Diagnose gearbox grind please
Discussion
Hello
MK2 MX5 owner here.
I have a grinding noise which is coming from my gearbox, at a certain short rev range (approx 2700-2800rpm)
This happens under load, no load, when moving, not moving, clutch in, clutch out, when moving up or down the revs etc etc - basically its just as soon as it hits the magic engine speed it will make a light grinding sound, but loud enough to hear when driving which is annoying.
Ive had it up on ramps getting the alignment done and asked the garage to have a listen for me, they held it at the magic rpm and identified it as definitely coming from the gearbox and it sounded rotational to them in nature.
What the hell could it be, is it terminal or is it just a bearing or something that can be replaced at the next clutch change?
Just for info, the car drives fine. Its done 60k, and is on the original clutch as far as I know. The release bearing is a bit noisy, but goes quiet with the clutch in. I had the original fuji torsen diff replaced with a 2nd hand proper Torsen one as the original diff sheared a couple of tabs and was grinding away. (common fault with late mk2's) and I am pretty sure the grinding noise started not long after that, I have read up about the diff and gearbox being connected by a Powerplant frame and the alignment of that can be critical.
Thanks for any advice.
MK2 MX5 owner here.
I have a grinding noise which is coming from my gearbox, at a certain short rev range (approx 2700-2800rpm)
This happens under load, no load, when moving, not moving, clutch in, clutch out, when moving up or down the revs etc etc - basically its just as soon as it hits the magic engine speed it will make a light grinding sound, but loud enough to hear when driving which is annoying.
Ive had it up on ramps getting the alignment done and asked the garage to have a listen for me, they held it at the magic rpm and identified it as definitely coming from the gearbox and it sounded rotational to them in nature.
What the hell could it be, is it terminal or is it just a bearing or something that can be replaced at the next clutch change?
Just for info, the car drives fine. Its done 60k, and is on the original clutch as far as I know. The release bearing is a bit noisy, but goes quiet with the clutch in. I had the original fuji torsen diff replaced with a 2nd hand proper Torsen one as the original diff sheared a couple of tabs and was grinding away. (common fault with late mk2's) and I am pretty sure the grinding noise started not long after that, I have read up about the diff and gearbox being connected by a Powerplant frame and the alignment of that can be critical.
Thanks for any advice.
seany87 said:
Hello
MK2 MX5 owner here.
I have a grinding noise which is coming from my gearbox, at a certain short rev range (approx 2700-2800rpm)
This happens under load, no load, when moving, not moving, clutch in, clutch out, when moving up or down the revs etc etc - basically its just as soon as it hits the magic engine speed it will make a light grinding sound, but loud enough to hear when driving which is annoying.
Now be very specific about what you're saying here.MK2 MX5 owner here.
I have a grinding noise which is coming from my gearbox, at a certain short rev range (approx 2700-2800rpm)
This happens under load, no load, when moving, not moving, clutch in, clutch out, when moving up or down the revs etc etc - basically its just as soon as it hits the magic engine speed it will make a light grinding sound, but loud enough to hear when driving which is annoying.
Engine running, foot on clutch and car in any gear, car stationary.
NOTHING inside the gearbox is turning, so it cannot make any noises. If there are noises, the problem is not in the gearbox.
stevieturbo said:
Now be very specific about what you're saying here.
Engine running, foot on clutch and car in any gear, car stationary.
NOTHING inside the gearbox is turning, so it cannot make any noises. If there are noises, the problem is not in the gearbox.
Been thinking more about this at the graveyard shift at work.Engine running, foot on clutch and car in any gear, car stationary.
NOTHING inside the gearbox is turning, so it cannot make any noises. If there are noises, the problem is not in the gearbox.
Dont think ive tried it with the clutch in, car in gear AND stationary. Pretty sure ive left it in neutral (but experimented with clutch in/out) when Ive been stationary and listening for the noise. Will try and have it stationary and in gear on the way home if I can do it without disturbing people asleep in houses
Ok, tried this before with the car in gear, clutch in and stationary and it still does it.
Bear in mind its engine speed related I am quite confident its not an engine issue, unless somehow the noise is travelling to the box. I honestly cant think what it is, can someone shed some light on it?
Bear in mind its engine speed related I am quite confident its not an engine issue, unless somehow the noise is travelling to the box. I honestly cant think what it is, can someone shed some light on it?
Right, next port of call then is to remove the heatshields one by one and see where I go from there. Is there definately nothing in the box like a bearing that could cause this then? Ill remove a heatshield and take it from there next week when Im off. Reading up on it, heatshield rattles are pretty common on '5s
seany87 said:
Right, next port of call then is to remove the heatshields one by one and see where I go from there. Is there definately nothing in the box like a bearing that could cause this then? Ill remove a heatshield and take it from there next week when Im off. Reading up on it, heatshield rattles are pretty common on '5s
If the clutch is down, car stationary and in gear nothing in the 'box is moving so it can't be the gearbox. If its related to a certain engine speed only it must be some sort of resonation.....I'd go with heatshield or loose bracket too.Hello again 
Right, heatshield wont budge and is on nice and solid, doesnt seem
to be loose or catching on anything. With an assistant revving the engine and me underneath, the heatshield is not the source of the noise. The noise seems to be coming from the gearbox/flywheel direction where it bolts to the engine. Sounds almost like something rattling around steadily in there.
