Indentifying diffs

[uax12]

Having finally run out of ideas for where the vibrations are coming from in my van*, I want to change the diff to a 4.22:1 version. Now I have some spare ones, but have no idea what they came out of!

Can anyone tell my the part numbers of the varing diffs please?

Also does anyone know what the speedo number will be to match?

Many Thanks

Andy G

* I've changed engine and box, new engine mounts, steady-bar rubbers (nd not too tight!), checked prop bearings, it can only be the rear axle. The vibrations come at about 55mph and stay from there on upwards, any other ideas??

[bmcecosse]

Welcome to the forum ! The diffs are all marked with the ratio - so just inspect the crown wheel on each diff. For a 4.22 diff you need a speedo with approx 1400 tpm. It's unlikely to be the diff causing vibs - are you sure the vibs are not simply wheel balance related ?

[uax12]

Certainly have tried the wheel-balancing front, hasn't seemed to make any difference. The vibration has been there for about ten years, it's just that I'm now using the van as a daily driver, and I'd like to be able to keep up with traffic (hence why the 4.22 diff). Interestingly have looked at one diff and the crown-wheel didn't have a ratio maked on it, just the part number.

It has in the past been so bad that the screen has shattered. I just wish I could get to the bottom of it!!

Andy G

[aupickup]

have you checked the prop for balence
try swopping the wheels around
uj joints

as bmc says doubtful to be the diff

[uax12]

How do I check the prop for balance?

Andy G

[bmcecosse]

All diffs are marked - look carefully - 4.22 diff will be marked 9/38.

[aupickup]

you can add weights
or find a place that will balence it properly for you

i would say this could be your problem, as it does it a t a certain speed

[MarkyB]

What about a bent wheel rim? or a tyre bulge?
55mph is the speed unbalanced wheels tend to start wobbling.
try swapping the wheels from back to front and see if it feels different.

[PSL184]

It sounds like a prop problem to me and the only way to be sure is to take it to a specialist to have it balanced properly (no pun intended)

[bmcecosse]

Or simply try another prop. You could unbolt your prop from the diff - and then bolt it back on after rotating it 90 degrees. May just work.

[bigginger]

Not possible. Has to be 180 degrees

[bmcecosse]

Ahh yes - so it has! Well spotted Andrew - still worth a try though.

[Declan_Burns]

I had exactly the same problem. Prop balancing is quite expensive. BM sell propshafts secondhand at a reasonable price. They even posted it to me in Germany for 15GBP! Couldn't complain about that and it solved the problem. Check the UJ's and regrease before installing.
Declan

[bmcecosse]

The prop may be bent - if someone has carelessly put a jack under it at sometime, or allowed the car to become 'stranded' on the prop. I would say - if the vibration was enough to break glass - that this is the most likely cause.

[mike.perry]

Prop shaft sounds favourite to me. I had the problem on my Series MM so I didn't have a spare. I had the shaft overhauled with new ends and rebalanced and it has been perfect since. I can't remember it being too expensive but it was well worth the effort.
Wheel balance shows up through the steering wheel, prop shaft just vibrates the whole car.

[Kevin]

One other thing that can cause strange vibrations is if the gearbox steady cable is done up too tight instead of the slack just taken out of it, but as this has been going on for a long time it does rather sound like the prop, you could try a couple of large jubilee clips on it to see if it alters the vibration range.

[uax12]

Thanks for all the thoughts, I played about in the rain on Monday, and swapped the prop for the nice clean one which I had painted up for my GPO van, and what do you know? Yeap thats right the vibration has gone. Well almost, theres a singey bit as you hit 62-65mph but so much better than before! Infact I can now chug around at 30 mph in top which it just wouldn't do before!

The old prop will have to be balanced up (if I can find somewhere that will do it!) before I use it on the GPO van.

I haven't changed the diff yet, but now I know i'm looking for a 9/38 l'll have a hunt through the box, and my next free long weekend I'll try and swap it over, so that I can save a few more pennies!

Thanks again all

Andy G

[bmcecosse]

Well done - just check carefully that prop shaft isn't bent - in which case scrap it and get another!

[Kevin]

Just so you know what you are looking for.<br><br>

[NIGEL15]

An old trick of the trade used to be the use of large jubilee clips fitted around the prop towards the back end and a bit of trial and error. The worm bit of the clip acts as a weight and by trying it in different places you can often improve or even get rid of vibration.