02 GT, 5-speed, 28,000-miles. Recently (few months ago) had FRPP 3.73s. More recently had Bullitt suspension with FRPP UCAs (the ones with the stiffer chassis-side bushings) installed. LCAs are stock, bushings in diff housing where UCAs connect are also stock.
Problem: Have noticed of late that right around 110KPH (68MPH) I'm getting a "hum" coming from the rear of the car when the drivetrain is loaded in acceleration. If I let off the gas, I don't hear it. If I modulate the throttle to load & unload the gears the noise comes and goes. I wouldn't classify the noise as a "howl" or a "whine"...it's just a hum, almost like it's coming through the chassis. I don't notice it at higher or lower speeds though my Steeda exhaust is quite loud so it may be masking it. Around town I hear no noises from the rear other than the usual, lovable dump-truck noises these things make (and it made before the gear change...)
There's no driveshaft vibration (it's the OEM shaft) and the car hasn't been abused; no high RPM clutch dumps, no slicks, no real burnouts even...not even chirps into 2nd or 3rd. Spirited driving sure, no abuse. The gears were broken in for 500-kms (312-miles) with gentle driving, nothing over 50-mph etc after installation. Synthetic 75W140 oil & FRPP friction modifier were used during the gear change. New FRPP bearings & races were used (can't recall if the carrier bearings were renewed or not at the moment...the pinion units definitely were.)
I was thinking the new UCAs with the stiffer bushings may be transmitting more noise into the cabin, "normal" noise that the OEM bushings masked. That the noise isn't there all the time, at all speeds (or varying with speeds) makes me think it's not in the rear itself. Maybe the damper mass on the differential is now "out of tune" with the new gears...
I'm loathe to take it back to the shop to have them take the rear cover off to verify backlash or preloads or to check the mating pattern again. Well, unless the concensus is that something is wrong back there.
Any ideas other than gear setup problems? Anyone experience any similar noise with new UCAs with stiffer bushings? Is the Mach 1 (3.55 gear) diff damper different than the 3.27 GT damper? Could it be bolted in place of the GT damper?
Problem: Have noticed of late that right around 110KPH (68MPH) I'm getting a "hum" coming from the rear of the car when the drivetrain is loaded in acceleration. If I let off the gas, I don't hear it. If I modulate the throttle to load & unload the gears the noise comes and goes. I wouldn't classify the noise as a "howl" or a "whine"...it's just a hum, almost like it's coming through the chassis. I don't notice it at higher or lower speeds though my Steeda exhaust is quite loud so it may be masking it. Around town I hear no noises from the rear other than the usual, lovable dump-truck noises these things make (and it made before the gear change...)
There's no driveshaft vibration (it's the OEM shaft) and the car hasn't been abused; no high RPM clutch dumps, no slicks, no real burnouts even...not even chirps into 2nd or 3rd. Spirited driving sure, no abuse. The gears were broken in for 500-kms (312-miles) with gentle driving, nothing over 50-mph etc after installation. Synthetic 75W140 oil & FRPP friction modifier were used during the gear change. New FRPP bearings & races were used (can't recall if the carrier bearings were renewed or not at the moment...the pinion units definitely were.)
I was thinking the new UCAs with the stiffer bushings may be transmitting more noise into the cabin, "normal" noise that the OEM bushings masked. That the noise isn't there all the time, at all speeds (or varying with speeds) makes me think it's not in the rear itself. Maybe the damper mass on the differential is now "out of tune" with the new gears...
I'm loathe to take it back to the shop to have them take the rear cover off to verify backlash or preloads or to check the mating pattern again. Well, unless the concensus is that something is wrong back there.
Any ideas other than gear setup problems? Anyone experience any similar noise with new UCAs with stiffer bushings? Is the Mach 1 (3.55 gear) diff damper different than the 3.27 GT damper? Could it be bolted in place of the GT damper?