Technical Brake instability at high speed

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Technical Brake instability at high speed

bulldog5046

faster! FASTER!!!
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Howdee,

when braking very hard from a good speed, say 100 down to 40 or even a stop the rear end of the car seems to get very 'floaty' and sways making it difficult to control the car and undoubtedly looking pretty dodgy!

do i need to adjust the rear braking bias to prevent this or if it just a case of new pads and discs all round?

i cant really remember if it was like it before or if my old one was so looking for advice.

Cheers,
Ry
 
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bulldog5046

bulldog5046

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hmm... its still on standard dampers so could well be, i will let you know once they have been replaced (wont be very soon mind!)
 

NumanR

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The easiest to check dampers is a static check, with the hand brake off bounce the suspension up and down through as much travel as you can and when you release the suspension the car should setltle in one cycle, if it continues bouncing this indicates the dampers are poor. A dynamic test is to go on a large roundabout with bumps, we have one near our dealership which when they eventually resurface it is going to ruin my test route. Drive around the roundabout at a safe but faster than normal speed and hit the bumps, if all is well, the car will stay stable and tight to the bend, if the dampers are weak or faulty the cars rear end will bounce towards the outside of the roundabout. You dont need to go too fast and dont do it in the wet, but you will feel a definate kick in the pants when the car shifts.
 

Notorious131

speed kills... and??
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Sounds more like a suspension prob', check for play in the bushes on the trailing arms and/or in shocker mounts.
As said earlier very much doubt it would be brake bias and is n't it a self adjusting bias on Mareas anyway??
Load dependant??
 

mountainmachine

Bravo 155 HGT
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Nope brake bias would cause rear end lock up or poor braking at rear, neither would make the car feel "floaty"

When i went for my MOT with the Volvo i was told that the break bias was off, ie it was breaking more on the front right than the front left, i fixed the problem as it was just break dust and such like on the pad carriers causing it. At high speed it did feel a bit strange, and would imagine if that happened at the rear is would feel floaty.
 
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bulldog5046

bulldog5046

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the reason i thought it was maybe the bias was because i can feel the front of the car dig into the road and the back lifting up like the wheels coming off the floor.

i figured more rear bias would keep the back down?
 

NumanR

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No what you find is that the brakes dont get any better at the front so if you have excessive dive (due to weight transfer) the suspension at the front may have gone weak or the rear is lifting due to weak dampers. Anybody who has changed dampers when they have been shot will know that the resistence to movement disappears, so they are easily stretched and compressed. Whilst the springs are used at the rear to maintain ride height under normal driving conditions, the expansion phase of the rear shocks is used when the car goes light (under braking). The resistence to expansion reduces front end dive by not allowing as much weight transfer to the front. It works in reverse on the front where the compression phase is used along with the springs to reduce weight transfer.
 
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bulldog5046

bulldog5046

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with you now, wont be changing the suspension until after turbo project then i will be fitting FK adjustable coilovers so we will have to wait and see.
 

Notorious131

speed kills... and??
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Bulldog if your going to coilovers, I hope your ready for a very hard ride, I've got Koni adjustables and there bloody hard ride on the soft setting.
I understand what you mean about the brake bias now, I think you may be correct about that after all.
I had an old Lancia HPE which had an automatic front/rear brake bias system, which was basically adjusted according to the ride height of the rear of the car.
If you loaded the car up and the back end lowered due to the weight, then the valve would partially close reducing braking force to the rear disc brakes.
If you got the car loaded up you wouldn't notice it working because of the weight in the back of the car and the weight transfer under braking.
 
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bulldog5046

bulldog5046

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Dont do 100mph (in UK) & it wont happen;)

becomes an issue seeing as she's been visiting the track ;)

Bulldog if your going to coilovers, I hope your ready for a very hard ride, I've got Koni adjustables and there bloody hard ride on the soft setting.
I understand what you mean about the brake bias now, I think you may be correct about that after all.
I had an old Lancia HPE which had an automatic front/rear brake bias system, which was basically adjusted according to the ride height of the rear of the car.
If you loaded the car up and the back end lowered due to the weight, then the valve would partially close reducing braking force to the rear disc brakes.
If you got the car loaded up you wouldn't notice it working because of the weight in the back of the car and the weight transfer under braking.

yeah i am looking for a lovely solid ride, where did you manage to get your Koni adjustables? are they Marea specific or bravo/a?

i was going to buy the bravo kit and modify the rear's to fit.
 
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Notorious131

speed kills... and??
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Koni kit is Marea specific something to do with top mounts..??
It took alot of finding and cost way too much £450 inc PI springs trouble getting Koni springs on time and thats with alot of discount.
Goes round corners VERY well if you know what I mean.
But it is very very hard ride...!!!
 

custard

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right now your complaining of it not being right under braking.
so you put a performance hike over sorting the suspension/brakes
 
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