Getrag 260 is leaking - but why?

[bmw-slangen]

Damn, I thought that was a solid metal post. Actually, when taking a closer look at some older photos of two E30 differentials, it looks like that metal post actually have a small hole!

Have a couple of differentials on the garage floow, will take a closer look at this area for sure! Thanks for the info!

[Wanganstyle]

Interesting - didn't know that. Have been throwing around many E30 differentials, but never seend anything that resembles a vent hole or non-sealed passage.



@Wanganstyle : Where is that vent hole / non-sealed passage located on the differential?

thread a few down has a decent photo of the vent itself leaking; if you look inside the cover on bmw differentials there is an interesting block off there behind the vent.

https://www.r3vlimited.com/board/showthread.php?t=417708

[bmw-slangen]

the rear differential is vented. when the vent is clogged there will be leaking from the speed sensor o ring area

Interesting - didn't know that. Have been throwing around many E30 differentials, but never seend anything that resembles a vent hole or non-sealed passage.



@Wanganstyle : Where is that vent hole / non-sealed passage located on the differential?

[Wanganstyle]

Sorry, must have missed some posts here.

@Digitalwave : I don't have the physical knowledge in this area, but would REALLY like to see or read a scientific paper (from like SAE or similar) around this.
I've only heard that enclosures with rotating parts should be vented to avoid pressure buildup. But I can't really come up with a physical explanation why pressure could build up. And I don't like or is satisfied with "I've heard", I want to know why.

For example, my rear differential is not vented - and there is a lot of stuff rotating in there.

The only explanation I can come up with is when gearboxes are working hard the fluid and gearbox heats up, this will in turn heat the air inside the gearbox and if in enclosure that would for sure increase the pressure inside to such a degree that the radial seals might not be able to handle it properly over extended period of time.




@LowR3V'in : Good question. The "new" breather simply acts as an height extension of the original breather outlet to avoid fluid overflow.

You could instead just extend the existing "breather tower" to be 10-15 cm higher, that would be just as effective and solve the problem equally good. However that solution is somewhat impractical :-)

Fluid overflow happens when the gearbox oil is pushed towards the front of the gearbox and at the same time you have a fairly high RPM.

the rear differential is vented. when the vent is clogged there will be leaking from the speed sensor o ring area

[zaq123]

Why does the tranny pressurize when it's not venting properly?

Very simple explanation...temperature change. The same goes for diff, transmission etc. We all have seen what happens to closed water bottle when it's sitting in the sun or in the cold. All that would never happen to open/vented bottle

Sent from my VS985 4G using Tapatalk

[bmw-slangen]

Sorry, must have missed some posts here.

@Digitalwave : I don't have the physical knowledge in this area, but would REALLY like to see or read a scientific paper (from like SAE or similar) around this.
I've only heard that enclosures with rotating parts should be vented to avoid pressure buildup. But I can't really come up with a physical explanation why pressure could build up. And I don't like or is satisfied with "I've heard", I want to know why.

For example, my rear differential is not vented - and there is a lot of stuff rotating in there.

The only explanation I can come up with is when gearboxes are working hard the fluid and gearbox heats up, this will in turn heat the air inside the gearbox and if in enclosure that would for sure increase the pressure inside to such a degree that the radial seals might not be able to handle it properly over extended period of time.




@LowR3V'in : Good question. The "new" breather simply acts as an height extension of the original breather outlet to avoid fluid overflow.

You could instead just extend the existing "breather tower" to be 10-15 cm higher, that would be just as effective and solve the problem equally good. However that solution is somewhat impractical :-)

Fluid overflow happens when the gearbox oil is pushed towards the front of the gearbox and at the same time you have a fairly high RPM.

[LowR3V'in]

what does the new breather fix exactly?

[Digitalwave]

Why does the tranny pressurize when it's not venting properly?

[zaq123]

Old breather design





new breather design



Mybimr's pics

[e30davie]

What an interesting outcome. Who would have thought.

Least its a relatively easy fix!

