Hello:
This weird vibration happened after I put on the winter tyres, so I thought it was just the tyres being out of round or maybe a little off balance as they were stored standing up. The vibration is weird because it happens intermittently, and when it does I can feel it in the seat of my pants and even the headrest. It almost felt like the brakes were catching and releasing very very quickly and it felt like it was coming from the rear, nothing in the steering wheel.

So I jacked up the car, and checked the drive shafts, flex discs and wheels. I had the nagging thought that it was brakes, but how can brakes cause such a vibration? I noticed that the passenger side rear wheel brake line looked pinched and there was a cut in it, but no fluid leakage so I thought nothing of it. Turned the rear wheels in neutral and found the wheels really stiff to turn (does the shaft turn with the wheels? Mine did) and I reckoned it was stiff cos of that connection. A buddy of mine thought it was the motor mounts. I didn't think so, cos when the vibration happened, I put it in neutral and coasted the car and its still vibrated. In fact, its almost like a hard pulsing.

Fast forward to this morning. The vibration was worse, when it finally came. Comes after about 20 km or so. This time, it felt almost like my rear end was bouncing up and down!! Then I had to do a hard stop due to some idiot cutting in front of the guy in front of me. After that, the next time I braked, the pedal went almost all the way down to the floor before it caught!! I drove really slowly to work then and numerous times when I needed to brake, the same thing happened. As I exited the highway, I tentatively stepped on the brake and what the hell...it was back to normal!!

So at this time, I really don't know what's going on. The brake reservoir is full. There's a slight pulsing on the brakes when I use it (probably my discs need changing, but I just changed them Feb 2008). Sorry for long post, but I've tried to be as detailed as possible. Any ideas?

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1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

Maybe there is air in the system. Did you try to pump the brake when it went all the way to the floor. the failure would indicate that there is a leak, or maybe air got into the lines. If you cant find a leak I would try bleeding the lines, and go from there.

Well, I suspect the damaged brake line is a hint. Is it still intact, and are you sure both halves of the brake fluid tank are full?

It's possible that the brake line was crimped and causing the brake to drag. That could cause the fluid the heat up and boil. Did the brakes recover when they cooled off?

Replace the damaged brake line immediately, brakes aren't something to mess around with.

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TC
Current stable:
- 2004 Mazda RALLYWANKEL
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Past: 135i, GTI, 300E, 300SD, 300SD, Stealth

Never thought of that. Yes the line is still intact, but there's a visible break in the outer sleeve. Doesn't seem like any leakage though but I will check both chambers in the brake reservoir (forgot about the back one!). I didn't realise that a crimped brake line could cause the brake to drag and cause the fluid to boil!! Come to think of it, the loss in braking happened right after that panic stop and after the whole highway drive not using the brakes, the braking power came back. That kinda explains it. But what of the vibration?? Could that be the brakes as well? Or are we looking at more expensive things? Thanks for the replies guys!

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1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

I wouldn't be surprised if a dragging brake could cause a vibration, possibly a warped rotor. I would deal with the brakes first, then see if the vibration is still there.

OK, thanks for that. I was told that if the brake pedal squishes all the way to the floor (like mine did), its likely the master cylinder is shot. So it looks like this is going to be an expensive repair for me...brake lines plus master cylinder is probably $200++ at a time when I can ill afford it.

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1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

I wouldn't assume the MC is bad. Just replace the line and bleed the brakes, then see what happens.

OK thanks. I will do that first and see. Will report back after its done.

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1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

Marko !!

Silly question.Are you missing any lug nuts by any chance?
Cheers from down under!
Big Dan
Southport,Surfers Paradise Australia

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Cheers
Big Dan MEng

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I never think of the future.It comes soon enough.

Bens is onto a good point there.
If the wheel is not mounted correctly, the rotor is under stress or out of position leading to vibration and pad rub that can lead to overheated brakes...

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2009 Mercedes ML320 Bluetec

How's your rear shock? If it's bad, then it may have let the brake line stretch when you jacked up the car since the shock supports the wheel carrier. If the shock doesn't do it, then the brake hose is the next in line.

That may explain both symptoms - the vibration/bounce and the bad brakes.

Your parking brake isn't frozen, is it? Maybe 20 km to warm up and over heat? That's an outside possibility but more likely if the temps are dropping to freezing now.

Hey Big Dan...whilst you're down under enjoying all that sun, we've been drowning in water here!! Thanks for the thought...but no, I checked all tyres and just yesterday, I took them off to replace the brake hose...which, is par for the course with my car, always seems to be an adventure. In this case, the crimped brake hose came out easily enough. The other side nut was frozen to the hard line. In the end, I had to cut it off and lug it to Lordco, where thankfully, they had almost the exact same length of hard line with the correct metric head. Gosh whatta chore!!

Anyway, long story short, this morning on the drive to work, guess what...yep, the bloody car started vibrating again!!!
What gives?? I'm pretty sure the brake is releasing since there's no more crimp in the hose to stop it from doing that, but damn that sure feels like brake grabbing. Still, the vibration happens at any speed, and goes faster with speed. At almost stopping speed (near lights) it feels like the way my brakes do...grabbing cos the bloody rotors must be warped.

I noticed on taking a bend in the road though, that a left bend creates some light clunking in the rear. What gives?? Axles?

Geez, why did you have to run off down under man.

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1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

Hi Yak...the rear shocks. Hmmm The bounce test doesn't show any problem with the shocks. I do know that when the back is loaded with adults, the rear sags a fair bit...thought it was normal.

How do you mean that the shocks support the wheel carrier? When I took off the old brake hose, it was hanging pretty tight, but it didn't feel like it let down when the hose came off. I thought the springs hold the weight no?

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1987 300TD
1984 300D
755,000 KM and going strong
BC Canada

Well, if the brakes are dragging, they should be getting hot after a few miles. Carefully feel the wheel after the next drive, if one wheel is hotter its probably dragging. Does the master cylinder feel OK now?

The thumping does sound like a bad CV joint. Take a look at the boots and see if any of them are cracked. You might of had two separate issues.