Jumping out of gear

This site contains affiliate links for which LandyZone may be compensated if you make a purchase.
wickford90

wickford90

Well-Known Member
Posts
3,623
Location
wickford essex
image.jpeg
prior to my S2 rebuild the gearbox was jumping out of 1st and 2nd mainly when you lift of the accelerator , I have now stripped the gearbox all down and its in bits on the bench with no apparent problems all teeth and gears are good no excessive bearing wear, are the detent springs the ones held in by 2 L bracket , holding in a ball bearing.only small thing is when I took off the gear change cover this small bolt was laying in there.
 
endfloat will effect gears jumping out you can have too much for a few reasons ,loose mainshaft nut, badly fitted bush length, wear in thrust washers or badly chosen thrust washers etc, l shaped brackets do hold the detents for 3rd 4th on rhs and rev lhs(spring and ball )as does the brass plug on the top, it does 1st and 2nd,where was bolt ,there is a bolt adjuster going through top from rear
 
I've had 30 years in the motor trade and during that time I've only ever seen 2 genuine reasons for a
wickford90 said:
View attachment 92645 prior to my S2 rebuild the gearbox was jumping out of 1st and 2nd mainly when you lift of the accelerator , I have now stripped the gearbox all down and its in bits on the bench with no apparent problems all teeth and gears are good no excessive bearing wear, are the detent springs the ones held in by 2 L bracket , holding in a ball bearing.only small thing is when I took off the gear change cover this small bolt was laying in there.
Click to expand...
I overhaul gearboxes often on a professional basis and when they jump out of gear, 99% of the time it's either because a) on crash boxes the flanks of the gear teeth have worn or b) on synchromesh or dog boxes the dog teeth flanks are worn. This wear is quite subtle and hard to be sure about without considerable experience. I would recommend getting a professional to have a look at the gear teeth for you just to make sure. All the stuff in Haynes manuals about detent springs and balls is just wishful thinking. A perfect gearbox will not throw out of gear even if you remove the detent springs and balls... I have in the past tried this with brand a brand new gear set in order to prove a point.
 
Vintage-and-Classic said:
I've had 30 years in the motor trade and during that time I've only ever seen 2 genuine reasons for a

I overhaul gearboxes often on a professional basis and when they jump out of gear, 99% of the time it's either because a) on crash boxes the flanks of the gear teeth have worn or b) on synchromesh or dog boxes the dog teeth flanks are worn. This wear is quite subtle and hard to be sure about without considerable experience. I would recommend getting a professional to have a look at the gear teeth for you just to make sure. All the stuff in Haynes manuals about detent springs and balls is just wishful thinking. A perfect gearbox will not throw out of gear even if you remove the detent springs and balls... I have in the past tried this with brand a brand new gear set in order to prove a point.
Click to expand...
correct end float is vital apart from dog teeth
 
jamesmartin said:
correct end float is vital apart from dog teeth
Click to expand...
Correct endfloat is important. But I have to be honest, 30 years in the trade have taught me that 99% of the time it's worn teeth that cause jumping out of gear. Other fixes cure it for a few miles or even a few thousand miles but in practise it's nearly always the teeth. Sure, sometimes it's endfloat but usually it isn't!!
 
image.jpeg
Sorry but I don't know what all the parts are called, the only wear I could see was here.the teeth sit further forward than the rest. Hope that makes sense.
 
wickford90 said:
The bolt was loose under the gear change plate, where the three rods are, don't the the proper name.
Click to expand...
I have to be honest... I haven't done a series box for years: I specialise mainly in other classics. That looks a little like the bolt which might hold the selector fork to the selector rail. If that's what it is then the selector will be loose on it's rail (shaft) which could result in only a partial engagement of the gear. This would cause your problem if it is the case. The reservation I have is that the end of the bolt isn't particularly well formed - selector locating bolts usually have a machined section below the thread to engage with the selector rail. The selector fork is the bit which engages with the gear itself.... is this a sliding fit on the selector rail (the bit with the detents in it which slides backwards and forward whe you engage the gear)? If so this could be your problem. It's a lot of work to fit a gearbox... I'd still recommend getting a professional opinion on the condition of the teeth if at all possible in order to avoid tiresome extra work!
 
