'With the benefit of empirical research behind him, Dave Bulman gives you the inside information on TR7 rear suspension.'

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Barnaby Ferguson
5 years ago
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1 'With the benefit of empirical research behind him, Dave Bulman gives you the inside information on TR7 rear suspension.' At the time of writing, the strengthened rear axle appears to be standing up well to the punishment it is getting. The initial problem was a failure of the two puddle welds holding the left hand axle tube into the differential casing. This is a common problem with many rally cars and is usually solved by fitting a bigger, stronger and unfortunately, heavier item. The mid-range axle, as fitted to the five speed TR7 is a very good unit and is certainly strong enough for the best you will ever get out of the 2-litre engine. Unfortunately it appears that the masses of torque available from a modified V8 can be just that bit too much. The axle must therefore be modified for serious competition with a V8, but these modifications should present little problem for the enthusiast. Before I describe the way in which I have strengthened my axle, there is, as already mentioned, the possibility of using something entirely different. BL Motorsport sell a competition axle based on the Salisbury 4HA casing which is used by a number of other manufacturers, and even in a certain dumper truck. This comes fitted with mountings for a Panhard rod and four parallel link suspension. A much cheaper alternative is to 1 / 9

2 be found on many scrap heaps, fitted to Jaguars and Scimitars. The mountings on these will, of course, have to be modified to suit your suspension set-up, but they are undeniably very strong. Eagle Rally Services have built a TR8 with one of these axles, and for anyone who wants more information, I suggest they contact Jack Coultard. I should perhaps point out that BL Motorsport do intend to use the standard mid-range axle for the rally V8, and consider that it will be of advantage due to its weight saving of nearly 20kg. The only delay in introducing it has been due to a shortage of LSD's which has only recently been overcome. I have been assured that the halfshafts are amply man enough for the job. So how can you overcome what is apparently its only weakness, ie: the fitting of the tubes into the differential casing? These tubes are normally pressed into the casings and welds are built up on the tubes through holes already in the casing. These welds are not intended to bond to the casing, but act as spigots or retaining pins. Unfortunately there are only two of these 'puddle' welds per side, and on my car, the two on the I hand-side sheared and fell out. The tube then twisted, putting the suspension mounting points out of line and causing the axle to move to the right and the nose of the differential to rise. The propshaft hit the tunnel and prevented further movement, allowing the car to be driven gently off the stage. 2 / 9

3 All that appears to be necessary to solve the problem is to increase the number of puddle welds to four per side. This, however, is not very easy unless the extra holes are drilled during manufacture. The best way is to drill two holes each side, 12.4mm in diameter, through the differential casing and tubes. These holes should be spaced between the existing puddle welds, and the axle then stripped and the swarf collected and carefully removed. Short lengths of 12.5mm diameter steel rod can then be tapped into the holes to give a good interference fit. These pins should protrude slightly inside the tube and also above the surface of the casing. They can then be tack welded to the casing. With my axle I have gone even further than just described and added a 5mm thick stiffening plate. This extends across the rear of the axle, effectively holding the two tubes together, It is welded to each tube using the spacing blocks shown in the drawing, and is held against the differential casing by the bolts which hold the cover. The bolts are 5mm longer than standard, and a layer of Araldite is used between the plate and the casing to seal it. Although the plate is probably not necessary, if you do make one, do not let it extend below the diff casing. Also, before welding, clamp the whole assembly to the axle and tack weld the blocks to the plate; next remove the plate and weld the blocks up properly. You must then clamp it back on the axle when cold and tack weld first one outer block and then the other, followed by the inner ones. Let it cool, and using the opposite sequence, lengthen the welds and repeat the process until it is welded to your satisfaction. This should prevent any distortion of the axle. 3 / 9

4 One final point: do not weld the tubes directly to the casing. It may help for a short tine, but it will usually weaken the tubes which will then fail, or the casing itself will crack. At this stage of the build, a decision will probably already have been made on whether to use the standard suspension layout or fit a Panhard rod with four parallel links. I have used the standard system with the front end of the lower links raised by 25mm (see TR Technique No3 ).At the time of writing I have had no problems, there is no tramp, and all the links are rose-jointed. It is a fallacy that the axle will act as a torque tube in this case, and this can be easily proved. Unfortunately this is not the case with the Panhard rod system, and if you do use it, do not rose-joint all the links; use at least one rubber one, preferably at the front end of a top link. It will also be found advantageous to raise the front links by the man already suggested. At the moment I do not intend to offer any advice on which system to choose. I prefer the standard rose-jointed layout, and it is obviously less costly. We hope in the future to obtain a driver's opinion after a back-to-back test. It may also be pointed out that the standard system produces loads across the differential casing and these probably contributed to the initial failure. This does not, however, imply that the modifications to the rear axle are unnecessary if a Panhard rod is used, because the torque reaction on the 4 / 9

