Need help with brake problem

[Bigfoot1969]

Hello all,

When I've used the brakes a few times the car starts pulling to the left under braking. That's the short story, I'll now elaborate.

I bought a road legal track car last October. The guy who stripped it out removed the yaw sensor which meant the traction control light was continuously on but otherwise it didn't cause any problems. I did a trackday at Bedford and the brakes were working as you would expect, although there was a lot of brake fade so I bought some CL RC6 pads and Brembo HC discs. I then did another trackday at Bedford. The brakes were amazing. At lunch I changed the damper settings on my Spax RSX coilovers from medium to hard but when I went back out on track the car started pulling to the left under braking. I finished the afternoon session without incident, although I nearly took out cones in the braking areas a few times and I must have been close to spinning it.

When I take the car out for a drive on the roads it brakes in a straight line for the first few hard presses of the pedal, then it starts pulling to the left when I brake.

I put new pads in thinking that one side may be glazed but that made no difference.
I put new discs on thinking that one side may be glazed but that made no difference.
I had the wheel alignment done but was told that the setting were already good.
I replaced the rubber brake hoses with braided ones but that made no difference.
I replaced the brake fluid with racing blue but that made no difference.
I swapped the front suspension units over side to side to see if it started pulling the other way but it didn't.
I bought a new caliper for the offside front but that made no difference.
I took it to a local garage for them to check all of the suspension mounts but they couldn't find any play.
I took it to a Clio specialist who checked the ABS system and he gave it the all clear.
I took the ABS fuse out to disable the system but that made no difference (other than to cover both lanes of the dual carriageway with Uniroyal smoke).
I replaced the steering wheel angle sensor but that made no difference.

I've got the car booked it to have a yaw sensor fitted so that the traction control will be operational. I don't expect this to fix the problem as it didn't have a yaw sensor when I bought the car and it has braked in a straight line for one and a half trackdays.

Can anyone suggest what to look at next ? Are there valves in the abs pump that could be sticking ?

Any advice much appreciated.


Mark.

 

[reedy107]

lower arm bushes ??

ball joint ???

arb bushes ???



just thinking out loud

 

[Chrisgti6]

mis-aligned or loose front subframe?

 

[reedy107]

master cylinder shot ?

s**t in pipe to the right side ??

 

[coverman]

Tyre defect only apparent when hot?

 

[reedy107]

what u mite have to think is the left side is fine but the right side is not braking at all hence the pulling

 

[philfree]

Spax damper adjustment doesn't work on one side, one damper stays on soft pulling on this side under braking?

Edit: Never mind, didn't see you swapped strut which made no difference

 

[marinemackay2003]

rear brakes all ok?

 

[Bigfoot1969]

I've had two garages check for play in any of the bushes etc. and neither could find any play.

I have a set of track wheels and tyres as well as my road wheels and tyres and it's the same on both.

The rear brakes aren't binding but other than that haven't been investigated.

I was half expecting it to be the suspension as the fault appeared after I changed the damping setting, but the fault didn't change sides when I swapped the suspension side to side.

I read that the rubber brake hose can internally break up and broken off pieces could act like a valve. I've replaced the hoses that attach to the calipers. Are there any other hoses further up the line ?

I have seen a picture of an ABS pump and it looks like it has what appears to be two lines in from the master cylinder and then four out to the wheels. Are there any valves in either of these two items, and this might sound daft but would I be able to swap the two brake pipes around going into the abs pump for the front wheels to see if the problem swaps sides as this would identify a blocked pipe ?

 

[Welsh.Dan]

I've actually got the same thing on my car. New discs, pads all round, fluid and braided hoses too.
Strangely it isnt a constant thing, some days it won't do it at all. Mine only pulls under extreme braking. No sign of it even slightly pulling under low-medium braking.
I can repeatedly do emergency stops, and out of 10 in a row, it will pull to the left maybe 3 or 4 out of 10. Other days I try emergency and it doesn't pull at all. Its so strange. I greased all sliders in caliper when I did the pad change.