Just looked at your pictures and trying to focus on what's happening. Is your S2 still fitted with the original box.... it might be me but the close up looks quite like a Series 3 suffix D box with all synchro?
 
Vintage-and-Classic said:
Correct endfloat is important. But I have to be honest, 30 years in the trade have taught me that 99% of the time it's worn teeth that cause jumping out of gear. Other fixes cure it for a few miles or even a few thousand miles but in practise it's nearly always the teeth. Sure, sometimes it's endfloat but usually it isn't!!
Click to expand...
depends on the box , later lt77s and r380s theres no provision for altering it only variance with gears machined size, on series boxes its a known issue, so you need to equally ensure dog teeth are good as well as the endfloat , later suffix d boxes had coffin shaped dog teeth(like all modern boxes)in an attempt to improve gear hold which it does unless endfloat is too great
 
Probably not the original, but it only has synchro on 3rd and 4th unless 1st and 2nd were knackered. Only drove it for a few miles after I bought it before stripping it for rebuild, the box is a 251******* suffix B
 
wickford90 said:
Probably not the original, but it only has synchro on 3rd and 4th unless 1st and 2nd were knackered. Only drove it for a few miles after I bought it before stripping it for rebuild, the box is a 251******* suffix B
Click to expand...
have you any pics , id be surprised if dog teeth were not worn
 
jamesmartin said:
depends on the box , later lt77s and r380s theres no provision for altering it only variance with gears machined size, on series boxes its a known issue, so you need to equally ensure dog teeth are good as well as the endfloat , later suffix d boxes had coffin shaped dog teeth(like all modern boxes)in an attempt to improve gear hold which it does unless endfloat is too great
Click to expand...
Interestingly all synchro and dog boxes have coffin shaped dogs. It's just that on modern boxes it's so pronounced that you can see it with the naked eye. The earliest of these designs came out in the 1930s and when you make new gear sets up for them the "coffin shape" is made by only a few thou. Oh yes... I'm afraid that I measure in thou because I am resigned to the fact that I am a complete dinosaur and proud of it! You are quite correct: The LT77 / R380 is unique amongst British boxes (as far as I'm aware) because of their taper roller design but otherwise end float is important. Nevertheless I have to speak from experience of countless gearbox rebuilds and also manufacture of new gear sets: It's nearly always the teeth at fault. You can sometimes eke things out little longer with careful assembly but after 100,000 miles for a pre - 1980 gearbox and about 300,000 miles for a modern gearbox the teeth/dogs are nearly always worn in my experience.
 
Vintage-and-Classic said:
Interestingly all synchro and dog boxes have coffin shaped dogs. It's just that on modern boxes it's so pronounced that you can see it with the naked eye. The earliest of these designs came out in the 1930s and when you make new gear sets up for them the "coffin shape" is made by only a few thou. Oh yes... I'm afraid that I measure in thou because I am resigned to the fact that I am a complete dinosaur and proud of it! You are quite correct: The LT77 / R380 is unique amongst British boxes (as far as I'm aware) because of their taper roller design but otherwise end float is important. Nevertheless I have to speak from experience of countless gearbox rebuilds and also manufacture of new gear sets: It's nearly always the teeth at fault. You can sometimes eke things out little longer with careful assembly but after 100,000 miles for a pre - 1980 gearbox and about 300,000 miles for a modern gearbox the teeth/dogs are nearly always worn in my experience.
Click to expand...
yes they are generally very worn on series boxes of any suffix, they arent many i dont change,unless its not long been rebuilt , rev gear on a r380 are quite often too long before the others ,if you look at the difference between a suffix d and previous youll see what i mean,both gear and synchro are shaped on d not previous i also use thou ,but a new 2nd gear in a series 2 box will still jump out on sudden inputs if its end float is too great ,1st as a sliding gear depends on gear teeth usually the layshaft gear with it been the smallest and setting up ie full engagement
 
wickford90 said:
View attachment 92646 Sorry but I don't know what all the parts are called, the only wear I could see was here.the teeth sit further forward than the rest. Hope that makes sense.
Click to expand...
thats 3rd gear and going from the pic it looks like teeth have a slight step at to root,but its 2nd and 1st i though you were worried about, 2nd is the gear directly behind 3rd and 1st the sliding gear at the rear
 
wickford90 said:
Not sure what ones the dog teeth are but I will get some close up pics of all the gears and put them up tomorrow.
Click to expand...
OK here's the anoraks guide according to one man's narrow viewpoint:

During the time period we are talking about gearboxes fall into these categories:

"Crash" boxes
Dog boxes
Synchromesh boxes
Pre-selector boxes
Automatic boxes
Continously variable boxes.

