Knighthawk108

Hi all,

I've read through many threads about crunching/grinding gear issues but none seem to relate to my exact issue. If I have missed one out I apologise for this post.

Car is an 04 UK ap1 facelift, 67000 miles, is my daily driver but not abused, only driven hard on a weekend country road or if necessary. Never had an issue with the car, sails through MOT's, services etc.

So when the car is cold, it shifts fine in every gear. Can be a bit stiff but loosens when heated.
For the last week, When the car heats up, it will grind into 6th. Does this from any gear, and if I double clutch, in to neutral then into 6th. But it only does this when the car is hot??

First thing I've done is change the MTF but the issue remains.

Any ideas on a next step?

I'm not a mechanic and I'm learning as go with this car. Rather attempt things myself before putting it into a professional.

Cheers

Chuck S

Skipping gears is not the best practice according to what seems like consensus here. Shifting into 6th should be made from 5th following this advice. No need to release the clutch in 5th, just select it before selecting 6th to slow the synchros.

Grasping at straws here:
Have you greased the shifter? Requires removing the console and shift lever to get in there. It's possible to put the stick back in backwards but I recall that just locks out Reverse.

What did you put in the gearbox? Heat and friction are related. I don't have a stiff gearbox at any driving temperatures so I'm wondering what's in there. I've used OEM Honda manual gearbox oil and Royal Purple SyncroMax.

-- Chuck

DanielB

I've seen this said elsewhere on this site but without an explanation of why this is bad. Given the large difference in gear ratio between 1st and 2nd that the synchros handle all the time, it seems like going from 4th to 6th by skipping 5th shouldn't be an issue. Curious if anyone can give an explanation.

To the OP, it does sound like the 6th gear synchro is worn but that's strange as it's not the one that wears first (typically 2nd and 3rd gear). You said that double clutching minimizes it, but that confuses me a bit: double clutching is useful when you need to increase the speed of the input shaft to match the speed of the next gear - in other words, when you're downshifting. But going into 6th can never be a downshift on a 6 speed gearbox Perhaps give some thought to how you're doing the double clutch on an upshift as that might give us another clue?

Other than that, I'm with Chuck S and wonder what type of oil you have in it. I doubt that's the cause of the issue, but you might be able to minimize it with a thinner oil and adjusting the speed of your shift into 6th.

Knighthawk108

I didnt say double clutching minimises it. I said I tried from every gear, including double clutching. As in clutch in and shift out of 5th, rev, clutch in and shift into 6th. I tried every possible way to shift into 6th to see if the problem was from every gear and to see if any option minimised the grind. Non did. I never double clutch usually I was just testing. First thing I done after the issue appeared was change the oil and the issue persists. It had hondas MTF in it and I replaced it with comma 80/90 GL5

I think it is the synchro but wanted to see if there was any other ideas before I went further with that option!

twohoos

When double-clutching up a gear, don't rev when in neutral; just 5th, clutch in, neutral, clutch out, clutch back in, 6th, <MAYBE a rev here if engine rpm has dropped too much>, clutch out.

Had the trans fluid ever been changed? The factory-fill MTF was crap until at least 2006. Sucked when hot, and degraded over time. But the "newer" Honda MTF (last 10 years or so?) is a pretty good all-round fluid. Other brands of MTF are really hit-and-miss with this trans, so it's still possible that the right fluid could help.

Knighthawk108

I don't think it had been, need to read through the history again to be sure but I don't remember seeing it. Good to know, thanks! I'll get the newer MTF from honda tomorrow, see if it helps. Am I right in saying they filled it at factory with more MTF than you would use when changing the oil? Like 1.6l to 1.4l? There was a little more oil than I expected come out the overfill when I took that off before draining it.

twohoos

A little overfill doesn't hurt, and might help. Just jack up the fill-bolt side of the car a little higher. I try to get ~1.8 US qt in there.

flanders

Transmission should take ~1.5 liters to fill it when changing oil, do not use GL5 fluid!
Honda MTF3 is pretty cheap and works very good so no need to try anything else.

Chuck S

I'm suspecting the use of 80/90 GL5 (hypoid gear) oil is too thick for the box. That's pretty much the spec for the differential with a different gear structure.

The oil needed in the S2000 gearbox is more akin to motor oil than gear oil. Motor oil is permitted in the gearbox as the owner's manual states (Emphasis added.)

-- Chuck

Knighthawk108

Thanks guys, I'll change it over asap and see, can get MTF3 tomorrow