6 speed ‘box - 5th to 4th trouble

[braddo]

My 6-speed gearbox baulks from 5th to 4th on track days. Has anyone had a similar experience?

With normal driving (or if stationary) it flicks down from 5th to 4th very nicely. On a track day I go to change down and it doesn’t slip into 4th, so sometimes I’m braking like crazy and trying to keep to keep on line while jiggling around for a gear. It led to an off-track excursion today.

[AndrewGP]

Give Phil a call at Road and Race Transmissions on 01959 525105 , he’s the go to man for Caterham 6 speed boxes and should be able to advise you.

[braddo]

Thanks, I'll try them.

[fordy999]

it's not at all expensive to have Phil refresh a 6 speed. You'll need to get the engine and gearbox out of the car and take the box to him but otherwise it's all fairly simple to achieve.

[Murph7355]

braddo said:

My 6-speed gearbox baulks from 5th to 4th on track days. Has anyone had a similar experience?

With normal driving (or if stationary) it flicks down from 5th to 4th very nicely. On a track day I go to change down and it doesn’t slip into 4th, so sometimes I’m braking like crazy and trying to keep to keep on line while jiggling around for a gear. It led to an off-track excursion today.

If it works when you're... under less pressure...are you sure it's the box?

That's not meant to be as rude as it sounds, but a long time ago I was told that you needed to use the 'H' deliberately on the 6spd (down-left-down. Don't try and cut corners. When you're on the hurry up it's all too easy to get into the habit of dragging the lever across the gate rather than being deliberate with it. That plane is easiest for this as the box is sprung to it.

[braddo]

Taking a straight(ish) line from 5th to 4th works nicely all the time except for when I've been on track for a while. At that point, the 'H' route works but only slowly and it's baulky getting from neutral into 4th...

[DCL]

If you haven't already, you may want to try Redline MTL. As with most GL4 gearboxes, the oil can be the cause of generic gear change issues like this. If it has ever had GL5 (or labeled GL5/GL4) in it then it will have damaged the surface of the yellow metal parts (synchro) and even some oils that are sold purely as GL4 can have the wrong properties for yellow alloy synchro. If it recovers with MTL you can then go back to a regular GL4 as MTL tends to produce higher levels of wear.

[Murph7355]

braddo said:

Taking a straight(ish) line from 5th to 4th works nicely all the time except for when I've been on track for a while. At that point, the 'H' route works but only slowly and it's baulky getting from neutral into 4th...

I think (but could be very wrong) that straightlining it can damage the selector forks over time. It may be that this is what has happened with yours. If they're worn/bent to "suit straightlining it in a hurry it could cause issues with using it properly.

Contact the guys noted above. It's all readily fixable, if a ball ache.

Edited to add... Give Phil a call. Describe the symptoms. He'll give you the best advice.