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post #1 of 11 (permalink) Old 05-19-17, 12:34 PM Thread Starter
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Brake problems

I have a 92 f150 straight six, 5 speed manual, 4x4. The problem occurs At 30mph or higher when I begin to slow down to either turn or come to a complete stop but is worse when coming at a complete stop. The vehicle will have a hopping/ or bump effect is the best way to describe it. I've had the shocks replaced with new ones installed. Next I am ready to install the whole tie rods assemble, along with the upper/ lower ball joints and bushings replaced with new ones due to they are ready to replace from 25 year old factory ones with new ones. The question I have is will this help solve the problem or is there something else involved?

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post #2 of 11 (permalink) Old 05-19-17, 01:31 PM
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Re: Brake problems

To me its sounds like the rotors could be warped. When holding steady brake pressure does it feel like the brakes sort of catch then let off with each revolution of the wheel? If so that's probably what it is.
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post #3 of 11 (permalink) Old 05-19-17, 05:50 PM
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post #4 of 11 (permalink) Old 05-20-17, 02:32 AM
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Re: Brake problems

I got to agree 100% with this comment below article

" Well, no. Parallelism and run out are both SAE checks. Sure, brake dust buildup can cause a pulsation, but saying a brake rotor will stay true is just false. I also am Master Certified and Advanced Level (L1) multiple times. Since the author brought up his credentials. "

If not the case , the different clock dial gauges I've used over 50 yrs in checking disc / rotor run out before replacing , must all have been faulty . The surface table that I sometimes checked the replaced discs/ rotors on to see visually how bad some were must have been knacked also .Brake dust build up contributed to a very small percentage .
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post #5 of 11 (permalink) Old 05-20-17, 04:27 AM
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Re: Brake problems

As I said; yes disk brakes can warp but (especially in my recent experience with move to more synthetic pad materials) it's more often a cementite glazing (or pad material transfer) issue. A simple run out test on a disc rotor with a dial gauge on one side will also not distinguish between a warped disk and a high spot caused by the transfer of pad material to the disk rotor. At the very least the run out test should be done on both side of the rotor. If the gauge indicates the same high spot on both sides it is often due to transfer of pad material and this material will not always be readily visible. In any event, the usual treatments for warped disks (replacement or skimming) will also address the pad material transfer issue.

It's always a controversial issue and we had the debate on this Australian forum here too: https://fordforums.com.au/showthread...ht=myth+warped the reply from Race Brakes on the second page is probably a fair view; i.e. All rotors can warp and there has been an increase in resin/pad deposits on rotor faces over the years and also more noticeable with slotted rotors as the build up can happen around the slot.

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post #6 of 11 (permalink) Old 05-20-17, 04:46 AM
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Re: Brake problems

Some other causes of a pulsating pedal:

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post #7 of 11 (permalink) Old 05-20-17, 04:46 AM
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Re: Brake problems

Perhaps it's a matter of semantics:


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post #8 of 11 (permalink) Old 05-20-17, 07:23 AM
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Re: Brake problems

I think we have to differentiate between ordinary , run of the mill brakes on most cars on the forum and high performance / racing brakes which are a completely different kettle of fish .You can usually easily see with the naked eye high spots and pad transfer on the discs unless you are Stevie Wonder .Not normally a common fault with brake jobs I've done , being honest but had a few .I remember removing an inboard disc on a car that was so thin you could have shaved yourself with it ( not quite , but you get my drift ) Slotted discs are liable to build up off dust and s**t but no big job to spend some time cleaning out .In different dealerships I replaced a lot of discs under warranty because of warping and they had to be returned to the factory to verify that was the cause and had been correctly diagnosed before we were paid out or claim rejected .I must have been o.k in my methods of testing as I cant remember any comebacks .Maybe the climate in different countries has a big say in brake problems , dry hot countries with high temps as opposed to the European wet roads .Also driving styles .Todays braking systems get more complicated by the day and this trend will continue .I found using the rolling road brake tester a great time safer in diagnosing brake faults as is todays modern test equipment which is essential on checking a lot of cars .One of those subjects we could debate for ever , but getting back to original post , I think JWKO was on the money with his reply and would be where I check firstly . Lets not digress to much from original enquiry .

