Differential advice please

[dalgrae]

I have a 4.55 ratio diff fitted to my car which I have some doubts about as it gets noisier the higher the speed I go 40 mph plus , it does not clunk or snatch on take up or on over run ,but can someone please advise me on a correctly set/adjusted diff what amount of radial freeplay would I expect to have on the driveshaft / propshaft flange location . On mine when I twist the propshaft by hand I have approx 1/2" to 5/8 " radial freeplay which to me seems a lot , as said previously no cluncks or knocks are apparent when I drive my car .If I have to replace the diff where is the best place to source one and do I have to go for new or used

[mike.perry]

Make sure that the noise is not rear wheel bearings

[dalgrae]

Thanks Mike any easy checks I can carry out to verify the bearings or do I just replace them

[MarkyB]

There is often a lot of play but it isn't very symptomatic of anything as the only time you might notice it is going into reverse.
I trust there is some reasonable oil in it?
What kind of noise does it make?

[bmcecosse]

As above - try an oil change. EP 90. The free play doesn't sound too bad to me.

[dalgrae]

Thanks for the advice I changed the oil in the diff as soon as I bought the car using EP90 until it just came out of the filler plug so it has only done approx 150 miles , the noise starts to appear in the late 30s MPH and gets worse with speed it is a sort of groan/rumble there is also a sort of cyclic whirring noise , with the amount of backlash I presumed maybe wrongly the noises were the crown wheel/pinion .I have no fore/aft movement by trying to pull the propshaft back and fore only this radial free play ,the car has only 100 miles ago passed its first MOT with me and I watched the examiner give the rear wheels a good inspection during the test so I have assumed the rear hub bearings are OK

[MarkyB]

I'd take a close look at the universal joints on the prop shaft, there shouldn't be any play in them and they wear out a lot more often than diffs.

[bmcecosse]

Possibly best to just pick up another final drive -not expensive, and a chance to drop the ratio down slightly!

[dalgrae]

Please advise reference the ratio change what should I be looking for other than a 4.55

[bmcecosse]

4,22 !

[dalgrae]

Just removed the propshaft from car and after a bit of a struggle I managed to remove the u/joints a few are still perfect but the rest have a variety of markings on them from parallel to the bearing grooves, some have angled grooves and a couple have cross hatch grooves , they all still had plenty of grease in them , my question is how much damage to the bearing surfaces is required to cause any problem / noise . I have ordered new u/joints for the rebuild

[MarkyB]

I didn't mean that closer look!
Just make sure the is no play in them which is best done on the car.