The ones which we are interested in for the purpose of this discussion are:
Crash boxes
Dog boxes
Synchromesh boxes.

Dog boxes and synchromesh boxes are very similar: Synchromesh boxes are dog boxes which have a mechanism to synchronise the gear speeds during changes.

Therefore we can consider two different type of gearbox: Crash gearboxes and "constant mesh" gearboxes. Both synchromesh boxes and dog boxes are "constant mesh" boxes. In order to see how this looks have a good look at your S2 landrover box: 1st and 2nd gear are of the crash type: Can you see how the whole gear itself is moved by the selector along the mainshaft in order to engage it with the appropriate layshaft gear? Now look at third gear on your Series 2 gearbox: Can you see how it is always in "constant mesh" with it's corresponding layshaft gear? In order to engage 3rd gear you have to move the synchro cone along its corresponding hub and this locks the 3rd gear itself to the mainshaft: once this has happened there is a drive all the way through the 1st motion shaft (input shaft) to the laygear cluster and back from the 3rd gear on the lay cluster to 3rd gear on the mainshaft and then on to the output shaft. The male and female teeth which engage third gear are the dog teeth. Notice that 1st gear and 2nd gear aren't of the constant mesh type and need no dog teeth to engage them to the mainshaft... they slide on splines on the mainshaft and although they aren't in constant mesh with the laygear cluster they are always turning with the mainshaft.

Now have a think about how any manual gearbox car drives.. from any time in the late 1930's up to the present day: Try resting your hand lightly on the gear lever and then accelerating and decelerating the car. Do you notice that when you accelerate it actually pulls the car further into gear? When you decelerate this phenomenon disappears. Why does this happen? because the teeth on the dogs of the synchromesh gears have an angle ground on them which causes them to "pull in to gear" under load. Why doesn't it completely throw out of gear when you lift off the throttle? Because of the "coffin shape" on the teeth which causes them to retain their engagement on the overrun too.

But what about crash gearboxes? Land Rovers up to and including seres 2A have crash 1st and 2nd gears and synchromesh 3rd and top gears. Crash gearboxes are not constant mesh and need the whole gear to be slid along the mainshaft so that it engages with the corresponding layshaft gear. The flanks of the gear teeth also have to be ground so that they pull into gear on load and stay in engagement on overload. The crash gears on a Land Rover are sophisticated ones: They are not straight cut gears so they have a mathematically very complicated profile which keeps them relatively quiet (have you ever heard the gear teeth of a 1920s box... ouch!!!) and yet still generates thrust which is contained within the confines of the holding profile. Once the flanks of the teeth on the crash gears or the dogs on the synchromesh gears wears outside the design limits then the thrust will no longer be contained and the gearbox will throw out of gear.

Note also that 4th gear on the Land Rover is "top gear" No gear meshing is involved but the 1st motion shaft (input shaft) is locked to the 3rd motion shaft (output shaft) resulting in a 1:1 ratio. This is the definition of "top gear" 3rd Speed in a 3 speed box is "top gear" and 4th speed in a 5 speed box is "top gear" because this is the 1:1 non - geared ratio. 5th gear in a 5 speed box is geared up so that the 3rd motion shaft speed is greater than the 1st motion shaft speed: overdrive.

Anoraks. You just have to wear one ;-)
 
Vintage-and-Classic said:
OK here's the anoraks guide according to one man's narrow viewpoint:

During the time period we are talking about gearboxes fall into these categories:

"Crash" boxes
Dog boxes
Synchromesh boxes
Pre-selector boxes
Automatic boxes
Continously variable boxes.

