What is the maximum thickness for rear brake pads?

dllubin

dllubin

Don
I was in the process of installing my new rear calipers and pads but ran into a bit of an issue. I did the passenger side and got everything on with barely enough room to turn the disc freely. I went to the driver side which has a newer (thicker) rotor and could not get the caliper over the pads on the rotor. Yes, the pistons are fully retracted, screwed in, and aligned. I even chamfered the ridge at the edge of the rotor to make sure it was not in play.

I started taking measurements and found that these pads are 11.7 to 11.8 mm total thickness. That surprised me as there are several posts here indicating something in the 9.5 to 10.5 mm range. I managed to find the manufacturer spec sheet (metalligroup Hybrix 088.0 pads) and it says 10 mm.

Anyone with insight as to whether or not 11.8 mm pads should fit? That is an extra 3.6 mm of material over the nominal 10 mm value.

Also, what are the options for thinning down the pads uniformly? Unfortunately, I no longer have access to a milling machine. Not sure doing figure 8s on a piece of sandpaper would be the way to go. I'm guessing 0.5 mm per pad might do the trick.

I also plan on contacting the supplier to find out what's up with these pads.
 
dllubin said:
I also plan on contacting the supplier to find out what's up with these pads.
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I think I'd start there.

Although I do not know what the actual specs should be or what can fit. But if they are too thick to fit, then that answers the question...they are too thick. I've noticed a huge difference in new pad thicknesses from different manufacturers (for any vehicle). Usually it is a case of being thinner, but I've found some that were thicker than normal and BARELY fit.

I believe this is with brand new calipers, so a couple of things to double check. Make sure they the correct calipers. Make sure both calipers are properly centered over the rotors. Does the left caliper have the same width (pad space) as the right one? Make sure there is no hydraulic pressure from the lines pushing in. Make sure the rotors are properly seated to the hubs and the calipers to the spindles.
 
some brands of brake pads include anti squeal sheet metal plates attached to the backside. Very typical for modern vehicles but they have to be removed for Fiats. If your pads came with them, pull them off.
 
After sending a message to the supplier about the pads, I got this response:

"I checked dozens of the rear brake pads and they all seem to be too thick by a bit to fit into the calipers. We have contacted the manufacturer, but I'm sure it will take a while to get the replacement pads from Italy. I have ordered some more pads from a US supplier and we should get those here before the end of the week. We will send you a set as soon as they come in."

At this point, I might throw the old pads (less than half worn) on just to get the car on the road. I've got less than 5 miles on the new engine and I'd like to drive the car while the weather is good.
 
Going by my past ownership experiences with 124's, X1/9's, 128's & 850's, I can tell you that there are at least 3 different pad thicknesses between the models, all with the same general outline profile/shape.

The 124-X1/9-128 front pads are really thick. The (post-'68.5) 850 front pads are about medium thick. The 124-X1/9 rear pads are comparatively thin, & should have a locating nub on the backside (not all do, it varies with manufacturer).

I've had vendors send me the wrong (thickness) pads per order on multiple occasions over the years. Sometimes they're mispackaged (manufacturer error or supplier repackaging), sometimes just the wrong ones were grabbed off the shelf. It sounds like you have a decent vendor who's at least giving good follow-up. ;)

If your vendor supplies 850 front pads as well, they might have accidentally given you those instead of 124-X1/9 rear pads (an easy mistake).
 
rachaeljf said:
Rear pads are same outline but 7 mm thinner than the fronts.
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Then the new ones you got should be good replacements for the fronts - so hang on to them. I don't see any harm in using the old pads until your replacements arrive. And I agree, it is good that the vendor confirms the error and is willing to replace them for you.
 
Jeff Stich said:
The 124-X1/9 rear pads are comparatively thin, & should have a locating nub on the backside (not all do, it varies with manufacturer).
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Interesting, I don't think I've ever seen them with those nubs. I assume they locate with the groove on the piston (park brake side)?
 
Jeff Stich said:
Going by my past ownership experiences with 124's, X1/9's, 128's & 850's, I can tell you that there are at least 3 different pad thicknesses between the models, all with the same general outline profile/shape.

The 124-X1/9-128 front pads are really thick. The (post-'68.5) 850 front pads are about medium thick. The 124-X1/9 rear pads are comparatively thin, & should have a locating nub on the backside (not all do, it varies with manufacturer).

I've had vendors send me the wrong (thickness) pads per order on multiple occasions over the years. Sometimes they're mispackaged (manufacturer error or supplier repackaging), sometimes just the wrong ones were grabbed off the shelf. It sounds like you have a decent vendor who's at least giving good follow-up. ;)

If your vendor supplies 850 front pads as well, they might have accidentally given you those instead of 124-X1/9 rear pads (an easy mistake).
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Actually, the box the pads came in lists all the models the pads fit and it includes the X1/9. I suspect the right packaging got the wrong product put inside at the factory, especially since the supplier's entire inventory has the problem.
 
