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MG MGB Technical - Pulls to right under braking

My 69 MGB GT is having an issue of pulling to the right under braking. It is really only noticeable at higher speeds above 35 mph or so and is not a violent pull but enough to require attention. It did it before and after I changed the flex lines on it so the system has been fully bled and that did not cure it. I also tried backing off the passenger side rear adjuster and that did not help either. All tire pressures are even side to side. Car tracks straight otherwise. Any ideas?
Can the brake failure switch cause this issue?
I did recently change pads and rotors as well and when I did so I had a hard time opening up the Pass. side caliper to get the pads in, when I compressed one piston the other would pop out and when I tried to compress them both they wouldn't budge until I opened the bleed screw, so something was keeping fluid from returning back toward the master. Again I suspect either the brake failure switch or the caliper itself. Open to advice though.
Bill Mertz

I had a similar problem to you - pulling to the right and difficulty bleeding LH caliper - which turned out to be LH flexible hose.

Obviously something is restricting the pressure. Did you have any problem bleeding the LH side? Have you centred the shuttle in the PDWA? I'm not sure if that could be an issue, although presumably the warning light would be on if it wasn't centred?
Dave O'Neill2

Bill - Since you experienced the problem you described in you query, I suspect that Dave O'Neill is correct his his assessment of a blocked flex hose (not allowing the fluid to bleed back into the master cylinder). If this is the case, I would probably opt for replacing all three hoses. Cheers - Dave
David DuBois

Bill says that he replaced the flex hoses, so I'm presuming that's not the issue, but some similar restriction.

The issue that I had with bleeding was when I used an eezibleed, I couldn't get any fluid or air out of the LH caliper. I think if you bleed with the pedal, you exert more pressure, which may overcome the restriction.
Dave O'Neill2

Yeah I replaced all three flex lines (after suffering a failure on the right front-- it had a tiny hole in it coincidence?). The problem remained before and after. Think I'm gonna make sure there is no oil or grease on the rear shoes then tackle that caliper. It bleed fine using the old pedal method but didn't want to push fluid in the reverse direction
I haven't tried centering the the shuttle in the switch, and I have the switch light disconnected. Starting at that caliper and working backwards toward the master seems like the thing to do.
Bill
Bill Mertz

It is unlikely that the rear brakes will have any effect on the pulling right. Have you tried changing the pads from one side to the other? If this make no difference try changing over the discs. Are the front tyres the same age and make/type? Is the wheel alignment correct - different castor angle from one side to the other could cause it. Get onto a smoothe piece of tarmac and brake hard enough to lock the wheels from about 15mph and swee if the skid mark starts at the same place.
Good luck.
Garth
Garth Bagnall

"It is unlikely that the rear brakes will have any effect on the pulling right."
Not true, I've found that rear brake faults will easily cause a pull. It will not yank the steering wheel out of your hands like a front brake problem, but it will certainly make the car pull.
Most common are contaminated linings, shoes installed incorrectly, and bad brake springs. Crushed steel pipes on the rear axle are common; check anytime the car gets retrieved by a towing service!
I do the lockup test Garth mentions anytime I have a pull, or poor braking performance. Especially easy to lock up just the rears and look at the marks, and common to find one side working much later than the other, or not at all.

FRM
FR Millmore

Have you tried the U bolts to see if they will tighten up any more. I suspect that the LH rear ones could be slack allowing the axle to move rearwards during breaking and so artificially applying RH lock causing the car to pull to the right.
Iain MacKintosh

Check the orientation of the shoes, each is 'handed' but can be installed either way round. From what I've been able to determine they *should* be orientated so that a point on the drum, rotating as if the car is travelling forwards, passes over the 'empty' or unlined section of each shoe before it passes over the lining. Left-hand side attached as an example, but the right follows the same principle. I don't know how much effect one orientation has compared to another, but unless they are identical different orientations side to side will make a difference. Different adjustment side to side ditto, and I've also had pulling to one side when a front damper wasn't damping any more.

Another check is to remove the pads and push the pistons back - removing any excess from the reservoir to prevent overflow, then have someone slowly operate the brake pedal while you see which piston moves first, block that and see how much extra pressure is needed to start the next one moving etc.


PaulH Solihull

My 72 GT as had a tendency to "wander" left under braking. I keep improving matters because there were various issues when I bought it. 1. O/S rear shoes were in back to front. 2. Perished suspension bushes. 3. Unbalanced front dampers. 4. "Soft" brake flexibles. 5. Play in rack. 6. Slack "U" bolts on axle. At present the engine is out and i'm replacing the X member/chassis pads, again which are perished, plus the bottom trunnions. Hopefully that will be it. The fact that mine doesn't "pull" i.e., you can't feel it at the wheel, suggests to me that it's rear end generated or there is play or inequality up front allowing it to err down the road camber. My V8 however, "weaved" quite violently, with snatches at the wheel, under braking. After hours of investigation at the front, all fruitless, the problem turned out to be generated from araes of "polished" corrosion on the rear drums. Changing the drums cured the problem..........!
Allan Reeling

One more thing to watch out for is the orientation of the almost imperceptible cut-outs in the front calliper pistons. They should be oriented towards the axle (from memory) and if they aren't all the same then one or more pad can begin to bite slightly before the others. This can show up as a pull under medium braking which eases up as you brake even harder. If they aren't right then the pistons can be carefully rotated to make them so.
Miles Banister

It's probably a bit late to add this, but I had exactly this problem a while ago, and cured it as Miles describes.
John Bilham

This thread was discussed between 17/11/2011 and 26/11/2011

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