T-5 NWC Rebuild, noise only in 4th gear above 55mph

Looking for some input on a rebuilt NWC T-5. The T-5 is in a Jeep but when I asked this question to Jeep guys, most either respond with "get rid of the T-5", or they go on and on about what lube is "correct" in the trans. I figure there's more knowledge amongst you Mustang guys. Fwiw, the box has synchromesh oil in it right now, and it had ran primarly ATF before.

At any rate, rebuilt a NWC T-5 that had run low on oil. When I pulled it apart, the gears and teeth all looked good. Mesh patterns didn't look abnormal. The gears didn't have any scorch or dark patterns. Replaced all the normal parts, bearings, blockers, etc, and had to replace the 5th/reverse lever as one of the legs was cracked.

I get zero transmission noise in 1st thru 3rd regardless of speed, which indicates to me I set the input preload correctly. Once in 4th and around 55mph (roughly 21-2300rpm), it starts to make noise.

I would think that if it were bearing noise, it would happen in 1st-3rd, and maybe 5th, but if it were gear noise it would happen at all rpm/speed while in 4th. When the transfer case is in neutral (no load on the drivetrain) and I run it through the gears, no noise.

The clutch, pressure plate, throwout bearing, pilot bushing, and slave cylinder were all replaced along with the rebuild. New u-joints at the axles and transfer case as well. Shifter is stock for a Jeep and is rock solid.

Could this be a gear issue? Input shaft out of round? Something else I'm not thinking of?

I've also heard that the T-5 is notorious for being noisy and since it's in a Jeep with zero soundproofing, I could just be hearing the normal trans noise.

Appreciate any thoughts. Thanks.
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It's not that these T-5's are inherently noisy, it's just that by this point most have been run low on fluid(or wrong fluid), which starves the bearings between the input and mainshaft and causes trans whine. (or damages the gearing which also causes whine) As a result, most folks now think the T5 is noisy because "they all do that". The reality is if you buy a brand new T-5Z or rebuild a T5 well with all new quality parts it will usually be silent. Sometimes a aftermarket shifter does bring out a little gear whine, but you would hear that in all gears.

What does the sound sound line? Whirring? Buzzing?

I've never worked on a NWC and have never run into a "whine only in 4th" issue myself, so i'm spitballing here.

4th gear actually passes the load through the least amount of bearings as the input and mainshaft are locked 1:1. I would suspect the issue may be the input shaft bearing, as when it's engages 4th, there's no side load on it through the clustergear. That offset might be enough to change the load on the bearing and the way it produces sound.

I'd have to hear it in person and try to pinpoint if the sound is at the front of the T5, or the rear. I'd also have to play around with putting load on the trans and coasting and see if that changes the sound (indicating it's a gear wear issue). In otherwords, this sort of thing i'd need to see in person before i can definitely say what i think the issue is.
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When put in a Jeep the T5 isnt sitting very level especially when theres a lift kit and your trying to keep driveline angle not so steep which is wrong..

When you have to do that you need whats called a dropped transfer case and or somebody who can change the angle on the rear and front axles..



When a stickshift transmission isnt mounted level front to back and mounted dead straight to the rearend they develop noises and shift problems as the gears are trying to sideload on the shaft towards the lower end of the angle plus it makes the fluid ride more at the tailshaft too...

tremec has a driveline inclinometer app that turns your phone into an inclinometer to tell you if your driveline is in spec...........

Another thing is making sure your crankshaft centerline is properly aligned to the center of the bellhousing hole using a dial indicator and correcting it using offset dowel pins...Industry standard is .010" TIR but I shoot for .005" and under........

I like the offset dowels from Robb MC..They have a setscrew that holds the pin in place so when a clutch needs to be done the setting isnt disturbed when the bellhousing is removed..



Good Luck


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I have never put a dial indicator on a stock T5 bell housing but maybe I should...dunno. Have not had an issue on my Coupe or the SROD bellhousing with the TKO in the Bird. I know you need to on the Lakewood and McLeod bell housings and most require some offset.

So just to clarify, it only do it in 4th and it starts around 55 mph (2100-2300 rpm). Wasn't clear on if the noise continues up to redline / shift point and also in 5th or not and if so what rpms or speeds. What does the noise sound like? If is is cyclical like a washing machine then I can tell you my TKO did this and it ended up being input shaft preload being waaay too loose out of the crate. I chased that crap for a couple years before I talked to Joe Dederichs at Dederichs Motorsports in the DFW area. He had a hunch that was the issue so I checked it and sure enough. Took two shim packs to get the correct thickness shims I needed so set the preload correctly and all the issues went away.

So with that what did you set the input preload at? I set my T5 at zero on a fresh build as it will loosen up really quick. What fluid are you running?