MG-Cars.info

Welcome to our Site for MG, Triumph and Austin-Healey Car Information.

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGB Technical - Brake evaluation

My 67 B GT has started to have a slight pull to the left when breaking. I assume that means one caliper is not working as well.

Any thoughts on what would be the way to start as to diagnosing the problem?

Brake system is original single line system. Calipers were both purchased as rebuilt back in 2006. All new hoses were installed at that time.
Bruce Cunha

First, check to be sure that the pressures in the front tires are equal. The pressure in the left front tire might be low (sometimes it's the simplest things.....).

Next, check the alignment of the front suspension.

Only after performing the first two should you begin to look at the front brakes. Let us know what you find, then we can proceed from that point.
Stephen Strange

Bruce, Your right hand hyd. hose may have collapsed internally preventing the pressure reaching the calliper.I know it sounds a bit strange, but this happened to me on an MGYA a few years ago allowing the other side to do all the braking,therefore the pulling. Owen
O McNeill

This has usually been sticky pistons when my car has done it. It has pulled up in a straight line since it had stainless ones fitted. I think this complets all possible causes.
Stan Best

Bruce, I too had a similar issue. I go with Owen on this. In the end I replaced both front flex lines, bled the system and that was the end of the problem. Worst case would probably be the caliper itself needs to be addressed.

As I've learned with these cars, time is not our friend, so part replacement become the norm.

cheers

Gary
79 mgb
gary hansen

Ok, Tire pressure is perfect. Car tracks fine when going down the road and letting go of the wheel. Issue only appears with breaking. So, will start with the hoses.

What are the opinions on what hoses are the best?
Bruce Cunha

I had a problem with a collapsed flexi-hose. When braking, the car would initially pull to the right, then pull up straight.

Another symptom was that I couldn't get any air or fluid out of that bleed nipple when using an eezi-bleed.
Dave O'Neill 2

"Slight pull" can be an inop (RH)rear brake, frequently a crushed pipe on the axle. Also leaky or stuck cylinder or bad oil seal. Find a nice clear country road and at about 30mph stand on the brakes hard enough to lock the rears. Get out and look at the skid marks. They should be equal both at start and release points. I am astonished at how often I find that one or both rears are not working at all.
If you are confident in your car control ability, jab the brakes hard and fast, and look for front lockup as well. Same thing.
Last car I tested (last year) like this had only the LHF working, good thing I had a firm hold on the steering! Rear shoes on wrong, oily, rear pipe crushed, 2 hose were original 1963 and one 1976, all restricted. Even the LHF was slow to come on and slower to release. Had a fresh state inspection sticker and new paint.
Make sure you are pointed straight ahead on these tests or you will be sideways or worse!

FRM
FR Millmore

Quite right FRM. At the end of the day, if it is unclear, you should go thru a proper diagnostic sequence. Check all brakes. But historically, do you know whether the brakes have been attended to in terms of; Linings, seals, including piston calipers, rear wheel cylinders, finally hoses. It is true that inner linings of hoses (rubber ones) can collapse. It is relatively uncommon. My 38 year old hoses were still good when I changed them, but a bit perished on the outside. Water contamination in the hydraulic system does not do any good. Look at the linings,( brake) at the rear, if they show contamination of brake fluid there is a rear wheel cylinder leak. This may manifest as an early lock up at the rear, one or both sides if both leaking, with concominent deviation of track.There may be a leak at the front calipers although less likely, but with corrosion the pistons could stick. Discs could be out of true, might manifest as a pulsing as brakes applied. All this can be long winded, but, depending on age of the car and perhaps dubious history I would be inclined to overhaul the lot. You will be rewarded but perfectly adequate stopping power and it will not be expensive. Remember, what often seperates one from a nasty accident are the tyres and brakes. Do not skimp on these! Mike
J.M. Doust

I know that you have done a lot of work to your car over the years, but it sounds to me like you are experiencing a sticking right caliper. Even though it is only going on 5 years, since the rebuild, it is not out of the question that it could be failing. My'67 did the same thing and when I had previously replaced the calipers, I had installed stainless steel flex lines. I replaced both calipers, last Summer, and found that the right side, too, was not functioning properly. RAY
rjm RAY

Tried the breaking suggestion and it is the right brake. Rears are locking up fine and pull is much worse when I stomp on the breaks.

Will do the lines this weekend. So, the next question. If the line does not fix the issue. Get a rebuild kit or just get a rebuilt caliper. Rebuild calipers are about $63 to $122. Not sure why there is such a difference in price.

I also note they use the term loaded or unloaded. Any idea what that is referring to?
Bruce Cunha

Loaded calipers have pads in them; unloaded calipers don't
Peter VanSyckle

"Unloaded" is a bare caliper, "Loaded" has pads and retainers included, obviously useless unless you do both sides, since the pads won't match. You have to guess on "semi-loaded"!
It is highly unusual for hoses to die in less than 10 years, unless there has been some nasty substitute for real brake fluid used. In that case, all other system seals are suspect.
The only thing that normally makes calipers stick is blistering of the hard chrome plate on the pistons, normally when you push the pistons back to fit new pads. That means the rebuilder either did not fit new pistons, or the plating was defective, or there was water in the system. Way around future trouble is to rebuild yourself, using SS pistons, available from TRF and others. SS pistons and seal kit are at the low end of your quoted prices.

FRM
FR Millmore

A non-damping damper can cause pulling to one side - BT, DT. However if very gradual brake application causes progressively more pull as the brakes are applied, it probably is a weak caliper, on the right for a left pull. The weakness could be caused by a sticking piston, partially collapsed hose, contaminated pads etc. However a sticking piston is also likely to stick on and cause that side to get very hot, unless it is so stuck it isn't moving at all. With all the pads removed and very slow application of the pedal check if one or more pistons aren't moving but the other are. there is bound to be some imbalance, but it should take only very light restraint of a moving piston to start a non-moving one moving. I freed-up an impecunious pal's pistons by easing the pistons forward as far as a fully worn pad would allow, wrapping a length of cord with a bit of brake fluid on it one and a half times round the piston, and pulling the cord back and fore to 'polish' the piston.
PaulH Solihull

You can even purchase new calipers, from VB, for under $70 a piece. RAY
rjm RAY

Not to start the debate again, but I use silicon brake fluid, So water should not be an issue (system was fully drained, cleaned and refilled when I rebuilt it.

Not saying there could not still be corrosion. I will find out this weekend when I change the brake hoses.

Does anyone know if any rebuilders use Stainless pistons? I would rather have these in even with silicon.
Bruce Cunha

There is one other thing to check. Each piston has a slight cut out, and those cut outs are all supposed to be correctly oriented. When I first acquired my B the cut outs in one caliper weren't correctly oriented. Over time that resulted in slightly uneven pad wear, and more importantly the pads didn't retract evenly when the brakes were off. This was all barely noticeable by eye, but on the road it showed up as a slight pull to one side when the brakes were applied, but almost disappearing as the braking force or time increased. Twisting the pistons back into line and replacing the pads solved it.
Miles Banister

This thread was discussed between 10/07/2011 and 13/07/2011

MG MGB Technical index

This thread is from the archives. Join the live MG MGB Technical BBS now