The ones which we are interested in for the purpose of this discussion are:
Crash boxes
Dog boxes
Synchromesh boxes.

Dog boxes and synchromesh boxes are very similar: Synchromesh boxes are dog boxes which have a mechanism to synchronise the gear speeds during changes.

Therefore we can consider two different type of gearbox: Crash gearboxes and "constant mesh" gearboxes. Both synchromesh boxes and dog boxes are "constant mesh" boxes. In order to see how this looks have a good look at your S2 landrover box: 1st and 2nd gear are of the crash type: Can you see how the whole gear itself is moved by the selector along the mainshaft in order to engage it with the appropriate layshaft gear? Now look at third gear on your Series 2 gearbox: Can you see how it is always in "constant mesh" with it's corresponding layshaft gear? In order to engage 3rd gear you have to move the synchro cone along its corresponding hub and this locks the 3rd gear itself to the mainshaft: once this has happened there is a drive all the way through the 1st motion shaft (input shaft) to the laygear cluster and back from the 3rd gear on the lay cluster to 3rd gear on the mainshaft and then on to the output shaft. The male and female teeth which engage third gear are the dog teeth. Notice that 1st gear and 2nd gear aren't of the constant mesh type and need no dog teeth to engage them to the mainshaft... they slide on splines on the mainshaft and although they aren't in constant mesh with the laygear cluster they are always turning with the mainshaft.

Now have a think about how any manual gearbox car drives.. from any time in the late 1930's up to the present day: Try resting your hand lightly on the gear lever and then accelerating and decelerating the car. Do you notice that when you accelerate it actually pulls the car further into gear? When you decelerate this phenomenon disappears. Why does this happen? because the teeth on the dogs of the synchromesh gears have an angle ground on them which causes them to "pull in to gear" under load. Why doesn't it completely throw out of gear when you lift off the throttle? Because of the "coffin shape" on the teeth which causes them to retain their engagement on the overrun too.

But what about crash gearboxes? Land Rovers up to and including seres 2A have crash 1st and 2nd gears and synchromesh 3rd and top gears. Crash gearboxes are not constant mesh and need the whole gear to be slid along the mainshaft so that it engages with the corresponding layshaft gear. The flanks of the gear teeth also have to be ground so that they pull into gear on load and stay in engagement on overload. The crash gears on a Land Rover are sophisticated ones: They are not straight cut gears so they have a mathematically very complicated profile which keeps them relatively quiet (have you ever heard the gear teeth of a 1920s box... ouch!!!) and yet still generates thrust which is contained within the confines of the holding profile. Once the flanks of the teeth on the crash gears or the dogs on the synchromesh gears wears outside the design limits then the thrust will no longer be contained and the gearbox will throw out of gear.

Note also that 4th gear on the Land Rover is "top gear" No gear meshing is involved but the 1st motion shaft (input shaft) is locked to the 3rd motion shaft (output shaft) resulting in a 1:1 ratio. This is the definition of "top gear" 3rd Speed in a 3 speed box is "top gear" and 4th speed in a 5 speed box is "top gear" because this is the 1:1 non - geared ratio. 5th gear in a 5 speed box is geared up so that the 3rd motion shaft speed is greater than the 1st motion shaft speed: overdrive.

Anoraks. You just have to wear one ;-)
Click to expand...
true except with a lr series box 2nd is constant mesh and helical cut with dog teeth,only 1st and rev are sliding straight cut hence the whine ,in that it slides into mesh with 1st layshaft gear and slides to lock 2nd to main shaft,
 
You must log in or register to reply here.

Similar threads

tony109
Jumping out of 3rd gear on over-run
Replies
10
Views
2K
Gun7354
Gun7354
B
Disco2 TD5 Can only select one gear
Replies
8
Views
441
Bugz
B
9
2nd gear noise only on overrun
Replies
1
Views
468
tottot
tottot
T
Gear selection problem
Replies
3
Views
419
miktdish
miktdish
D
Series 2a with a Suffix F gearbox. Full Synchro?
Replies
5
Views
909
cornish rattler
cornish rattler
Back
Top