sonett43

recently picked up an 85,000 89 Turbo. previous owner had it for a year, only 500 miles, owner before that pretty similar story....was buying a house and the toy had to go. West coast car, one long term owner, very well cared for.

The flip 2 owners ago had new rotors installed but can't remember why, except he had Zimmerman rotors on-hand and thought it was time....

so, here's the story, car runs great for the first 20 minutes, once warm, if you even tap the brakes the whole car shakes, not necessarily thru the steering wheel....but it sounds like it is coming from the front right.

First guess was the RF caliper was sticking, looked good, no rubbing noises when off the ground, so I swapped in new brake hoses all around.

problem remained.

I guessed maybe the front right had some disintegration, when I bled it's some small rubber chunks came out, so I pondered maybe a new rotor was warped.....ordered a front right rotor, swapped it on, problem remained.

maybe my ears are wrong, took one of those rotors and put it on the driver's side as a test, I know the cooling fins are specific left to right. problem remained. Swapped all the rotors back to where they belong.

Wear on the rear rotors looks perfect, no high spots, I don't suspect the rear rotors.

Does anyone have a suggestion?

Thanks

MAGK944

It’s unusual for the front brakes, suspension, or even the tires to cause the whole car to shake, it’s usually just the front of the car that will shimmy and you’ll definitely feel it through the steering wheel. Also, as it only happens when you attempt to slow down, try testing by not using the brakes. Instead downshift and use engine braking to see if the shaking persists.

First thoughts, I suspect you have a clutch or torque-tube issue, listen for any increased noise from the drivetrain when decelerating.

maybeillbuyit

I've had my share of brake related issues, problems and noises can be difficult to track down, at least for me. I would say small chunks of rubber point to maybe the flexible brake lines deteriorating inside. Changing them can't hurt if they are original to the car. I've also removed calipers but kept the lines connected, then pried up on the boots and had a good look at the piston going into the caliper. Any rust? Or compress the pistons into the caliper and see if any are stuck or dont come back out smoothly. Rebuilding calipers isn't really that hard to do either. Good luck. Or as MAGK944 says, maybe its not the brakes, control arm bushings?

Tiger03447

Front wheel bearings? Does the shaking get better or worse in turns? Just a thought...

Zirconocene

Maybe you guys can educate me, but what rules out the tie rods as a potential culprit? My thinking is that warm up period observation is significant, and maybe some of the aluminum components are playing a role, as they expand more with heat than the steel parts.

In addition to the good ideas you've gotten from other people, I'd take a look at the other bushings in the suspension that might be getting funky as some of the components heat up.

Good luck

jeyjey

Forward tilt and warm hydrostatic oil causing the exhaust side engine mount to collapse?

Shaking or vibrating?

odurandina

all of the above
adding to those possible issues
bad motor mounts
worn ball joints

PaulD_997C4S

Tire.
Swap left and right front tires and see if issue follows.
If not then suspension worn, or something loose, possibly ball joint or control arm bushing.

sonett43

Motor mounts are collapsed and on order.

I’ve decided I’ll buy the other front rotor just because and I don’t love how the brake pads look. Almost like they are disintegrated from excessive heat. So I’ll do pads, and swap the new rotors back on. And sensors.

at this point I’m willing to blame the motor mounts but I’ll check back in when the parts arrive.

all bushings, especially control arm bushings, ball joints, tie rods. Everything looks very clean and tight.

944Fest (aka Dan P)

The motor mounts on these cars are purely transformative. I don't know of any other front engine rear transaxle mass produced sports cars out there where the drive line is a rigid tube from the front pulley to the rear of the far aft trans. It will work but it has to be supported correctly! When the front mounts pop the whole assembly, rotating mass pitches down, throwing off alignment of everything hoping to miss rubbing or altering an alignment downstream. You might as well get one of those 'new car smell' air fresheners because the car will drive like a new car after motor mounts.