Final Drive Unit

[Guest salty_monk]

Easier for you to read this than for me to explain.....

 

http://en.wikipedia.org/wiki/Constant_velocity_joint

 

http://en.wikipedia.org/wiki/Universal_joint

 

By the way.... if you get one of the "glue together" boots you'll find you can trim it before you glue it together. Not sure if I'm a huge fan of that type but many have had a lot of success with them.

 

Dan

[Guest timswait]

A UJ does not turn at constant velocity. If the input is spinning at constant speed then after going through a UJ deflected at an angle the speed will be faster through some of the rotation and slower through other sections. If this is drving a wheel then it will be felt as vibration. The effect can be cancelled out by passing through a second UJ deflected at an equal and opposite angle to the first (as long as the joints are aligned). This is why UJs are fine for prop shafts (as long as the diff and gearbox are parallel - see the thread on turbo's broken prop), but should not be used on driveshafts to the wheels. A constant velocity joint does spin at constant velocity, so is used on driveshafts.

Arg.. beaten to it!

[Grim]

so why are cv joints not used on driveshafts?

[Guest timswait]

Do you mean why are CV joints not used on prop shafts? Don't know, I presume probably cost, they tend to be a bit bulkier and a bit heavier too, so I guess when a UJ will do the job you may as well use it.

[Robbie 2B]

After a weekend of investigation, head scratching, pulling the prop shaft out, head scratching, checking and greasing the UJ's, head scratching and re-assembly the fault is still evident. All bets are now with the differential being the defective item. Yes I realise that a series of gears, running in an oil filled enclosure, should be the last thing that fails but all other suspect items have been given a clean bill of health.

 

If anyone local has an unwanted standard differential sitting around in their garage, beer tokens and collection are available. Original was from a 2 litre carb sierra sapphire. If not, it will be a trip to Bridges at the weekend.

 

Thanks for everyone's help.

 

Best regards

 

Robbie

[Guest chris brown]

so why are cv joints not used on driveshafts?

We know you meant UJ's and they have been in the past. Ever driven an old Landrover in 4WD on full lock and had the steering wheel kick all over the place that demonstrates well that UJ's are cyclic. Another one I know of is the Rover P6 as in the photo but with the De Dion suspension the inner and outer were kept pretty parallel

[Guest salty_monk]

Robbie,

 

That should be a 3.62 ratio diff. It's not a huge job to swap it over.

 

I'll be very surprised if it turns out to be the culprit.....

 

Dan

[Grim]

i meant "why are cvs not used on propshafts", thanks tim for the andyspeak translation, and sorry chris for that kerb ball!

[Guest chris brown]

"why are cvs not used on propshafts",

Price I suspect

[Guest pmk159]

so why are cv joints not used on driveshafts?

 

Found this:

 

http://cvcoupling.com/index.php?option=com...4&Itemid=52

 

Basically they are not used in high load applications due to the small surface area of the loaded part of the joint, ie the area of each ball on the sliding guide surface. The above link describes it better.

 

Paul

[Robbie 2B]

Just to complete the tale.

 

I got a 3.62 differential from Bridges last Saturday, (£45 already removed from car).

 

When it finally stopped raining I changed the diffs over on Friday night.

 

Have now been for a number of runs (30 plus mile) and the problem appears to have gone!!

 

One thing I did notice was when I had the prop shaft out there was a small square of curved plate (40 mm by 50 mm) which had been spot welded near to one end of the prop shaft. I take it that this was Robin Hood's method of balancing the prop shaft. At least it shows that the prop shaft had been on a balancing machine.

 

Thanks for all the interest and responses.

 

Robbie

 

PS That Hamilton boy did well!

[Guest chris brown]

One thing I did notice was when I had the prop shaft out there was a small square of curved plate (40 mm by 50 mm) which had been spot welded near to one end of the prop shaft.

PS That Hamilton boy did well!

That is the normal method of balancing a prop Robbie so perhaps they do the job properly. BTW when did RH start making there own props when I got my kit they wouldn’t sell the prop and it was listed as free with kit but not sold separately due to agreement with the manufacturer.

 

That Hamilton boy did well. He did that.