Back in my 4WD days we used to extend vent tubes to stop water getting into diffs and gearboxes. I have no more to add to this anecdote.

[zaq123]

E21,E30,E36,E46,E90,E91,E92,E93.... the above breathe is the only design currently offered to all the above models +

There is no pickup tube, what you see in the breather valve is what you get. On older models there is similar but open valve is buried under that little tube/black cap

Interesting!

I was under the impression that all E30 Getrag 260/5 did have the plastic cap, and the one-piece-metallic was used in E34 Getrag 260/6 and others.

So then you might encounter the one-piece-metallic on late E30's then.




I only have some theories why this actually happens (would like in the future to chop up a Getrag 260/5 and have a closer look).

But I suspect that the pickup point/tube for the vent hole at the top is located at a "non-optimal" spot inside the gearbox.
Under normal conditions this pickup point/tube is in free air and the venting works just fine.
But when under heavy breaking the pickup point/tube is submerged and the pressure inside builds up slightly and simply pushes up fluid (instead of air) through the tube and it flows out from the vent hole.

Just a theory, but I suspect that is what happening.

And this internal solution maybe was updated on later gearboxes, we really don't know how many changes Getrag made internally on the Getrag 260/5 during the lifespan of the E30.

[bmw-slangen]

Interesting!

I was under the impression that all E30 Getrag 260/5 did have the plastic cap, and the one-piece-metallic was used in E34 Getrag 260/6 and others.

So then you might encounter the one-piece-metallic on late E30's then.




I only have some theories why this actually happens (would like in the future to chop up a Getrag 260/5 and have a closer look).

But I suspect that the pickup point/tube for the vent hole at the top is located at a "non-optimal" spot inside the gearbox.
Under normal conditions this pickup point/tube is in free air and the venting works just fine.
But when under heavy breaking the pickup point/tube is submerged and the pressure inside builds up slightly and simply pushes up fluid (instead of air) through the tube and it flows out from the vent hole.

Just a theory, but I suspect that is what happening.

And this internal solution maybe was updated on later gearboxes, we really don't know how many changes Getrag made internally on the Getrag 260/5 during the lifespan of the E30.

[zaq123]

interesting....
I watched the vid and it looks like you had the fluid already sitting in the tube vent....before you started the drill. Maybe there is something wrong with the vent valve (under the tube)?

BMW redesigned that part 3 times for E30. The latest one eliminates the plastic cap, tube and the open top vent valve. It looks like it is all one unit now

p/n 23131204841

[Digitalwave]

Just wanted to thank bmw-slangen for helping me out on the issue, both with this thread and via PM.

I have had every leak imaginable on my Getreg 260. Input seal, output seal, selector rod seal, detent pin cover. After finally curing all of them, I was horrified to see more fluid covering my tranny! It didn't take long to notice it is coming from the top breather vent. When I would move my vent cap after driving the car, it would hiss letting the pressure from inside the tranny out.

I disconnected my exhaust, shift linkage, CSB, tranny support bracket, loosened the motor mounts, removed the clutch slave cylinder, and removed the bracket/brace under the bellhousing that sits behind the subframe (preventing your motor from shifting too far forwards if you have bad driveline mounts). This allows you to drop down the tranny enough to give a little more clearance to install the breather hose.

First push off the plastic vent cap. You're going to be working blindly, but tighten your hose clamp a little bit so it's not too loose on the 1/2" hose, and then slide it over the breather nipple based on feel. Tightening the hose clamp is the hardest part with the limited space, but mine went on and it was on there solid. Raised the tranny back up and checked the hose. It doesn't have much room, especially the large 1/2" hose, but it wasn't pinched so it should flow freely. Then I ran the hose up near the fuse box and capped it with a breather filter from the auto parts store.

If you track or even autocross your car you should go ahead and do this! I wish I had known last time my tranny was out, as it would make the job a lot easier.

Thanks again bmw-slangen!

[TobyB]

Sometimes the best way to learn is to learn by doing!

Glad you got it fixed.

t