Technical Time for new axles, but....

[nzbobc]

Well, being newbies and low on the learning curve, we're learning (sometimes the hard way) about the nuances of these cars. This time, we snapped one of the axles but letting out the clutch too quick. Looking at it closely, it had been snapped earlier in its life and had been welded back together..

I've been reading online and in Haynes about axles and replacing them and felt good to go until I looked closely at the axles: They're different from everything I've seen/read. Ours have universal joints in them. Each axle appears shorter than what's shown elsewhere. Each axle connects to a universal joint, then to a shorter axle, which connects to the wheel hub.

So, kind folks, what can you tell me about these? This 500 has the 650cc motor and wheels off of a 126. I don't know if the transmission/differential is from a 500 or 126.

I'm seeing where I can buy the beefier (i.e., thicker) axles to handle the torque of the bigger motor but here's where I'm scratching my head:

• It looks like I can buy these replacement axles which means I'd toss out the universal joints and the axles on both sides of the joint.
  
• But, do I need to replace the hubs? Are they the same/different?
  
• I'm worried that the angle of the new axles leaving the differential will be different and will muck up the meshing and/or bearing preload (I'm getting this from reading the Hayne's manual-Chapter 6-Transmission-Sections 7 and 8- Restoration of the Final Drive and Meshing the Crown Wheel and Pinion)

Any thoughts/knowledge on axles with differentials?

Thanks,

-bob

 

[oopsadaisy]

Firstly welcome to the forum.

That sounds like a really strange set up you have there - I don't think I have ever seen a 500 or indeed a 126 with universal joints in the drive shafts.

Any chance of a photo?

 

[Toshi 975]

If you have a gearbox with syncro on 2nd, 3rd & 4th then it is 126. I guess from your previous posts that you have a tuned engine so the drive may have been uprated (or bodged!) It could be that the tripod drive couplings have been fitted. I have got some for my 500 but have not fitted them yet. Can you get any pics?

 

[lilgreencar]

Does yours look anything like this:

http://www.motomax.pl/eng/fiat126/instr_126p/instr_126-B-F_eng.html

 

[tjmra]

Never seen this before so curiosity forces me to ask a couple of questions.

Now that the rubber coupling is gone, what takes up little bit of give that they used to provide?

Also, for a numpty, what is the benefit?

Regards

Joe R

 

[RogerNZ]

"Now that the rubber coupling is gone, what takes up little bit of give that they used to provide"

Exactly, the standard rubber coupling cushions the effect of sudden forces in the drive train. If you go to UJ's then you are wise to use a later model clutch disc which has springs that serve that purpose.

 

[nzbobc]

Hi folks,

Thanks for the interest and the welcome..

I've been attending to other things so, it's taken me until now to get some photos to you. Here's photos of the same axle from the left wheel to the differential.

As you can see, it's not the same as the setup as that shown in the link posted by lilgreencar.

Anyone recognize this type of setup and specifically, the best course of action for replacement since the right-hand axle is snapped?

Cheers,

 

[RogerNZ]

Hi, it's just a different version of the same thing really. If you remove the axle and UJ I am confident you will find you can fit a standard axle and rubber block coupler.
Cheers Roger

 

[nzbobc]

Thanks for that Roger but any thoughts that if I do replace these with straight axles, will I be mucking up the angle of the axles coming out of the differential and meshing?

While I'm comfortable working on cars including engines, I have only rudimentary knowledge about transmissions and differentials (!) That's why I'm asking about the meshing and bearing pre-load (stuff I read but have no understanding of)...

Cheers,

 

[Toshi 975]

Not seen a set up like that before on any 500 or 126. If you say the drive shafts have been welded then I would think it is a case "when in New Zealand do as the Kiwis do" , that is make use of what you can get hold of.
I will be back there at Christmas & if you are anywhere near Rotorua I would be interested to have a look.
The drive must have a sliding spline to allow for movement of the suspension & gearbox. I can see from the picture that the splined flange coupling which normaly sits on the end of the drive shaft has been reversed & fitted on the outer stub axle to enable the connection to the UJ. I would guess that it is held with a nut in order hold the rear wheel bearings together. Looks like a clever idea as long as the shafts do not break.

 

[nzbobc]

Hi Toshi,

I'm down on the S. Island-Christchurch so and I hope to have this all in the past by the time you make it back so, you'll have to just rely on photos, I'm afraid...

But, here's a couple more....

-bob

 

[the hobbler]

Morning Bob;
you have a very interesting variation of 'UJ' connections on your 500---very similar to the factory set-up on the last of the works Abarth 1000s. You are going to have to remove the gearbox, whatever repair you decide to do so why not have a really good look at getting the present halfshaft PROPERLY repaired, poss with a new and properly welded sleeve. This could turn out be a much more economical repair. Don't forget of course to have the other shaft checked--it may need some preventative work.
Looking at the first 3 pictures you posted, I would have to assume that the OUTER half of the coupling (which on normal cars is the part that slides on the drive-shaft) is secured to the stub-axle with a large nut and that the coupling on the drive shaft is the part that slides, hence the fitment of a retaining circlip.
If you do decide to go back to original factory spec. driveshafts, go for the 25mm 500 shafts and couplings. Even if you have a 126 gearbox fitted, you must still fit 500 shafts as the 126 shafts are too long. Whichever way you go, all the best and keep us in the picture.

