Clio 200 third gear crunch ( ktec rebuilt 7 months ago)

[Hsustyler]

Gearbox had work done by K-Tec Racing July 2025. Invoice shows:

• 3rd gear synchro ring replaced
• 4th gear synchro ring replaced
• 3rd and 4th synchro hub replaced due to crunching
• New genuine Renault slave cylinder
• Filled with Millers 75W90 FS

Car has covered under 7kcmiles since.

Now it’s doing this:
Consistent slight crunch going 2nd to 3rd.
Consistent slight crunch going 4th to 3rd.
Everything else is clean.
Engine off it goes into gear perfectly.
If I rev match, it reduces the crunch.
It's only ever 3rd gear engagement.

- Before I start pointing fingers, I’m going to drop the 75W90 out and put the correct 75W80 GL4 in.

Those who know these boxes:
Does this just sound like 3rd synchro again?

Has anyone seen 75W90 cause this specifically on 3rd?

Anything else worth ruling out before assuming internal?

Would you bother checking cables or clutch hydraulics given it is gear specific?

Looking for experience based input.

 

[Clio_fool]

@NorthloopCup will probably confirm your suspicions. No wonder K tec shut their workshop 🙄.

 

[NorthloopCup]

It’s worth bleeding the clutch to rule that side of things out first, but it’s a good chance the synchro is goosed again.

 

[RSRowe]

Has anyone seen 75W90 cause this specifically on 3rd?

Yep. Had this happen and seen it happen.

It’s worth bleeding the slave, but the damage has been done now. In my opinion, if it was an issue with the operation of the clutch, chances are it would affect every gearshifts (not just the ones into 3rd).

Fuchs sintofluid made a significant difference to the crunchiness of my original gearbox. I got an additional 12 months out of it on track before it got really bad again.