Any experience with T3 upper trailing arms?
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Joined: Dec 2018
Posts: 84
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From: St. Michael
Thanks; couple points:
1. The commercially available part for the watts link does not help axle stud strength, only link stud strength. The axle stud itself needs bracing for side-loads. I've rallied tarmac escorts for over 30 years and am very familiar with the system. It is easy enough to do by welding two more studs to the axle either side of the main stud and bolting on a cross brace like an escort.
2. 6-link is the most effective location setup for a live axle. It would be helpful if the links were longer but not an option for pre-1982 group 2 FIA historic regulations which dont allow changing axle or body brackets. One thing is for sure, the standard RX7 live axle setup is much better than every other car being rallied at that time except for the Escort RS and Fiat 131, both of which were homologation fiddles. Asconas, mantas, sunbeams, chevettes etc. are all agricultural compared to the RX7.
3. The watts link on the RX7 is not too high. The car is already prone to understeer due to its lack of engine braking, mid-engine layout, low ride and long wheelbase. If the rear rollcentre was any lower the cars wouldn't turn.
4. Your idea of a spherical bearing is a good one but I'd need to use two of them to stop the link tilting. I'm off to check that now.
I'm happy with the axle articulation I've achieved and am in the process of sorting the watts. Bilstein dampers already sorted, then spring rates to fine tune.
1. The commercially available part for the watts link does not help axle stud strength, only link stud strength. The axle stud itself needs bracing for side-loads. I've rallied tarmac escorts for over 30 years and am very familiar with the system. It is easy enough to do by welding two more studs to the axle either side of the main stud and bolting on a cross brace like an escort.
2. 6-link is the most effective location setup for a live axle. It would be helpful if the links were longer but not an option for pre-1982 group 2 FIA historic regulations which dont allow changing axle or body brackets. One thing is for sure, the standard RX7 live axle setup is much better than every other car being rallied at that time except for the Escort RS and Fiat 131, both of which were homologation fiddles. Asconas, mantas, sunbeams, chevettes etc. are all agricultural compared to the RX7.
3. The watts link on the RX7 is not too high. The car is already prone to understeer due to its lack of engine braking, mid-engine layout, low ride and long wheelbase. If the rear rollcentre was any lower the cars wouldn't turn.
4. Your idea of a spherical bearing is a good one but I'd need to use two of them to stop the link tilting. I'm off to check that now.
I'm happy with the axle articulation I've achieved and am in the process of sorting the watts. Bilstein dampers already sorted, then spring rates to fine tune.
It should be possible to find a metric spherical bearing that fits the Watts Stud that is welded to the rear axle. From there you would need a bearing holder that would be welded to center link to replace the rubber bushing. That said, doing this will be adding allot of extra load to the watts stud that is in single shear from the factory. Support brackets that made this a double shear mount used to be available because cars on 13" DOT racing tires have caused these things to crack/fail. And that was with rubber bushings every where - Pro 7 racecars.
In the end, I think you guys are spending allot of effort and money to "improve" on a bad design. Yes a watts link is superior to a panhard rod but the factory watts location is too high and the fact that it has unequal length arms and is off set dramatically creates binding at travel. A simple panhard rod using 1/2" or 5/8" rod ends that is located at the same level as the lower shock mount would work allot better. The 4-link suspension in the second post on this thread has an extremely long panhard rod and as a complete package, that suspension worked better than any thing you can do with the OE suspension/watts link.
As far as panhard rods, I am not referring to the T-3 panhard rod setup. You need to fab a couple of mounts and run a proper straight panhard rod. Some of you have done at least that much work already
In the end, I think you guys are spending allot of effort and money to "improve" on a bad design. Yes a watts link is superior to a panhard rod but the factory watts location is too high and the fact that it has unequal length arms and is off set dramatically creates binding at travel. A simple panhard rod using 1/2" or 5/8" rod ends that is located at the same level as the lower shock mount would work allot better. The 4-link suspension in the second post on this thread has an extremely long panhard rod and as a complete package, that suspension worked better than any thing you can do with the OE suspension/watts link.
As far as panhard rods, I am not referring to the T-3 panhard rod setup. You need to fab a couple of mounts and run a proper straight panhard rod. Some of you have done at least that much work already
It depends on what you are doing with the car and if you are restricted to the OE suspension then you have to do the best you can. For road racing and autox the OE watts link is too high and given the opportunity, we have always opted not to use it.
We have a couple of RX7s in our shop that has a custom made watts link that is welded to the rear of the axle housing. Both work well but the fab work is pretty extensive and it added allot of weight to the rear axle housing. Neither of these cars have a roll center that is as low as the one on my car with a panhard rod. Charlie Clark at KCRaceware.com built both of them including the suspension pictured in the second post. That car won the SCCA Runoffs in the rain.....so it worked really well.
A better watts setup would be to put the watts pivot on the chassis and attach the arms to the rear axle housing. It keeps the weight off of the axle housing but it does require more fabrication.
I run a panhard rod because the are easy to fabricate, they work in a race car that doesn't have/need that much suspension travel and 2 rod ends are way cheaper that 5.
We have a couple of RX7s in our shop that has a custom made watts link that is welded to the rear of the axle housing. Both work well but the fab work is pretty extensive and it added allot of weight to the rear axle housing. Neither of these cars have a roll center that is as low as the one on my car with a panhard rod. Charlie Clark at KCRaceware.com built both of them including the suspension pictured in the second post. That car won the SCCA Runoffs in the rain.....so it worked really well.
A better watts setup would be to put the watts pivot on the chassis and attach the arms to the rear axle housing. It keeps the weight off of the axle housing but it does require more fabrication.
I run a panhard rod because the are easy to fabricate, they work in a race car that doesn't have/need that much suspension travel and 2 rod ends are way cheaper that 5.
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