Experience with Spax rear shock absorbers

Andy Torode was faced with replacing his worn out telescopic shock absorbers and posted a message on the V8BB in May for some help. This note sweeps up the postings and later email from Gordon Hesketh-Jones. (Jun 07)

I have a Spax tubular shock absorber conversion on my MGBGTV8 fitted some time ago and they are on their way out. I obtained a set of Gaz shocks to change them over, but they do not appear to be long enough. The Gaz shockers are 17.125" from centre to centre of the holes fully extended, but the existing Spax must be an inch longer measured on the car - good job I checked before getting them off! My car was a 1973 car but was re-shelled into a rubber bumper body at some point and the ride height is quite high. Can you get replacement shock absorbers in different lengths to cover the different heights? Moss and MGOC seem to have a "one size fits all" approach according to their catalogues.

Gordon Hesketh-Jones responded: "Some 5 to 6 years ago I carried out development testing for Spax and fitted seven or eight different pairs of prototypes to my chrome bumper MGBGTV8, then reported the results to Spax each time after approximately 500 miles. I still have a few pairs in my garage and they measure from 13.75" up to 15.75" centre to centre. How were you measuring the Spax - were they compressed/static or was your car jacked up?

The old Spax which I first fitted 15 or18 years ago were indeed very long and could be seen to be sticking out below the bottom of the rear springs. For all modern telescopics you need to take off the plates under the springs and reverse them side to side. This is a complicated procedure but I can send you step by step instructions if you let me have your email address. Pretty well all after-market shock absorber manufacturers produce upper mounting plates with the stud boss off centre, so that reversing the plate will usually cope with 1" to 1.5" of different shock absorber length. On the Bilstein, Koni and Spax fitting instructions, the MGB/MGC require the longer operation, but on the rubber bumper MGB and all MGBGTV8s they require the shorter operation.

Recently I fitted a pair of Spax to my wife's rubber bumper MGBGT to replace the Bilsteins and the improvement in ride is unbelievable. The chief engineer at Spax is very helpful - you can contact him at tony_shakeshft@spaxperformance.com if you feel you need more help. I could bring a free pair to Silverstone next month if it would help - but don't mention this to Tony!"

Andy Torode replied "my shock absorbers do indeed extend below the springs when viewed from the rear. I do not know how long ago the kit was fitted. The measurements of the existing setup mentioned earlier were taken with the car up on stands placed under the front spring hanger, and the rear axle hanging against the straps."

Gordon Hesketh-Jones provided more information on his experiences with Spax shock absorbers as a follow up to the information requested by Andy Torode: "the original "long" Spax were purely based on oil and its movement between the various chambers under compression. They worked fine but the problem - for me at least - was the protrusion below the rear springs which regularly became damaged in rough-road driving in rallies and tours. At that time Spax did not make shorter versions, so I first tried Bilsteins and then Konis - but when combined with our 550lb rear springs both of these induced an incredibly harsh ride

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even on motorways, together with equally strong complaints from my wife. Spax then produced their early "shorter" versions and I bought a pair - the ride was greatly improved compared to the Konis and others but there was a serious "chattering" noise from the Spax. I complained to the supplier and was sent replacements FOC but the same noise was present. This is when I contacted Spax and then the series of testing started with Tony Shakeshaft sending down all sorts of variations.

Eventually it transpired that the new units, which work on a combination of oil and gas, were setting up a harmonic vibration with reference to the MGB bodyshell; I witnessed equivalent tests at their factory where there was no "rattle" but as soon as we popped the same pair onto my V8 at the factory, the rattle returned. Note however on the later versions I have here, the rattle is only audible when driving at low speeds; at higher speeds the rattle is drowned out by general V8 engine and wind noise. I understand that the harmonic vibrations are smoothed out - but then I am not really a mechanical engineer. The measurements of the units I have here were all taken "static" in my garage - that is not extended as per your V8BB posting.

To fit the new shorter Spax you have to take off the spring retaining plates from below the springs then swap them side to side, mounting them "upside down" with the hole for the old lever shock absorber drop arm now at the front, and pointing down. What can happen when you do this is that the whole spring assemblies can come apart and getting these hefty items together and back into place again is a pretty frustrating and time-consuming task. To avoid this I have evolved the following process from fairly bitter experience:

1. Jack the rear end up with your jack under the differential, then use axle stands to keep the axle up as high as possible.

2. Next, use two more axle stands (or substantial blocks of wood) to support the spring on the side you are starting first, say 3" either side of the link (retaining) plate - these stop the spring on the side you are working on from coming apart.

3. One more support - use yet another axle stand/set of wooden blocks under the brake drum of the side you are not working on - if you do not do this then as soon as you undo the last bolt on the side you are working on, then the whole axle will tip over with your side going up in the air and the U-bolts will come out of the assembly giving you much grief. Use chocks of some form to make sure that items (2) and (3) above are really tight up against the spring or brake drum.

With the five supports in place you are ready to start, however note that if the long U-bolts which secure the spring assemblies are worn on the inside, then torque-steer will result so it might be a good idea to buy a set of these before you start, and to change them one by one as you work on each side. I am assuming that the existing Spax brackets at the top will suit the new Spax units - in my experience the brackets for the modern Spax, Koni and Bilstein are very similar and can be interchanged. I do not have any spare top brackets.

As mentioned previously, the units I have in stock are prototypes so will give a light rattle at low speed - I just ignore it because I know that the shock absorbers work perfectly. I do have a spare set of link plates which I could lend to you but it would be essential to have your own pair back in exchange - with a spare set it means that you can finish one side totally before rearranging all of the supports".