K10 Gearbox Failure Modes

[SammoHung]

I have read that the K10 box is weak but I would really like to understand the modes of failure (i e what ypes of breakage occur and how it happened)

My particular interest is in the manual 4 speed

1)Do they fail mainly because they are crunched or short shifted under high torque conditions?

OR

2)Do they fail mainly under “in-gear” acceleration…but the torque gets too high


Also for either case; is the ‘strength’ of the K10 gear box significantly effected by normal wear due to high mileage….or is it just plain PAP even when new!?


If the case is that “they fail under normal “in-gear” acceleration…does anyone have any info on which gear is the weakest over the others and what sort of torque the box will pop at in that gear (and / or load)


I guess this is subject is not straight forward and has many dependencies & variables…but any solid info / case examples would be appreciated….


For example if you have had a box death….what were the circumstances (power / torque / driver behaviour) and what was the care history of that box

Cheers to anyone who can help me here…

 

[Micra 110]

Some good questions there (Y)

One thing i've never understood over the years is when someone says their gearbox has 'gone' they never seem to try to find out what the cause was.
It's obviously easier to buy another gearbox but sometimes it would be nice to know 'why' it happened.

 

[Arnold]

I've had two gear boxes go on me, but both identical faults.

The short ratio 5 speed i have in my car now, lost 3rd and 4th gears. The problem was with the hub inside the box, it wouldn't disengage those gears once they were in, and it took some major abuse of the gear stick to release. In the end, i just had to avoid those two gears.

My wide ratio gearbox in the super s had no oil in lol, and i also lost 3rd and 4th gears. Bummer this time though was i was coming back from Edinburgh to the south coast!

When i had my 5 speed repaired, i was told by the engineering company on the phone that it's a very common fault with these cars. I can't say what caused the fault with it originally, maybe lack of oil?

Replacing the gearbox might be cheaper, but who knows what faults will arise with it. At least with a recon, it's warrentied and will be alot more reliable!

 

[Speedle]

this would be interesting to answer these questions samo as its the weak point of the car and limits the amount of power you can tune the car too, i'd say the safe limit for power mods on a k10 gear box is about 75-80bhp as when they start going over 80 and heading towards 90bhp the boxes seem to have short lives

personally id put it down to the internals in general being week, lets face it these cars were build to be cheap so the metals/materials used in the box are probably of a lower grade.

hence why the turbo and super turbo have totally different gearboxs compared to other k10's

 

[bobsp16]

this is true speedle once you start making power over say 75@flywheel then its not going to last long,and yes before somone says somthing like you race micra's its not going to last long.
when i have a box fail it mosty one of 3 things
1st ,,most common thing is it will jam in a gear or starts jumping out of a gear
2nd,,we do change gear really quick and sometime it will selected 2 gears at once and smashes everything inside or locks the box up solid,i have heard this happen on road cars
3rd ,,strips some teeth off a gear

I have stripped down some boxes after thay have failed and i found bent selector forks so i think the problem lies in the selectors being weak

But this i have found that some boxes do last longer than other,ive even tried a new recon one and it lasted no longer than one thats done 80k+.
One thing i no is try and find out were the car has came from because city cars spend most of there life in the lower gears and there gearboxes dont last me as long as a car thats come from the country side were all gears are used.
4 speeds last longer than 5 speed boxes

 

[Speedle]

so it looks like we have three choices then, tune to around 75//80bhp and stop or find a way to improve the box or find another box that fits the ma10/change its internals using parts from another nissan

 

[Ed]

I have busted about 5 k10 boxes in K10s I have had, and have seen at least that many go in others.

Most common failure I see is input shaft bearing failure. Creats that really common K10 whine noise.
Second is damaged/broken selector etc, where engaging gears is very hard (badly ajusted clutch) so you slam it in and damage the gears.
I have never seen one shread gears.

 

[SammoHung]

Thats some great info guys ..cheers!

So...it sounds like most of the failures are caused by case number 1) in my original post...and not so often case 2)?

does this mean that with a certain degree of care, the K10 box could tolerate some where between 75 & 100 bhp mods if gear changes are smooth and clutches are set up right?