 

[Bambino]

Is this a variation on the Abarth 'pendolare' IRS ?

I would second a good repair of the broken halfshaft and a check of the unbroken halfshaft. It's an interesting setup that should keep your wheels perpendicular to the road under most conditions.

Chris

 

[babbo_umbro]

Is this a variation on the Abarth 'pendolare' IRS ?

I would second a good repair of the broken halfshaft and a check of the unbroken halfshaft. It's an interesting setup that should keep your wheels perpendicular to the road under most conditions.

Chris

I don't understand why this type of drive shaft would change the geometry and reduce camber change at the wheel, which is governed by the swinging arm. However, this setup is still much better in concept than the original (and would allow you to alter the geometry if you wanted to), except that, because it's much shorter, the UJ has to accept a fair degree of articulation, and the original Fiat UJ, concealed within the rubber boot on the side of the gearbox, is certainly being subjected to considerably greater angular movement than it would experience with the original-length shaft, and the rubber boot is also being pushed through greater angles.

 

[Bambino]

I'm no great suspension expert, but I guess I was thinking of vertical movement of the diff assembly not being coupled to the wheels through solid axles. The distal UJs will isolate the wheels and they will be more likely to remain perpendicular to the road surface. Like in the photo attached.
Chris

 

[the hobbler]

sorry lads, but you're talking through your backsides---(1) drive-shaft design alone will not alter rear wheel alignment/movement--it is controlled by the design of the hub location. As Bob's car still has the original swing-axle/wishbone arrangement, the vertical movement of the wheel will stay as per original. (2) The inclusion of Hardy-Spicer U/Js will not alter the alignment angles of his drive-shafts---the inboard ends of the drive-shafts are located/driven by square 'slide-rings' on the drive-shaft pins--a very simple form of joint articulation which allows for drive-shaft angle change. The main reason for fitting U/Js onto the drive-shafts is that it removes the potential weakpoint of the original rubber/alloy couplings.
The Abarth 'Pendolare' rear suspension not only had Hardy-Spicer type U/Js on the rear-axle (and I think they retained the rubber/alloy couplings, so reducing the length of the drive-shaft even more) but the rear wish-bone was of a completely different (tubuler) design in order that the rear wheels could move in a more vertical alignment. The 'Pendolare' rear suspension was only fitted to the final, most powerful version of the '1000T/Cs'--never on any '500' variant

 

[dragonwagon]

Considering the performance potential of a 500, even with a 650 in it the rubber/alloy couplings are plenty strong enough if in good order. The semi trailing arm rear suspension will by design allow significant camber change between full compression and full droop (but less than a VW swing axle setup). Driveshaft design is irrelevant in either case. Only with full wishbone based IRS is a double jointed shaft a must to allow constant camber angles without excessive pressure on the diff. Looking at those strange shafts with almost central UJ's I'd be somewhat wary of inducing failure of the simple slide joint inboard end and the resultant wrecking of the transaxle. For what it's worth I'd revert to standard 25mm shafts and couplings.

 

[Bambino]

sorry lads, but you're talking through your backsides

Yeah - but you're listening

I read about the pendolare suspension ages ago and thought that someone had attempted something like that on this car. Obviously didn't work too well ....

Chris

 

[babbo_umbro]

I'm no great suspension expert, but I guess I was thinking of vertical movement of the diff assembly not being coupled to the wheels through solid axles. The distal UJs will isolate the wheels and they will be more likely to remain perpendicular to the road surface. Like in the photo attached.
Chris

The drive shafts are not a part of the suspension (here - as opposed to some Lotuses for example) so they have no influence on the motion of the wheels - see another post. However, shortening the part of the drive shaft that's inboard of the UJ MUST increase the angularity on the coupling within the diff, and place extra demands on the oil seal - which has obviously been leaking, though that's not unusual.

You need to align the pins within the outer UJ with those on the inner joints - as on the UJs at either end of a front engine/rear drive prop shaft - to prevent placing large bending loads on the shaft, which is what I suspect has happened here. Remember these are not totally articulated joints like you find at the outer ends of front wheel drive drive shafts.

 

[nzbobc]

So, I'm thinking that my best option is to stick with the axles that have the U-joints and beef them up.

I'm thinking this because I was just digging thru the box of parts that came with the car, and in it was a differential and pinion gear. So, maybe the newer axles (with U-joints) required a new differential? There's no obvious signs of wear/damage so can't think of why it would be replaced other than because of the axles.

If so, I'm not inclined to swap it out and put the older differential back in just to get straight axles. My reasoning is that I'm concerned with bearing pre-load and meshing between the crown and pinion gears (Haynes says this is hard to do).

Make sense?