rear brake moan... - Ford Mustang Forums : Corral.net Mustang Forum
 
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post #1 of 13 Old 10-11-2015, 10:16 PM Thread Starter
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rear brake moan...

This weekend at VIR my car developed a terrible brake "moan" while taking right hand corners. The first couple of sessions on Saturday it was not too bad but became worse during the third and forth sessions. I am running Raybestos ST43 pads on the rear with Cobra calipers and the "anti moan brackets"... The differential is the stock "Trac Loc". Upon inspection of the rotors the left rear rotor is "bluing" while the right rotor appears "normal".

Saturday evening I pulled the left rear caliper off and the left axle appears to have ~.100 to .125 end play. The left axle also appears to have a very slight "up and down" movement, my "guesstimate" would be ~.010 "up and down" movement of the axle. Unfortunately, I didn't pull the right caliper to compare the axle end play or "up and down" play...

Prior to putting the caliper back on the car I swapped the rear pads from side to side and took it out for a drive. Of course I was not at speed but there was no more moan. During the first session this morning all was good for the first couple of laps. At the end of the long straight on the third lap the "moan" returned but as I applied more brake pressure the "moan" went away... In right hand corners after, with no brake input, the "moan" returned. I got a "point by" and drove deep into #1, a right hand corner, and the "moan" then became a grinding noise. I then backed off and came into the paddock... Upon inspection I could not find any witness marks of the caliper bracket hitting the rotor.

I have searched and found some posts were others have mentioned having similar issues. However, I could not find a clear solution.

I don't have a great deal of experience with the "Trac Loc" diff or with the type of bearings in the 8.8 axles. I have been drag racing and had a spool and had 9" axle ends installed in the 8.8 that was in my drag car... Is it plausible the "Trac Loc" is just worn out and the excessive end play of the axle is causing the pad to drag while cornering? Is it considered "normal" for there to be "up and down" play in the axle shaft with the type of bearings in the 8.8 ends?

Thanks in advance and any suggestions will be appreciated...


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post #2 of 13 Old 10-11-2015, 11:06 PM
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It's very possible, but before further conjecture, what axle housing, what axles, and what rear caliper setup are we talking about?

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post #3 of 13 Old 10-12-2015, 07:37 AM Thread Starter
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It's very possible, but before further conjecture, what axle housing, what axles, and what rear caliper setup are we talking about?
MFE... The housing and axles are stock equipment for a 1994 GT. The calipers are the stock Varga Cobra calipers with just "white box parts store" Cobra rotors. I am using the Ford "anti-moan" brackets...

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post #4 of 13 Old 10-12-2015, 12:02 PM
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Man,I wish I could be useful here but I've had the same issue for over a year. I bought a replacement caliper in the rear and I think the moaning started after that but it's tough to recall. It became less annoying as the pads wore some but I still hear it a bit and have had to tune it out because after pulling off the track and inspecting a zillion times I never could figure it out. I've replaced my diff as well but still hear it and I know a co-racer who says he hears something similar on his 96 cobra. So I hope this mystery is solved by someone eventually.
Are the anti moan brackets those little clips on the ends of the pads?
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post #5 of 13 Old 10-12-2015, 12:54 PM
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Up and down movement at the wheel sounds like worn out wheel end bearings. Probably a separate issue from the brake issue.

The end play in the axle may be getting a little too high for your rear disc setup, causing the rotor to drag on the pad during turns. I think worn differential clutch packs are the most common cause.

https://forums.corral.net/forums/gene...-8-8-rear.html
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post #6 of 13 Old 10-12-2015, 02:17 PM
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The alldata spec on endplay is pretty tight.

End Play, Max. 0.762 mm (0.030 inch)

I think mine is more than this but then I have a Torsen diff so I don't think I have any adjustments.
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post #7 of 13 Old 10-12-2015, 05:48 PM Thread Starter
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Thanks for the replies... I am going to order a diff rebuild kit and replace the axle end bearings while I am in there. Hopefully that will cure the issue or at least make it better...

Another issue I am having is a high speed vibration. I had "chalked it up" the possibility of the tires being poorly balanced and was planning to have them rebalanced. After doing searches on the issue of the brake "moan" it appears the vibration could be caused by a bent axle or the axle bearings being worn...

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post #8 of 13 Old 10-12-2015, 09:11 PM
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Typing all this when I could just call you......

Same rear, brakes, etc. My rear rotors are "beveled" from rubbing against the caliper brackets. You can see significant material missing from the caliper bracket where they rub. The pads also wear significantly crooked. I've installed several sets of rear calipers and brackets........no change. I had 33 spline axles milled to 28 so thy fit in the 8.8 rear with no change. I even tried running with/without those little pad holders without change.

Try putting the car up and running in gear to look for rear wobble. I could see some on mine, especially on the dyno but the new axles really didn't change anything. I've finally decided it's just normal but check it quite often............but I do everything wrong

If racing is like sex.....why would you want it to only last 10 seconds. (road races last 25 to 45 minutes!)
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post #9 of 13 Old 10-12-2015, 09:52 PM Thread Starter
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Typing all this when I could just call you......

Same rear, brakes, etc. My rear rotors are "beveled" from rubbing against the caliper brackets. You can see significant material missing from the caliper bracket where they rub. The pads also wear significantly crooked. I've installed several sets of rear calipers and brackets........no change. I had 33 spline axles milled to 28 so thy fit in the 8.8 rear with no change. I even tried running with/without those little pad holders without change.

Try putting the car up and running in gear to look for rear wobble. I could see some on mine, especially on the dyno but the new axles really didn't change anything. I've finally decided it's just normal but check it quite often............but I do everything wrong
I thought for sure after hearing the "grinding noise" while taking #1 at VIR I was going to see a ground out area on the rotor but I didn't find anything... I did notice uneven wear on the pads... I am planning to put it on jackstands and see if I can see any unusual wobble with the rear. The "moan" of the brakes really does not bother me that much what bothers me is the left side rear rotor being blue while the right side rotor appears "normal"... Either way, I have to rebuild the rear end... As you have so many times pointed out, everything on the car has been rebuilt and the rear end is the only remaining component... however, the housing was thoroughly cleaned and painted... LOL!!!

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post #10 of 13 Old 10-13-2015, 07:10 AM
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My rear rotors are "beveled" from rubbing against the caliper brackets.
You're running the Cobra-specific brackets?

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post #11 of 13 Old 10-13-2015, 04:18 PM
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You're running the Cobra-specific brackets?
I really think so but since you ask.......I'm wondering. I've ordered/asked for the cobra rears when I bought new ones so I assumed that's what I was getting. I think the GT rear brackets do not "connect" each end while the "cobra" bracket is connected...correct?

If racing is like sex.....why would you want it to only last 10 seconds. (road races last 25 to 45 minutes!)
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post #12 of 13 Old 10-13-2015, 10:39 PM Thread Starter
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You're running the Cobra-specific brackets?
yes, cobra specific brackets....

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post #13 of 13 Old 10-13-2015, 10:52 PM Thread Starter
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Originally Posted by t500hps View Post
I really think so but since you ask.......I'm wondering. I've ordered/asked for the cobra rears when I bought new ones so I assumed that's what I was getting. I think the GT rear brackets do not "connect" each end while the "cobra" bracket is connected...correct?
I always thought the only difference between the GT brackets and Cobra brackets was the distance the caliper was spaced from the centerline of the axle... I do believe there is a slight difference between the calipers in that the Cobra specific calipers does "connect" the ends while the GT and V6 calipers are "open"...


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