I guess its more due to the forces in the box (torque) and inertia (load) rather than the 'power' that does the BUSTING

I wonder what the results would be if someone with a sacrificial K10 box (grin) were to 'somehow prevent' the out put shaft from moving through more than (say) 45 degrees with respect to the casing and then bolt the whole lot down to the floor/wall and using a beefy torque measuring device (big strain guage and a winch?...lol) apply force to the input shaft in the forwards driving direction (in each gear starting with 4th?) until something gives and record the torque figure at this point?...or am I taking this too far??LOL

 

[Ed]

100bhp no problem but the clutch wont take it. And I would have the high load bearings replaced as a matter of course anyway.

Just do it, 100bhp is still not much at all in the grand schemes of things - youll be fine and its cheap experiment even if it does go bang!

 

[SammoHung]

LOL

OK advice taken!!


Cheers Ed

 

[RTLkyuubi54]

bit of a highjack of the thread but its to do with g.boxes. When i put my new engine in i wanted to start it, but couldnt because it was in gear, I try to change gear but it wont have it, the selector wont move. So i to start it i have to put the clutch in. If i let the clutch out 1/2 way it started to rattle badly. Because of this i think the selector fork is ####ed.

Also since the auto driveshafts and manual shafts are different, i havnt got any driveshafts in atm. and because of that i think its fubared my differential up. It feels off centre from the driveshaft hole. I can also spin 1 of the sun gears but not the other. Could of the diff moved out of place because of the missing driveshafts. Also is there anyway to put i back in the proper place without having to strip the box?

Many thanks Ryan.

 

[SammoHung]

crikey this is above my head i'm affraid

 

[bobsp16]

bit of a highjack of the thread but its to do with g.boxes. When i put my new engine in i wanted to start it, but couldnt because it was in gear, I try to change gear but it wont have it, the selector wont move. So i to start it i have to put the clutch in. If i let the clutch out 1/2 way it started to rattle badly. Because of this i think the selector fork is ####ed.

Also since the auto driveshafts and manual shafts are different, i havnt got any driveshafts in atm. and because of that i think its fubared my differential up. It feels off centre from the driveshaft hole. I can also spin 1 of the sun gears but not the other. Could of the diff moved out of place because of the missing driveshafts. Also is there anyway to put i back in the proper place without having to strip the box?

Many thanks Ryan.

i made this mistake once,,,,NEVER,,,,,start your engine with no drive shafts in...when i did this it shot and smashed the planet(sungears) out the side off the caseing

 

[Arnold]

100bhp no problem

But for how long! Both K10 Paul LX and Pietro were both running 90+bhp on standard boxes and they both went wrong! Nobody else has really tried. I'd be quite cautious about approaching that power without uprating the gearbox first

 

[Ed]

Gearboxes are cheap and easy to change, and usually fail due to abuse or not power related problems. So try it first before you spend money on one.

 

[SammoHung]

Could of the diff moved out of place because of the missing driveshafts. Also is there anyway to put i back in the proper place without having to strip the box?

Many thanks Ryan.

Yes and I think it's strip or replace unfortunately (Replace recommended)

I’ve come back to this thread cos the poor 5-speed 1.2 transplant out of Ems old Datsun gave up the ghost just over a week ago while Liz was out and about in it

Here are the symptoms as Liz described it:

during the drive the gears got stiffer and stiffer to change (all gears)
untill eventually while in 3rd gear the lever would not change to 4th (stuck in 3rd)...so Liz thought ....Limp home in 3rd gear....but eventually the transmission popped into neutral but the lever was still very jammed

Anyways, after getting recovered to home I swapped in a very nicely cared for 4-speed from thunderbird two (the £30 minter donor car) and the silver bullet was once again tickety-boo...

So since the mashed 5-speed transmission was destined for the skip, I decided to split it open for a peep and this is what I found...


