Gearbox and axle upgrades

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Axle Linking

Postby Neilyman » 21 Aug 2005, 11:37

Many Thanks to Harry for this article

Harry Flatters wrote:OK, here's my understanding of the situation - apologies if I'm teaching any grandmothers to suck eggs!

The standard Chevette / Kadett / Ascona / Manta set up is 4 link - two trailing arms, the torque tube, and the panhard rod (Andrew Duerden refers to this as 3 link in the Sportpart Manual, apparently discounting the panhard rod). The trailing arms give forward / rear location of the axle, the panhard rod gives lateral location, and the torque tube prevents the axle rotating around the halfshafts - in the real world this stops the axle tramping. Early Mantas and Kadetts had steel torque tubes (stronger) - these were replaced in later cars by alloy torque tubes to reduce weight. The Manta B might look as if it’s got more mounting points than the Kadett because of the big wide torque tube bracket they use, but in fact they’re the same.

The Chevette HS was built, homologated, and initially rallied with the alloy torque tube axle from the Kadett C GT/E. It was already known that GT/Es had a problem with the front torque tube bearing failing (due to high torque levels, not high BHP) and this was also the case in the works HS, so from June 1977 the Salisbury 4HA axle was homologated and used. This was subsequently replaced by the Ford Atlas axle until the transfer of the Group 4 HSR homologation into Group B, when GMDS were forced to change back to the 4HA. For the 180 odd BHP of a typical clubman’s 2.3 SC, a torque tube is probably adequate if the Manta A steel one is used, unless you think you’ll benefit from the improvement in axle location.

The 4HA and Atlas were mounted with a 5 link system (called 4 link in the Sportpart Manual) - two top and two bottom trailing arms and a panhard rod. This system goes back years - at least to the early 60's if not before. It has the advantage of giving very good, strong location to the axle with lightweight components.

At the time the HSR was evolved it looked as though the FIA were going to ban the alteration of suspension mountings and linkages, so the HSR was built and homologated with both top links and a torque tube, to keep the option of using either set up. It's not good having both, though, as the two set ups fight each other, which is why the roadgoing HSR has slightly quirky handling.

One disadvantage of a panhard rod is that it makes the axle move in an arc as it goes up and down. This doesn’t matter on the loose, and they’re stronger, but some tarmac cars had a Watts linkage for lateral location. This has a vertical arm, pivoted in the centre, fixed to the diff casing; a short arm like a panhard rod goes from each end of this to the chassis on either side. I think I’m right in thinking that Rover SD1s had Watts linkages.

On the body, the 5 link system uses the bottom arm mountings of the standard Chevette. The top arms are mounted to the vertical panel behind the front seats that forms part of the rear seat base. To do this you have to cut two slots in the floorpan in front of the rear axle, 26” between centres, and weld in sheet steel boxes for the arms to move in; it’s normal to remove the curved part of the seat base (support for the squab) at the same time.

The works cars – or at least the early ones – only had one mounting point at the front of the 5 link boxes. If you make a vertical series of holes for mounting, you can adjust the handling by changing the angle of the top links. This will increase or decrease the amount of oversteer you get. The drawing in the Sportpart Manual shows such a mounting.

The HSR road cars were built without spring pans on the axle, and used the ‘gondola’ type lower trailing arms from the FE Victor; these were used on rally cars, but all the ones I’ve seen - and my HSR - have had strengthened Viva / Firenza / Magnum lower trailing arms. If you wanted gondola lower arms the Rekord E / live axle Carlton ones might also be an option but I haven’t checked the length.

I’m not aware of 5 link Manta axles having been used widely. However, my HSR had one – I’ve still got it (no, it’s not for sale!). I can’t see why you can’t remove the torque tube, undo the pinion shaft nut and remove the barrel spline from the pinion shaft. This should expose (if I remember right!) a standard spline that the barrel spline is fitted to, enabling you to fit a standard prop flange. You may have to set up the pinion preload etc. again, as you’d release the pressure on the collapsible spacer by doing this. This looks to be exactly what’s been done to mine – I did take some photos, but they’re out of focus – I’ll get some more when I can. Unfortunately, I don’t know what flange has been used on mine, but I would think it’s a fair bet that something like a Rekord one would do the job, or maybe even the one off the front end of the torque tube! The difficult part is the spline – if you have something with the right spline and know a good welder and a good turner you could make or modify a flange to suit.

The Salisbury axle was fitted to a number of 50’s and 60’s cars, notably pre XJ6 Jaguars – if you find the right car, you could get it disc braked and LSD equipped! Atlases are still readily available, but unfortunately arms and legs are involved! The Rekord E and FE Victor had a 5 link rear end as standard, but I can’t find any reference to these axles being used in competition. This may be just because they’re too wide, but if I remember right I think the Carlton / Rekord E diff is a bit fragile.

I assume you've got the drawings from the Sportpart manual. Meant to say if you're getting the mountings for the top links welded to a Manta axle, make sure you use a welder who has a good understanding of shrinkage and pulling, and knows how to clamp it and spread the heat, or you could end up with a bent axle!

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Neilyman
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