Brakes: Disc Brake Pad Backing Plate Comes Loose Repair: Adhesive, Bonding, Epoxy, Tuffbond 230, ...

[tomhoo]

Over 1/2 the pads I've ever serviced have the backing "sheet" separate.

I believe this is a non-critical issue because the brakes do not fail when this happens and also, have you ever seen conventional pads separate from their backing plate (about 1/4" steel)? (answer = no)

I have looked for "Friction Bonding Adhesive" and yes, Henkel/Loctite makes it but only in massive quantities.

I have found the following candidate methods after internet research:

1. JB Weld - lots have recommended it with success stories. No failure stories
2. eBay - someone is selling "Brake Lining Adhesive Bonding Kits" which appears to be an epoxy with no specs.
3. Tuffbond 230 - an epoxy sold in India for brake shoes and clutch lining
4. Henkel - unobtanium, bonds with pressure and temperature (over 300 deg F).

Also read that the backing plates do not get as hot as rotors since the pads act as insulators.

Again, the backing sheet is almost an afterthought as far as I'm concerned and what is the worst that can happen? They'll just delaminate again.

For now I'm thinking just try the JBW although I have asked the eBayer for more specs on his kit. It is $20 shipped for something like 20 20 CC's of epoxy.
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EDIT:

This may be a moot point. Although I have a basically new set of pads, 2 of which separated. I'm getting my Toyota Sumitomo 2-1/4" pots SS sleeved and if I have any sense at all should run EBC Green Stuff and be done with it (!)
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EDIT 2:

Just checked: JB Weld withstands temps up to 550 deg F which isn't too shabby. Might be the most expeditious approach.

[Mike Van Veghten]

I'd be very, VERY carefull with this.
1. I've never had pads fail like you mention, motorcycle or car, and I've beat on the motorcycle brakes pretty hard.
2. Brake pads and rotors can get "MUCH" hotter than 550 degrees (F) fairly easilly.

Remember it's not only your life you may be taking a chance on, it may also be the persons life across the intersection..!

I'd be buying for higher quality new pads than the ones you've had fail.

Mike

[tomhoo]

First, I've never seen a non Stude/Jag pad separate from the backing plate.

I have seen about 50% of Stude/Jag pads separate from the backing "plate."

Conventional pads use thick and structurally rigid pads to distribute usually a circle line load from the piston over the entire face of the pad. This is exacerbated with modern pads which are very long.

The Dunlop pad "backing" has no structural purpose. It is merely a piece of thin, flimsy sheet metal which engages the "nail" on the piston. Its only purpose is to connect the pad to the piston during retraction - a load which is negligible compared to braking loads.

Again, the piston is a flat solid surface - not a circular line. It does not need to have its contact load distributed via the backing plate - it already is due to the solid flat face piston. This means you could drop pure friction material in the caliper cavity and have it work w/o any kind of backing (you would have to drill a small hole to clear the "nail head" that protrudes from the piston.) Many people are driving right now with separated backings and don't even know it.

Are you familiar with the Dunlop system? I've never seen another brake pad that had a thin, sheet metal backing - they are always "plate" thicknesses.

I'd like to know why you think this is a critical.

As far as getting hotter than the 550* F, yes to rotors and pads, but what about backing plates and caliper pistons? I don't know what the caliper seals are rated at but they definitely cannot with stand rotor temperatures which can actually be luminescent (red) - something the Dunlop are capable of.

Granted, I don't like the idea of a 550* adhesive limit, but when you consider how easily the backing "sheet" comes off these pads, I don't think anyone else was that concerned. Again, on average, 1/2 of all Dunlop used pads separate.

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FYI: From AP Racing's site (they make racing brake systems and many, many styles of racing calipers.)

"Because race Brake Clipers are sometimes subjected to very high and unpredictable operating temperatures, they must be examined and seals must be replaced on a reular basis to maintain efficiency and safety. Seal life is governed by the time at temperature which should therefore be kept as llow as possible by provision of cooling airflow. For guidance only AP Racing offer the following recommendations (temperatures measured on the outside of the Caliper adjacent to logo):

* Calipers that regularly run at up to 200*C - Re-seal every other event
* Calipers that run intermittently from 200*C to 220*C and agove - Re-seal as soon as possible
* Reduce "soak" temperatures after the car has come to rest where possible (e.g. do not leave foot on brake pedal when stationary with hot brakes) as this can cause excessive caliper temperatures."

200* C = 392* F
220* C = 428* F
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EDIT:

Here is a study done by the Washington State DOT regarding brake system temperstures - FEM compared with experimental.

