86 300E Brake rotors..turn or toss???? - PeachParts Mercedes-Benz Forum

ChinaClipper · #1 01-30-2003, 01:10 PM

Any ideas what the minimum thickness of my 86 300E Rotors would be? Better to toss or have then turned? Horror stories? Thanks Scott PS Any good Ft wheel bering grease ideas?

timreid · #2 01-30-2003, 01:48 PM

ChinaClipper

How many miles on your 300E, and do you know if your car rotors been replaced or turned before?

enjoy your drive, timreid

ChinaClipper · #3 01-30-2003, 01:53 PM

Dunno if PO had them turned or not, 123K, 10K by me....Any hints on the min thickness? I know they are stamped on the rotor, but sometimes covered in rust etc, so I want the spec before I remove them!

Jim Anderson · #4 01-30-2003, 01:55 PM

I believe the cost of turning is comperable to the cost of a new rotor.

maheath · #5 01-30-2003, 02:13 PM

Maintanence Manual procedure 4251. Some excerpts:

Check brake disks for score marks and cracks. Cracks in a circumferential direction up to 0.5mm in depth are permitted.

Ventilated brake disks with hairline cracks up to 25 mm in length, which may show up under high loads, need not be replaced. Replace disks with open cracks and score marks deeper than 0.5 mm immediately.

Wear limit:
Ventilated front brake disks - 19.4 mm
Solid front brake disks - 9 or 10 mm
Rear brake disks - 7.3 mm

maheath · #6 01-30-2003, 02:14 PM

Almost forgot... Don't turn them, replace them.

haasman · #7 01-30-2003, 02:24 PM

Any group opinions on slotted or cross-drilled disks? I intalled a set of cross-drilled disks on the 300E and I really like them.

They seem to extend pad life, work very well in wet conditions and under severe use.

Haasman

#8 01-30-2003, 02:50 PM

Cross Drilling was done on a very specific application some time ago to allow gases from a particular pad type to escape. I think they are popular not because of their function in most applications, but because they look cool.

Have a great day,

md21722 · #9 01-30-2003, 02:55 PM

IF the discs are within spec for turning & the price is reasonable, then turn them.

haasman · #10 01-31-2003, 11:52 AM

Larry - I disagree.

I spent about $10 more per front disk for the cross-drilled and I think it is well spent.

During the winter rains the difference in stopping in the wet is amazing. Pad life continues to be much longer than I had experienced without. Driving in the Sierras last summer with a full load of luggage and people, the brakes never even smelled hot.

I think the fronts only are the way to go unless one autocrosses or does a lot of competitive/ club driving since 80% +/- of all braking is done by the fronts.

Since the '91 E has the wheels that don't allow a lot of veiw into the brake area, the visual effect for my car is nill.

Haasman

stevebfl · #11 01-31-2003, 12:16 PM

Never turn a MB rotor. If there is a sufficient lip on the rotor to be at decision time then it is already at the wear tolerance. There is only a mm to 1.5mm wear on most MB rotors.

The roughness achieved in almost all machine turning is too rough for good braking and pedal pressure.

csnow · #12 01-31-2003, 01:32 PM

Toss 'em.
We all know how prone they are to warping, and a thinner disk has less ability to dissipate heat.
Besides, at $35-40 each, is overhead of taking them to a machine shop +service cost really worth it for a DIYer?

csnow · #13 01-31-2003, 01:42 PM

Quote:

Originally posted by haasman

I spent about $10 more per front disk for the cross-drilled and I think it is well spent.

During the winter rains the difference in stopping in the wet is amazing. Pad life continues to be much longer than I had experienced without. Driving in the Sierras last summer with a full load of luggage and people, the brakes never even smelled hot.
Haasman

I would caution anyone who lives in roadsalt areas against cross-drilling. I have had really poor results with this.
The problem is that abrasive road debris gets trapped in the holes, and causes premature wear of both the rotor face and pads where there are holes.
Since the outer 1/4 inch or so has no holes, this diameter wears more slowly.
After 1 winter or so, your swept area will be reduced to just that outer 1/4 inch, and your braking capacity will be very poor.
Best of luck.

haasman · #14 01-31-2003, 04:26 PM

I have never heard of this. Seems possible. I wonder if Mercedes has issued some sort of service bulletins on this now that the S class come with cross-drilled as standard?