My dealer says I need new front pads and rotors and that the job will cost about $500. I have looked at the front rotors and the wear on them is trivial. The pads look like they need replacing though. I looked only at the outside of the rotors assuming that the rotor wear rate is even with that on the inside of the wheel. Can anyone tell me what the recommended thickness is to replace rotors or should they be replaced everytime the pads are changed.

Thanks,
DTF
1994 E320 Wagon

Find out if the rotors were measured. If they say yes, ask what the measurement was. If they don't know get a measurment and confirm if they are at or below min spec. Min spec on those rotors should be 19.4 mm. The spec is stamped on the rotor hub in case I'm wrong.

Please excuse my ignorance - but 19.4 mm measured from where to where? What I am seeing is a very small 'lip' on the outer edge of the outside rotor that can't be more than 1 mm high.

Thanks for the input,
DTF

1994 E320 Wagon

DTF:

I dont know if his specs were right, but he is reffering to the minimum(By law) thickness of the disc itself. You can read this with a micrometer, all shops and parts stores that resurface or "Turn" rotors have to measure the thickness to see if the rotors need replacement. Anyway, 500 bucks sounds really really steep.... You can get the OE parts from Partshop for about $50-60 per rotor, and $25-30 for a set of pads... overall about $150 for premium quality parts with no sales tax.. There is even an Do-it-yourself article on this site that shows you how to do a brake job on your specific car with very basic tools. Give the DIY section a look and then cruise through Fastlane parts, you might find auto maintenance an interesting hobby :)

Best of luck and welcome to the forum

Jason M.

...for that sort of lip, I would suggest a new set of pads will sort it out for you until the next time for a pad and disc change. I have never favoured turning brake discs, they are cheap enough to be able to purchase a pair of full thickness new ones. It is almost the same as using someone else's oil out of the sump drain at the local garage when you take it for an oil change. Buy new ones and ride safe and confident. It is after all, only a few dollars for new brakes. ( well, I think so ! )

I've just been messing around in this area on my '87
300TD.

Minimum rotor thickness is 19.4mm, as discussed above.
This is the *width* of the rotor measured where the
pads have worn it down.

It's important to note that 19.4mm is the minimum
thickness the rotor must have *after* the new set of
pads is worn out. Hence it must be thicker than 19.4mm
when the new pads are installed - but by how much I
don't know. The service manual may specify the thickness
at which rotor replacement is required during a pad
change.

I think the thickness of a new set of rotors is about
22mm. Hence if you have a 1mm lip on either side of the
old rotors, you're sitting at about 20mm thickness vs.
19.4mm as the minimum. I think you're on the borderline
of needing new rotors. Given that the brakes are the
primary safety system in a car, I'd sure replace my
rotors. (Did, in fact.)

BTW, the price sounds absurd. I purchased new ATE rotors
from my favorite vendor for $28/each. Front pads were
another $28 or $29.