Green Machine Front Damper Replacement

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Spacenut
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Joined: Thu Feb 20, 2014 9:43 pm
Location: Hampshire

Green Machine Front Damper Replacement

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Some of you with long memories will remember that I changed my old SPAX rear dampers for AVO double-adjustables back in 2016. You may also remember that the replacement was not straightforward, with the SPAX dampers being pin mount and the AVO using spherical bearings top and bottom, which meant welding in new top brackets.

The front damper replacement was no less problematic, perhaps one reason why it has taken me so long to get around to doing it. I initially ordered the AVO dampers through Demon Tweeks, but the dampers that arrived, although correctly labelled, were in fact a different specification; the open length was 2” too short and the dampers were designed for 2.25” diameter springs instead of the 1.9” diameter springs I use. Having returned to dampers to DT I re-ordered and received exactly the same type again. In the end I went direct to AVO, which in hindsight I should have done in the first place, and received exactly what I asked for a few weeks later. However, that was not the end of the story, as comparison between the new damper and the old SPAX unit revealed that the open dimension between the spring mounting plates on the AVO damper was smaller than the SPAX unit, which necessitated the purchase of a new shorter coil spring with the same spring rate (225 lb/in).

Here are the two assemblies, side by side.

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Furthermore, using spherical bearings instead of the SPAX rubber bushes necessitated the use of spacer bushes, which you can see here…

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These were purchased from DT at the same time as the dampers. Now seemingly on the home straight, my next discovery was that the damper mounting brackets on the lower wishbone were not tall enough to accept the AVO bearing carrier, and worse still, the damper fouled the suspension upright at full droop…

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Unfortunately the solution to this problem required modification of the wishbones themselves, not an option to be considered lightly – once the original brackets were cut off, there was no going back. My chosen solution would have to work, otherwise the car would be unusable.

My plan was to purchase a pair of universal damper mounting brackets (the same Allstars ones that I used for the rear suspension upgrade), which would have to be welded on to the lower wishbone once the original brackets had been cut off. As the lower balljoints have been on the car since the chassis was built in the early 1990s I thought I would replace them too. The balljoints are from a Mk4 Cortina, modified to remove the large cast extension and located with 3-off M8 bolts. The third bolt isn’t strictly necessary to locate the balljoint, so this time around I decided to omit this bolt, which would also provide more clearance under the damper.

A pair of new Quinton-Hazell balljoints were purchased, and we modified as shown…

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Then it was just a simple matter of removing the lower wishbone – two spherical bearings attaching the wishbone to the chassis, and pop off the balljoint with a balljoint splitter. How hard could that be?

For the OSF, no problem at all. The balljoint popped out of its taper with only a modicum of persuasion from my trusty balljoint splitter. Once on the bench, I removed the old balljoint from the wishbone, took a deep breath and cut off the damper mounting brackets. I then ground off the old welds and smoothed off the surface ready for the new bracket. This would have to move further inboard compared to the old mounting location, so the new brackets would overlap a reinforcing bar, so I notched the bracket base first.

I tack-welded the bracket to the wishbone and then reassembled to check clearances…

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As you can see, there is now adequate clearance between the upright and the damper, and the brake pipe bracket does not foul the knurled bump adjuster either.

Confident that I now had a solution, I seam-welded the bracket into position and plugged the redundant balljoint mounting hole at the same time. The quality of the welding is up to my usual standards (rubbish), but one thing I can say with complete confidence is that the brackets are not going to part company with the wishbone anytime soon!

I cleaned off all of the old paint and rust from the wishbone before priming and painting it, ready for reassembly the following day…

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Quality work I think you will agree :D

After some careful reassembly to ensure the fresh paint didn’t get chipped or scratched, the end result looks like this…

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After the success of the OSF modification I thought the NSF would be even more straightforward. How wrong I was. The bottom balljoint wouldn’t let go, so in the end I had to remove the brake caliper and the disc and hub assembly to gain access, and then cut off the balljoint taper with a hacksaw. This allowed me to remove the wishbone and do the necessary modifications, but still left me with an upright with a taper stuck in it :(

The removal of the old damper bracket and the welding all went smoothly, and by the end of Day 2 the OSF wishbone was ready to refit, so I turned my attention to the upright. Now on the bench, I showed it some heat, bashed it with a hammer and tried pressing out the remains of the taper with a bench vice, all to no avail. Some research on T’internet revealed that the method of choice was to bash the upright with a club hammer, which physically distorts the forging and pops the taper. Never fails, they all said. Still sceptical, I called my friend Sean (also conveniently on holiday this week) and asked if he could bring his hammer...

Less than an hour later, the taper was free and I could get on and rebuild the NSF suspension! Just a couple of minutes with the club hammer was all that was needed. What a relief! A quick check of the taper bore showed signs of corrosion which was either the cause, or a consequence of the stuck balljoint. Either way, I cleaned the taper bore thoroughly to make sure it didn’t happen again.

With the modified wishbone fitted I could build up the suspension again. First the upright, followed by the new damper, then the brake disc and hub, then finally the brake caliper.

Once back on 4 wheels it was clear that I had overcompensated for the re-positioned damper brackets and shorter springs – the ground clearance under the front axle was a mere 2”! Great for a circuit racer, but hopeless on the road. So it was off with the wheels again and wind the spring plates up a bit.

A quick run around the block to settle the suspension and my original 3.5” front ride height was restored. Barring some minor tweaks to level each side we should be good to go, once I can find some more super unleaded fuel that is :D

I have left the bump and rebound settings on full-soft for the moment. This corresponds to a standard off-the-shelf damping ratio, which is typically around 3:1 rebound-to-bump. If that proves to be too bouncy I will dial in some more rebound, but I need to get some miles on the clock first.

Damper replacement finally completed!

Lauren

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