Steering judder under braking

[80Sprint]

I have tried to resolve this but I am getting nowhere so far.

I am running trackerjack brakes with Sierra discs and calipers. All new when fitted and probably only 2000 miles since. The car is lowered on Spax and polybushed.

Discs and pads checked and all seems ok.
Disc run out is 3 thou
I greased the guide pins.

Wheels look like they could have lost a weight but it has no shake at 100mph ( on the track of course )

Could it be something in the suspension ?
Is 3 thou still too much ?
Could the wheels be ok at speed but still give issues under braking ?

Any help appreciated.

At Goodwood next weekend but no time to sort it now.

Tks

Mick

[tony g]

3 thou is too much for me. I was always told to aim for 1.5 thou max. Ive said before on this subject,the hub to disc interface can affect this a bit and in my experience (2x TJ conversions) the hub needs gentle filing to mach the disc. Mark the hub to disc so it goes on the same way every time you strip and build it. (of course you can try all 4 positions first to get the lowest number. Even cruddy/dirty hubs can upset the numbers.
Just remove a tad of metal/crud for a good clean up and keep checking. Got mine to under a thou in the end, worth the effort.

Tony

[Carledo]

I've fitted 4 sets of TJ now without a problem (must confess one set, on my Sprint, has not yet been tested) the set on the Carledo has done 10k + including trackdays, it will need new pads soon! But i'm pretty careful on assembly, making sure everything is spotless.

It definitely SOUNDS like disc warp though and 3 thou is right on the upper limit of what I would accept as viable.

FWIW, might be worth checking BOTH faces of the disc for "bulges" as this can give judders too, just tip-ex 8 or 12 marks around the edge of the disc and gather readings on both faces at each point and compare.

Steve

[gmsclassics]

A few thoughts from my experience:

I always adjusted the wheel bearings up so that I had zero play, but just ran freely. Sometimes I used shims so I could get a setting between the turns of the castellated nut. Good grease and Timken bearings (Chris Witor).
I tried to get as close to zero run out on the discs. Thoroughly cleaned both surfaces and used small pieces of wet paper between disc and hub for the final adjustment. Only wet so they stick while disc is refitted.
Tyres would need a cleaned up with a wire brush to remove rubber they had picked up from the track and the fronts would need rebalancing often.

I would do the above after every second race meeting, or sooner if any issues arose.

I also found that the poly bushes on the front drag struts (mine are adjustable) would wear /tear themselves to bits unbelievably quickly so I had some very hard / tough ones made. They have lasted well and tightened up the front end.

Could the wheels be ok at speed but still give issues under braking ?

Yes, absolutely. Braking on the track is always full on and changes the dynamics significantly. Any deficiency will be magnified hugely.

There's an example of steering judder in my car in this video https://www.youtube.com/watch?v=6-iVG8Gtgo4

Geoff

[xvivalve]

With this appearing in the 'last post' section of my browser titled "Steering judder under bra..." I had been hoping for a somewhat different content of discussion!

[xvivalve]

https://www.youtube.com/watch?v=UiU_HVl_dH4

[Galileo]

Oh my!