Brake troubleshooting..help!

sharpshooter677 · 05-01-2009, 09:10 PM

1974 911

Replacing rotors and pads all around...Regarding my front calipers which apparently stock are "M." However, with M pads part number # 911-351-938-00-M168 the actual pad height at about 1.7" does not cover the full face of my Zimmerman rotors..which right now i cant find the part number...

Also, i tried "S" pads, but they dont fit my caliper..wutever!
My rotors experienced this same problem, that the pads did not fully cover the rotor, which is why I am replacing them. Should I try "A" pads for the later 911?, or is it possible the calipers were changed...So the rear pads I bought which are the same as the front pads # 911-351-938-00-M168 which fit my front calipers...

So I guess my question is there a 74 pad the at height is about 2" or is it possible my front calipers are not "M" calipers. Does anyone know the dimensions of the"A" pads even though the guides fit for "M"..or do the have the same pattern!?!?!?!?!?!?

Flieger · Flieger's Garage

Don't panic. What exactly do you mean by "the pads do not completely cover the rotor."

Usually, the problem is pad overhang.

The pads do not cover the entire rotor surface. There is a little space (a few millimeters) on the outer rim and there is a larger area in the center around the hub that do not get swept by the pad.

Can you post photos to better illustrate your question?

ossiblue · 05-02-2009, 08:16 AM

Flieger has nailed it if I understand you correctly. M calipers are the same, front and rear, and use the same pad. It is normal that the pad does not sweep the whole rotor surface as he pointed out.

sharpshooter677 · 05-02-2009, 09:37 PM

FRONT ROTORS

Sorry for the bad pic...i got home from work late tonight..figured i'd jsut take a pic with the wheel still on, u can see it anyway...so yeah i see wat you mean max with the outer part..but should the surface around the hub be untouched as much as it is?...these are with the "M" rear pads...

sharpshooter677 · 05-02-2009, 09:40 PM

Um...fresh rotors help with the visibility...you can easily see where the paint was left behind...green arrows is cool...red arrows is what i am wondering about...so are you saying i can leave it like that??

Flieger · Flieger's Garage

I would run with that for a while. After a few dozen miles, you could pull the pads to make sure they are wearing over the entire pad surface. If so, that is fine.

The new rotors and pads will take time to bed in and show the wear pattern correctly, though.

sharpshooter677 · 05-02-2009, 10:40 PM

You think so?..It doesnt seem like to big of an issue. As long as i get adequate stopping power all around. Ill judge after I finish the whole job. Also, hub seals. Are they not available on pelican parts? My front hub seals are in decent condition able to re-use, but i figured I would get new ones. Not a big deal i guess.... Thanks MAX!

Flieger · Flieger's Garage

Do you mean the grease caps that cover the cotter pin for the outer wheel bearing?

I have no experience with hub seals.

Remember that for the first few miles, until you start to use the brakes hard enough to bed them in completely, you will have uneven and unpredictably low stopping power compared to broken-in parts.

Cheers,

VFR750 · 05-03-2009, 04:56 AM

This seems to be normal. The outermost 3-4mm of the edge should not have coverage by the pad.

You really have to drive 50-200 miles to fully bed a set of pads.

BTW, did you say if the wear surface and pad sizes on the removed rotor/pads were different that the new ones? Were they different?

djpateman · 05-03-2009, 05:47 AM

M calipers take M size pads.
S calipers take S pads.
A calipers take A pads.
S & A are the same area, but different thickness. M is much smaller area.

sharpshooter677 · 05-03-2009, 07:00 PM

Quote:

Originally Posted by VFR750

BTW, did you say if the wear surface and pad sizes on the removed rotor/pads were different that the new ones? Were they different?

...you have it right..the removed rotor/pads have the same wear as the new one i put on (pictured)...which is onereason I would be replacing them. So, the wear is exactly the same as the rotor/pads before it. So thats normal then?...sounds good..

sharpshooter677 · 05-03-2009, 07:02 PM

Quote:

Originally Posted by Flieger

Do you mean the grease caps that cover the cotter pin for the outer wheel bearing?

I have no experience with hub seals.

Remember that for the first few miles, until you start to use the breaks hard enough to bed them in completely, you will have uneven and unpredictably low stopping power compared to broken-in parts.

Cheers,

Yes exactly.. I really am sure it will pose no problem, he looked fine after a thorough cleaning.