On-car brake lathe
 

I just noticed this item on E-Bay:
http://cgi.ebay.com/ebaymotors/SNAP-ON-KWIK-LATHE-YA180-TO-TURN-ROTORS-ON-CAR-NR_W0QQitemZ140089074426QQihZ004QQcategoryZ63695QQrdZ1QQcmdZViewItem

item: 140089074426
Described as a "Snap-On Kwik-Lathe YA 180 lathe:
"This tool is for turning disc brake rotors without removing them from mostly import cars which I saw mentioned somewhere in the instructions. I have never used it but it seems to be in very good condition with all the threaded adjustments turning and moving easily. Included is a box of carbide replacement tips shown in closeup of the cutters on the machine. There is a selection of mounting bolts, bushings and nuts however I'm not sure whether they are enough for every import variation. The foam insert nesting the tool in the carrying case is pretty beat up by whoever put the machine in and out of its box. The working parts, like I said, are in great working condition. The manual is a Zerox copy and it's very light but readable. The machine itself weighs about 28 pounds but packed about 35lbs. What you see in the pictures is all you get but if I can answer questions please ask and I will try to answer."

Has anybody used these with Mercedes brakes? How are they? Is it still a current-model piece of machinery? I'm guessing that they use the drivetrain to turn the disc, so wouldn't work on Merc fronts, but maybe on the backs.

I am a believer in just replacing the rotors. They are soft and intended to be replaced, IMHO. Get them too thin and they will warp. They are cheap.

My experience here is limited to the 124 chassis.

It's a good deal, but Mercedes aren't FWD
 

From Snap-On:
>>YA180A On-Car Brake Lathe Overview:
The YA180A On-Car Brake Lathe mounts in place of the brake caliper and enables the technician to resurface a front wheel drive car's brake discs while they are still on the car. Special mount fixture reduces set-up time by providing a quick reference for spacer requirements and correct link spacing as well as cutting tool centerline. The unit mounts in place of the caliper and the vehicle turns the rotor during machining. "Dead-on" accuracy in only 8 to 12 minutes<<

I guess you could use it on the rear wheels of RWD cars??

I saw it in action on a Japanese magazine - there should be an external spinning tool that spins the hub at a certain speed that's lathe friendly.

don't know how this one works without one.

The on car brake lathe is made for FWD cars where removing the disc, either for turning or replacement is costly. Some models of Honda come to mind, at a price of $350-20 years back, ouch.
Not needed for Benz as the discs are readily removed for turning or replacement.

I have a friend from the Third World who tells me that an important part of any DIY brake job there is to put the car up on jackstands, start it and put it in gear, and go over the rotors with a sanding block (DO NOT DO THIS!).

^ how is that going to flatten out brake rotors that are genuinely warped?

That's the main reason we use these lathes is it not?

The on car brake lathes are becoming more and more common around shops of all kinds and they work well. The advantage is to the shop. They can set it up to turn the rotor and not have to pull it. The rotor turning takes place while the tech is doing something else in tandem and he doesn't have to wait for the rotors to come back from the shop or in a big shop he doesn't have to cart the rotors to the other end of the facility.

The machines do an okay job, nothing more or nothing less than removing the rotor and having it done on a stationary lathe.

All that said, it is a none issue on an MB. MB rotors are: 1) Too thin to cut and have enough mass left for an adequate "heat bucket," 2) MB rotors are cheap anyway, 3) probably too many rotors are replaced unnecessarily.

Measure your rotors thickness and compare to the spec. If they are within thickness spec and you do not have a pulsating pedal, put pads on them and forget it.

Also, a pulsating pedal is often not a warped rotor at all. Todays most common cause of pedal pulsating is the use of tire foam without covering the wheel. It takes very little overspray of tire foam to cause a slick spot on the rotor that allows the other portions of the rotor to get hot while that spot stays cool. It then leads to a partial glazing OR an actual warping.

Cover wheels if you use tire foam.

I didn't say it was a good idea, I'm just telling you what they do...

Wow! That's the first I've heard of this issue.

Would figure that most tire foam users would be meticulous at wheel cleaning as well, and after washing, the rotors would have gotten wet and be sufficiently cool to not be affected at all.

To add to that, Tire Foam overspray wipes off of wheels with a swipe of a cloth...I would suspect brake pads would remove the emulsion from the discs with a couple of turns of the wheel (sufficient to also remove the oxidation left from washing too).

I mention this because I'm a Tire Foam junkie...I use it on all the vehicles.

Only warpage issue I had was with the 300E two summers ago, and that was because I let the rotors get dangerously thin one time.

Julio,

I expect that you are pretty careful with tire foam. Not everyone is. They just spray it all over.

The stuff does not simply get wiped off by the pads. It reacts with the pads to glaze a portion of the rotor. Sometimes this problem will clear itself up after awhile but if a hard braking is done from speed while a glob is still on the rotor, it can be permanent or near permanent, requiring the rotor to be cut or replaced. I've seen it.

I'll take that tip under consideration...thanks!

Tire foam?
 

Larry, forgive me for being a complete idiot, but what the heck is tire foam?

I dunno what tire foam is but...
 

Maybe you can describe how ANYTHING could stay on a brake disc at "speed?" As for me, I use P21S and flood the discs and calipers during washing to get rid of some of the brake dust.

BTW, the experts will tell you that MB discs are not turned but instead are ground with a blanchard grinder.

I expect that during the manufacturing process that virtually ALL brake rotors are finished with a grinder, not just MB. That really has nothing to do with the reason for not turning MB rotors.


Tire Foam is a product that was first sold under the trade name "No Touch," but now is sold by Armor All and Son of a Gun. It is a rubber protectant that you spray on tires and it is in the form of a foam on contact. It then soaks into the rubber to some extent and gives the rubber a dark, shiny look.

This substance is oily, that's why it reacts differently than "P21S" which I assume is a cleaner of some sort.

Think about it, will an oily substance cause problems with the brakes as opposed to a cleaner. I think sOoo.


BTW, no one has to believe me on this, I am just reporting what I have seen. Sometimes you can theorize until you're blue in the face and you just can't totally explain things.