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MG Midget and Sprite Technical - Another Armstrong damper question

About three years ago I bought a pair of 30% uprated front dampers for my mk3 Sprite from a well known eBay trader and classic car specialist. After about a month, the left side one started leaking from where the spindle protrudes from the damper body, but as I'd only just got the car back on the road after a long restoration I was reluctant to strip it down again, send it back and wait for them to send me another one under warranty, so I soldiered on with it.
I am now in the process of fitting Superpro bushes all round, so I thought I'd try and do something about the leaking damper while I was at it. Judging from the sound of air being moved around inside it when I move it up and down (disconnected from the upright), I don't think there is much oil left in it, although it is still providing some damping effect.

Am I right in supposing that fitting a new seal at the spindle is not a DIY job and am I correct in thinking that when they are classed as being "uprated" it's not just thicker oil but rather different valves and stronger springs inside them? If this is the case, I would consider buying some damper oil from Moss and refilling them both. I can't afford a pair of Peter Caldwell's ones this year, maybe next year, but until then I need to get the car back on the road for this year.
Apologies for such a long convoluted thread.

Bernie.
b higginson

You're right, it isn't a DIY job. Considering it happened almost immediately after buying the shock, they weren't properly rebuilt in the first place. You might check to see if the rebuilder offered a lifetime guaranty (as does Caldwell). If they are reputable, they might still repair the shock under warranty.

Uprated shocks do have different valves. The same fluid should be used as in a standard one.
David Littlefield

David. Thanks for your instant and definitive answer confifming what I thought.
I don't have any kind of receipt and as you mention, they weren't done properly in the first place, so I doubt if the warranty would be a lifetime one. They only cost £80 for the pair, so I guess it's a case of you get what you pay for. But I will get a pair of Caldwell ones eventually. A freind of mine has just done it and the price worked out favourably compared to a new set from Moss even with surcharge for the exchange core units not being practical to send to the States factored in. The guaranteed no leaks was worth the little extra that was paid.
I think I'll repaint them, fill 'em up and put them back for another year.

Bernie.
b higginson

How are they assembled, that makes disassembly a "not a diy job"?

Just wondering.:)
Lawrence Slater

Lawrence. I meant that fitting a seal at the spindle is not a DIY job as I think it may involve special tools. I've seen a few comments on here over time to that effect, so I assumed it was true. If you or anyone else can tell me different and how to do it, I'd be very grateful as I'd love to stop it leaking.

Nice pic of your car in the shop window in MASCOT by the way.

Bernie.
b higginson

Here is a description of what Caldwell does for the shocks that he rebuilds.

http://www.gerardsgarage.com/Garage/Tech/ShoxWS.htm

Note that the shocks were originally designed to leak to lubricate the bearings. Often, fluid was not replaced quickly enough, which would result in damaged bearings, then heavier leaking, then more severely damaged bearings, etc.

Throwing in some packing or washers may slow the leaking, it won't stop until the shocks are rebuilt properly, which requires machine work and specialist knowledge. Much more than just a matter of replacing some seals and washers. Hence, not a DIY fix.
David Littlefield

here is a decent link describing their construction:

http://mgaguru.com/mgtech/suspensn/fs119.htm

one of the biggest challenges regarding DIY damper service is that the arm is pressed on

and here's a link to the best source for dampers these days:

http://mgaguru.com/mgtech/suspensn/fs122.htm

Give Peter a phone call, he has posted on the MG Enthusiast BBS several times, describing what is necessary to rebuild them.

hope this helps

Norm
Norm Kerr

Hi bernie,

No I don't know how, as I never attempted it. I really did just wonder, as you mentioned it, why we couldn't do this as a diy job.

If feasable, then I might even go back to the front lever arms, and sell my FL conversion. So I'll have a good read of the links that have been posted by David and Norm.

I've even got two half decent pairs of front lever shocks in my loft to have a play with. :)
Lawrence Slater

Well after reading those links, I reckon I have neither the kit nor the inclination to do a lever arm shock rebuild. Guess the FL conversion is on my Sprite for the duration, until I find something else.
Lawrence Slater

Since the damping effect is produced by the pistons forcing oil through those small holes, why shouldn't they be uprated by simply using a higher viscosity oil?
Guy

Hi Guy,
the problem with using a higher viscosity oil is that the mechanism that connects the pistons to the lever arm is not capable of sustaining the higher forces, apparently it is a different effect, mechanically, when the valving is changed, rather than viscosity.

