TR2/3/3A Tr3a brakes pull to left on hard braking

[badornato]

what is the most likely cause and what would be the best way to diagnose?

disk brakes .. minimag wheels. problem started only a month ago and is not noticeable on light braking
only when I really stand on the brakes the steering wheel pulls hard left.

 

[TR3driver]

Since it only happens when you get on the brakes hard, I think you can rule out a stuck caliper or similar problem. I would double-check that you don't have worn out pads, maybe try swapping pads from side to side.

After that, I would be looking for anything that lets the front suspension deflect under a heavy load to the rear. When I had a TR3A that pulled like that, it turned out that the rear lower suspension mount (on the RH side IIRC) had pulled loose from the frame. The front mount was still holding the pivot in place, but the pivot rod would bend under heavy braking, allowing the suspension to deflect and the steering to turn the wheel to the inside.

I had just gotten the car running and drove it that way for a few weeks, holding the wheel hard when I had to stop; until someone pulled out in front of me and I couldn't keep it from jumping the median! Fortunately I hadn't been moving very fast and got stopped before it veered into oncoming traffic, but the experience convinced me it had to be fixed sooner rather than later! Oddly enough, the alignment shop had not spotted the problem.

 

[Geo Hahn]

Basic but I'll mention it anyway - have you checked your tire pressures?

It can be hard to spot a low tire by just looking. Set them to whatever you decide you like but they have to be the same left to right.

 

[charleyf]

If it is braking and pulling to the left, could that mean that there is a problem with the right side caliper NOT braking? Something like a bad brake hose that expands rather than holding the pressure and pushing that pressure into the caliper?
Charley

 

[Foura]

When I bought my 3A in 1968 (!!!) it had brand new pads. I drove it for many months without an apparent problem. One night I did a panic stop, and the car immediately went out of control. I managed to get it stopped without hitting anything and drove it home. I found that the previous owner knew that it had a frozen piston in the left front caliper. By putting new pads in, the small amount of play in the bearings allowed the working piston to push the disc against the frozen pad and the brakes appeared to work OK. Despite putting a huge amount of pressure into the caliper, the brake shop could not budge the piston and I had to get a new caliper.

I would not rule out a stuck piston. My problem only showed up under hard braking. It is not a hard job to pull the pads and see if the pistons are all moving OK.

 

[CJD]

Binding caliper, leaking caliper, grease/oil/brake fluid on one pad.

 

[groupdeville]

Also check or replace your front flexible brake hoses. Preferably replace, so that part of your braking system is baselined.

 

[pdplot]

Check the right brake pad for grease or oil.

 

[badornato]

bingo. the hard pull to the left was caused by leaking hydraulic fluid on the right brake pads.

 

[Geo Hahn]

Well shoot, I knew that. I didn't mention it in 2016 because I had not experienced it - but my TR4 developed a hard pull (to the right in my case) about a month ago and it was a leaking caliper. Never did see any smoking gun (other than wetness) as the seals and caliper all looked fine -- but replacing everything 'rubber' resolved the problem.