Can anyone tell me what gives away a hydro upper arm from a dry apart from the mounted bumpstop? Measurements, obvious features etc..

I don't have two to compare against around the garage, and I have it from a hydro subframe converted to dry. I'd like to make sure I am refurbishing the right type of top arm...

_________________
SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

A dry arm has the shocky bolt hole a loose fit on a 3/8" bolt (I guess 10.0mm diameter).
A virgin hydro arm has a hole about 8.5mm diameter.
But if it's been drilled out it's hard to tell from a dry arm.

If you have one of each to compare, the big knuckle joint hole on a dry arm is slightly closer to the top pivot shaft.
Some racers use hydro top arms instead of dry, as it increases the spring rate a bit.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Yeah, I've checked the holes and they look pretty vigin with no signs of a dodgy drill going through or a burr. I'll have to see if I can find a dry arm to compare against.


Now I've blasted the bare arm back, the number can be seen - 21A1480 so I'll see if I can't find a part number reference.

EDIT: Well from the CD reference it has 21A611 and 610 (Right & Left). Though it shows a dry suspension in the diagram it is supposed to be for Cooper S as well....hmmm

_________________
SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

In the Mini Kingdom book the number is close to a hydro one 12A1482 or 12A1479.
Cheers Pete

_________________
A recent study found the average Aussie walks about 900 miles a year
Another study found Aussies drink, on average, 22 gallons of alcohol a year
That means, on average, Australians get about 41 miles per gallon

Kind of makes you proud to be an AUSSIE

My Mini Car Clinic book says
dry- 21A2690, 21A2691
hydro- 21A1479, 21A1482.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Definitely a 1480 on the arm I have blasted back, but will take that as a hydro from those numbers as they are far removed from the dry type numbers.The knuckle joint looks like it is spaced out a little further (6mm (ish)) from the inner edge of the machined pad.

_________________
SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.

It was common BMC practice to make part numbers and casting numbers 1 or 2 apart.
eg the C-AEA648 or 649 cam.

_________________
DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.

Yep that makes sense now that you have mentioned it. Thanks for the support.

In goes the new needle rollers!

_________________
SooperDooperMiniCooperExpertEngineering

All garage work involves equal measures of enthusiasm, ingenuity and a fair degree of irresponsibility.