Im stumped
Next step? change the oil again (only had it done 10k ago) and see if any metal bits pop out?
Forgot to mention, the gearchange seems to be getting slightly notchier and once or twice its felt as if it hasnt gone into gear properly even though the clutch pedal is right down, which has caused me to grind the shift by mistake. A couple of times ive had to pump the clutch to get it into first at the lights as well.
Right, heatshield wont budge and is on nice and solid, doesnt seem
to be loose or catching on anything. With an assistant revving the engine and me underneath, the heatshield is not the source of the noise. The noise seems to be coming from the gearbox/flywheel direction where it bolts to the engine. Sounds almost like something rattling around steadily in there.
Im stumped
Next step? change the oil again (only had it done 10k ago) and see if any metal bits pop out?
Forgot to mention, the gearchange seems to be getting slightly notchier and once or twice its felt as if it hasnt gone into gear properly even though the clutch pedal is right down, which has caused me to grind the shift by mistake. A couple of times ive had to pump the clutch to get it into first at the lights as well.
Edited by seany87 on Tuesday 17th July 17:21
Assuming you have actually read my posts, and the instructions. It would make it physically impossible for it to be a gearbox problem if it makes a noise under the circumstances I stated.
If you are adamant it is not an engine noise, or heat shield. And insist the noise is still in the bellhousing area, it could be a clutch or flywheel problem. In which case a failure there could either be a simple loss of drive, or a catastrophic one depending on why it is making a noise and what could fail.
Either way, it needs a competent person to look at it, and soon might be a good idea.
If you are adamant it is not an engine noise, or heat shield. And insist the noise is still in the bellhousing area, it could be a clutch or flywheel problem. In which case a failure there could either be a simple loss of drive, or a catastrophic one depending on why it is making a noise and what could fail.
Either way, it needs a competent person to look at it, and soon might be a good idea.
I had something very very similar.
Turned out to nothing to do with the gearbox, (which was my 1st port of call too, It's only when changing the box for a different unit - for a different reason, I realised that it wasn't the box...
It was one of the copper heater matrix pipes which connect the engine bay rubber pipes on the exhaust side of the engine bay to the heater matrix behind the dash. They were vibrating at a specific RPM point.
Took a LONG time to figure out where that noise was coming from
Turned out to nothing to do with the gearbox, (which was my 1st port of call too, It's only when changing the box for a different unit - for a different reason, I realised that it wasn't the box...
It was one of the copper heater matrix pipes which connect the engine bay rubber pipes on the exhaust side of the engine bay to the heater matrix behind the dash. They were vibrating at a specific RPM point.
Took a LONG time to figure out where that noise was coming from
seany87 said:
Hello again
Forgot to mention, the gearchange seems to be getting slightly notchier and once or twice its felt as if it hasnt gone into gear properly even though the clutch pedal is right down, which has caused me to grind the shift by mistake. A couple of times ive had to pump the clutch to get it into first at the lights as well.
That will just be the slave cylinder dying. A very common and cheap problem to fix on an MX5.Forgot to mention, the gearchange seems to be getting slightly notchier and once or twice its felt as if it hasnt gone into gear properly even though the clutch pedal is right down, which has caused me to grind the shift by mistake. A couple of times ive had to pump the clutch to get it into first at the lights as well.
Edited by seany87 on Tuesday 17th July 17:21
Richyvrlimited said:
I had something very very similar.
Turned out to nothing to do with the gearbox, (which was my 1st port of call too, It's only when changing the box for a different unit - for a different reason, I realised that it wasn't the box...
It was one of the copper heater matrix pipes which connect the engine bay rubber pipes on the exhaust side of the engine bay to the heater matrix behind the dash. They were vibrating at a specific RPM point.
Took a LONG time to figure out where that noise was coming from
Thanks for thatTurned out to nothing to do with the gearbox, (which was my 1st port of call too, It's only when changing the box for a different unit - for a different reason, I realised that it wasn't the box...
It was one of the copper heater matrix pipes which connect the engine bay rubber pipes on the exhaust side of the engine bay to the heater matrix behind the dash. They were vibrating at a specific RPM point.
Took a LONG time to figure out where that noise was coming from
How did you sort it, replacement??
I still havent had chance to get it looked at. Still drives fine for now will get it looked at in time.
seany87 said:
Thanks for that
How did you sort it, replacement??
I still havent had chance to get it looked at. Still drives fine for now will get it looked at in time.
Took the glovebox off and noticed if I applied a lot of pressure to the A/C box the rattle stopped. I ended up wedging something behind the box and the pipes as removing said box to access the pipes means taking the dash out which I didn't want to do.How did you sort it, replacement??
I still havent had chance to get it looked at. Still drives fine for now will get it looked at in time.
If you don't have A/C then the concertina pipe which replaces the box is very easy to remove, so you'll be able to do a better job.
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