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Strengthened Stub Axles All That?

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glemon

glemon

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I am looking at parts and upgrades for my TR250, one of the things I have seen in the catalogs, not cheap, is the upgraded front stub axle kit for most TRs.

Then I read the Roadster Factories claims about the brake getting spongy under certain circumstances and the reason being flex in the stock items.

Darned if I didn't have a TR4A years ago that did this not matter what I did to the brake system.

So is the upgrade kit necessary on most cars or a case by case basis kind of thing or a lot of money that could be better spent elsewhere?
 
I never noticed knockback until I read about the phenomenon in the Friends of Triumph e-mail list. I then paid attention as I braked and found that I had been pumping the brakes once before applying them "for real" without realizing it. It had become an automatic reflex. It doesn't bother me, so I'm not worried about it.

On the other hand, the new owner of my old racecar experienced knockback and he thought his brakes were fading! Caused some anxious moments until other racers explained that he was feeling knockback and not brake fade. He changed to the upgraded axles.

So I'm trying to say that if you're not bothered by having to pump the brakes once in a while, spend the money on something else. If you are bothered, go with the upgrade.

Edit: By the way, nothing you do to the brakes will cure knockback. It's all about the rotor moving inboard/outboard due to the wheel bearing clearances. That's why your old car did it no matter what you did to the brakes.
 
I'd say it's necessary only if the low pedal bugs you. Takes some pretty spirited driving to even demonstrate the problem, so unless you're in the habit of thrashing your TR250 around curves, likely you'll never notice the low pedal.

The factory did install a cure in the brakes for awhile, known as a residual pressure valve, but it was deleted during the TR4 run. Only partially effective, and everyone hated having the front brakes appear to drag. Most people disable the RPV (on cars that have it).
 
I never really noticed that problem with my brakes all of these years, but I did install the HD kit when I rebuilt the front suspension a few months ago. I've only driven it 30 miles because of the winter weather, so I really can't comment one way or the other.
 
I too have been "feared" into interested on these "enhanced" parts.
For a weekend and fair weather only driver are they really a necessity?
 
Tomster said:
For a weekend and fair weather only driver are they really a necessity?
Click to expand...

No.

The brakes don't work any better with the upgraded axles, you just have less pedal movement when applying the brakes after not applying them for a while.

The stock set-up allows the rotor to move inboard/outboard a little as you motor down the road or track. This small movement pushes the pads, and therefore the pistons, into the caliper cylinders. When you apply the brakes, the pistons have to move out of the cylinders this distance before the pads contact the rotor. This extra distance means that your foot has to move the pedal farther. Might scare you if you're not ready for it, or might mess up your heel-and-toeing, but the car will still slow down.

The upgraded axles are made so that there is no side-play in the rotor, so it doesn't push the pads (knock them back, hence the term "knockback") into the calipers.

Save your money for something else unless the knockback bothers you.
 
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