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Old 06-15-2017, 01:03 PM   #1
DSG2003Mach1
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"Thumping" sound on decel?

any thoughts on what to look at? Im not sure if its just a byproduct of tolerances in the aftermarket parts or what

Truetrac 31 spline diff
Moser 31 spline axles (with c-clips)
FRPP 4.10s
MT ET streets in case that somehow matters.
Also has Steed upper and lower control arms (might be transmitting more noise?)

on decel I'll get a rotational thumping type noise from the rear of the car. If I put moderate pressure on the brake pedal it will stop.

When originally chasing this I found that my rotor pros rotors had a little wobble to them (we'rent true). Those have been replaced, did not check the new ones before installing them. I also saw that the driver side rear rotor was very close to the caliper bracket, I spaced the bracket out with washers and now both sides the rotor appears to be pretty well centered in the caliper. Apparently thats not uncommon with aftermarket axles.
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Old 06-15-2017, 01:52 PM   #2
311-420
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Re: "Thumping" sound on decel?

Did this come out of nowhere or did it happen after a launch? Does it have a drive-line feel to it or a suspension feel?
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Old 06-15-2017, 02:19 PM   #3
TRbetngu
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Re: "Thumping" sound on decel?

http://www.mach1registry.org/forums/...t=gear+install

Check this out. Maybe it is the problem, maybe it isn't. Worth a shot!
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Old 06-15-2017, 02:39 PM   #4
DSG2003Mach1
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Re: "Thumping" sound on decel?

I looked at that link, theres no noise while accelerating or cruising. Im going to do some better trouble shooting this weekend if itll stop raining for a bit.

this setup has made the noise from the beginning and it doesnt always do it. This rear end setup came out of the MM&FF project car, it did it on that car when I had it and does it on mine too. I just havent been able to drive the car much until recently so now Im noticing/chasing gremlins like these
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Old 06-19-2017, 01:39 PM   #5
Tommy Z
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Re: "Thumping" sound on decel?

Is the noise in sync with the speed from which you decelerate? I.e. is it faster when slowing down from 70mph versus slowing from 40mph?
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Old 06-19-2017, 02:17 PM   #6
DSG2003Mach1
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Re: "Thumping" sound on decel?

yes, it decreases as speed decreases, its in line with wheel speed. Unfortunately I didnt get a chance to play around with it this weekend to see if it matters being in neutral vs in gear or trying to figure out if some sequence of events triggers it
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Old 06-19-2017, 04:46 PM   #7
01yellerCobra
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Re: "Thumping" sound on decel?

My guess would be the diff. Those worm gear diffs are known for making more noise than others. When you press on the brake you're probably applying just enough force to take up whatever slack is in there.
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Old 06-19-2017, 06:54 PM   #8
DSG2003Mach1
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Re: "Thumping" sound on decel?

If that's the case I can live with it just trying to narrow it down
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