TR2/3/3A The flexing front spindle and no brakes syndrome?

I've been driving my TR3 for over 20 twenty years and have never experienced this phenomenon. I always thought I drove pretty aggressively in daily driving and a few times doing fast parade laps on a racetrack. Is this something that just happens after really hard driving like say in racing conditions. How many have experienced the no pedal situation and what were the circumstances? I can't really afford the the upgrade at this time.

I have had a TR4A and a TR250, both do/did it. My brakes didn't go away, but the pedal gets noticeably softer and close to the floor after hard cornering, the TR250 has fat, sticky tires, which I am sure doesn't help, but my fuzzy memory is that the 4a did it worse in 165s, so maybe varies from car to car.

The factory installed a device on most TR3 to deal with the problem, known variously as a restrictor valve, or residual pressure valve. If it is working as designed, you won't experience the low pedal. The valve is housed on top of the 5-way connector near the RF wheel.


My personal experience (with the valve disabled) has been that although I notice the pedal is low after hard cornering, it's never been so low that I don't get good brakes without having to pump. It's more disconcerting than dangerous, IMO. But it does depend on things like how tight you set the front wheel bearings (the workshop manual is wrong, IMO*); and in one case I discovered that the axle was actually out of round enough to let the outer bearing move up and down a bit. And while I run wide, sticky tires (205/55), I use TR6 steel wheels, which aren't the most rigid wheels in the world. Good alloy wheels might well result in more spindle flex.

YMMV

*The procedure for setting the bearing clearance was updated several times; the workshop manual says to tighten to 10 ftlb and then back off by 1.5 to 2 flats but that was written before disc brakes were introduced. "Practical Hints" says to back off by only 1/2 flat, while the TR4 workshop manual specifies backing off only to the nearest hole, then measuring the clearance at .003" to .005". If the nearest hole is too loose, the nut is sanded down until the next hole gives the desired clearance.

Randall Does the restrictor ever get gummed up and need cleaning? Why are they N/A and why did you disable yours?

I don't know if these fit anything other than the 6 or 250, but HP660 solved that problem.
http://trf.zeni.net/TR6-TR250GB/index.php?menu=A&page=191

Yes, the "uncle jack" spacers will fit TR3-4 with front disc brakes. Jack Drews developed them for his TR4 race car. So will the uprated spindles (HP661).

I believe the RPV can get gummed up or even rusty, the one in the photo was both. Not too obvious, but there is actually some metal rusted away from the small piece near the big spring. Old DOT 3 brake fluid is surprisingly corrosive and this car was a "barn find".

I disabled mine because it also makes the front brakes drag just a bit. Not enough to hurt anything (probably), but enough to annoy me. IIRC, that would have been about 1975, and the TR3A I had then (more of a backyard find) had some interesting braking problems. I eventually figured out that one of the front suspension mounts was torn loose from the frame, but it took an embarrassingly long time to figure that out. (In my defense, three different professional shops couldn't figure it out either.) Under hard braking, it would turn left no matter how hard you tried to turn right.

The valve was actually deleted later on; the TR4A SPC shows it as "Special order only" but I've heard that later TR4 didn't have it as well.

No idea why they are N/A; probably just not enough demand to make it worthwhile reproducing them.