I did think of getting new front calipers but by the sound of your attempts it doesn't seem to have fixed the issue.
I'll try a few more stops on way home from work and see if mines still doing it. Brakes performance are brilliant other than this occasional, bizarre pulling issue.

 

[Chrisgti6]

A slight camber in the road can cause it to pull under hard braking

 

[Welsh.Dan]

Yeah it can do.
In my situation it's something to do with the car as you can hear the one tyre screech and not the other, and you can feel the weight of the car shift dramatically, as if the one side braking harder than the other. I have a trackday booked in a 2 week's so should be a good shakedown of the brakes. One of the other more mechanically experienced CS members can drive it and maybe shed a bit of light on the situation for me.

 

[Bigfoot1969]

With mine I need to be aggressive with the brakes to get the problem to show up. The first few times I brake hard from 70mph to 30 mph there is no pulling at all. After that it will pull to the left every time and you need to countersteer to avoid going off the road/track. The pull is progressive though, it doesn't suddenly pull. I'm having the yaw sensor fitted on Saturday and I'm going to get a quote for fitting a replacement abs pump/master cylinder/brake lines. It would be nice to have a good idea which part (if any) is causing the problem so I only have to replace that part. Ironically I sold my previous car which was a Westfield Megabusa because it had a clunking transmission noise that nobody could diagnose

 

[Welsh.Dan]

Sounds pretty much identical to my issue. I was going to replace master cylinder but I'm afraid of throwing money at random parts in the hope of fixing it.
Problems like this are the worst as its not easy to diagnose. My local garage don't know what it could be either.

 

[Bigfoot1969]

I've now had the yaw sensor fitted by Mick at Diamond Motors (great service and would thoroughly recommend) and as I expected the fault remains. I say expected because the car has never had a yaw sensor fitted whilst in my possession but hasn't always had this brake problem. I had the yaw sensor fitted because for MOT purposes it made sense to fix the system rather than rip it all out. Whilst on a test drive Mick suggested it might be worth considering looking at the rear end as the pull to the left could be the back end stepping out to the right. I've so far swapped the coil overs side to side and fitted new pads, to no avail. I've just bought a 30mm socket so I'm going to swap the disks over and then get a pair of well used cheap second hand calipers to try. I'm then going to look at replacing the master cylinder, ABS pump module and brake lines. Dan, if I can identify what fixes it I'll be sure to let you know so you don't have to have any unnecessary expense.

 

[STEVE.M]

Is there a compensator valve on the rear beam?Any play in the rear beam bushes?I would bleed the whole system including the rears.

 

[Bigfoot1969]

I had the brake fluid replaced when I had the braided hoses fitted so it can't be that.

I'm putting it through an MOT soon so I will ask them to look especially closely at all of the bushes etc.

Last night I swapped the disks over and I could see a build up of rust on the inside face of one of the disks that covered the bottom half diameter of the disc (if that makes sense). Also the inside pad had worn at an angle. It looks like the piston hadn't been lined up properly when the pads were last changed so the knob on the back of the pad wasn't sitting in the channel of the piston which resulted in half of the pad not touching the disk. I took it out for a test drive but it was raining so I couldn't test it properly. I'll take it out again when it's dry.

 

[st3ve]

Sounds like a sticky caliper to me.

 

[Welsh.Dan]

Sounds like a sticky caliper to me.

I'm starting to think the same in my case anyway.
Have been doing numerous E stops in mine over last few days and the issue has reduced massively.
When I first noticed it, it was quite a dramatic shift in weight.
Tried a few stops on way home and on the odd time it did pull it was nowhere near as severe.
With all these hard stops, it does make me think I'm easing/freeing something as the issue is easing off. Have a trackday on Wednesday so that will definitely be a good test.

 

[Bigfoot1969]

So I've been out in the dry and performed numerous emergency stops. It was initially pulling to the right under braking (good sign as I had swapped the rear disks over side to side) but after a while it started braking in a straight line (I guess the rust was getting worn off the disk by the pad and was starting to grip properly). I'm going to do more testing but I am stunned by the fact that it looks like an incorrectly fitted rear pad caused all of this.