Squeaking/Grinding Sound Starting in 1st 6MT

Recently I've noticed a strange noise coming from what I suspect is the input shaft starting in first. It occurs for a brief moment (< 0.5 seconds) right at peak torque transfer as the truck starts to move. It sounds like a higher pitched squeak/grind almost like what a squeaky sway bar bushing would sound like. Zero other issues or noises, shifts are smooth, etc. Noise happens in 2WD and 4WD, but does NOT happen when starting in reverse.

Clutch and flywheel were replaced about 5k miles ago (centerforce flywheel, competition stage 2 clutch), with no issues until now. Redline MT90 (

$29 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75W-90 GL4) fluid was also swapped in at this time.

I had a shop take a close look at it and confirm that the noise is most likely coming from the input shaft bearing. They recommended to keep driving it until the noise becomes worse, then to consider swapping in a remanufactured transmission.

Is this something that requires immediate attention? If so, is a full trans swap the best thing to do, or could a reasonably competent DIYer like myself handle replacing the bearing?

Any input or thoughts on this would be greatly appreciated, thanks in advance!

EDIT: I've triple checked U-joints, carrier bearing, U-bolts, trans and motor mounts, heat shields etc. U-joints were replaced with OEM spicer ones at the same time as the clutch. Carrier bearing was swapped for the poly one Inland Empire Driveline sells. New trans/motor mounts installed as well.

 

Check your U-Joint's first.

 

That's what I thought too at first, but AFAIK they are in perfect shape with <5k miles on them. I've edited my post to convey this better, thanks for pointing it out!

 

I just noticed the same type of noise only on take off, and I have to push to about 3k rpm to hear almost sounds like brakes. I am lifted and do have some play on my rear yoke of driveshaft, gonna swap out ujoints this weekend. Hopefully not the rear diff, or transmission

 

"I had a shop take a close look at it and confirm that the noise is most likely coming from the input shaft bearing."

OP, the bearing on the input shaft is a great big thing and I would be a bit surprised if it is at fault, but not saying it can't happen. Actually when I first saw one I was somewhat impressed by how robust it appeared...

The bad news is that the entire transmission has to be disassembled to get to the thing. I've had a couple apart and can state that it is a job for, let's say, the very dedicated. The transmission is heavy as all get out and you will need to obtain or improvise some special tools.

I would probable recommend to you that you get a second or third opinion before deciding to dig inside.

 

Thanks for the input on this! At this point, I'm seriously considering dropping the trans again just to have a look around and see if there's anything obvious going on there. By any chance, would you suggest checking anything else (besides what I've already checked) before dropping it? I'll post pics of the input shaft/clutch etc. if I do end up taking the trans out again.

 

I am running a Centerforce clutch and flywheel setup up (installed in August/Sep '23) and my grinding is horrible when engaging 1st gear. I called Centerforce and they said they know about the "Chewbacca" sound. They gave me the run around for a bit but agreed to have me send back the whole kit. I have to purchase a new setup and they will refund me. It's still a pain in the ass having to pay for more labor when they know about this issue.

 

Update: Pulled the trans last weekend, took a good look at everything and noticed some pretty bad grooves on the shaft where the throw out bearing rides. Ordered the URD sleeve/upgrade kit, installed it and got the truck back together today. Noise is STILL happening! I will note that it sounds different from before, but not really any better. Beginning to suspect the pressure plate, which is weird because I saw no sign of any issues when I had it apart. At any rate, looks like I'll be pulling the trans again as soon as I can afford to replace the clutch kit.

Also, @Taco'09 was correct, I measured less than 0.0005" play in the input shaft, seems highly unlikely the input shaft bearing is to blame.

This is very interesting! In your discussions with Centerforce, did they provide an explanation of what is causing the sound? I have their HD flywheel, but the clutch is from competition, not centerforce. Do you know if the flywheel is the cause of the sound? I saved my old flywheel, I guess I could always try swapping it back in just to see what happens...

 

Did you replace the throwout bearing when you had the transmission out?

I remember that on mine, and another one I have here in storage, the thin aluminum quill (snout) of the transmission would sing like a bell when I would flick it with something. It certainly would amplify any resonate noise IMHO and this kind of leads me initially to the the T/O bearing.

On the other hand, the silence when starting in reverse has me perplexed. Does the sound change pitch, diminish, or anything else if you rest your foot on and slightly depress the clutch pedal?

 

I just read through this and wasn't surprised that it wasn't the input shaft on the transmission. The only few input shaft bearings that I have seen that were bad the only symptoms they showed was a markedly strong vibration under a load.

Chirps and such are usually caused by the clutch throw out bearing.

 

I did replace the TOB when I did the clutch initially last summer. I tried to get the URD upgrade, but they were on backorder and I needed the truck so I had to resort to putting an autozone special (Dorman brand I think?) TOB in. Surprisingly, when I installed the URD upgrade the old TOB was in perfect shape: no play, spins smoothly, etc.

Noise still doesn't happen starting in reverse, or when shifting between gears 2-6 while moving. Only way I can get it to happen is starting in first for a brief moment during torque transfer. Since my original post, I've made some more observations:
1: Starting in 1st with slightly higher engine RPMs seems to significantly reduce the noise. Usually I rev to around 1.25-1.5k RPMs before starting to release the clutch. If I rev to 2k RPMs instead, I can barely hear the noise at all.

2: The noise is noticeably worse starting on uphill grades. Often, I don't it hear it at all starting on even a slight decline, or if the truck is already slightly moving. Starting from even a slow crawl (<1 mph) is enough to prevent the noise.

3: 4WD/2WD makes no difference at all. Starting in second gear still causes the noise.

4: Slightly depressing the clutch does not cause the noise. I've tried very slowly clutching in/out of neutral at stops and at speed, can't get it to happen. To date, the only way to hear the noise is to start in a forward gear from a complete stop on flat or uphill ground.

5: Shifting/transmission behavior is perfect, and trans fluid is clean with no evidence of internal transmission problems. I have experienced occasional difficulty shifting into 1st at a complete stop, but that has been happening since when I first got the truck over 40k miles ago.

All this seems to point to something more like a body mount/suspension kinda thing. My current thinking is that at moments of higher torque transfer, something is shifting/applying force on a worn out bushing or something like that. This would explain why the noise stops happening in situations where less torque is required to get the truck moving. I've triple checked motor mounts/trans mount, everything looks fine there. While I had the trans out again, I pried around on all front-end control arms/ball joints and couldn't find anything in the suspension that was loose or worn out. I did notice that one of the far front body (radiator?) mount bushings is loose and a bit squeaky. Going to replace those next since they're quite affordable and clearly need attention regardless. Will update here with any findings from that.

I've reached out to Centerforce as well to see if they have any more info on the flywheel/clutch kit problem reported by @SleeperTaco. I find it kinda hard to believe that a flywheel which matches factory dimensions (trust me, I checked it 5 times before I installed it initially) could be responsible for this, but at this point I'll take any leads I can find.