Did my mechanic misdiagnose my car?

[silviaz]

(context, my rb25det pull type gearbox was making a grinding sound on idle and when accelerating in the lower rev range but goes away with the clutch pedal in) I got a pretty hefty bill recently which I'm not overly happy about (only because the problem is still there), my mechanic told me a while back that the grinding noise I had in my car was the spigot bearing, long story short but he pulled it out and it looked like brand new, he said that it wasn't lubricated and ended up putting in a new one that was. I didn't think much of it, until I turned on the car went for a drive and noticed the car has the EXACT same sound, nothing has changed.

He said it had some noise which I have no idea what he's referring to and I told him that my gearbox was still grinding, when we went for a test drive he said it was normal. There's no way a grinding gearbox is normal. You can really hear the grinding if you're in a higher gear but your speed is low, I guess makes sense as the gearbox is working harder.

That's one issue, the other issue I noticed is there is a loud rattling sound especially when I start up the car and especially as I go up my driveway. Some other things to note is that the previous owner did a dodgy clutch install and also stripped one of the threads on the flywheel bolt which my mechanic all fixed up and put a new clutch kit in, which I'm not sure if that has something to do with it. I know a bit about the history of the car, it was definitely thrashed and tracked.

The car itself drives fine and doesn't crunch through the gears, there was wasn't much metal shavings on the gearbox. Do you believe my mechanic misdiagnosed my car? I'm trying to decide what next steps to take, I imagine I'll have to rebuild my gearbox eventually.

Edited October 9, 2023 by silviaz

[admS15]

I don't think you can blame the mechanic. He replaced what he thought and what is a common source of gearbox noise. It could be internal gearbox bearings that are causing your noise. Would have been an even bigger Bill. These boxes are a little noisy at low revs high load. I had a brand new one in mine before I broke it and it also had noise at low rpm.

I'd just put up with the noise and don't load it up at low rpm. Gearboxe is trying to tell you it doesn't like it.

[wildeagle44]

What type of gearbox mount are you using? A solid mount will transfer alot of normal whirring noise into the cabin. 
 

[GTSBoy]

Input shaft bearing, more than likely. More common on the skinny box, but still an issue on the fat box. Mine does it (groans and resonates at low rpm in higher gears).

[silviaz]

9 hours ago, GTSBoy said:

Input shaft bearing, more than likely. More common on the skinny box, but still an issue on the fat box. Mine does it (groans and resonates at low rpm in higher gears).

Funny thing is I wanted that replaced but my mechanic said it's a rebuild at that stage, I wanted that replaced because from what I understand it's not deep in the gearbox. 

[silviaz]

10 hours ago, wildeagle44 said:

What type of gearbox mount are you using? A solid mount will transfer alot of normal whirring noise into the cabin. 
 

I had them replaced to with oem style ones not solids, nothing to do with that. 

[silviaz]

11 hours ago, admS15 said:

I don't think you can blame the mechanic. He replaced what he thought and what is a common source of gearbox noise. It could be internal gearbox bearings that are causing your noise. Would have been an even bigger Bill. These boxes are a little noisy at low revs high load. I had a brand new one in mine before I broke it and it also had noise at low rpm.

I'd just put up with the noise and don't load it up at low rpm. Gearboxe is trying to tell you it doesn't like it.

Yeah, problem is would have been better to do it all at once but now I have to pay to pull out the gearbox again.

[joshuaho96]

4 hours ago, silviaz said:

Yeah, problem is would have been better to do it all at once but now I have to pay to pull out the gearbox again.

Weird to me how the mechanic didn't offer to just tear into it further at that point but that's just how it rolls with a lot of mechanics. They'd rather get the cashflow sooner than later.

[GTSBoy]

5 hours ago, silviaz said:

Funny thing is I wanted that replaced but my mechanic said it's a rebuild at that stage, I wanted that replaced because from what I understand it's not deep in the gearbox. 

Well, replacing a front bearing is not a "rebuild", nor does it trigger a need to rebuild everything in the gearbox. A dismantled gearbox with worn/aged parts can be put back together just fine. The only argument is whether the labour to do so is then considered to be wasted compared to doing a rebuild as well.

[silviaz]

3 hours ago, joshuaho96 said:

Weird to me how the mechanic didn't offer to just tear into it further at that point but that's just how it rolls with a lot of mechanics. They'd rather get the cashflow sooner than later.

Nah this mechanic is honest and for him he has a more "leave it if it's working" approach. Not always ideal because if for example I didn't replace my rear main seal and it leaked then I'd have to pay him again to pull out the box.

[silviaz]

2 hours ago, GTSBoy said:

Well, replacing a front bearing is not a "rebuild", nor does it trigger a need to rebuild everything in the gearbox. A dismantled gearbox with worn/aged parts can be put back together just fine. The only argument is whether the labour to do so is then considered to be wasted compared to doing a rebuild as well.

Yeah that's what I thought, I thought if all he has to do is take off the input shaft cover and replace the bearing behind it, that sounds like a pretty easy job but I'm not 100% sure as I haven't been able to find much information on the process.

[r32-25t]

3 hours ago, silviaz said:

Yeah that's what I thought, I thought if all he has to do is take off the input shaft cover and replace the bearing behind it, that sounds like a pretty easy job but I'm not 100% sure as I haven't been able to find much information on the process.

No it’s not that easy, you need to completely strip the box in order to get the input shaft out and press the bearing off it and press the new one on 

[silviaz]

1 hour ago, r32-25t said:

No it’s not that easy, you need to completely strip the box in order to get the input shaft out and press the bearing off it and press the new one on 

Ah ok, that's what I wanted to know. Thanks!