Lurching left at speed - possible castor problem?

[PaulZR]

Morning all

Curious to see if anyone has experienced something similar to this problem I'm having with my Cup-suspended 182. At motorway speeds (say 55 mph and above) when turning left on long bends, the steering angle will suddenly increase markedly with a slight movement of the wheel. Effectively the car 'lurches' to the left with a slight increase in steering input. It's only really noticeable at higher speeds and is a little disconcerting; feels like tramlining but happens regardless of road surface.

Few things to note:

• I have changed from original 182 alloys on bald, mismatched tyres to 172 Cup Turinis on all new tyres. The problem was exactly the same on both old and new wheels;
• Springs and shocks appear to be original (82k miles). Visual inspect suggests no leaks or breaks, and no obvious damage to any of the major suspension parts;
• Alignment done a few hundred miles ago. Don't have details but was done by racing car engineer who I know and trust.

I am no expert but am wondering if there's a latent issue in the front suspension and / or top mount that could be causing this. Anyone have any ideas?

Thanks
Paul

 

[adamlstr]

I had this a few years back (172 cup), after turn in and suspension load the car would increase it's turn rate - turned out to be the bottom NS ball joint had shat itself.

It's come back now, so I imagine it's something similar.

 

[sam JFM]

Have you checked your ball joints?

 

[PaulZR]

Cheers for the input.

Quick update: jacked the front of the car up this afternoon and gave both front wheels an exploratory waggle. No obvious play in either wheel that would suggest the ball joints are knackered. I'm no expert so will get the garage to confirm on my next trip, I think.

 

[adamlstr]

PaulZR my bottom ball joint didn't have any play that I could feel using hand strength, the only sign was that it was weeping grease/oil/fluid.

 

[PaulZR]

Interesting. Will get it up on a ramp and report back.

 

[TheCAB]

Need to get a bar in between to check, not always obvious by hand even when jacked up due to load from suspension.
You need to jack wheels up off ground individually, ball joint play won't show if car on ramps due to weight of car still being on ball joint

 

[PaulZR]

Hello again. Just to close this one off, eventually diagnosed the problem as... knackered ball joint. Huzzah! O/s ball joint was knackered, with the joint bit lifting in and out of the socket in which it sits*. £80 ish later, ball joint saved, problem solved.

Thanks for the help chaps.

*non-technical explanation.