Bad differential? - TCCoA Forums
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post #1 of 2 (permalink) Old 10-16-2009, 07:36 PM Thread Starter
6th Gear Poster
Join Date: Mar 2005
Location: Turlock, CA
Age: 32
Posts: 563
Bad differential?

When I installed my 3.73 True-trak approx 3 yrs ago, It always made noise. A humming type sound that is speed dependent, worst at high load low rpm 3rd gear, and decel as well. The noise is definately from the rear. I cannot notice it when I drive hard, especially WOT, but that may be because I just can't hear it over the PI motor.

The first bad thing I noticed after installing - shift into reverse, big clunk from the back. I also noticed, when I pulled in my incline driveway the first time, I held the brakes with tranny in drive, set the ebrake and then shifted to park. Thats what I have always done. The next day, when I released the e-brake, the car shifted backwards big time and clunked. Which gave me the impression there was just play somewhere.

That clunking has gotten worse over time, as has the humming. I had Darin build me a moderately built 4R70W, (which I love, arguably the best mod I have done!) but the downside to getting the wicked tranny is that the hard shifts have made the play worse over time. If I stab at the throttle it clunks hardcore and jerks/lunges the car. I get around it by tapping the brake every time before I depress the accelerator when coasting, which unlocks the torque converter and allows me to gradually accelerate lessening the clunkiness.

I have triple checked torque specs on diff and trans mounts, which were new poly ones just before diff was originally replaced.

There is just huge play in the drivetrain somewhere. Along with the true-trak diff and tranny by Darin, I got a one piece d/s from a GB on here, which was about 3-4 yrs ago. All were installed at same time. And I have checked the u-joints, seem a-ok.

I just lifted the rear of my car off the ground. When I turn the tire/wheel, there is what I feel is a lot of play before I can see the driveshaft and the other tire move, and it just feels like the diff is empty with no resistance, until it catches, clunks, and jerks the other tire and driveshaft. And this is with very slow turn speed of the tire.

If it was on one side, I would suspect the axle, but both are the same, so that would indicate it is internal in the diff right? When I had a mechanic check it out, they ran it with the wheels in the air. They told me the noise definately came from the differential. They showed me the 3.73 gears, and he told me that the wear pattern was absolutely perfect, which I can vouch for. His advice was that it was an internal problem and quoted me an obscene amount to R+R and rebuild the diff re-using the gears. He is the best mechanic I have come across, but I still don't trust mechanics in general, haha.

I just bought a traction lock diff 3.73 that I am going to replace it with. But I am wondering what exactly could be wrong...? Anyone have a clue? I'm not sure I will be able to tell without tearing it down (paying someone to do it because I don't know how) but can anyone venture a guess from experience?

All Glory to God!


96 LX PI/Jspec Pearl White. She enjoys eating ricers for breakfast
2002 PI 4.6L - Jspec Trans built by Darrin - 04 Marauder converter - Hayden 679 Trans cooler - Engine cooling modification - SCT Xcal2, tuned by Lonnie - 02 GT MAF and 99 GT Intake tube - removed silencer - 255 lph HP fuel pump - Aluminum Driveshaft - 3.73 TL - 245/60/15 BFGoodrich Radial T/A's - PBR front brakes - SCP Rear torsional load brace - SCP Solid rubber motor, transmission mounts - Rear Strut Tower brace and Diff cover brace by Rod
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post #2 of 2 (permalink) Old 10-16-2009, 07:44 PM
6th Gear Poster
Join Date: Jun 2003
Location: spring grove, il
Age: 37
Posts: 623
Pop the rear flange of the driveshaft off of the pinion flange and really check the rear u-joint. It is better to eliminate the easy things first than wrap your mind around 10 different scenarios at once. Did you atleast pry on the u-joints with a screwdriver to check them?

lowered, koni sport adjustables, 4.30 tl in aluminum housing, mark 8 trans, j-mod, 93 mark viii ds, antenna hole=gone, kooks headers 1.75" primaries, 2.5" catless duals, midmount magnaflow, 96-97 sport wheels with 255/50/16 sumitomo HTR Zs, optima in the trunk, new motor...94 mark 6/6/08
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