Random Aggressive pulling/ instability when braking

[Dgracing86]

Hi Everyone,

Hoping that someone can help me and apologies if this is a bit of a long post - I will try to keep relevant.

I have a 2001 1.6 puma rally car (ST150 brakes all around). I have no ABS (module removed). Running AP coil overs.

Every so often, when I brake the car pulls quite aggressively to the left - as if the car is crabbing and sometimes even wobbling slightly too. There does not seem to be any rhyme or reason - happens at low speed under light braking and also heavy/ hard braking. It happens from cold or when brakes are hot. Usually, if I come off the brakes and reapply, the issue sorts itself out. If I keep pressing the pedal, the car becomes unstable and seems to lock the rear right - as if the rear is trying to overtake me.

This issue only happens under braking - car handles perfectly at speed.



I can do 2 special stages and it won’t happen - or I can tap the brakes as I leave my house and it can happen. I am really struggling to think what can be causing this - I have checked/ changed the following:

-Rebuilt callipers all around.
-Fitted mintex “fast road” pads all around
-Changed rear axle/ bushes
-Changed front control arms/ bushes
-Changed tie rods/ rod ends and realigned
- bled brakes multiple times
-Fitted bias valve for rear ( has no impact on this issue)
-full nut and bolt check
- hubs/ bearings all tight/ appear fine
- probably forgetting other things I have tried


Does anyone have any ideas/ suggestions as to what could be causing this? Again, this is intermittent and random ( I have tried and tried to recreate the issue but it’s impossible)

Any thoughts/ suggestions would be massively appreciated - running out of ideas!

 

[yippeekiay]

Can't think what it could be with everything you've already checked.
Assuming wheels/tyres/balancing & alignment are good - which I don't think would be an intermittent cause, just a thought.

Throwing this out there but how are the roads you're driving on? Could it be the actual road condition?
You could be tramlining on a bad road, or simply braking on a less grippy surface at times & not realised that what all it was.
Bit of a long shot but who knows with not having ABS to sort out any dodgy surfaces.

Good luck either way

 

[John Woodward]

Can't think what it could be with everything you've already checked.
Assuming wheels/tyres/balancing & alignment are good - which I don't think would be an intermittent cause, just a thought.

Throwing this out there but how are the roads you're driving on? Could it be the actual road condition?
You could be tramlining on a bad road, or simply braking on a less grippy surface at times & not realised that what all it was.
Bit of a long shot but who knows with not having ABS to sort out any dodgy surfaces.

Good luck either way

I think that you've checked everything that I can think of, having read your post again, I wonder if it's possible that something in the master cylinder, pipes or calipers is acting like a non return valve, it's not something I've ever experienced, but had something similar at work, (not cars) which turned out to be a piece of debris acting like a non return valve.
Have any of the brake lines or pipes got any kinks or twists ?

 

[Dgracing86]

Thanks guys

Yes, bad camber on roads/ tram lining was an initial theory but I’m sure it’s not the roads - it’s such an odd feeling/ thing to happen that I really am struggling to explain. “You have to see it to believe it” sort of thing…

Interestingly - my latest theory was that perhaps there was some grime in the master cylinder which was having an impact on the front brake lines only (the fronts being plumbed into the outlet furthest from the car/ closest to the end) - for the sake of a couple bolts and some brake bleeding, im going to try replacing the master cylinder during the week.

Can’t believe I didn’t think about this sooner to be honest, but the fact John has mentioned it too gives me hope - aside from the MC all the lines are fine/ no blockages or kinks etc.

I’m fast running out of theories so eventually I’m bound to be right!

Will post how I get on!

 

[Dgracing86]

Hi guys

Just a quick update. Changed out master cylinder but made no difference - however after further investigation it seemed there was some debris in the brake line to front right calliper. ran a temporary brake line to drivers side front calliper and seems to have fixed the issue - seems problem was two fold - 1) the crap on the line causing occasional pressure loss to front right cause car to pull and 2) was the balance being all over the place with the rears which amplified the issue.

Cheers For the input glad it’s finally sorted - a bit annoying all it took was 15 minutes to fix in the end!

 

[John Woodward]

Hi guys

Just a quick update. Changed out master cylinder but made no difference - however after further investigation it seemed there was some debris in the brake line to front right calliper. ran a temporary brake line to drivers side front calliper and seems to have fixed the issue - seems problem was two fold - 1) the crap on the line causing occasional pressure loss to front right cause car to pull and 2) was the balance being all over the place with the rears which amplified the issue.

Cheers For the input glad it’s finally sorted - a bit annoying all it took was 15 minutes to fix in the end!

Really pleased to hear that you've got it sorted.