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One of the links wont let you read it without joining the forum .

The guy at home video where he suggests using racing pads to scrub deposits off brake discs , surely not advisable on standard discs as they are a different compound , heat range and more abrasive ?

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post #9 of 11 (permalink) Old 05-20-17, 01:44 PM
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Re: Brake problems

" Perhaps it's a matter of semantics: "

May well be .Let's not confuse the poster further with different opinions and say " it could be faulty discs / rotors " as in post#2 .

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post #10 of 11 (permalink) Old 05-20-17, 06:11 PM
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Re: Brake problems

Yes; I totally agree the bottom line is that skimming or changing the disk rotors will likely remove the judder.

But I am still interested in the "academic" aspects of the causes and cures of disk brake judder. What appears to be the transfer of material on to pads causing brake pedal pulsations certainly is a common issue on our Australian made Fords (although sticking calliper slide pins is probably an even greater cause of brake judder on them). I wonder if it is a climate related issue (little snow in most parts) or perhaps in part at least it is because Australia has successfully banned the use of pads containing asbestos while the US ban attempted was unsuccessful (see https://www.epa.gov/asbestos/us-federal-bans-asbestos etc.) and we a stuck with safer more synthetic material is our brake pads.

And cementite on rotors is apparently not usually visible to the naked eye. Google "cementite invisible" to get lots of references. But nonetheless I have to acknowledge a Google Scholar search on "brake judder" for me at least gave no definitive answer and no confirmation that pad material transfer was a common cause. Perhaps cementite is just a localised thickening of the rotor due to changes to the chemical composition of disk metal rather than transfer of pad material. As they say here: http://www.powerbrake.co.za/Articles.asp?ID=253 "When the temperature around these high spots reaches 650 – 700°C. the cast iron in that area will change structurally and transform into a material called Cementite. Cementite is far harder than the cast iron of the unaffected parts of the disc and will therefore wear considerably less as the disc wears down with use.”

One paper concluded (e.g. Interactive Effects of Thermal Deformation and Wear on Lateral Runout and Thickness Variation of Brake Disc Rotors ) that hot judder is caused by deformed rotors but almost most seem to agree all brake sourced judder is due to variations in disk thickness (DTV) and often attribute it to changes in the surface of composition of the metal of the disk rather than direct transfer of pad material. And this paper The role of raw material ingredients of brake linings on the formation of transfer film and friction characteristics suggested that "the transfer film on the rotor surface reduced the amplitude of friction oscillation". Similarly, The Role of Transfer Layers on Friction Characteristics in the Sliding Interface between Friction Materials against Gray Iron Brake Disks | SpringerLink had this outcome: "Results showed that the transfer layer formation was highly dependent on the relative amount of ingredients in the friction material and temperature. Among various ingredients, solid lubricants and iron powders increased the transfer layer thickness but no apparent correlation between transfer layer thickness and the coefficient of friction was found. Strong influence from individual ingredients was observed, dominating the friction characteristics during sliding. On the other hand, the thick transfer layers on the disk surface tended to reduce the friction material wear and the amplitude of the friction coefficient oscillation during sliding." If these two papers are correct often layering of pad material would actually reduce brake judder.

It seems I am not alone in being puzzled by the actual cause of brake judder. This paper noted "There are numerous publications available dealing with high frequency vibrations, such as brake squeal, including mathematical models for analysis and simulation. However, low frequency phenomena, such as brake judder and groan, have received much less attention. There is a growing interest from the automotive industry concerning brake judder. Even though few companies would admit that they have the problem, it is not unusual to meet people who have experienced the problem in their own passenger cars. Much of the knowledge concerning brake judder remains within the companies. Hence, very few people have the full picture." I guess it could be as suggested "an industry secret" or perhaps it’s just that nobody really knows.

One interesting finding was that relevant to the original post though was: " the causes for brake judder do not always relate to the brake system but also to other components" http://papers.sae.org/920554/

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