GearBox Repairs

[Os8472]

Ok I jokingly put a post about pulling apart a gearbox in the general chat section but now I've got the box apart I'm having trouble finding what went wrong.

First off the symptoms, the box made a loud grinding noise and slowly loss more and more drive till it had no forward drive at all, reverse still worked but nothing forwards, now before anyone says it THE CIRCLIP HAS NOT POPPED OUT, I put the problem down to the diff packing up but all the teeth are intact on the diff.

the only thing i could find were some damaged teeth on the first cog which meshs with the big cog on the diff but its not every tooth and its only the tips that are damaged, could this be the problem?

[Tony Walker]

looks like somethings got in there and chipped the teeth? hows the bearings for the diff look?

[Os8472]

er i haven't got the diff fully out, only been able to get the circlip out and the bit it holds in out as I don't the right size socket to undo the other end but I can feel any play in any part of it

[Tony Walker]

does it sound really noisy to turn? there usually a little noisy

[Os8472]

nope thats the thing, the gearbox was smooth and quiet and every gear selected perfectly just no forward drive

[Tony Walker]

with that gear being chipped and the fact that you have no forwards gear it would suggest a bearing screwed and sort of twisting the shaft locking it and chipping those teeth reversing turns the shaft the opposite way allowing it to move? boxes locking up id of thought would be a bearing fault.

[Os8472]

yep reverse is just fine, when the box finally lost drive there were no more noises from it. if you turn the input shaft by hand both the outputs turn freely until you put some load on them then they stop.

Diff bearing then?

its a jb3 014 tapered bearing diff, according to the cup manual, dunno if that makes any difference.

[Tony Walker]

difficult to say without seeing/feeling it

[Os8472]

There's no obvious play, feels ok

I guess I need to get the diff out to be sure, reading the cup manual it looks like you have to press it out of the casing from the drivers side of the box, that right?

[Matt@CodeRedMotorsports]

Did the nearside driveshaft loose some of its needle rollers at all?

[Os8472]

Nope

[THE MASTER]

to get the final drive out .
remove the oil seal on the drivers side of box . behind that seal there is a big nut , somthing like 50mm . your going to have to lock the diff in the box to get the nut off . once the nut is off take note of any shims washers etc. when the diff is out look at the planet wheels i got a fealing that they have gone awol

[Os8472]

to get the final drive out .
remove the oil seal on the drivers side of box . behind that seal there is a big nut , somthing like 50mm . your going to have to lock the diff in the box to get the nut off . once the nut is off take note of any shims washers etc. when the diff is out look at the planet wheels i got a fealing that they have gone awol

Excuse my lack of names of bits but are planet wheels the 2 small cogs that are sat 90degrees from the direction of the outputs?

[THE MASTER]

yup there the ones. planet wheels are the small cogs and the sun wheels are the bigger ones in the diff

[Os8472]

yup there the ones. planet wheels are the small cogs and the sun wheels are the bigger ones in the diff

In that case then there intact as I popped the circlip out and the first bit out

[THE MASTER]

ive only seen this once before .
the massive gear that is on the final drive, came away from the diff section
it the cog that this gear drives

[Os8472]

Right, ok I'll get the diff out completely tonight and take she'd loads of photographs and post them up

[Os8472]

Ok having trouble getting the right size sock to remove the diff so I'll take the whole thing to work tomorrow and pop in at friendly garage and see what the've got.

This is the internals of the diff with sun wheel held by the circlip removed



But one question and this will proberbly make me look stupid but is the cog that drives the diff marked 1 supposed to turn the inner diff casing marked 2?

[Matt@CodeRedMotorsports]

1 and 2 should turn as one.

[Os8472]

1 and 2 should turn as one.

Ah then I've found the problem, they don't, bugger

[Matt@CodeRedMotorsports]

So the big gear on the outside of the diff unit is free to turn and is separated from the diff?
They are pressed together normally.

[Os8472]

So the big gear on the outside of the diff unit is free to turn and is separated from the diff?
They are pressed together normally.

yep turns free of the centre bit, well somehow i've managed to part them lol

[Matt@CodeRedMotorsports]

Nice one!

[Os8472]

Torque FTW baby

[Matt@CodeRedMotorsports]

Now check the space between the two bearings in the other casing.... I wonder if there is a little crack between them....?

[Os8472]

Which bearings? The two in the end of the outer gear casing where the 5th gear end cover goes over?

[Matt@CodeRedMotorsports]

Yep.

[Tony Walker]

thats usually where they fail and crack there.

[Os8472]

Nope no cracks there

[Matt@CodeRedMotorsports]

That's amazing...! No cracks in the casing but a self separating final drive.

[Matt@CodeRedMotorsports]

thats usually where they fail and crack there.

Hey Tony, how many jb's you had apart and found cracks in that casing??

[Os8472]

That's amazing...! No cracks in the casing but a self separating final drive.

Just double checked, defo no cracks anywhere near those bearings or anywhere else on the casing

[Tony Walker]

id say a majority have cracked or chipped around the bearing, ive never payed much attention to my dad building them previously unfortunately, ill have to have a go at the next one lol. (more than likely will be mine lol)

[tiff_lee]

So that should be an interference fit but is now free to turn? wtf

[Phoenix Autosport]

Put it on eBay as a very rare option "an unlimited slip diff"

[Os8472]

Put it on eBay as a very rare option "an unlimited slip diff"

Hehe good idea but I think I'm still gunna try and fix this one.

[Os8472]

Bit of tech know how needed here, anyone know about the volvo versions of the jb3 boxes?

I'm sure i heard someone say the 3 numbers on them denote the final drive ratio, is that right?

I've got a M54 373E sat in my garage, it has the electronic speedo drive like a GTT box so it'd work and if I'm right it has a final drive of 3.73, whats the final drive on a Gtt box?

[SCHWARTZ]

iirc 3.563:1

[Os8472]

iirc 3.563:1

So that means this Volvo box is longer or shorter? Excuse my stupidity but I'm new to fiddling with gearboxes

[SCHWARTZ]

no idea matey guessing longer i just remember someone saying the final drive for the jb3.

[SCHWARTZ]

dono if it means anything but you can take 5th gear from the volvo box and fit it to the jb3 and that will drop 200rpm at the same speed.

[Os8472]

I'd better get my reading head on and read up on gear ratios me thinks.

Thanks bud

[Fordy]

So that means this Volvo box is longer or shorter? Excuse my stupidity but I'm new to fiddling with gearboxes

if the reno box is 3.72 and the volvo one 3.56 then the volvo box is longer