prop shaft

[MoggyTech]

Both the prop shaft AND the diff would need to be unique - seems 'highly unlikely' to me !

It's not often you are wrong, but your right again

[Innovator]

Marking the diff and prop flanges to ensure it goes back on the same way is an "old school" thought. It does not matter!

The flanges have registers (a recess on the diff flange and a raised spigot on the prop flange) that do the location. Assuming these are as designed ie clean without burrs the prop will locate accuratly. The amount of tolerance to put it out of concentric is so minimal it will not effect the balance.

When props are balanced they are bolted to a machine using a flange like the diff. From the experience of balancing hundreds of props I can assure you that we never balanced closer than the tolerance of the spigots, In other words if we put the prop on and pushed the spigot hard one way and balanced it then removed it and pushed it hard the other way it would still be well in our balancing tolerance.

Another tolerance that can effect the balance is the spider of the UJ. This can be pushed hard one way against the circlip. However a tap of the yokes with a hammer normally centralises.

[bmcecosse]

Where did you do this balancing Innovator ?

[Innovator]

I worked at Dunning and Fairbank, Leeds for over 5 years.

I would like to clarify one point I made regarding pushing the prop over on the spigot when balancing. The tolerances were so tight on our machined and hardened balancing plates I would guess I could move it in the region of less than 0.1mm. We often had to tap the flange home.

[bmcecosse]

I've often wondered how you prevented the prop shaft from 'whirling' on the universal joints - how did you hold it rigid ?
And someone was asking about having a special prop made up - will D & F do that ? Or just high volume work ?

[Innovator]

The balancing machine was a bit like lathe (see pic above). The "headstock" and "tailstock" can rock from side to side and any out of balance is detected here, amplitude and position. If a centre bearing is involved there is a plinth to bolt the bearing to. Some props have 2 centre bearings so there are another 2 plinth.

At one end we had a plate which the flange bolts to and at the other end a collet chuck that the gearbox end slides into. So the prop is held like it would be in a car. We had adapters for all props and if we didnt we would turn one up.

Dunning and Fairbank http://www.propshafts.co.uk/ (tell them John recommended you) can make any propshaft. A lot of my work was on the specials including a carbon prop bonded together. Carbon props are now a standard item. I refurbed shafts for the world rally champion. A lot of their work is one offs.

A lot of props are quite easy to modify as many share the same UJ so it is a matter of swopping flanges or yokes. Most parts are available new. For example they can make a brand new Minor prop except for the gearbox yoke

[bmcecosse]

Excellent - many thanks for the explanation! I have seen one in action on one of Mr Evans 'car reborn' programs - still a mystery to me how it can detect the position to add the required balance weight!

[southerly95]

Another tolerance that can effect the balance is the spider of the UJ. This can be pushed hard one way against the circlip. However a tap of the yokes with a hammer normally centralises.

Can you explain what to look for with the above extract. Our '65 convertible has a long standing viration prob over 50 mph, many thanks, John

[MoggyTech]

Another tolerance that can effect the balance is the spider of the UJ. This can be pushed hard one way against the circlip. However a tap of the yokes with a hammer normally centralises.

Can you explain what to look for with the above extract. Our '65 convertible has a long standing viration prob over 50 mph, many thanks, John

Unlikely to be your problem, more likely wheel balance or wheel bearing. The prop shaft yokes pivot on UJ's called Spiders which is a cross shape. The spider sits inside the needle roller cup bearings in the yoke assembly. These are retained by circlips in a groove in the yoke assembly. A visual inspection might show a larger gap between circlip and bearing cup on one side of the yoke, but clearance is minimal, so any displacement would be very small.

Check to see if your propshaft has a small plate welded onto the tube, usually near the front yoke. If it's missing, that could be the problem. Or underseal on the propshaft.

[southerly95]

Thanks it's been a long saga. All bearings, halfshafts, brakes, gearbox, suspension replaced in the last year, all new. Wheels balanced and swapped by substitution to test - no change. Prop uj's replaced and propshaft balanced - worse! Replaced propshaft with s/hand one made it quite a bit better, next I am going to line up 3 MM's I have acccess to that don't have vibro probs and try each of their propshafts by substituting!! It's a great life if you don't weaken lol.

[Innovator]

Another tolerance that can effect the balance is the spider of the UJ. This can be pushed hard one way against the circlip. However a tap of the yokes with a hammer normally centralises.

Can you explain what to look for with the above extract. Our '65 convertible has a long standing viration prob over 50 mph, many thanks, John

Unlikely to be your problem, more likely wheel balance or wheel bearing. The prop shaft yokes pivot on UJ's called Spiders which is a cross shape. The spider sits inside the needle roller cup bearings in the yoke assembly. These are retained by circlips in a groove in the yoke assembly. A visual inspection might show a larger gap between circlip and bearing cup on one side of the yoke, but clearance is minimal, so any displacement would be very small.

Check to see if your propshaft has a small plate welded onto the tube, usually near the front yoke. If it's missing, that could be the problem. Or underseal on the propshaft.

The cross can sit hard one way against one circlip and the other circlip is put in it doesnt touch the UJ cap and just sits in the groove. This happened occasionally and I would thicker circlips. Circlpis are available in different thickness. But as correctly stated this is so small in will not effect the balance noticably.

It sounds to me that your prop is not locating at the axle flange. Check the diff flange very carefully and ensure the prop flange is a snug fit. Rotate the flange and try moving it around. It should sit flat with no gaps or side to side play.

At the gearbox try lifting the yoke that slides into the gearbox. There should be no play.

Get a DTI and clock the prop to see how true it is. Total run out on the tube should be less than 1mm and more like 0.5mm. If you dont have a clock use a pencil held very still and turn the prop by hand.

I have also had terrible vibration due to a dodgy diff.

[bmcecosse]

I would ask for money back at the place that 'balanced' that prop shaft!