Peter says that is his theory about why some of the dampers he receives are stripped out inside (and scrap, because of it).


Norm
Norm Kerr

I should come clean on this - the reason I asked the question about using a heavier viscosity oil is because I have done exactly that for the last 10 years on my car. The damping on the front is very firm, the shocks don't leak and haven't blown up or disintegrated! One of these days I may try disconnecting the top trunion and just test to see how the lever arm feels when moved by hand.
Guy

Bernie

Assuming that you do have properly uprated valves, would it be worth getting a good non-leaking damper and swapping the valve over?
Dave O'Neill2

Guy and all. The thicker oil will definitely stiffen the action, but, it will have some undesirable effects, too. 1) It can get quite hot in use and might cavitate to the point of no resistance (usually about 20 minutes into a race). 2) We have seen stripped splines as Norm states, and while not exclusive to shocks with gear oil in them, it's pretty reliable. 3) Also, there are poppet valves in the bottom of each piston that allow reverse flow of oil through the piston as it moves away from the valve. We have observed that those shocks with "blown-out" poppet valves, where the ball and spring have come out are also almost exclusively on shocks with heavy oil. There are 3 different styles of poppet valves, and one looks to be better than the others, so if you have those pistons, you may be OK.
One issue peculiar to Spridget front shocks is the cylinder walls wear more than on most other Armstrong shocks... akin to an engine bore, there's a ridge that forms at the top meaning piston to bore clearances have increased. Perhaps heavier oil will "solve" this in the way 50W engine oil "solves" oil pump clearances?
The best method to stiffen the valving is to work with the valves themselves. It's quite easy on the front Spridget shocks. The rear shocks are more difficult, but in my opinion, they are better left stock or softer than stock.

Sorry to be so long winded. Peter
Peter Caldwell

Peter,
A genuine thanks for your advice. Its easy for shade tree mechanics" to think they know it all but still make big mistakes. My front shocks do seem to have survived my mis-use with heavy oil but I will know better for the future, or when something does go wrong!

My car has been modified bit by bit over the years in all sorts of ways - sometimes I think it would be nice to drive an absolutely stock version in original "as new" condition just to see what it should really be like!

I like that phrase "shade tree mechanic" - pictures of long warm sunshine days - Ahh, if only it were warm enough now to require the shade of a tree when spannering!
Guy

Guy,
I noticed Peter put >>shocks with gear oil in them<< so perhaps the oil you've put in yours isn't quite as thick as Peter was refering to

what weight/grade/thickness/viscosity of oil is in your shocks (whooops, sorry dampers) are you using
Nigel Atkins

50:50 mix of 20/50 and STP

Had to look up what I had used in my car notebook.
Guy

I happen to have driven a standard midget recently...
Wow what a change!

Bodyroll in corners
Rear squating under acceleration
And the front diving when on the brakes

But it was a lot more comfortable over bumpy roads.
Comfortable over normal roads to but I just could not carry the same momentum through the corners.

Altogether a very fun exercise.
But I am happy with the changes I made
Onno K

Guy,
an interesting mix, I no idea what weight the STP would equate to but 20/50 at least isn't in gear oil territory, if I'm right in think 75-90 region

I might be wrong, again, but standard shock is 20(?)

if you've used this mixture in the same shocks for 10 years and it's worked then it's a real world test, if the shock and then no good for rebuild later they're no worse that lots of others that can't last 10 months let alone 10 years

Onno,
you must be light I've never noticed the rear squating under acceleration when driving a Spridget
Nigel Atkins

In the '90s "reconditioned" dampers sold at £9.95 each. For that price, I doubt that they had any more reconditioning than a quick clean and a thin coat of black paint. The uprated ones sold for £12.95. I guess the extra uprating related to the use of red paint instead of black.

Oh, and STP has the pouring viscosity of Golden Syrup. But I haven't tried that in shock absorbers(yet).
Guy

This thread was discussed between 31/01/2012 and 01/02/2012

MG Midget and Sprite Technical index

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