In short, disc pads reached 800-1000*F and shoes, 300-400*F

As I expected, the Tuffbond 230 is specified for "shoes and clutches" which I thought was inadequate for discs.

So it looks like there isn't much of a solution.

Of course, the way most people drive their cars, 550#F might be good enough. I mean like how many people make their caliper paint change colors? ...caliper paint?

[tomhoo]

Turns out EBC uses a true backing plate - something I have never seen - of course how many people find EBC pads on a Studebaker, eh? (may be time to get the DP2120 Green Stuff and there is even DP3120 Red Stuff if you track the car)

From the www.viva-lancia.com website:

"Use pads with a steel back plate such as EBC DP2120 or DP3120. The steel back plate is already attached to the friction material. See the green picture below. Do not use the old fashioned pads. The modern pads are backward compatible with the old fashioned pads. You can also use them with the original Dunlop pistons which have the "mushroom" on top. In the box with the pads is fibre material for noise elimination. You may cut that to size and stick it to the back of the pads."

NOTE: One thing that is completely different with the Dunlop system is that the backing "plate" DOES NOT position the pad - the pad fits neatly in a nest. All other disc brake designs position the backing plate and then the glue holds the friction material on the backing plate. If a modern pad would delaminate, it would be a DISASTER. So you might say the Dunlop is more robust because it does not rely on glue for anything other than pad retraction which is not even a secondary issue.

[BrianC]

That's great info. on the pads, I had a set arrive with half back plates off. Now only fear in using them is the possibility of squeal or chatter or some other strange frequency.

[tomhoo]

BrianC, are you saying you got new ones where half have had their backing plates come loose?
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Some more "high temp" finds:

Actually, Permatex Ultra High Temp Copper RTV is good to 700*F.

So I search for 800*F and find (!) Rutland Seal it Right 800-Degree Latex, 10.3-Ounce Cartridge, Black for about $15 a full size calking tube. Latex, who would have thought.

Cotronics has

• Durabond 7025 1000*F Aluminum Putty, and
• Durabond 7032 2000*F Stainless Putty (has "excellent adhesion" and is machinable)

Versachem 83009 Inferno Metal Repair is good to 2000*F and I have used it. It is very weird - like metal flake in corn syrup. It flows like honey, but with just a few seconds with a heat gun, skins over and is stable. If you let it cool down, it turns liquid again (!) When it finally dries/cures it is very hard. Can be machine and sanded. Available at Autozone for $10. NOTE: I still have some of this. I'll try an experiment and see how hard it is to pull the backing off. EDIT: As I feared, it dried out once opened. NOTE: they claim "nano" technology for this product.

is good for 1000*F and intermittent to 1500*F. ("remarkable adhesion to clean and rusted metal) Autozone for $4.

NOTE: Versachem appears to be owned by ITW which also owns Devcon.

COPALTITE is a 1500*F sealant that does not harden (actually a good property) that is quite pricey $50 for a 5 oz. tube from various industrial supply houses.

Frankly, considering how poorly the OE backing "sheets" are attached, chewing gum might work.

[BrianC]

Yes, got them from SDI, the cost of returning them exceeds the cost of purchase?? At least from here in Canada. I'll track down the Durabond, thanks for the tip.

[tomhoo]

VERY INTERESTING FEM transient analysis which shows the insulating qualities of friction material: https://www.youtube.com/watch?v=KpEOkeZAJg4

• Rotor heats massively where contacting pad
• Pad @ rotor heats at a significantly slower rate
• Pad @ rotor never reaches rotor temp
• Heat transfer through Pad is poor
• Pad @ backing heats even more slowly and barely exceeds the rotor hub temperature.

This means the previous info I found,

• the pad is a poor conductor of heat (insulator) is correct, and
• the backing/adhesive sees "hub like" temperatures which are significantly lower than rotor and pad @ rotor temps.

CONCLUSION:

• 550*F JB Weld just might do the job.
• 600*F Red RTV just might do the job,
• 700*F Permatex Ultra Copper would most likely do the job
• 800*F Rutland Latex would be even better however latex is more unfamiliar than commonly experienced epoxy and RTV

[tomhoo]

Regarding ASBESTOS

If you wanted to design a pad that would keep the backing/adhesive at the lowest possible temperature, what would you do?

Use asbestos as the friction material.

Asbestos is legendary for its high temperature stability and very poor thermal conductivity - its an awesome insulator (good electrical insulators are almost always good thermal insulators: ceramic is another example.

