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what would make front end start to shake around 50mph? New brakes AND rotors May2020.

3319 Views 17 Replies 8 Participants Last post by  amc49
what would make front end start to shake around 50mph? New brakes AND rotors May2020. Thanks for reading
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What 'warped' rotors? I cut both drums and discs by the hundreds and there is really no such thing. The issue is really one of messing the cast iron friction surface up with embedded friction material off the pads/shoes. The effect is the same, you think the part is warped but throw it up on the machine and not warped at all. The difference is hitting cast iron or pad friction material ground into the disc, the difference in friction can be radical.

OP look at the ties, they can easily do that shake if loose. Jack wheels up in air and do a 3 and 9 o'clock tire yank looking for looseness.
You can't even do it that way as there will always be play in varying amounts in the wheel bearings. That alone throws the accuracy off. There is no such thing as zero runout either except for side to side, both sides will still vary at the same time and in the same direction though, the floating caliper movement cancels that. Why you MUST cut both sides at the same time. At least on a disc/drum cutting machine.

It's not even necessary to have zero runout. I used to send them out at up to .004" all day long and as long as both sides were cut at same time the discs never showed a problem ever. If the side to side variance goes any further off than .002" you got trouble though.

Balance? If the tire has worn out of round you can balance it to the end of the earth and it still shakes.

I have not a clue as to what overtightening lugs is as I go to 75ft.lbs. and any tighter and the lugs tear up. If you got discs warping for real I'd say dump the cheap crap discs that are not full thickness to wear out faster.

The axles pull forward on any FWD car under power. The brakes then pull them back again. Any slack you got in there moves from back to front under power and at neutral power the slack can be in the middle to let tire flop around in a shake and if the ties are loose why you shake then but it can then go away with a lot more power or hard braking and how you check for it along with the 3 and 9 tire check.

If you are not braking the problem is NOT brake parts.
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I never had any problems at all with the off the car lathe, you just have to know what you are doing at the machine. I had to retrain the guy who 'trained' me of course, typical of everything I do. I had to explain to the district managers how they messed up customer parts over and over. They didn't seem to care and much of the issue.

Digital reading side to side to zero means nothing to me, I can get it easily with no readout at all.
Next much do you use it now? The reason I ask is because so many parts now tend to come in undersize and cannot be legally cut any more. When I was in parts roughly 7/8 of the parts that came in needed to be replaced especially if disc, the new pads if semi-metallic simply eat the discs alive, the disc wear rate about the same as the pad. Now modern ceramics may have stopped a lot of that, it seemed to be headed there when I quit the shop. The cheap crap Chinese discs add to that by commonly machining the parts so they go below minimums even with only a couple months of use. I would check discs right out of the box to find them maybe .010" over the minimum number. The difference in expensive and cheap parts, the more expensive had the full OEM new thickness on them.
Read the last big paragraph at bottom of post #10. Your fix is there.
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