Manual Trans. Thud when shifting

[Enzo]

I think what’s causing this is when you trying to push the shifter into gear, the fork is pushing the synchronizer sleeve which that pushes the synchronizer towards the gear itself and when those two meet it’s causing the thud sound. So either the synchronizer isn’t biting good enough or the way it transfers fluid around doesn’t soften the blow when the synchronizer meets the gear.

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[aleccolin]

I my experience the thud is just a Getrag thing, my S4 does it too, and a full rebuild doesn’t even solve it. They’re just set up with more lash I I guess. BG fluid helped some, but ultimately I cured mine with a Tremec and a 1 piece driveshaft. There’s a reason they don’t put the MT82 in the GT350 or Mach 1.

 

[aleccolin]

I did a Magnum XL, Tilton clutch, MGW shifter, and QA1 driveshaft. There’s a whole bigass thread here with several of us that have done it. Not too bad, but not 100% plug and play either.

https://www.mustang6g.com/forums/threads/installed-a-tremec-magnum-xl-in-my-s550.115797/

Best bet is to go with Modern Driveline, Bowler, or Silver Sport Transmission and buy a whole package from one vendor.

 

[1MeanZ]

If you haven't been into the guts of a manual trans, then I don't expect this to make sense, but I'll explain as best I can.

The thud is caused when the main shaft (and countershaft) inside the trans suddenly change speed. The synchronizers are pretty grippy and causes the main shaft to comply very quickly. If you've ever held the front of your bicycle up and spun the front wheel really fast and then grabbed the front brake really hard, that shock of the wheel immediately stopping is the same thing your trans is doing and that's the thud you feel.

To eliminate the thud going into gear from neutral, push the clutch in and wait a second or two for the main shaft to stop spinning at engine rpm before you put it in gear. Also helps if you more gently or slowly put the shifter into gear vs just quickly stuffing it in. Moving the shifter more gently allows the synchronizer to slip a little bit instead of immediately grabbing. The harder you pull the shifter the harder the synchro will grip the mating gear, resulting in an immediate change in shaft rpm causing the thud.

The thud is also sometimes present at other times, like the 1-2 upshift for example. Same situation, rapid change in RPM of the transmission's internals as another gear is selected.

I assume this has been articulated previously in this thread, but I have the answer and it was faster to just type it here vs sort through 82 pages of clueless BS and false information...

 

[13GetThere]

Just noticed this thud today. It happens when I shift and before letting the clutch out, and it sounds like it's coming from the rear end. Sounds like this is a common issue that is not a problem.

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