At the point that the gear was cracked, the selector will have started to become stiff as the gear flexed causing the inner gear to become "not a cylinder" and the outer gear of the selector would tighten up as it tried to slide over the inner gear

Eventually another crack and another and another untill eventually there is no way that the selector could slide in either direction

Interesting stuff

In some of the pics there are two selector gears shown side by side...the left hand one is the 1st & 2nd selector gear that is in good order and the one on the right hand side is the FUBARed 3rd & 4th selector

 

[Ems]

Awww it died

Don't forget though that that was the original 1.0 gearbox, so was pretty ancient lol!! Glad you got it sorted though

 

[Ed]

Thats a common failure, and a relativly cheap repair

 

[Speedle]

nice pics sammo im very keen to learn more about the k10 gearbox so i can eventually create an uprated one using OEM parts from other nissans.

can you show me a picture of the input shaft and its bearings? i think i know what people mean by the input shaft but id like to see myself before i tackle changing the bearings

also the rest of the gear box seems in very good shape its defiantly worth repairing i reckon

 

[Arnold]

Sammo, i love how you've named your cars. Silver Bullet, Thunderbird 2 etc! Hilarous. Shame that happened, poor Liz! but i'm glad to hear the car lives on.

I know nothing about gearbox so interesting photos there

 

[curtis]

my 4 speed on my red K10 went all wrong, on the way back from donny 2007 i couldn't get the thing out of 3rd! not matter how had i pulled it wouldn't come out. but found a way, by flooring it in 3rd then renching the gear knob into 4th......oh and my clutch went the same day!

 

[whipit]

Gotta say that the k11 gear box internals do look very similar. Not really that surprising but worth noting.

 

[Ed]

All nissan internals look similar! Even pulsar gti-r are very similar, just larger!

 

[SammoHung]

can you show me a picture of the input shaft and its bearings? i think i know what people mean by the input shaft but id like to see myself before i tackle changing the bearings

Yes ofcourse, give me an few minutes amd I will add the photos here

also the rest of the gear box seems in very good shape its defiantly worth repairing i reckon

You have pursuaded me to keep it, but I will be shelving it incase / untill I another one goes....I could replace the broken gear but I am VERY interested in your OEM parts super combo gearbox mod....so I might wait and see (no rush ofcourse) what comes of this

-------------

one thing I was surprised at was the tiny bridge of metalwork in the gear that connects the 3 broken - bulky peices of the gear together....

I can see that when declutched and good synchromesh this part of the gear wheel should not see much (if any) torsion....but Im surprised that the designers didnt provide a bit more reinforcement here for thos irregular? moments when the gearbox is not matched during a gearchange


another observation is that: I recently came across the internals of a modern box from a small engine and the assembled gearchange mechanism similarities were uncanny!!....I didn't see the stripped gears on this individually though so I cant be sure if modern boxes with similar designs still have this matchstick crossection on the inner selector gers or wether thay have improved it.....(swap a modern one in??? are shaft splines & diameters common in the trade?)


Speedle: I can highly reccomend getting your hands on the cheepest box from ANY small manual and just breaking it open (lots of rags)..doesnt matter if its working or not, but I was well amaised when I opened this one ...loads of 'mysteries' were right there in front of me


<EDIT> heres the pics

the splined shaft on the end of the input shaft mates with the clutch...the first baring is neer the splined secton and the second baring is at the other end of the shaft and is housed in the transmission casing....get the oven warmed up to remove this i guess.....

Im not sure if these barings would see large radial forces since huge powers should only twist the shaft harder (torsion)...not cause radial or axial displacement....unless ofcourse the clutch is not ligned up properly in the centre....may be THIS is the main cause of input shaft baring failure (big power with not perfectly central clutch)...rather than just pure, fundamental power increase??

 

[Ed]

Think the main shaft failure is usually due to contamination and crap oil. The sideways forced that act on them are due to the helical cut gears.

Ed

 

[SammoHung]

The sideways forced that act on them are due to the helical cut gears.

Ed

Yes, ofcourse!! (slapping my hand on my head!!)...lol

and the helix looks about 45 degrees to that's 50:50 by vectors...

good greif...!!

so the barings take at least half of the forces and have to react (newtons 3rd) without squashing or breaking in order to deflect this back in to a rotory motion



....side note:

I was amaised by how heavy the gear train was in comparrison to the housing....most of the weight is in the gears themselved...the housing is ligh in comparrison......I would guess that the gear box has far more inertia than the flywheel (that people somtimes get lightened....a lightened gerbox would be good....<materials?>) sorry slightly off the topic

 

[Speedle]

wicked thanks Sammo, super helpful as always!!!

i'm going to get a new 5 speed box for my k10 this weekend if i can, ill then use my old one to experiment with and start learning how they work and how to dismantle and rebuild them