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TR4/4A Dedicated front coil over shock absorbers.


Jedi Warrior
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Has anyone fitted Mustang 11 QA-1 adjustable coil over shock absorbers,
Interested to know.... did you modify the spring tower and what length spring and spring rate did you use.


Jedi Trainee
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Has anyone fitted Mustang 11 QA-1 adjustable coil over shock absorbers,
Interested to know.... did you modify the spring tower and what length spring and spring rate did you use.

Do you mean Mustang II? That would be the downsized Mustang for the 1974 through 1978 model years before they went to the Fox body cars for 1979. On to springs bearing in mind that I have no direct experience with the application you mention but have done a fair amount of chassis set up in the past.

The stock front TR6 springs per Richard Good are ~305 lb/in and his performance front springs are 390 lb/in with a free length of ~8 7/8" and that ride height will be ~1" lower than stock. Unfortunately he doesn't mention the ID of the spring or diameter of the spring wire. He does note that for use on the TR4A that a spacer will be required.

It looks like the QA-1 Mustang II coilover uses a 2.5" ID spring and considering the lower damper mounts on the Triumphs and the ride height/preload adjustment nuts, I'm thinking off the top of my head that the QA-1 9" long spring (shortest QA-1 offers) might be a bit too long unless you put in a fair amount of preload but that in turn has the potential to lead to coil binding. My off hand guess is that an 8" spring, perhaps even a 7" one is the length you are looking for. As far as spring rates go, I'm thinking something in the 325 lb/in to 400 lb/in neighborhood is the answer without knowing anything else about your car. Of course if your suspension is heavily modified, then a full blown suspension analysis is in order. You might look at Swift Springs. They offer a wide variety of lengths and spring rates. The spring rates are listed in kgf/mm so 1 kgf/mm is 56 lb/in. A 7kgf/mm spring is 392 lb/in for example. In the 6 inch, 7 inch and 8 inch springs the range of spring rates go from 4 kgf/mm to a bone shattering 28 kgf/mm and even higher as spring length decreases. I think that you could run these without an issue in the stock spring towers but best to get some good measurements and confirm. Do run a spring pad at the top of the spring in the tower and while helper springs can be used when using shorter length springs, if you can find a spring that doesn't require too much preload to get you at your desired ride height without the need for helpers, you're probably better off.


Jedi Warrior
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"Tybalt", thank you for your comprehensive comments.
My forum post was bought about by my desire to obtain a much "softer" and adjustable ride than the factory spec of around 310 lb/in.
"Performance" springs are a no go for me. Ok for a track car.
The factory springs are about 11" free length.
Thoughts were to use 3" ID springs on the Mustang C/O shocks that can be bought outside QA-1, eg Eibach, perhaps even modifying the TR upper spring tower and/or the bottom spring plate to overcome using springs that may be too short.
My other options are to fit ordinary 250lb springs of suitable length, wire diameter, number of turns etc that would probably have to be especially made, or better still have variable rate springs custom made.
I remember someone on a TR forum many years ago, perhaps in Germany? offering to make variable rate springs.


Jedi Trainee
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I was operating on the assumption that with the use of coilovers you wanted to be able to adjust ride height with everything in situ. That is why I was talking shorter length springs as opposed to springs at or near stock length. As for spring rates, Swift offers a 4kgf/mm (224 lb/in) and a 5kgf/mm (280 lb/in) spring in various lengths at 1" increments and IDs of 60, 65 and 70 mm.

Here's the URL for Swift's US operation listing of metric coilover springs, I can't help but think that Swift has some sort of outlet set up in Oz as well:

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