Hydro vs rubber top arms

[66S]

Hi guys,

Apparently there are dimensional differences between Hydro top suspension arms and rubber. It is said that using Hydro top arms with rubber suspension gives negative camber. I think that some cars left the factory with incorrect arms (1071's??). Has anybody got any knowledge of this?


Regards

Al

[Henry]

I don't believe there is any difference in the length of the arm, only in the position of the hole where the suspension knuckle joint fits. The hydrostatic arm supposedly gives a firmer/stiffer suspension if used on a rubber cone Mini.

[Vegard]

But, obviously, the fitting if harder springs would have the same effect.

[guru_1071]

But, obviously, the fitting if harder springs would have the same effect.

thats not correct.

the knuckle is in a different place on a hydro arm compared to a dry one, so its the leverage that alters, so its the ratio of increase in stiffness vs position of the arm that alters.

[Vegard]

I agree.. However, is this something that we "need"?

[ivor badger]

Its not just the leverage, but the angularity is different. If you fit hydro arms to rubber car, it ends up on the bump stops before the spring gets near to taking the load.

[Tim Harber]

I agree.. However, is this something that we "need"?

Yes, of course you need them

Let me think , where could you buy them? Try Googling 21A1479 and 21A1482 (the arms)

My question (sensibly) is:

If the car was homologated as hydro (1275), does this not mean that any car that is converted to dry is
A- illegal for Appendix K racers
B- Should use all dry parts (like suspension arms)or can use a combination

Or is it a case that it was homologated dry (1071) and you are allowed any dry period parts

It occurred to me whilst building my new car as it came with a selection of Hydro and dry parts. The front subfame was hydro converted to dry , but the (deceased) owner had put the spacers between the top of the towers and the bulkhead(Dry only) and had forced (1977 on) teardrop mounts between the front panel and the front subframe as he must have felt this was part of what was necessary. Talk about wrong end of stick

[mike owen]

I use the hydro arms in my racer with hi los. The buffer under the arm must be much bigger or the hi lo can fall out of the donut when jacking up.
Mike

[sandman]

Mike, this problem occurs with dry arms too.... however the hilo's will need to be shorter with hydro arms.

Tim,
The 1275 S (FIA form 1300) was initaially homogated with dry suspension. The hydro stuff was ammendments homologated later - in Nov 1964.

Ivor, i think you got it the wrong war around... on hydro arms the leverage is greater so the trumpet will actually start pushing on the cone *sooner* - meaning your (dry) bumpstops will be way to short..

[ivor badger]

Mike, this problem occurs with dry arms too.... however the hilo's will need to be shorter with hydro arms.

Tim,
The 1275 S (FIA form 1300) was initaially homogated with dry suspension. The hydro stuff was ammendments homologated later - in Nov 1964.

Ivor, i think you got it the wrong war around... on hydro arms the leverage is greater so the trumpet will actually start pushing on the cone *sooner* - meaning your (dry) bumpstops will be way to short..

It was a long time ago. but I remember it didn't work and the failing memory says it had the suspension too low. If you used hilos screwed right out it might have worked, but my hilos couldn't do it.

[PatM]

Just to help those that are reading this topic and perhaps don't understand what is being said.

[mmm850]

I have a pair of arms with these numbers on them 17044z24jg3b and 17043z43jg3b are these hydro ?

[Spitz]

Well I'm watching this with interest now.
I have a set of wet arms. It was suggested to me that I fit these to my dry car to improve my track day cars handling.
( hinting that it either stiffens the suspension or gives neg camber ).

[mmm850]

Have you seen these I think one is hydro and one is dry they do not look the same


http://cgi.ebay.co.uk/ws/eBayISAPI.dll? ... K:MEWAX:IT

[medwaybeat]

I could never get a straight answer on this “racers knowledge” and all that. Fair play, if it gives you the edge why would you share. Vizard says too hard and Bill Sollis says if you can get them fit them. But when I bunged a wet sub frame up on ebay I was asked if I had the arms and sold them to a guy who works a reasonable well known tuning firm. I didn’t ask about set up incase I cried. So I guess if you’re going racing and spending very big money on dampers then yes.

[mmm850]

I have been thinking about this and I think that since the length of the arm is the same it will not effect the camber angle, as long as you keep the same ride hight, it will only stiffen the suspension, this is good for racing in a track but not for road use. (especialy on maltese roads as they are all offroad).