Rear sphere movement

Unread post by **Dommo** » 07 Feb 2010, 00:04

CitroJim wrote:
Dommo wrote:, but if anything ever comes of it I'll make sure a few bushes get made! I'll ask around for the liquid nitrogen when I'm on placement in hospital again (student radiographer, only 5 months to go until I'm qualified, yikes )
Hey, I wonder of you could x-ray a ram to get an idea of the internal construction of one Dom

That would be incredibly valuable!

Unfortunatly I doubt they'd let me do something like that, for some reason they're a bit fussy about stuff like that, even though it doesnt affect anyone!

v6, i had a quick look for cartridge bearings but there dont seem to be any the correct size which is a shame. A rose bush of the correct size would be nice! Well worth paying for I'd imagine.

Unread post by **CitroJim** » 07 Feb 2010, 08:24

Martin,

Yes, sorry I remember now! My memory sometimes is atrocious

I don't see the need for a rose joint at the lower end as the top has a fully articulating balljoint so why does the bottom need to articulate in all directions as well?

Mike, very interesting website there on the supply of liquid nitrogen

xantia_v6 wrote: So why can't you just fit a new rose bearing? e.g. see here

If there is a UK supplier and they can provide the exact size, it might be a goer Mike

The problem is that the inner sleeve is a good bit wider than the outer sleeve to fit properly in the yoke. If there is a supplier of plain rosejoints who deals in small quantities, the necessary dimensions are as follows:

Outer diameter: 24mm
Outer sleeve width: 13mm
Inner sleeve width: 23.5mm
Innser sleeve bore: 12mm

An outer sleeve width of 23.5mm would be OK as there is room to
accommodate it.

addo · Unread post by **addo** » 07 Feb 2010, 08:34

What I'm particularly curious about, is whether it's a post-welded one - where an end is TIG welded on after the unit is otherwise assembled.

If you can't figure how it would ever come apart, it's likely one of this type... Parting the weld in a lathe would allow service to be performed; manufacturing procedure then mimicked for reassembly.

Sounds like you need something along the lines of a CV boot spreader for fitting that gaiter.

Unread post by **Dommo** » 07 Feb 2010, 11:16

There is a bearing you could use that has the correct sizes apart from the inner race width, you could in theory make a spacer for it too, two 5.25mm spacers, one on each side of the inner race, and you'd be sorted. It sounds awkward to fit too but it should only be as difficult as changing bearings on modern full suspension mountain bike systems..

http://simplybearings.co.uk/shop/p8554/ ... _info.html

Unread post by **CitroJim** » 07 Feb 2010, 11:34

Dommo wrote: http://simplybearings.co.uk/shop/p8554/ ... _info.html

Very interesting Dom, well found! A bit of machining around it and arranging seals each end and it might well be a goer...

Unread post by **myglaren** » 07 Feb 2010, 12:28

Could you use solid CO² (-78°C) to shrink the bushes?

Easier to handle than liquid NO² and easier to get hold of I should think. We used to buy it by the pound, like butter, from the now defunct Durham Chemicals, who were only a mile away at the time. Came wrapped in aluminium foil and plastic.

Lasted most of the day if we stuck it in the freezer or wrapped it in thermal insulation.

We only used it to create mist and hoar frost for photographs, not engineering purposes.

BOC or Air Products will likely have it.

addo · Unread post by **addo** » 07 Feb 2010, 20:33

I am not sure if a needle roller bearing is suitable for the ram application. Gut instinct tells me it would risk Brinnelling.

Unread post by **CitroJim** » 07 Feb 2010, 20:37

addo wrote:Gut instinct tells me it would risk Brinnelling.

Good thinking Adam, yes, as it doesn't really rotate, just rocks...

It would most likely eventually suffer the same mode of failure as the 1.9TD/2.1TD Auxillary belt tensioner needle rollers do...

Unread post by **xantia_v6** » 07 Feb 2010, 20:51

The problem with this is not Brinnelling, it is that a needle roller only has one axis of motion. so is no better in this application than a nylon bush.

Assuming that the design needs 2 axis of movement, then you need a different type of bearing.

BTW, suspension bearings don't actually seem to suffer from Brinnelling, it doesn't seem to be a problem with PSA rear arms, and the old Jag IRS uses needle rollers at each end of the lower wishbones and these seem to last OK (until they get water in them).

addo · Unread post by **addo** » 07 Feb 2010, 20:56

They're all primarily in rotation - as I visualise it, the main force vector on an Activa ram lower bush is radial to the axis of fixing. That's creating a lot more impact type events on the rollers.

Unread post by **Dommo** » 07 Feb 2010, 23:02

Shame about that needle bearing, I did realise that needle bearings prefer lots of motion to a little back and forth motion, but they fitted them to quite a few downhill MTB rear shock linkages and they seem to last a few years, possibly not on a car though?

There may be two roller/cartridge bearings you could fit in the ram alongside eachother though? Then it'd be like two sets of bearing races in one, should be nice and strong then?

Also - one other question, today while removing the front ram I noticed that a hose going towards the front brakes was rediculously tight, the suspension as it servicelow and the steering wheel was at full lock to the right so it's at the worst possible place for that hose, but even so Citroen should have accounted for that surely??