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View Full Version : TR3 rear suspension mods.



karls59tr
04-23-2008, 06:00 PM
Has anyone done the rear suspension modification where an extra leaf is added to the leaf spring and a lowering block is placed under the axle? Anyone have a pic of this?

JerryB
04-24-2008, 01:26 PM
I'll comment on rear leaf sprung cars in general......

"""""" where an extra leaf is added to the leaf spring """"

...this will raise the spring rate of the spring package. Depending on the arch of the leaf, it may or may not raise the ride height.


""""""""and a lowering block is placed under the axle""""

..this will lower the car depending on the thickness of the block.

You did not state your objectives in doing all this. If you need more spring rate in the rear then you can add a leaf(s) or replace leaf(s) with thicker or wider leaf(s). Most British cars are plenty stiff in the rear to begin with so you might be going the wrong way.

You want enough spring rate and arch to hold the car up at the ride height you want, but not so much rate so the car does not skitter or walk out in the rear on hard cornering. Best case is not to use lowering blocks but get the springs where you want them as to rate and ride height. That and a Panhard or locating link and some good shocks and your there. Then you can proceed to sway bar issues.

karls59tr
04-24-2008, 04:12 PM
I'm just trying to make thr car handle better for the occasional autocross but basically its a summer driver.I've read that" At the rear suspension the leaf springs should be changed to lower the car and make it stiffer. Remove the two smallest springs and add one spring the same size as the two that were taken out. Install Delrin bushings at the rear of the springs and retain stock rubber bush at the front spring mount." As you say I dont think I'll use the lowering block for my intended use. What is a Panhard rod...what's it look like and how is it different from a rear sway bar? I've heard that a rear sway bar only increases the natural understeer of the car so is not reaaly needed on an early TR. Also "Even with stiffer springs traction bars can be added to the rear springs to prevent wheel hop on hard braking and acceleration." Would traction bars be over kill for a street car? Karl

JerryB
04-25-2008, 01:29 PM
"""""At the rear suspension the leaf springs should be changed to lower the car and make it stiffer."""""

well if thats what you want to do then add a thicker leaf in place of a thinner leaf, (s) (to stiffen) and re-arch
each of the leafs to get the rear of the car lower.


""""""""Remove the two smallest springs and add one spring the same size as the two that were taken out.""""

well thats unclear...define smallest.....(thickness or length) . Doing that you MIGHT just be trading spring rates.


"""""Install Delrin bushings at the rear of the springs and retain stock rubber bush at the front spring mount.""""""

Well that might be a Triumph thing in that the rear shackles MIGHT move around or the rear half of the spring package might be long(er). By replacing rubber with plastic you will reduce compliance in the suspension BUT you will have more NVH (noise, vibration and harshness). You might not want that in a street car.


""""""What is a Panhard rod...what's it look like and how is it different from a rear sway bar? """""

That is a suspension link that limits movement left and right of the rear end housing in relation to the chassis in cornering. There are other "limiting links" but the Panhard bar or rod is the simplest and easiest to fab up and is well suited to a live axle car. Made of DOM or CrMo tubing about 7/8- 1" od and using a spud on each end with screw in spherical bearings (Heim ends). Chassis bracket on the left and diff housing bracket on the right and bar mounted as close to horizontal as possible at ride height.

Sway Bar is basically a horizontal bar connected to the chassis with legs on each end that are connected to the diff housing (in the case of a rear bar). The stiffer (larger o.d.) of the bar the higher the resistance to twisting as the car rolls. It does nothing when the car is going in a straight line. It tries to limit the roll of the car.

"""""""I've heard that a rear sway bar only increases the natural understeer of the car """

Thats correct.

"""""so is not reaaly needed on an early TR""""

As just possbly the rear spring package is too stiff. Now if you change front springs to a higher rate and add a bigger sway bar to the front of a car, then you MIGHT add a rear bar. Thats a whole different issue tho.

"""""." Would traction bars be over kill for a street car? """"

I would have to say yes in your case. Unless you have big horsepower and can spin the tires at will. Clamping the back half of the rear spring package will help eliminate wheel hop. To add a link on either rear side on a leaf spring car is a movie. It mus not put the rear housing in a bind on bump or droop or IN ROLL.

If your serious about this I would soften up the rear spring package, lower the car a bit front and rear, add the correct tube shocks for the spring rates you will be using, and use all new rubber bushings in the rear leafs. Use plastic bushings in the front sway bar only on the chassis mounts. You might want to read up a bit...three books maybe no longer in print....1) Fred Puhn "How to Make your Car Handle" HP Books, 2) Paul Van Valkenbergs' chassis book...written about 1985 but still applicable today...and 3 ) Alan Staniforth's book on chassis and suspension.....listed in the order of "bestness" in my opinion.

karls59tr
04-27-2008, 07:10 AM
Very informative. Thanks for the info Jerry.

billspohn
04-27-2008, 11:34 AM
Be wary about softening rear springs on a TR-3.

The main objective at the rear is to keep the ****ed diff from hitting the frame and lifting, at which point all differences between a sports car and an oxcart are instantly lost.

This objective can be served by limiting travel, and the poster's objective of spacing the diff higher off the spring, thus lowering the frame vis a vis the axle may be beneficial.

I've run many TRs and if you can keep that axle sprung instead of bottomed (and keep the bloody front A arms from tearing off the frame) they can be made to handle almost reasonably. In fact just about up to the level of a stock MG... :-)

(PS - it isn't just TRs - all but the last big Healeys also had underslung frames)