> > My TR6 lever shocks are tired and worn out. They just don't dampen
> > enough.
As the resident pedantic word-weenie, I'd like to put in my spit-in-
the-wind comment about "dampen." Yeah, I looked it up to make sure,
and "dampen" is an acceptable word to use for describing what the
Armstrong levers do. But so is "damp," and I'd like to enlighten
people on why I think it's a better choice. "Dampen" is ambiguous,
though of course with Armstrong dampers both meanings apply: it means
to apply an external force that asymptotically reduces oscillations on
a moving object, or it means "to wet." The verb "to damp" means only
to apply this "damping" force.
Besides, shocks are called dampers, not dampeners, so it seems more
logical that they should damp, not dampen. Besides, it's simpler.
End of pedantry. Shall I bring in the port now, Mr. Wooster, sir?
> > Question: can I put in some "thicker" oil and compensate
> > somewhat for the worn out innards? My friend Bob tells me I can try
> > heavy duty shock oil for starters. Anything else anyone has tried?
> >
> > jim
>
> leaks in the lever shocks. Reasoning that thicker oil leaks out slower
> than that thin stuff in there, I topped them off with STP.
> This did two things: it slowed the leaks quite a bit, and made the dampers
> _much_ stiffer :-)
And it also dissolved your shocks' internal seals. It does give
stiffer damping, but only till the shocks come apart. Mineral oil
(motor oil, which is the base stuff used in STP) eats shock seals.
You can use motorcycle fork oil or the oil that goes in hydraulic jacks,
but there are a couple of problems with that approach. The main problem
is that lever shocks were designed back in the days when the valves were
sloppy but they made up for that with thick goop that took a long time
to work through the valves. Standard shock damping fluid is about equivalent
to a motor oil with a viscosity rating of 20; running shock oils with
viscosities up to 50 will stiffen your old Armstrongs up to racing levels.
There's a price: if it's cold enough (under about 40 degrees F), the 50-
weight shock oil solidifies like butter in a sclerotic artery, with similar
results: you can actually break suspension components because the shock oil
is thick enough that it effectively freezes.
The other problem with 50-weight shock oil is that basically, nobody
makes it any more. Shock technology has been gradually moving in the
direction of more precision in the shocks, letting the valves in the
dampers do the work rather than the thickness of the oil. This means
that modern motorcycle forks, for example, are designed to use zero-weight
oil, something that will provide roughly zero damping in an MG or TR.
For now, there are several options with your old lever-shod cars:
1. If they're leaking and worn anyway, go ahead and put in STP, what
the hell. You'll be replacing shocks every year or so anyway if you
race it, so you might as well make it really stiff and figure you're
paying Apple Hydraulics for the new seals anyway. This is the cheapest
but it's really sleazy.
2. For about $21 per corner, you can buy new high-performance shock
valves. These are original-type Armstrong valves that ahave been
adjusted to give stiffer damping. I've got a set at home that I need
to install and evaluate for a future article on MGB suspension. Can't wait.
They're definitely the cheapest non-sleazy solution, as it's less than
$100 for something like a 20-25% increase in damping stiffness. It's
also the only choice for a really careful vintage racer, as it duplicates
what would have been available in the Sixties.
3. For closer to $100 a corner -- and I'd love to have a pointer to these
people, as I've lost my old one -- there's an outfit in the Pac NorWest
that was developing reed-valve inserts that would replace the stock valves
in Armstrong dampers. These new high-tech reed valves have much faster
response characteristics; the spring-loaded valves in the stock dampers
basically become rigid at any frequency over something like 100 Hz, while
the reed valves can handle several hundred with much greater accuracy and
virtually no foaming. But in addition to the high-priced hardware, you
have to have your shock bodies machined to fit the reeds. (This place was
also trying to produce 50-weight synthetic shock oil, but I haven't
heard from them in a coule of years.)
For the interim, just be sure you have fresh fluid, and a full charge
thereof, in the shock body at each corner. You might be surprised at
the difference when you fill each shock; I know I was.
--Scott
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