Since all brake systems evolved from asbestos, they have striven to maintain this insulating property since it keeps all "downstream" components at lower temps. (Everything from the adhesive, caliper seals, and lastly brake fluid.)

This further reinforces the belief that the adhesive sees a much lower temperature.

OBSERVATION:

How many of us have worn pads down to the backing plate?

Guilty as charged!

What is interesting is that delamination does in face occur in little pieces as the friction material is worn down to near paper thicknesses. Even 1/16" of friction material usually stays bonded, but as you exceed that, where the "featheredge" should be, there will be little chucks that break off, maybe around 1/32" or less.

So in this case, YES heat gets to the adhesive and it fails. But only after the point where the pad should have been replaced.

And again, in a conventional design, if the friction material delaminates from the backing plate, the pad positioning is lost which is a critical failure. The Dunlop, however holds the friction material itself in a nest so this is a non-issue.

[tomhoo]

Frankly, I'd be inclined to favor the epoxy because of its adhesion and hardness. Again have not found any complaints about using JBW.

RTV is actually a good "glue." However, even it used as a skim coat, there are significant compressive pressure applied during braking. I don't know how repeated cycles would affect the RTV. However I would still not rule RTV out.

[StudeRich]

OBSERVATION:

How many of us have worn pads down to the backing plate?

Guilty as charged!

I take it you were talking about brand X Brakes in this instance? It is impossible to wear a Dunlap System Brake Pad down much more than to about 25% because of the "Stops" that prevent braking with under thickness Pads.

It is a pretty good hint when you have to "COAST" to a stop on the rear brakes, that you need Pads!
Don't try this in an Intersection!

[tomhoo]

Forgot about the Dunlop pads not wearing down to the "metal." Due to the nail head feature on the pistons, clearly they had to protect the pistons.

There are so many differences between the Dunlop and all other disc brake systems.

Too bad I couldn't get a "sheet" of Green Stuff and cut out some pucks (!)

[jnormanh]

Yes, got them from SDI, the cost of returning them exceeds the cost of purchase?? At least from here in Canada. I'll track down the Durabond, thanks for the tip. [ATTACH=CONFIG]43066[/ATTACH]

When you say "backing plate separated", I assume you're talking about the thin anti squeal shim , about .020 thick, which is loosely, or not at all, attached to the actual backing plate, which is usually about 1/8" think. Those shims do not need to be permanently attached at all, and in many applications are not. If they separate, braking ability is not affected. OTHO, if the actual "backing plate" separates, then the pads can move, or, indeed fly out of place and you'll have no brakes at all.

If never seen, or, in fact heard of, an actual "backing plate " separate from the friction material.

The shims are normally held in place because they "register" in the caliper, and are often coated with grease before installation, although some are glued.

[tomhoo]

jnormanh, you are not familiar with the Dunlop - it is totally unlike any other disc brake system.

Characteristics:

• No 1/8" Bonded Backing Plate
• No anti-squeal shim
• Bonded .030" sheet whose sole purpose is to engage the piston "nail head"
• Pad friction material is precisely located by the cavity it resides in you could actually run blocks of friction material with no bonded metal whatsoever (but you would have to provide a slot to clear the piston "nail head"
• Locating pad friction material is NOT accomplished through a bonded "Backing Plate" like all other disc brake systems.
• Pot seals are on the piston, not in cylinder grooves.

Everything you have referred to does not even exist in the Dunlop system.

I would suggest you research this system. Historically, it was the first disc brake system that was adopted by Jag, Stude, Ferrari, Lancie, Mercedes, Toyota, Datsun and the list goes on. You should first focus on the purpose of the piston "nail head" and the pad retraction feature.

The very next generation of caliper design put the seals in the pot and it has remained that way ever since.

Ironically, the first time I ever replaced seals in a modern caliper (a 2000 Windstar), I was shocked about the placement of the seals. I thought the Dunlop was the center of the universe!

[SuperHawk]

Just for what its worth, I would like to confirm what Tomhoo is saying.

I have owned and driven Stude factory equipped disc brake cars for well over 40 years. Hundreds of thousands of miles. And, yes indeed, those backing plates absolutely become delaminated from the asbestos pad material. It mostly happens when it is time to reinstall new pads. When you lift/pry out the old ones, half the time the thin metal backing plate becomes loose. I have had new ones come apart too, in which case I just don't use them , because I have more new ones on the shelf, and I just do not know what the consequences would be if a "defective" part was used.

This is just for info only, substantiating Tomhoo's experience.

Larry