Heavy Vibration While Braking

[Jetaway]

Folks,

I'm hesitant to post here because its not like my Z is by the side of the road somewhere, it isn't, its in my garage, but I do think I need to get this figured out quickly.

1972 240Z. Stock in any potential source of the vibration. Haven't done anything recently to the brakes, suspension, wheels, or tires.

The vibration is noticeable if you are on the look out (feel out?) for it at around 30 mph, by 40 mph noticeable, by 50 mph annoying, by 60 mph getting scary.

The vibration only occurs when the car is in gear and begins with the lightest touch on the brakes, its intensity increasing with pedal pressure. Occurs with gradual increase in pedal pressure or sharp braking. Doesn't seem to have an effect on stopping distance, nor grabbing / swerving, though I am not in the habit of nor do I think a full-on stop would be a wise move at this point.

At speed, in neutral: smooth. Not like silk, there is a bit of a vibration, but probably no more than 50% of the cars out there, and not severe at all. Even the "rhythm" of the vibration seems different, with the in-gear vibration cycling faster, though this feeling may simply be the result of much greater amplitude. It may have started as long as 3 weeks ago, entered my consciousness as something amiss 2 weeks ago, and it was only a couple of days ago that I tried braking at speed while in neutral. Pretty sure the vibration is getting more intense with time also.

The only thing I can rule out is the front brakes. I put in new pads and pins 3-4 months ago and pulled the wheels last weekend for an inspection and nothing seemed amiss. Now I at a loss to where to go next, and what I should be looking for, as the problem occurs at speed while I'll be looking at it going 0 mph in the garage.

Suggestions?

Chris

[superlen]

Sticking caliper? What did they look like when you put in new pads?

[Hunter260Z]

Had the same problem on my Chevy truck. Replaced calipers, two weeks later same problem. Replaced rotors, no problem that was a year ago. Rebuilding the front end would help.

[ZCurves]

Yep, warped Rotors. Rebuild Calipers, Replace Rotors. I say replace Rotors rather than have them machined because - They're cheap to replace and machining may provide a temporary solution, but because they have been 'Thinned', they tend to warp again. Don't forget new shims and lube the calipers so the pads can move.

[5thhorsemann]

yep, warped rotors. Rebuild calipers, replace rotors. I say replace rotors rather than have them machined because - they're cheap to replace and machining may provide a temporary solution, but because they have been 'thinned', they tend to warp again. Don't forget new shims and lube the calipers so the pads can move.

ditto

[bluezcrazy]

If you don't want to buy new rotors, I would suggest having them turned with an On Car Brake Lathe. That way it will rule out any wobble your hub may have too.

Bryce

[Jetaway]

Warped rotors? Even though the vibration is strong only when in gear? True, I didn't have them turned when I replaced the pads, with generic, six months ago, or ceramic two - three months ago but they didn't have any goofing. (Ruling out calipers as they were replaced when I put in the generic pads.)

If warped rotors are the problem, that would be great. Parts or service pretty cheap, not that difficult to pull off of the car. I'm knocking off work early today, so I can start in on it in about four hours. If anyone has another viable possibility, please speak now or forever hold your peace (piece?).

Chris

[5thhorsemann]

Piece (of mind)...............Peace!

[ZCurves]

While you are working on it, inspect the play in your Inner and Outer Tie Rods and Lower Ball Joints. When re-assembling make sure to follow the Torque-Specs from the FSM !

[Jetaway]

The spirit was willing, but the flesh was weak. The heat, high 90s, is not that unusual, but the humidity is and dragged me down. Even worse today, so it looks as if my main girl, Stella, will be doing transport duties for the next week.

Thanks all, the rotors shall be machined. They are non-stock, grooved and cross-drilled, which costs a bit more than standard, so even if I can only get another 20,000 out of them, it will be worth the money.

Chris

[Jetaway]

All better now.

Though quite the ordeal, some self-inflicted, most not.

I knew it would take awhile because the labor required is early equal to that of replacing the pads and the front wheel bearings and separating something or the other from the rotor that had become quite fond of staying together. Took the rotor in to Brake Master's. Nope, won't machine it? Why? Nope, won't do it. Why? Cross-drilled and grooved. Why? Because they are cross-drilled and grooved. So why won't you do cross-drilled and grooved rotors? Eats up the bits. Asked: Do you know anyone who will work on them? No.

Fine, so I go to Les Schwab's. They were OK with grooved, not so with cross-drilled. Bit may catch on edge and break the rotor. Grrrrr. Asked: Do you know anyone who will work on them? No. You'll have to buy new ones. "Not at $250 a piece, a mumbled."

Went home to take my kid out for lunch and to mull over where to take them. Try every place in town? Try my luck at a performance car builder? Monkeys! I'll try Monkey's.

No problem, $20 each.

Now this is how to make sure you don't get my business. I can excuse the Les Schwab guy because for all I know he arrived in town yesterday. But the Brake Master's guy has been here since I got here 13 years ago. A friend of mine, in his mid-30s, and born here has told me that Monkey's has always been here. Allowing that very young children aren't that good at remembering things, I'd guess 30 years at least. Especially because he thought it was a Monkey zoo. No way in hell the Brake Master's guy didn't know of Monkey's and knew, at the very least, they worked on brakes and worked on just about anything. I don't think I'll be taking my business their again.

Anyway: Shiny rotors (they look like the Motor Sport version) in hand, I return home to deal with a balky caliper. The piston wasn't frozen, but very tight. So I went to O'Reilly's and picked up a new one for $40.00 - $7.50 core charge. Yes, they had them in stock. Put it all back together, bleed the new caliper side. Come around to the other side, with an eight month old caliper and -- &&*! I had broken the S-shaped brake line that goes from the brake hose to the caliper.

No luck anywhere finding that baby. Decide to bend it myself. Took awhile, like 4 hours, but finally got it. Wouldn't seal up on the caliper side. I figured the problem was a "nose" on the connector and carefully cut it off, screwing up the threads in the process. Cleaned them up manually and --- still wouldn't seal up. Screwed in the other end. Hung up maybe 2/3rds of the way down. Finally determined that the new-old caliper had stripped threads. Tried tapping it out. No dice. Capitulated and went back to O'Reilly's and bought another caliper. (Yes, if you are counting, that's three in stock calipers for a '72 in six months at O'Reilly's.) Bought more brake tube, gave it to Monkey's and an hour later they called with it. Had to bend it a bit at home, but it is a tricky arse curve, but finally got it in, topped off the brake fluid, bled master cylinder, left, right, and master again.

The Z was out of action from Friday morning till Tuesday evening. I probably put 20 hours in on it including the running around looking for parts and service. But: No vibrations!

Thanks for pointing me in the right direction!

Chris

[5thhorsemann]

FWIW, ALWAYS take drilled and slotted rotors to a mcchine shop to be turned, they need to be done on a lathe, and cut in slow passes. A rotor machine at a brake shop is too agressive for the job. My 2 cents.