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Leaf Spring Sag

Keep it pinned to the road.

by dinofritz » Sun Jan 04, 2015 11:14 am

Hi everyone,

Oooh - I have the first post for 2015 - Happy New Year everyone, and another new job for the Interceptor.

While I'm fitting the new 17 inch rims and brakes and have the car up on the stands, I'm looking at the rear leaf springs and I've noticed that the passenger side's sagged (again). Roger Carroll had a look with me and suspects that the leaf spring wasn't properly hardened.

More than likely, I'll need to have them both out (again) to reset the offending spring, but rather than send them back to the same place (again), I think that I may try another spring / suspension place to try and break this cycle and get the job done correctly.

Now, my 74 Mk III has a total of 9 leaves, and I remember that some of the Adelaide owners had Southcott Engineering reset their springs in the 90's and added another extra leaf (supposedly, Southcott had the specifications all documented in their records, which corresponds to Richards comments re. the FF rear suspension). Only problem is that Southcott closed down around 5 years ago here, so I wonder if anyone in Adelaide (or indeed Australia) may have kept their specifications to upgrade to a 10 leaf setup.

Only other question - I seem to recall another restoration recently which showed an immaculately restored rear suspension with 11 leaves!

Does anyone have any specifications to properly upgrade / restore (even remanufacture if needed) the leaf springs, or have anyone in Australia (preferably Adelaide) who could do this upgrade (I'd prefer someone as close as possible, as originally the local shop needed 3 attempts just to get the rear springs correctly reset 1 inch lower than standard). I'm seriously considering fitting the coil over shocks if this turns out to be big $$$ again, or more hit and miss fitment with an untried supplier unfamiliar with Jensen's.

Your thoughts and experiences are welcome, over to you,

Cheers, Dino
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by Paulio » Wed Jan 07, 2015 3:38 am

Dino I don't like your chances, a friend just had his leafs done (or redone if you like) on a 35 Chev tourer and had them back 2 or 3 times with not much luck. I'm wondering if your not better off getting a new one made up or putting those adjustable coil over shockers in with the leafs so you can set the height?
cheer,
Paul
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by dinofritz » Wed Jan 07, 2015 1:06 pm

Paul,

What you have described is EXACTLY what happened to me around 15 years ago when I was finishing my car and had a local spring maker reset my rears 1 inch lower - it took them 3 iterations to get it right (and I was the bunny who took them home and refitted and returned them each time)!

Two years later and with me setting up the wheel and headlight alignment, the shop noticed that the passenger side rear spring had sagged 15mm, so off it was again to reset. And now, it's the same spring, and Roger Carroll and I believe that the spring wasn't properly tempered the last time.

At least I'm glad that I've discovered why my rear end is so soft - it should definitely have 10 springs (mine has 9), and some owners have fitted an 11th leaf to give improved handling.

I may have a chat to one or two other leaf spring shops here to check their experience and willingness to help (and the final $$ factor), because I may be seriously tempted to go down the coil over route if needed.

Cheers, Dino
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by hemi » Sat Jan 10, 2015 7:26 am

Hello all.

Dino - this may well be one of those annoying replies that does little to address your query, however.....

MINES GOT TWELVE LEAVES !!!! and no evidence of a tow bar or entry stickers to the Baja 1000!

Eleven leaves appear to be of the same gauge, with the lowest being a bit thicker and only about 250mm long.

The car sat up pretty high (for my liking) but I was told it had the correct stance/height for a Mk2. Anyway, I've since dropped it a bit to suit new tyres and now it looks more the ICBM (Inter Continental Ballistic Missile) an Interceptor should.

My workshop manual (Mk2,3,with SP and FF inserts) is the same as the one you've posted.

Also, I built up a V8 Capri in the early 2000's and getting the rear springs set at the correct height was a 3 time job - at Lovells Springs in Strathfield (NSW) - since moved. So perhaps the coil overs may be the best bet...

All the best,

Matt.
Interceptor II
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by dinofritz » Mon Jan 12, 2015 1:56 am

Hi Matt,

12.........aargh!!!

The more that I'm speaking to leaf spring manufacturers, the more that I'm seeing that resetting the springs is a bit of a dark art, with an element of experience, experimentation and trial and error involved.

One of the shops clued me in on this when I was discussing leaf thicknesses, when I gave them the measurements (inches), they converted back to metric (mm's), and said "oh, we'd probably remove two of the imperial thickness springs and fit three metric leaves to get near the same result".

But can it really be that hard to get things close (or even exactly correct) - Rik and I were discussing that they replaced the 2 inch wide leaf springs on his with 50mm wide ones. Normally I think that 0.8 of a mm would be a close enough width, but we do live in an age where metals can be plasma and laser cut to incredible tolerances, so is a 0.8m difference really that hard to achieve?

Anyway, more on this soon - I'm learning a lot about parabolic leaf springs at the moment and I think that this is the preferred way that I would like to go (if I can find anyone in Australia that makes them)!

Cheers, Dino
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by Paulio » Mon Jan 12, 2015 5:47 am

I'm going to play the devils advocate here Dino, have you considered carbon fibre leaf springs- they're just starting to enter the market, already used in the current corvette I think. If you could obtain a set of those to fit ...... lighter, stronger, more progressive, no rusting ...etc. Just cost I'm guessing?
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by dinofritz » Mon Jan 12, 2015 7:18 am

Actually, yes (but still waiting on a reply from the manufacturer):

http://www.owensprings.co.uk/carbon-fib ... f-springs/

It actually looks like there is no-one with the capabilities to manufacture parabolic leaf springs in Australia, so I'm searching further afield.

Owen Springs are one that I've contacted last week (as they mentioned that they are the only UK based manufacturer of parabolic springs), plus they mention that they have the specifications and drawings of thousands of classic vehicles, but the carbon fibre / composite springs have me wondering.............

Will keep you all informed,

Cheers, D
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by Paulio » Mon Jan 12, 2015 9:52 am

Great! I'm always up for someone who can afford R&D both fiscally and mentally for the group :lol:
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by hemi » Mon Jan 12, 2015 8:51 pm

Didn't the Channel 9 Camaro, driven and largely built by Kevin Bartlett, have fibreglass (leaf) springs ??

Matt.
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by Interceptor3 » Tue Jan 20, 2015 5:53 am

That reminds me, I must do something about my coilovers, and fixing the squeak in the back end. And the runout problem on the back brakes...
Nigel Honey
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'08 Mitsubishi Lancer Evolution X MR
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