Rear end waggle under hard braking / snaking scary results?

[c3dpo]

Hi all,

I've tried searching and failed

I have a 172 cup and under moderate to heavy braking from 45+ MPH, the rear end "snakes" if that makes sense?

I thought this could be a caliper binding, or such. Cleaned up both front calipers and while the brakes became more potent, the snaking is still there.

90% of the time its on direction, i.e. passenger back end wants to come around. Though after my brake clean up, the issue went the other way????

I know my rear shocks are fooked on one side, so have replacements for those (though they aint returning to start position after compression and not sure if thats normal or both of mine are fooked)?

Could it be that, or is this likely to be ball joints? If so, does anyone have a link to ones that have the right diameter hole (I think they come in 10 and 13mm)? Or must you pay for the whole lower arms with new bushes and ball joints.

Again apologies for asking all this, I've tried searching the net quite a bit, but not finding much on it.

Thanks very much

Dean

 

[theduck]

Rear shocks.

 

[NorthloopCup]

Your brake compensator valve could be seized as well. If it's seized in the closed position (as they do move - only by a small amount though) it will be getting more pressure to the rear brakes. That would cause it to snake under braking, but only if it's heavy braking really.

You need new rear shock absorbers first though as from your description they are 100% fooked.

 

[mikekean]

I found on my Cup that was in perfect working condition that under heavy braking the back end would become very loose. I think there just like this stardard tbh, makes them pretty exciting to drive, a decent set of coilovers would help settle it though.

 

[Advikaz]

I didn't think the cups had a compensator valve on the rear? Correct me if I'm wrong....

 

[NorthloopCup]

I didn't think the cups had a compensator valve on the rear? Correct me if I'm wrong....

Yes mate they do. They're the single reason why the majority of cups fail mot every year! Lol

 

[mikekean]

They have one but there is no arm on it, so i cant possibly see how it could go wrong as the pressure is set to a fixed figure..

 

[Gavin J]

My brothers (52 plate) 172 cup has a compensator valve and it does have the arm connected (had seized and stopped any fluid going to the rear brakes) so it seems its a bit hit and miss as some are and some are not - dealer confirmed this aswell....

 

[NorthloopCup]

The compensator has a arm on it, but it's not connected to anything. The arm on the compensator is held in the up position by a spring that attaches to the chassis. This keeps the compensator in the closed position, but when the brake pedal is pressed, the arm deflects downwards to reduce the pressure to the rear brakes.

The arm on the compensator only moves in relation to the pressure applied, ie, less pressure = less movement, more pressure = more movement. It reduces the pressure by a set amount at full pressure.