Hello all,
I run a hillclimb mini and have a frustrating problem at the moment..
I had a new box built up using a jack knight dog kit by a reputable miglia builder chap. At the same time I changed to a KAD internal gear linkage kit so i'm a little unsure where my problem lies..
The car is completely solid mounted so i know my mounts arent moving, in 1st, 2nd and 3rd I have no issue but when i shift into 4th all is well until I back off the throttle and unload the gear slightly and thats when I hit problems, the car jumps out of gear...
Can anyone shed any light on my issue, I'm pretty much ruling out the KAD linkage as it works very well in to every gear, am I right in thinking I may have an issue with the gearbox??
I'm guessing but when I let off the accelarator the engine/body may flex which causes the box to pull out of gear..
But why is this happening...??! Please help..! I thought dog boxes went into gear easily, not out..! 
I'm racing this weekend so any help would be much appreciated..
Andy
You don't say if this is a rod-change or which version of the JKD dog box you are using. You also don't mention if this JKD gearset was new or second hand. You mention a "new box" but you don't state if the dog gearset was new. You refer to a "KAD internal gear linkage kit". Do you simply mean a KAD Quikshift or something more involved? I don't understand your use of the word "internal" since the KAD Quikshift, one of which I own, is strictly EXternal and has no parts internal to the gearbox.
Can you please clarify things by answering my questions?
It's a matter of fact, not opinion, the the most recent version of the JKD dog box(raced in 2004-2005) had very serious and well-documented problems with the box jumping out of gear. This happened in all 4 gears, not just fourth gear and it happened in gearsets that were fairly new, in their first 2-3 races. You need to find out if you have one of these ill-fated gearsets. The chap who put your gearbox together should certainly know if you have one of the troubled gearsets. If you are unlucky enough to have one of these gearsets, you will absolutely need to replace it as no reasonable or affordable remedy is possible. This could obviously present delicate issues between you and your mechanic.
Right. The following test assumes that you do NOT have one of the troubled gearsets which simply need to be replaced.
I can't tell from what you are saying if it's the box or the shift mechanism that is causing your problem. But, rather than remove and disassemble the gearbox to see if it has problems, I would try the following test to see if you can figure out if your problems are with the shift lever/linkage or with the gearset.
As an alternative to the following test, you could simply elevate the front two wheels of the car(just enough to get them out of contact with the ground). Then run the car in fourth gear with the shift lever/linkage disengaged and try the accelerate/decelerate cycling to see if it jumps out of fourth gear. Please be safe while conducting this test. One disadvantage of this test is that the weight of the car being accelerated/decelerated is not able to be replicated as a test condition.
This next method may sound crude, but effective, but I think I would try it. Choose a safe area in which to conduct this test. An area with minimal traffic and no stop signs or stop lights for a goodly distance. With the engine switched off and the car parked, I would use the shift mechanism to place the box into fourth gear. I would then disconnect the shift lever and its linkage from the selector shaft that enters the back of the gearbox, thus leaving the car in fourth gear. A single roll pin should be the only thing holding the pieces together. Since you're probably going to have to tow the car briefly to get it up to speed, you could place the gearbox in fourth gear and disengage the shift lever/linkage at home and then tow the car, using a rope, to the test site. The car is now in fourth gear without any means to change gears.
With the engine running and clutch disengaged, I would then find a way to get the car moving, with the clutch in. When the car gets going fast enough for, say, second gear, I would let the clutch out gently and then try to drive the car, in fourth gear(only) because you are unable to change gears with the linkage disconnected. The engine may lug for a while, but shortly you should pick up enough speed to match fourth gear, engine speed and car speed.
With a little bit of driving, alternating between acceleration and deceleration, you should be able to repeat the conditions which originally caused the box to jump out of fourth gear. If the box jumps out of gear, you know that the shift lever and its mechanism are not causing it to jump out of gear.
If the box does NOT jump out of fourth gear, you should assume that it is the shift lever and its linkage that was causing the box to jump out of gear.
If the box jumps out of gear with the shift linkage disconnected, the problem must be something inside of the gearbox that is allowing the dog ring and gear to disengage with any influence of the shift lever and its linkage. I cannot think of anything other than the dogring/gear engagement teeth that could allow the box to slip out of gear.
Please let us all know what you find out. I sincerely hope that you did NOT get sold one of the troubled JKD gearboxes.
