In my technical services corner one problem keeps cropping up with renewed fervor; sagging IRS Triumph rear springs. Wc thought a technical recap would help, and since I REALLY like these squatty-tailed monsters, I volunteered to write this column!
An array of problems results from worn and sagging springs. Mismatched or upside down trailing arm brackets can cause fits in spades, and can push people to unbelievable measures. You can ask me about it sometime. If your car leans in one direction or drags it’s tailpipe on the ground and squats like an east-Hungarian bull frog when you let the clutch out, then sit hack and grab something cold to drink.
It’s worth mentioning that IRS frames ate extremely prone to rusting and should be checked very carefully around the trailing arm mounting brackets for thin metal (this is the lowest point on the car where water collects). Serious clunks could mean a bracket that’s about to pull loose. Avoid buying a car with repair patches around this area. Their bellshaped design renders IRS frames extremely prone to accident damage. Be sure the frame is solid and straight before diagnosing suspension problems.
Checking the mounting bracket types (1-notch, 2-notch or 3-notch) and positions will often show why a car leans excessively. Ensure that all brackets are correct. Bracket positions on TR4A-6 up to CC61570 are: 1- notch inner, 2-notch outer. Longer springs of increased rate were used after CC61570 to cope with settling problems. The brackets were changed then to provide anti-squat geometry. Positioning was now 1-notch outer, 3-notch inner, and remained so to the end of production.
Aside from chassis damage, there are two causes of tear camber problems on these cars: the springs and chassis mounting brackets. The accompanying chart shows the springs Triumph fitted to the TR4A-TR6 models. I always replace rear springs when I buy a TR because they’re cheap and they provide a good reference point.
Fined length and spring rate are critical on these cars because the spring determines rear wheel camber. Changing mounting bracket shims adjusts only the toe-in; it docs not alter camber. As Triumph changed the spring specifications, they altered the rate in relation to the fitted length. All factory springs were of a non progressive rate (i.e. the rate did not change as the spring was compressed).
Triumph offered at least two uprated springs, part No’s. V-499 and V-739. These are thought to have been offered only for TR6s. The former was for competition use only, while the latter was offered as an heavier-duty stock replacement, rated at 450lbs. To deal with complaints of settling springs and excessive camber. Triumph issued Service Bulletin 75-F-l in January, 1975, informing dealers of aluminum packing piece, part No. 64-20-01 (Moss #675-065) which fitted between the spring and the control arm to rectify the condition in “most cases”.
Today, most suppliers offer one or more “stock” springs and perhaps a “competition” version, but everybody has their own idea of what a “competition” spring is. A number of these “competition” springs actually worsen the condition; most have the length of an original “stock” spring, but are made from a coil with an outrageous rate. Installed, these springs have little or no “give”, causing a car’s tail to poke up at the sky; altogether inappropriate behavior for a Triumph. The increased rate gives a ride stiff enough to shake your fillings loose. Congratulations – you just traded one extreme for the other.
We at Moss take our IRS Triumphs very seriously. When we set out to have springs made, we came up with a couple of nice and workable solutions. Wc offer a stock-grade spring, 675-035, as a replacement “long spring” for all TR4As, with a-normal ride height and a bit stiffer ride than the weak original versions. For TR250-TR6 up to CC61570 we offer the 675-045 stock spring. Ride height may vary slightly from car to car with this spring (due to different vehicle weights – see chart), but you can expect a nice wallowy ride as Triumph intended.
If you’re interested in something above the stock springs, we offer a really nice blue painted spring set which compares to factory spring V-739, and is my personal favorite. Unlike originals, this spring is progressive, meaning it gets stiffer as it’s compressed more. This is nice – you can bounce the car easily at first, yet after 1/2 inch of travel it stiffens up quite a bit. This gives a comfortable ride with lots of control.
I’ve fined this set to both a TR4A and a TR250 with wonderful results. I’ve also suggested this set to a number of our customers who report good results on both early and late TR6’s (post ’73 cats may require packing piece 675-065 to maintain stock ride height, as this spring is shorter than stock versions). In my opinion this spring is what the factory should have used to give a nicely controlled but not too stiff ride .
That about finishes things up on springs. For those seeking all- out racing goodies, we offer a selection of competition-grade spring sets on a special order basis, directly from Triumph Tune in England. Please contact any Moss salesperson for details.
by David Eichelbaum