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I’m having an issue where my car pulls to the left a bit upon the initial application of the brakes (seems to be worse after driving without braking for a bit). My thinking is that the left side front brake is binding causing it to heat up a bit and then not work as well, but I’m not sure. It isnt extreme, the brakes aren’t smoking or anything, but it definitely is not perfect.

I checked the steering and there is absolutely zero play or backlash in the system between the wheels and the steering wheel. Absolutely no play in the ball joints. After the car was sitting for a day I lifted each front wheel off the ground and they both spun fairly freely by hand. I then started the car and pumped the brake several times and checked the wheels again. First the brake light didn’t stick on or anything like that and the pedal returns. Each wheel could still be spun by hand relatively easily, but there was definitely more friction in the system and the left side spun slightly less freely than the right side. I then unplugged the vacuum hose to the brake booster while the car was still running and the wheels went to somewhere in between where they had just been and where they were before starting the car (in terms of spinning freely).

Any advice would be greatly appreciated. The car is a standard Cooper S with a brake booster that was newly rebuilt a year ago by a professional. The brake master cylinder is new as of less than a year ago. The brake hoses are not new - no visible issues, but they are probably 35 years old.

I guess you've checked the tyre pressures and the front tracking.

I would eliminate the brake pads first by replacing them. Process of elimination by checking and/or replacing the cheapest items first.

Sticking caliper pistons is another simple check while you're down there. Suitably sized block of wood between them and press the pedal. Will hold the block and release it PDQ

The car was aligned shortly before I noticed this so I assume it is still fine, but perhaps they did a bad job. Tire pressure is also fine. I guess I could replace the pads - as you say they are not expensive.

Or just swap them over if they are quite new and let them re-bed in perhaps?

How old are the Flex Hoses to the Brakes ?

I don’t know the age of the hoses but I strongly suspect they are 35 years old.

I'm not too sure how the hoses come into this equation. Thinking on my feet, on a single line system, when you press the pedal and load up the pressure to, say, 100 psi, then regardless of the bulges or blockages in the hoses - and they can only bulge so far before they split - then the pressure throughout the system (leave out the rear regulator as it's irrelevant here) is 100 psi. There will be more fluid in the bulged hose, but the pressure will be the same. That's the nature of the beast.

A truly blocked hose is easily identifiable when you try to bleed that part of the system

I've been having the same issue with an MGA recently. Try doing a few sharp stops from a reasonable speed, then pull over and feel the brake disks if you can. If one feels hotter than the other you know one is sticking on. Maybe easier on an MGA with wire wheels than a Mini...

In the end, IIRC, after also checking the hoses it turned out to be swelling on one of the piston seals that was blocking the return of one of the pistons.

You can test that by putting a block of wood between the pistons and pressing the brakes. Release brakes and outer slipper seals should retract and release block of wood very quickly.

Yet another interesting thread

The hoses can and do swell internally as they age and eventually, will act as a one way (or non- return) valve. The reinforcing of the Hose prevents them from swelling on the outside as this aging occurs, so looking at them, it's hard to gauge their condition. There's high pressure from the Master Cylinder pushing the fluid in to the Brake Caliper, but very low pressure on the fluid for it's return. Eventually, it will result in the Brakes locking on, but before they get to that, they become slow to release.

It's also because of this effect that they fitted the Over-throw Nuts to the Clutch.

Factory advice is to replace all rubber parts of the Hydraulic Systems every 40 000 miles / 3 years. I know few of us would do them every 3 years, as I don't clock up 40 000 miles in that time, I change mine every 4 - 5 years.

If your hoses are circa 35 years old, you'll get a pleasant surprise once changed how much better the Brakes feel.

Something else to check is that the Steering Arms really are tight on the Hubs. Often rocking the Hub by the 3/ 9 O'clock position by hand doesn't exert enough pressure to show if these are moving, you really need to take them apart and look for signs they have been moving. I have found that the LH one is more susceptible to this (in Keep Left countries) as that tends to be the worst condition part of the roadway.

Tie rod bushes???

Cheers, Ian

The tie rod bushes seem tight.

Based on the comments here and knowing that rubber doesn’t get better with age I’m going to rebuild the front calipers and then I might as well replace the hoses while I’m there. Thanks for the help!

Ok I have an update that I want to post just in case it helps someone in the future. TLDR Spider was right - it was the flexible brake hoses in the front. I started by rebuilding the calipers and I’m glad I did because they definitely needed it. However after doing that it actually made the problem slightly worse (I guess because the brakes were working better). I now just finished replacing the front brake hoses (what a total pain in the neck on a car with a brake booster - access is terrible). Probably took me three hours to do what should take 5 minutes. As soon as I did the problem was fixed.

Here is what I believe was going on (with slightly more astute description of the original problem).

When I would hit the brakes, the harder I got on the brakes the more it would pull to the left. Then after the initial surge the car would straighten out a bit. Difficult to fully judge this because you compensate for the pill with the wheel.

I believe that the right brake hose was more restricted than the left hose which basically caused it to act like a damper. So when I hit the brakes hard the left brake would work better while it took a second for the pressure in the right brake to build up. Then when releasing the brake the calipers were slower to release on the right side because of the same damper affect. This caused the brake dust to be significantly more on the right side than the left side.

Here is a picture of what the offending hose looked like - I don’t know how big it should be, but that looks awfully small. It’s probably worth noting that there was no indication of a problem when bleeding the brakes - fluid would flow thru the hoses just fine.
Finally I wanted to point out what I would consider to be a design flaw with the original Lockheed Cooper S calipers. When rebuilding them I could see that there is just a single hole to connect the outside half of the caliper to the inside half of the caliper. The bleed screw is of course on the inside half of the caliper along with the inlet. So what happens when you change your brake fluid is the new fluid just flushes the inside of the caliper but it never gets to the outside half of the caliper. When I was taking mine apart there was some really nasty old fluid and water on the inside half. For those who have these brakes I would recommend taking the calipers off and disconnecting from the hoses every so often to let all of the fluid drain out of the calipers in order to get the old stuff out. Maybe lots of calipers are this way - I have no idea, but clearly a bad design.

Good to get your feed back on the issues found and i will take on your Tip regards the old fluid within Brake Calipers.

I’ve had exactly the same problem on my mk 2 and just like you, it was the hoses. It showed up when I initially replaced just one hose.

I had the same problem years ago. Practically changed everything in the front suspension and it turned out to be throwout shim in the diff bearing was incorrect allowing the bearing to "float". Shimmed it up with the engine in situ and the problem disappeared.

Thanks for sharing - good to have confirmation that this can be a problem

I have a similar situation which I haven’t bottomed yet on my mk1. In my eleven years of ownership it has always pulled to the right on acceleration and left on deceleration ( or possibly just straightens up off power ). It was really bad when I first got the car but I’ve improved it by making adjustments to suspension geometry…..camber, toe out, tie rod length, corner weight etc. All this has been a suck it and see guess using tape measure and visual checks……which have generally worked good enough for me in the past on my road cars. I know that the diff is shimmed correctly…….and have rebuilt the engine / box while in my ownership ( I was hoping to find issues there at that point but None ) The next thing I am going to replace are the suspension cones ( I already have the MS Evo cones ). I’m thinking that if the cones are all different ages and conditions, and I have been setting ride height / corner weight to compensate the differences, then this could be contributing to my pulling ? Also, I realise that there’s no substitute for going to a suspension set up specialist who has the correct equipment and expertise.