Bent Input Shaft Manual Trans 3rd Gen

Hey all.

So I took my truck in to the dealer when the transmission was slipping and making a whirring noise. When I put the clutch in the noise stops so assumed it was something with the clutch. I've got 170k on the original clutch so figured it was time to replace. I know my first mistake was taking it to the dealer, but I called around and couldn't find a local mechanic that would take me on. I'm new to the area.

They replaced my clutch but then informed me that once they got it back together the noise was still there and it's actually because the input shaft is bent.

I wish they'd told me before they did the work because I could have sourced a junkyard trans and tried a little harder to get a mechanic. Now I have a new clutch in a transmission with a bent input shaft.

Wondering if anyone with a manual trans has had this problem? It is not leaking and is operating normally. It's just noisy when it's idling. Wondering how long I can expect to drive it with a bent input shaft.

Thanks for any input.

 

Bent input shaft? Wut. Did they provide anything to document that? Noise stopping with clutch pedal application would make me think the throwout bearing was having an issue, I'm pretty sure even just a couple thou of runout on the transmission input shaft would be causing some noticeable vibration that increased with engine rpm as the trucks accelerating.

 

Sounds fishy AF.
I mean even IF it was bent,,, why did they button it up without calling first?
IF it is bent, they should at least remove and install the replacement at no charge to you.

 

This. Good Call. As Chew said, why would they reassemble it? I would guess Throw Out Bearing as well.A better question is how did the shaft get bent?
I bent an output shaft on a raised chevy 4x4 (being stupid) and it was catastrophic to say the least, I guess from your post that the truck is still driveable.
I say second opinion from a decent mechanic is required.

 

Bent input shaft...?

Let's think about this a minute.

The input shaft is supported on the front by the pilot bushing/bearing on the end of the crankshaft and in the rear by the front bearing of the transmission - just how was this supposed to get "bent"?


Just to be clear, when you say "put the clutch in" I'm going to assume you mean depressing the pedal to the floor. If you do this at a stop the transmission input shaft stops spinning - if the noise stops as well that indicates the front bearing of the transmission is making the noise.

Question: Do you have an aftermarket shift knob? If so, transmission noise that travels up the shifter is sometimes more noticable.

The bearing right in front of the gear on the input shaft is usually the culprit.

 

actually no pilot bearing or bushing on ours, because the input shaft is fully supported by 2 bearings and so there is no use or benefit for a pilot. So technically it could be bent but I don’t understand how that happens.

Transmissions utilizing pilot bearings usually have a super short input that ends right after it connects to the counter shaft just inside the transmission, and so it needs the pilot bearing for stability. Ours doesn’t have the input connect directly to the counter shaft, so it’s different. Still, a bent input shaft seems unlikely.

 

First off thank you all for your input, I really appreciate it. I'm kicking myself for not starting this thread earlier, I've been suffering in silence for too long.

To answer Toy_Runny, Chew and Bill: I thought throw out bearing at first and so did the tech at the dealer. They replaced the throw out bearing, turned the flywheel, and new clutch and pressure plate. They said there was no way to tell if the input shaft was bent until it was put back together. I don't have the paper work they gave me in front of me, but I'll review and see if they mention a bent input shaft anywhere when I get home.

Rusty: Very good questions, thank you. Yes, when I put the pedal to the floor the noise stops.
Yes I have a very cool blank white ball for a shift nob. Just to add to the confusion of any would be thief. The noise is most noticeable from the outside however. It's a rattle, like something is loose.

To everyone wondering how it could have gotten bent. Could I have done it by overloading the truck? I did drive to Alaska in 2023 and hit some trails in Utah along the way that were a bit on the technical side (for me). I run a Project M camper (400lbs) and we were loaded for a few months on the road. I wasn't pushing the payload capacity, it was just camping gear and a dometic fridge. But could taking it up some steep, rocky stuff with a bunch of gear have done it?

Thanks again everyone.

 

I don’t know how the input shaft could be bent, but technically it could also stop making noise once the clutch is pressed because the input will stop spinning at that point due to being disengaged from the flywheel.

Have any audio recordings of the noise? A throwout bearing noise is pretty distinct and if it’s not that and is the input, I bet we could hear the difference.

Overloading the truck shouldn’t be the input shaft. It might not even be bent, you might just be unlucky with a worn bearing allowing the input to wobble or something. Hard to say.

 

I am not a tech, so the real techs here please chime in if I am off base here. This still sounds like booshit. They couldn't simply put a small and true straight edge on it to verify? I not a machinist and I have more than one. Furthermore, wouldn't a bent input shaft make reassembly/clutch alignment more difficult?

 

About half of the exposed input shaft is covered by the front throwout bearing support snout, so without doing more work to remove that you wouldn’t really be able to get a straightedge on it.

The clutch alignment argument might have some merit, but it might just be off by such a small amount that it doesn't affect the clutch too much.

I think really all we can add any further input on would be if the shop showed him photos/video of it acting up and he posted it here. Otherwise it's just word against word. I will say that after browsing a bunch of threads here, this would be the first time I've heard of this one happening.

 

If you are moving, the input shaft will still turn with the clutch engaged, it would be driven by the rear wheels at that point.

A bad bearing would make more sense. There is no way that I can think of to bend an input shaft with the transmission installed. If it is bent, it was done while the trans was out. (dropped) Either way, a dial indicator would've confirmed while the trans was out. I also wonder what kind of shop would put a trans back in with a bad input shaft? Why the hell would you charge someone to assemble something that has to be disassembled again? It doesn't take much to take the trans back out, but still...effing do it right.

 

I agree, a bending the input shaft does not make sense without some sort of damage occuring when it was removed. The force it would take to bend that shaft with everything together wpuld be ridiculous, and I'd expect other, serious engine/trans/transfer case damage as well.

 

Just throwing this out,the second gens had an issue with the shaft wearing and the solution was to use a URD sleeve. Do third gens suffer the same.

 

No. Second gen had an aluminum snout built into the housing. Third gen have a replaceable steel snout built into a cast iron cover that bolts onto the front of the transmission. No issues known from this design.

 

Another question(s). If it was a bent input shaft would it have gotten worse by now? Would I see leaking or other progressively worse symptoms? I've been driving it like this for over a year and the sound hasn't gotten louder and it shifts fine.

If I put a youtube link in here would you guys be able to watch it to hear what I'm talking about?

Thanks everyone. This is really helpful.

 

Hard to say on if it would get worse. Put it on YouTube and post the link, that will definitely help.

 

Ok right on. Here is the link: https://www.youtube.com/shorts/VhKAzP04Gk0

Let me know if the sound isn't clear and I'll make another one.

 

I definitely hear it and it definitely isn't the typical chirping throwout bearing. It could be the bent shaft or more likely, a bad bearing letting the shaft wobble or something. The input stopping when you press the clutch in would be why it goes away in that scenario.

I'm curious, have you done fluid changes at any interval on the transmission?

 

did they drop the transmission on something and cause this? The shaft didnt just magically bend

 

I took it in because of this noise unfortunately.

BL: Haven't done the trans fluid recently. Do you think that could help?