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TR4/4A TR4 DISTANCE PIECE between axle and leaf

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G

Gblake2613

Jedi Hopeful
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What is the prpose of this distance piece on the TR4? When rebuilding the rear is it better to run earlier springs w/o the distance piece or later springs with the piece?

Thanks,

Greg
 
Hi Greg,

My understanding is that Triumph went to the distance piece and matching spring arc to try to tune out some tendency to bump steer on the earlier cars. So, presumably, the later springs with the distance piece should improve handling a bit.

However, to be honest I don't recall ever experiencing much bump steer on my older TR4 that lacks the distance piece and uses the earlier leaf springs. It does now have some added spacers between the axle and spring, that lower the rear of the car about 1-1/4" (they actually were made from wooden 2x4s when I bought the car... talk about a DPO!), but these are homemade and nowhere near as tall as the distance piece used by the factory. Oh, and the car now has competition rate rear leaf springs, although I can't report on the performance since the car is not yet back on the road.

So based on my own experiences with it I don't think I'd bother converting a car one way or the other. IMHO, just be aware of the differences to get the correct parts used in whatever setup your car has.

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According to Triumph Workshop Manual the distance piece and re-cambered road spings were used to reduce roll steer. There is a short discussion of this in Tuning Standard Triumphs by David Vizard. I have the Vizard book in my computer in PDF, I got it off the internet. Maybe someone knows where to find it. I converted my early rear suspension some years ago when I was into Solo II more than I am now, not sure it is worth the effort. The curious thing about the highly arched road springs is the lateral inacurracy with which they locate the rear axle. In other words the distance between the spring where it mounts to the axle and the frame will not be the same on both sides. I guess you could fool around and bend the spring eye to adjust it. After noticing this on my TR, I crawled under my pickup with a tape measure and found the same thing. The moral of the story is: don't watch Monk while working on your car. You won't measure and you won't think about it.
 
[ QUOTE ]
Alan,

Where did you source your competition springs? Do you know what rate they are?

Thanks,

Greg

[/ QUOTE ]

Hi again Greg,

Sorry, I don't recall exactly where I got the heavy duty rear springs. They were purchased 5 or 6 years ago, I think. They came from one or the other of the major U.S. vendors, I'm sure (Moss, VB or TRF). They are Triumph part #304008 for TR4 and the distance pieces aren't used with them.

The "competition" spring rate is 155 (+/- 5%) lb/in. (Compare to 128 lb/in for both types of stock springs, which are part #208636 up to car CT23382 w/o the distance piece, and part #209964 for CT23383 and later with distance piece.)

I find the rear ride height a bit high with the competition leaf springs by themselves, but it's pretty easily adjusted by putting spacers between the axle and the spring, which also requires specially sized u-bolts. Custom made aluminum spacers or distance pieces (probably somewhere between 1 and 2" thick) can be used to set the ride height just about anywhere that works best for any particular car setup. I've looked for but havent found any useful adjustable wedge type spacers. Most are too wide (made for bigger 'Merican cars with wider leaf springs).

Let me correct something. In my first response I wrote that I thought Triumph added the distance pieces and recambered the spring to help reduce "bump steer". I think Mark is more accurate in his response that they were installed to try to correct "roll steer", which is a bit different. (Of course, the 20% stiffer springs I'm using will also reduce roll steer, without the distance piece, although the ride might chatter my teeth a bit more.)

At some future time I'd like to fiddle some more with the rear springs & shocks and see what can be accomplished. I'd like to try a monoleaf spring combined with an uprated shock (possibly tube shocks, or larger/adjustable lever shocks). There are various other options, too, such as slightly tapered shim plates to correct for spring twist, roller-type rear hangers, adding a panhard rod, etc. But, frankly and realistically, IMHO all this is aimed at getting the last 2 or 3% out of a primitive suspension that's already suprisingly effective on these cars, in terms of handling if not ride comfort.

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