend to leak )

Strange and MW's c-clip elims are much better

Yo can get small 28spline shafts ( I never twisted ) and large diameter 28 or 31 spline shafts. These are basically the same large diameter shaft with the splines machined on.
I twisted the splines on both of these. I can only assume because there was less give in the actual shaft itself compared to the small 28 spline shaft.
They're all the same price from Moser anyway.

I think I might have a set of Moser c-clip elims here ( with larger bearing ) and defo have a 28 spline Ford racing Torsen LSD if anyone's interested.

 

I've got the standard Ford Posi and am keeping the C-clips and seen they do shafts for what I want.

I was under the impression all 31 spline shafts use the big bearing?

 

I had a one piece prop on my escort stuck with it for a few months untill i couldnt take the vibrating any more ,swapped it for my 2 piece and all was good again

 

Simon as Stevie says just because the 31 spline are bigger dosnt mean there better ,mine in the escort were only 28 spline and didnt break or twist with 8800 rpm launches

 

Oh don't get me wrong, I'd prefer to go 28 spline in a way, but I have a 31 spline diff so am limited to 31 spline shafts without changing and there's no point in doing that really.

 

I think they do, but you can get 28/31 both with the larger bearing.

Only issue with c-clips is if they break, your shaft falls out. Probably with disc brakes not such a huge issue. But with old drums it could be a huge issue. Most drag rules insist on c-clip elims so the shaft should never be able to leave the axle, although I'm sure the changes of them ever failing is remote.

 

I don't know whether I have 28 or 31 spline shafts tbh, mine still have the C clips but I am running 20mm thick rear discs with 1mm clearance either side in the caliper carrier so my shafts are never coming out

My axle came out of a Fox Mustang 5.0GT which was an 84 model I think, it has an LSD but its been sooo long since I looked inside it that I can't remember if its a plated type or not. Can you tell anything externally??

 

That's what I heard but thought the same as you've said - that the disc/calliper will stop a proper incident...I should think/hope.

 

Can't tell from the outside as far as I know.

Fairly sure that early Fox body Mustangs ran 28 spline. Well, at least I hope so as Wisbech told me they don't and haven't done 31 spline shafts

 

Most of the OEM LSD's are simply the Traction Lok one, dont think any had a proper plated LSD

 

I'd bet mine are 28's, my car isn't going to be really heavy and will prob only have about 450hp so I'm hoping it will all hold together.