Author Topic: Suspension geometry change under braking  (Read 269 times)

Rolo

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Suspension geometry change under braking
« on: 28 June 2020, 01:20 PM »
My car tracks fairly straight with a slight drift left.  Under hard braking, the geometry changes so that I have to turn the wheel pretty far to the right.  I'm thinking that a bushing is worn or soft and allows a big change in the geometry.

Anyone have experience with this?

rumb

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Re: Suspension geometry change under braking
« Reply #1 on: 28 June 2020, 02:37 PM »
One thing to consider is brakes.
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ptashek

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Re: Suspension geometry change under braking
« Reply #2 on: 28 June 2020, 03:32 PM »
Rumb makes a good point. I'd first check the calipers (could be sticky), pads and rotors. Next I'd check the shocks and springs, and then the track rods.
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daantjie

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Re: Suspension geometry change under braking
« Reply #3 on: 28 June 2020, 04:51 PM »
Agreed, pulling to any given side under braking is a classic sign of brake issues.  I have to say this is one area where my 6.9 outshines even modern cars, the brake feel and response is top shelf with no fade, shudder or any kind of pulling.
Daniel
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floyd111

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Re: Suspension geometry change under braking
« Reply #4 on: 28 June 2020, 09:49 PM »
yes, if this were a <20 years old car, I'd say check/adjust the alignment, and wait for something to go 'clonk, clonk", indicating bishings or shocks are gone.
These older cars, heavy cars, might need a step-by step check to be sure. Too many "maybe's" to consider, at too much risk. Calipers, disks, pads, bushings, shocks, springs, and maybe even other stuff I dare not mention as a layman among mechanics. :)
Give it a proper check, and start with whatever is visible without having to take things apart, hope it's something simple and cheap.

revilla

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Re: Suspension geometry change under braking
« Reply #5 on: 28 June 2020, 10:34 PM »
Experienced the exact same issue here.
Breaks definitely!
But there’s something much more specific to check: the pistons in the calipers. In my case it was one rear/outer piston that was sticking. They weren’t expensive. I changed the seals too of course. After that the drift was gone.
Hope it helps.
Robert
W116 1977 280SEL & 1979 280SE

rumb

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Re: Suspension geometry change under braking
« Reply #6 on: 29 June 2020, 04:47 AM »
The rubber brake lines if old can also cause problems.
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Randys01

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Re: Suspension geometry change under braking
« Reply #7 on: 30 June 2020, 02:01 AM »
qik test...jack front of car off the ground. have a pal gently apply the brakes and check the comparitve rotation resistence of the front wheels. Bet the right hand one just bites whilst the left just rotates. It's all in the feel. If this be the case explore the difference between r and l pad wear. if a noticeable difference exists the one the with the least wear..the lh..will now point the finger at the front lh brakes.. so either seized piston or double check for wall thickness fatigue in the flex line. Before pulling anything apart, treat it to a brake bleed. hily unlikely that air has got into one side of the system but may be there is some history here we don't know.

Rolo

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Re: Suspension geometry change under braking
« Reply #8 on: 03 July 2020, 08:50 AM »
The brake hose theory is intriguing.  Rotors and pads are new.  I just serviced the calipers.

Rumb, Are you thinking the line on one side is expanding and softening the fluid pressure?

I may be mistaking for geometry since it only occurs when the nose is going into the pavement.  Braking from high speed is straight, but really hard braking coming to a stop with a lot of nose dive is not.

UTn_boy

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Re: Suspension geometry change under braking
« Reply #9 on: 03 July 2020, 09:05 AM »
The brake hose issue Rumb is referring to isn't as you're thinking.  First of all, these are to be renewed every 10 years for good safety measure.  Most people never abide by this rule.  What happens is that the inside passage way of the brake hose collapses.  It ends up acting like a check valve in that fluid will either be allowed to pass or not.  Sometimes the fluid can pass but not return, which leaves the brake applied even after the pedal is released. 

If it's not a brake hose, then it has to be a sticking caliper or air in the system. 
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ptashek

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Re: Suspension geometry change under braking
« Reply #10 on: 03 July 2020, 05:42 PM »
Instead of replacing rubber with rubber, do yourself a favour and go for Stahlflex hoses. They'll outlive the car, and probably the landfill they may eventually end up at ;)
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