2nd gear crunch

[ptr_drvr]

Hello folks.

After my mammoth drive from Kent to Munich in the Caterham, my mileage has reduced significantly, but now that I'm more comfortable pushing on in the car I've noticed a significant crunch when changing up from 1st to 2nd gear.

The issue is only when the revs are high, and the speed with which I change gear doesn't seem to reduce the issue. Additionally, it is only when changing up from 1st, and not when changing down from 3rd.

A quick search of the forum led me to this thread which suggests a threshold of 4.5k rpm but I haven't checked my car against this. I too have the 5 speed box, but i don't know what oil has been used in it. This thread doesn't seem to offer a conclusion to the problem, so i'm looking for any suggestions or experience others might have?

Cheers, Pete.

[Tom_Arundel]

It`s usually 3rd that goes crunch. Maybe bleed the clutch slave cylinder and check that your seat position is getting full travel on the clutch pedal. It is important that the correct oil is in the box, if in doubt change it, the wrong oil will wear out the syncro. cones.  3rd-2nd is a different syncro. cone from 1st- 2nd so maybe worn.

P.S. unless in traffic I don`t use 1st gear, the car will pull away just as quick in 2nd if you use low revs. I did a 0-60 back to back test using 1st -2nd and 2nd only and the times were identical!  Actually, most of the time it`s a 3 speed box just like the early cars !! 

[John Vine]

If you haven't already done so, I suggest you first of all discuss this with GP Sevens.  That way, you'll get their advice and record the problem should it later turn out to be a warranty issue.

JV

[ptr_drvr]

Yes, of course John, thanks. But i'd much rather check if there's some common knowledge here on a simple fix first.

Tom, I did wonder about getting the clutch pedal all the way down, but i'm certain I am. And the evidence of only one gear change being affected would suggest that's not the issue. I'll look into this more once i've spoken to GP Sevens.

 

[timb2117]

Totally agree with above but - just a thought - I had similar in a  6 speed box, tried the redline MTL as suggested by many it seemed to make the problem a bit less bad.....

Ended up having box stripped by an amazing but very "backyard" but genius old guy who sucked his teeth so hard they nearly fell out when i mentioned synthetic oil "it'll glaze your synchro's so they cant get up to speed fast enough to do their job" - PLEASE don't shoot the messenger! 

He rebuilt with fresh synchros, abraded the surfaces and recommended only straight 40 engine oil, also of note I put fresh clutch in,  Its running great now.

Be aware many many people on here swear by the redline and I am not disrespecting their experience, just relaying my journey. 

 

[ScottR400D]

#5 I think gearbox oil requirements are very well understood by the manufacturers these days. Certainly some synthetics shouldn't be used but I'm yet to be convinced that a straight 40 engine oil would give you all the protection needed, especially in hard use. 

[ptr_drvr]

#5 - Thanks for posting your experience, useful to use as reference.

[timb2117]

thanks Scott I DO totally agree with you, change it regularly, and he can have it back for rebuild as and when...