5 differential has still to be transmitted through the axle tubes to the links. This torque is equal to wheel torque, and the two standard puddle welds are too small to take the torque from a modified V8. In order to lower the car, the lower rear suspension links can be cut away as shown in the photograph. With the rear springs supplied from BL Motorsport, this will give an ideal ride height for tarmac, and a sirnple spacer can be used for rougher events. To modify a link, cut or chisel off the existing spring support, put a saw cut through to the depth required, and fold over the sides. The spring support can be replaced and the complete unit welded along the joints. The maximum amount of metal you can safely remove is about 25mm, and an extension should be welded to the spring support to prevent the spring jumping out. If the standard arm is, retained, it will give a compromise ride height suitable for normal club and loose surface events, provided the correct competition springs are obtained. The springs to use are either 185 or 210 (the units are pounds of force per inch). The majority of TR drivers are now going for the lower rate, although one notable exception prefers to use the higher one. The dampers to use are 180/110 (Bilstein rates). If the car is intended purely for tarmac, use 275 springs with 250/1 20 dampers. Alternatives to the Bilsteins are adjustable Spax or Koni dampers. 5 / 9

6 One point which many people overlook is the provision of good bump stops. The ones already on the car can come off if the bonding proves to be insecure. If this happens, any severe crashing out will bend the bump stop mounting, and possibly break the damper or its support. To avoid this, I have removed the standard rubbers and welded a 3/8 UNF nut in the centre of each mounting. Into these I have screwed one half of a Rover 3.5 engine mounting rubber. It is then possible to experiment with the size and shape of bump stops, and in the future I hope to try certain ideas to effectively give progressive springs and hopefully produce terminal oversteer. The present set up has proved effective, and on the few occasions that the rear suspension has crashed out, the thud has felt reasonably undamaging. It should be noted that on these occasions I did not have a spacer under the springs, and the crashing out was anticipated. The position of the brake pipes can be seen in the photographs. They should be kept hidden behind the axle and secured to prevent undue flexing or vibration. They can also be covered with rubber tubing to protect them from flying stones. If you are stilt using drum brakes, shields must be made to protect the pipes where they enter the wheel cylinders. The flexible pipe from the axle to the body must also be protected with a coil and should be long enough to accommodate full movement of the axle, even when the dampers are disconnected. The handbrake cable may need to be shortened so as to fit neatly without fouling the exhaust system.. The pivot arm can 6 / 9

7 be reversed so it is above the axle centre line, and an additional support for the cable should be fabricated on differential cover. the The differential ratio you choose is not so important with the V8. Since the engine has so much torque over a wide rev band, it will happily cope with the standard 3.9 to 1 ratio. This gives about 120mph at 7000 rpm in fourth, depending upon which tyres you choose. This leaves fifth gear for the brave, and also helps with economy if you intend to use the car on the road. I am still using this standard ratio with a completely standard gearbox and see no reason to change at the moment, preferring to keep the money for use on events. The next alternative for the mid-range axle is a 4.5 to 1, and if you intend to keep to a maximum of 7000 rpm, this is probably as far as you should go. For the initial testing of the car well as the first two events, we were without an LSD. I was amazed at the grip we had, and for anybody with a low budget, or doing purely tarmac events, the car is obviously competitive without one (remember, we were lying fourth overall on the Chieftain before we had the puncture). For wet or very slippery events the LSD is essential, and BL Motorsport have now got them in stock. Because the drum brakes are self-adjusting, there is the possibility of the brakes locking after severe use. If the drums get very hot and expand, they automatically adjust to take up 7 / 9

8 the slack, and when the drums cool they contract onto the shoes and lock. The way to get over this is to modify the adjusters to give more free movement of the shoes before automatic adjusting takes place. To do this, file the return stops down by about l mm. When the car is driven normally after doing this, the pedal travel will be slightly greater. After the drums have reached competition-type temperatures, the adjusters will move, and when the drums cool again, the brakes will have "firmed" up. If the brakes still tend to lock on cooling, file a little bit more off the stops. The linings to use are VG95s, which can be obtained from BL Motorsport. Do not forget to bed these in, and then remove the drums and dust them out before a competition. These linings are not really suitable for normal road use because they need to reach a decent temperature before they work properly. I have also found on other cars that they appear to all glazed the drums if used lightly over long periods of time. Finally, there are a number of minor points worth noting which concern the back axle and rear suspension. Firstly, always use good bolts on the rear suspension links. The standard bolts are perfectly all right, but never replace them with a weaker variety. It can also be of advantage to plate the bolt holes on the rear axle. Secondly, if you use the competition propshaft (which is probably not necessary for the clubman), the flange on the 8 / 9

9 back axle will have to be drilled to match. Thirdly, each rear spring can be fastened in place by a keeper plate at the top of the spring. This makes it easier when changing dampers, and also stops the spring jumping out if a damper breaks and the axle drops. The rubber pads at the top and bottom of each spring are not necessary. Lastly, if you use drum brakes and you compete on a very wet event with lots of deep puddles or fords, check the linings as often as possible at service points. After four miles at a very wet quarry, plus 30 miles of wet testing at Bagshot one of my drums finished up full of a beautiful shiny, muddy mixture - hence no left rear brake. Next month we start on the engine, and discover just what a low budget car the TR really is. 9 / 9

Step 5 Install the frame rail insert into the frame.

Step 5 Install the frame rail insert into the frame. COR-6372S, COR-6372D 63-72 C-10 Rear Coil-over KIT Tool s for the job Car Lift Floor Jack Chalks Jack Stands Standard Wrench set Standard Socket set Spring Compressor Phneumatic/ Electric Grinder Phneumatic/