Although it isn't the case in your situation, I also recall someone here (Bernice?) saying Mazda RX7 pads are the same shape and/or somehow interchangeable with X1/9 pads? Or maybe they are larger surface area but will fit as something of a upgrade? But they are available in a greater selection of performance compounds (not that Don is looking for that, just relaying info).
 
Dr.Jeff said:
Then the new ones you got should be good replacements for the fronts - so hang on to them. I don't see any harm in using the old pads until your replacements arrive. And I agree, it is good that the vendor confirms the error and is willing to replace them for you.
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I don't remember if the front pistons would clear the nub, but I suppose they would be easy to grind off. The vendor is Auto Ricambi. I've had good luck with them in the past for the few things they sell that fit the X. Last time I adjusted my valve clearances, they had the best selection and lowest prices on shims. They were also the only supplier of rear calipers I found that actually had them in stock and was not marking them up 2-3X.

I had an idea for somewhat accurately thinning down the thick pads. I've got an abrasive drum that fits my radial arm saw. It is basically a grinding wheel shaped like a drum so it should be more than wide enough to run the pad through in a single pass without missing a spot. I figure I can run the pad through on the saw bed which should result in uniform cuts on each pass.
 
I think if it were me I would look into the possibility of removing the 'nub' and using them as front pads before trying to make them thinner. By the way, I did not realize they had the nubs when I posted earlier.

However the grinding drum you have for a radial saw sounds very interesting. Not for this application, but there could be lots of other uses. If possible please post some pictures of it the next time you have it set up. Where did it come from?
 
Dr.Jeff said:
I think if it were me I would look into the possibility of removing the 'nub' and using them as front pads before trying to make them thinner. By the way, I did not realize they had the nubs when I posted earlier.

However the grinding drum you have for a radial saw sounds very interesting. Not for this application, but there could be lots of other uses. If possible please post some pictures of it the next time you have it set up. Where did it come from?
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My father bought the saw new in 1954. It was made by DeWalt back when they were owned by AMF. It was the first radial arm saw designed for non commercial use. It is built just like the commercial ones with heavy castings for most critical parts but just smaller. It will take up to a 10" blade. Unlike most of the homeowner type radial arm saws that came later (using extrusions and sheet metal), this one can hold tolerances as well as a table saw. It appears that the market has moved on to miter saws now. I'm not sure anyone makes radial arm saws anymore, at least for residential use.
 
Thanks Don. I'm very intrigued to see how the drum attachment works. That's the kind of stuff I make to work with my equipment.
 
Dr.Jeff said:
Although it isn't the case in your situation, I also recall someone here (Bernice?) saying Mazda RX7 pads are the same shape and/or somehow interchangeable with X1/9 pads? Or maybe they are larger surface area but will fit as something of a upgrade? But they are available in a greater selection of performance compounds (not that Don is looking for that, just relaying info).
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Gen 1 RX7 pads are the same "shape" but are thicker and will not install - actually sounds like what has been experienced.
 
How funny. I was just installing Auto Ricambi's new 38 mm rear calipers on my Scorpion along with a set of their ceramic brake pads and I'm having the same issue -- they just won't fit. I'll check the brand and measure pad thickness to see if they are the same as Don's.

As an aside, Auto Ricambi has given me excellent customer service in the past. I bought a set of pistons that were out of spec (turns out the rest of their supply was too) and they were exchanged for the next oversize without hassle or extra cost on my end even though I was past the return date.

EDIT: My problem was user error. I hadn't considered that I need to align the slot in the piston with the nub on the pad backing plate as was pointed out earlier in this thread. My RTX brand ceramic rear pads measured 10 mm exactly including the backing plate but not the raised nub. They fit perfectly now.
 
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According to FedEx, my correctly sized pads should be here tomorrow. Hope they show up early enough to install tomorrow.
 
Amazing how easy the brakes go together when the pads are the correct thickness. The replacement pads were Ctek (Centric) metallic. They came with shims attached and fit fine with them left on. Total thickness with shims ~= 10.5 mm.
 
Glad it worked out well. I saw your other post about driving it. I think the new pads just needed to bed in, which is what you saw in the braking improvement after driving awhile.

Now that you have the issue resolved, I'll go a bit off topic. Brake pad materials have always been an interesting topic. Lots to choose from and lots of mixed (and contradictory) information out there, plus many opinions. The manufacturers seem to be very vague about what they are made of, if they tell anything at all. Metallic, semi-metallic, ceramic, organic, OEM, composite, carbon, and many more. It makes sense to have different materials for different applications/uses, but I wish there was more uniformity to the way they are described so the consumer can have a better idea to compare and choose from. For that matter, I wish all makers were required to state the composition of the product; so many don't even bother to say anything.
 
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