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MG MGB Technical - Lever Arm Damper test

Hi All

The rear end of my GT has felt like a space hopper recently. Suspecting that the lever arm dampers were implicated, I disconnected the drop links and moved the arms up and down to try and assess them. They seemed weak but I couldn't quite be sure. (Long time since I fitted them. Terrible memory.)

So, having bought some recon units from Moss, I thought it might be useful to find some numbers which would indicate effectiveness, for future reference.

In the spirit of improving the sum of human knowledge, this is what I found. With each damper clamped upright in a vice a 10lb weight (e.g. sledge hammer head) took the following times to pull each lever from the top of its range to the bottom:

Old N/S damper 6.5 secs
Old O/S damper 5 secs
New N/S damper Infinite (it never reached the bottom)
New O/S damper 28 secs

Hopefully this info will be useful for others too!
T H Brearley

Thanks for that.
paulh4

I’m not sure what that tells us about your new n/s damper.
Dave O'Neill 2

Great thread idea and information.

But have I misunderstood things as that all sounds bad to me, I was concerned about all the dampers but particularly the new O/S damper as I thought it takes great effort to move the arm, 10lbs doesn't sound a lot?

ETA: - found it, JT vid, see 0:54 in - https://www.youtube.com/watch?v=ZKrQAi4V2Iw

Nigel Atkins

More than 10lb would be required to move it quickly, but in theory any weight enough to overcome the mechanical friction should move it.

The point Dave is making that at some point - hopefully near the end of travel! - the mechanical friction is overcoming the test weight on that one damper.

Personally for rebuilt I don't see it as that bad - as long as with some additional force it did continue to move. It's how soon in its downward travel it stopped, and how much additional force was needed to get it moving again, that is important.
paulh4

Fair enough, 10 lbs just didn't seem that much to me, and with your explaining I see Dave's point about the new nearside damper.

I wonder how they'd compare with a set from Peter Caldwell, or Stevsons or a new set from Moss.
Nigel Atkins

Yes I should have said that the O/S damper moved slowly through the first 2/3 of its stroke before stopping. It could be pushed all the way down with a firm hand.

I chose 10lb because it gave a reasonable number of seconds to measure. It is actually quite heavy. Try throwing a sledge hammer around.

Nigel - I have to defer to John Twist, but maybe the rear shocks are designed to be a little less firm? I agree, figures for a brand new (not recon.) damper would be interesting to compare.
T H Brearley

10 lbs is very heavy to me now, although only a fraction of the weight of my one of wife's kitchen-sink-and-all handbags.

I wondered if the rear GT damper might be different to roadsters but see they're not and looked at Paul's site for model variances.

Paul,
unless this experiment was also carried out in October 2009 you've got the date wrong.
Nigel Atkins

I have some NOS rear dampers, so I’ll see if I can find a suitable weight.
Dave O'Neill 2

That'd be really interesting Dave.

Decades back I'd have loads of small lbs and kilo weights at home but that was a different lifetime.
Nigel Atkins

4.5 litres of water weighs 10lb, near enough.
T H Brearley

Surely you'd use a (UK) gallon. :)
Nigel Atkins

Which was exactly 10lb, as originally defined.
paulh4

Did the same thing a few years ago, more to match a pair rather than to compare new against old.
1. I used an MGB flywheel which gave me decent fall rates.
2. Compression and rebound are set to different rates, so you are measuring rebound.
3. I put a pulley on a roof beam and did the same thing but pulling the lever up.
I did know at the time what the proportional difference was, but can't remember.

It's not a difficult job to alter the damping piston spring rates.
Look at The MG Guru, he has a detailed account.
Allan Reeling

OK, I’ve checked a couple of NOS dampers. One took 11 seconds and the other took 9 seconds.

I used a Lucas M35J starter motor, which weighs 9lb 12oz.
Dave O'Neill 2

I installed BIlstein rear shocks from Moss after blasting through the cheaper one that uses Monroe shocks (junk). This changed the handling characteristic completely, especially cornering. It can be rough on the kidneys but it is a much more stable ride than the lever shocks.

