Grinding Noise when changing into 3rd and 4th

[Nathan19]

A couple days ago I started noticing it was hard to get into 3rd and occasionally would “crunch” when I got into gear as if I haven’t had the clutch pressed down funny. Yesterday this also applied to 4th gear. I’m assuming it’s the Clutch (I don’t know much about transmissions).

If it was the clutch how much of a chew on is it to do? I’ve heard mixed reviews that it’s not hard to do a clutch just awkward and time consuming while others say it’s a nightmare, not seen anyone mention the clutch on a clio. I’ve tinkered with cars for a bit, doing my own repairs etc. I work as a Maintenance technician apprentice in a factory so I’d say I’m able to physically do it.
Just wanting someone who’s done it before to give me some tips as I’ve heard some people mention dropping the subframe etc. I have 3 days to do it so shouldn’t be too bad right?

[Scrump]

What car/engine/year is it?

[Nathan19]

Scrump said:

What car/engine/year is it?

It’s a 2015 Renault Clio 1.2. Yes I know, not the best car - but it’s what I’m stuck with while I’m saving up for my dream car.

[E-bmw]

If the engine is the same series as the 07 1.6 16v Clio it was actually quite easy, even having long bolts to allow the bell housing to remain in place, but it is still a big and time consuming job.

Lots of bits need to come off/be moved out of the way still.

[guards red]

Don't know anything about the clutch in this particular car but I think you at first check that the hydraulics to the clutch work correctly and that it is being disengaged fully.

Also that the gearbox has sufficient trans oil in it.

[catman]

If it's going into 1st gear ok and you can pull away without any problem and then change into 2nd ok, it's not likely to be the clutch.

[GreenV8S]

If it's only affecting specific gears it's most likely to be worn syncros on those gears.

[Nathan19]

GreenV8S said:

If it's only affecting specific gears it's most likely to be worn syncros on those gears.

Ah okay, as I said I’m not too clued up in transmission. That sounds like a shop job. What exactly would need doing/ how much is this gonna hurt the bank?

[voram]

I agree with both catman and GreenV8S

IMO you need to start with a gearbox oil change - not just to change the oil but mainly to see whether what comes out is oil or oil + bits of metal. If the drain plug us magnetic just looking at the inside of that may give you some clues.

Question. Do you have a habit of resting your hand on the gearlever while driving along? That can potentially be very unkind to synchros.

[Nathan19]

voram said:

I agree with both catman and GreenV8S

IMO you need to start with a gearbox oil change - not just to change the oil but mainly to see whether what comes out is oil or oil + bits of metal. If the drain plug us magnetic just looking at the inside of that may give you some clues.

Question. Do you have a habit of resting your hand on the gearlever while driving along? That can potentially be very unkind to synchros.

I occasionally rest my hand on the gear stick, not all the time and not with pressure but I have caught myself doing it. I’ll have a look at the gearbox oil. What exactly do the Syncros do?

[GreenV8S]

voram said:

Do you have a habit of resting your hand on the gearlever while driving along? That can potentially be very unkind to synchros.

That is more likely to wear out the selector fork. The synchros won't care since they are no longer slipping at that point.

[GreenV8S]

Nathan19 said:

That sounds like a shop job. What exactly would need doing/ how much is this gonna hurt the bank?

You either live with it, or get the gearbox fixed. In most instances that means getting the 'box replaced with a similar reconditioned one.

You can mitigate the problem by slowing down the gear changes into the affected gears. On a low value car a gearbox replacement could easily be expensive enough to write the car off, but the car can keep going for many years if you drive around the problem. On the other hand a driver who just keeps shoving it into gear and graunching every gear change could destroy it quite quickly.

[spikeyhead]

Learn to double clutch

[voram]

Nathan19 said:

I occasionally rest my hand on the gear stick, not all the time and not with pressure but I have caught myself doing it. I’ll have a look at the gearbox oil. What exactly do the Syncros do?

Well, resting your hand on the lever doesn't necessarily do any harm but if the lever is moved partly towards a gear and held there the shift fork will apply pressure to the synchro and wear can take place.

Synchros make the difference between modern gearboxes and old-fashioned crash gearboxes. It's the synchro which helps to make up for any mis-match of rpm between the various shafts in the gearbox. There's a handy video here,
https://www.youtube.com/watch?v=nM4CuWlnJY0

Synchro wear can be in the cones and/or baulk rings if you drive with them partially engaged by having the gear lever moved from it's central resting position.

One way to cause increased wear in a transmission is to rush gearchanges, so the components don't have time for the synchros to do their work before the next gear is engaged and cogs get crunched together rather than engaging smoothly when they're both rotating at the same speed. The more accurately the driver rev-matches the less work the synchros have to do. Nonetheless, car modifiers who fit "short shift kits" increase the risk of accelerated wear because gears are jammed in faster.

[GreenV8S]

voram said:

if the lever is moved partly towards a gear and held there the shift fork will apply pressure to the synchro and wear can take place.

Only if the gear is not engaged. Once the gear is engaged there is no movement between the contacting parts of the synchro hub and no wear can occur. The only movement is between the selector fork and the hub. That can wear the selector fork over time if you drive with pressure on the lever, but that's a separate problem not related to graunchy gear changes.

[voram]

GreenV8S said:

Only if the gear is not engaged.

The concept of "engaged" is not black and white. The whole job of the synchro is to deal with partial engagement - hence the cone clutching mechanism, as explained in the video I posted earlier.

Sure, the fork applies pressure to a rotating part but the rotating parts then have work to do between disengaged and fully engaged. You don't want the cones constantly dragging and causing accelerated wear. It's the opposite of jamming gears in too fast before the cones have done their job, which will tear up teeth.

Another video here, with focus (at 6 minutes to 8 mins) on the cone clutch and application of pressure which causes the cone clutch to "grab".
https://www.youtube.com/watch?v=MXsRfbOiBhE

[GreenV8S]

voram said:

The concept of "engaged" is not black and white. The whole job of the synchro is to deal with partial engagement - hence the cone clutching mechanism, as explained in the video I posted earlier.

Understood, but in the scenario where you're driving along and resting your hand on the gear lever the hub is fully engaged and there is zero slip across the synchro hub and no possibility of wearing it.