Subject: [TR] TR3 rear spring specification

From: "Randall" <[email-masked]>
Date: Tue, 17 Feb 2015 16:23:57 -0800

In the factory TR2-TR3 workshop manual, the rear spring diagram on page H-3 gives the nominal laden camber for the rear springs as
7/8".  But there are two specifications next to that, one for "blue" and one for "red".

Does anyone know what the colors signify?  The SPC does not list any alternate rear springs except the later 330306 passenger side
spring that is supposedly identical to the drivers side except for an added spacer.  The diagram was published long before the
330306 spring was added, so I doubt that is it anyway.

And if there were a performance spring option available (like the front springs), I would expect it to have a different spring rate
but roughly the same ride height.  The workshop manual lists only one spring rate.

I'm trying to work out whether my old springs really were way too soft; or the new springs I got are way too stiff (and ride much
too high).  So I do have a practical application, not just random curiosity.  The fact that a piece fell out of one of the old
springs the other day says that it was probably too soft (cracked), but its mate seems to match very closely with another original
spring that I was given.

-- Randall 

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From: "Randall" <[email-masked]>
Date: Wed, 18 Feb 2015 17:28:08 -0800

> I was also told that most if not all makers of 
> reproduction TR springs just made the TR4 springs because it 
> was cheaper 
> make one set than two sets with different spring rates.

That's certainly a very interesting story, even if it is an old husband's tale.

Anyone have the TR4 spring specs handy?  They don't seem to be in the workshop manual.

I'm not quite done with my experiments yet, but so far both original springs that I have tested are quite close to the TR3 manual
but just a bit stiffer (about 8%, lending credence to Jonmac's story).  However, the new spring checks almost 75% stiffer than the
spec!  (222 lb/in rather than the spec 128)  It seems unlikely to me that the TR4 weighs that much more than a TR3, but maybe the
standard springs were stiffer (relative to the TR3) for more reasons than just body weight.

-- Randall

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From: "Randall" <[email-masked]>
Date: Sun, 22 Feb 2015 11:02:34 -0800

> > make one set than two sets with different spring rates.

Just thought I would follow up to the group with the results of my research.  It turns out that the TR4 spring specs are in the TR4
workshop manual, I was just looking in the wrong place.  According to those specs, the standard TR4 rear springs were the same 128
lb/in rate as the TR3 springs.  The only difference appears to be the ride height, which is just a bit taller (at the same specified
load).  And TRF at least, does supply the TR4 springs to fit TR3.

I've measured the spring rate on several springs now.  The new one I got from TRF several years ago is clearly way, way too stiff;
220 lb/in instead of 128.  'TR4Tony' (a TR4 racer in the UK) has confirmed that this rate is too stiff even for the race track as it
causes the rear end to bounce over the bumps instead of following them.

Two of the original springs that I measured were slightly stiffer than the 128 lb/in rating (140 and 145), which I think supports
Jonmac's report that the US got stiffer springs than the UK did.  I plan to install those on the car in the next few days.

The other original spring was a mate to one of the first two (removed from the same car at the same time) and looked identical to it
in both construction and condition.  However, it was significantly softer than it's mate, only 110 lb/in (which is undoubtedly why
the owner chose to replace them).  The likely explanation, I think, is that one or more leaves are cracked, perhaps only partially.

On a related note, the "too soft" spring that I left on the car while considering the conundrum of why the new springs were so stiff
finally broke, and dropped part of the bottom leaf on the street!  Looking at the break, part of it was still quite shiny,
indicating that part had just broken; while most of it looked rather rusty.  I cleaned and looked for any cracks before installing
it a few years ago, so either it started to crack right after I installed it, or the crack was already there and I missed it.

-- Randall