I added a leaf to the springs the last time I had them arched. After about 50,000 miles, the ride height is perfect.

I have run Koni tube shocks on the 1971 Midget since 1976 and also found the handling greatly improved.

Glenn Mallory

Well that's muddied the waters Dave. :)
Nigel Atkins

Bilstein fan at last -best thing since sliced bread--welcome that man--I had 5 of them on my midget racer

Back to lever arms
This measuring with a weight is ok but you have to realise that you are measuring rebound with this method not actual bump, to measure compression you need to rig up a lever that swings out the other side of the shocker
Rebound is usually quite a bit stiffer than bump
Rebound should be set so that if you push down on the car it returns back to normal hight, if it returns and bounces up past ride hight thendown again it's too soft --if it takes anymore than about a second to return it's too stiff it just needs to return up and stop ,no bouncing at the top just up and stop
Compression is set to suit the weight of the vehicle and the comfort level required, usually the softer the better
If you remove the valve assy from the shocker and have a peep at it,there is a spring with a shaft through the middle with a nut on the end (soldered to hold it in place)
The washer between the spring and the body adjusts the compression-more washers makes it stiffer
The nut on the end is the adjustment for rebound -
tightening it stiffens the rebound--fairly touchy adjustment, 1/2 a turn makes a noticeable difference
Bump dampening is usually around a 1/3 of rebound stiffness
It's a messy job ,but with the shock out of the car mounted up on something it can be an interesting project matching a pair of shocks
William Revit

time beat me--
2 springs in there-
the outer spring and washer is the compression adjustment , the inner spring and adjusting nut for rebound

willy
William Revit

What weight oil should go in these shocks?

Cheers

Gary
79MGB
gary hansen

Not generally oil, but hydraulic fluid. The WSM states "Armstrong Super (Thin) Shock Absorber Fluid No. 624. (If this fluid is not available any good-quality mineral oil to specification SAE 20W can be used, but this alternative is not suitable for low-temperature operation)."

I use hydraulic-jack oil, despite claims of it 'foaming' which I've never been aware of, I'd have thought foaming in a jack would be more of an issue. Others recommend motor cycle fork oil as it apparently has a seal-swelling agent.
paulh4

Gary,
a copy and paste of a previous post of mine elsewhere -

>>Opie Oils - "The SAE figures give a good guide to relative oil viscosities, however, the ISO figures, related to the true viscosity at 40°C, give a more accurate assessment of damping capabilities."

Peter Caldwell of World Wide Auto Parts (USA) who used to post on here and is very well respected for his better than new exchange service on LA dampers cautions about using thick oil, 30w max (I know you put 15w).

"Stick with the 20W oil recommended (AW68 spec). At most use 30W (AW ISO 100) Best are synthetics like Silkolene or Redline suspension oils. They hold up under heat waaaaay better than standard hydraulic oils.... and these shocks get hot."

AW I think means anti wear, AW68 would be AW ISO 68 and 15w is shown as ISO 46.

IIRC Peter said there were several ways of mechanical uprating (not oil) but IIRC for DIY heavier valve springs (but as always don't go on my memory).<<
HTH


Nigel Atkins

Nigel, et al:

IIRC, the use of different hydraulic fluid "weight" was mentioned as a way of attaining different ride and handling characteristics.

Cheers

Gary
79 MGB
gary hansen

Gary,
it often is but I don't think that's the correct way to do it, think revalving is the way (it'll be in the Archives) or Malc Le Chevalier on S&M section does info (and kits again?) for Spridgets.

Just to confirm for oil -
Peter Caldwell posted -
"Stick with the 20W oil recommended (AW68 spec). At most use 30W (AW ISO 100) Best are synthetics like Silkolene or Redline suspension oils. They hold up under heat waaaaay better than standard hydraulic oils.... and these shocks get hot."
Nigel Atkins

Silkolene 20w Motorcycle fork oil, is what I use. Heat stable, unlike the original!!
Allan Reeling

This thread was discussed between 26/06/2020 and 03/07/2020

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