Transmission Breather, crack pressure?!?!

Mauro_Penguin

Mauro_Penguin

Punk in Drublic. #BlackLivesMatter
Motorhead
Background: About 4 months ago I decided to inspect some of my fluids. I went and removed the fill plug on the trans and noticed a faint whistle coming out as I slowly removed the plug. I thought it was a little strange, it turns out the fluid was a little low also. I went ahead and topped it off with another half a quart of gear oil (I had half a quart of Amsoil Severe Gear oil from last time I changed it). Topped it off and drove it until now.

Today: I was changing some fluids out, hooray! The time came to swap out the Trans gear oil, and when I opened the fill hole the transmission started whistling again! It seems as though it had a build up of pressure inside that couldn't vent despite the breather vent by the pivot shaft.

I check the axle seals and and all the bolts, and everything is still tight with no leaks. I had some spare hose, so I plugged the drain plug back up and shoved the hose inside the fill hole. I placed my soft supple mazda loving lips on the hose and gave it a good blow. All the pressure came back out through the hose. I did it again and blew harder (a little more tongue and neck this time), same thing. Now I'm thinking, "maybe I'm blowing too hard and overpowering the crack pressure of the breather vent." So I gave it a third light blow of air and put my fingers surrounding the vent (think rusty trombone), nothing came out.

I'm a little concerned that the pressure might lead to axle seal leaks, or even worse a leak into the bellhousing. Im considering removing the pivot shaft and replacing the vent or modifying it somehow, and also replacing the pivot shaft seal and bearing for good measure.

Has anyone ever had/heard of this? Or maybe if anyone knows the crack pressure to that piece if crap breather? My GenPu only has 50k miles on it, which is the real head scratcher...

Thanks for the gayz...

(Mod's feel free to move, I may have posted this in the wrong area.)
 
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So no one on this forum has noticed pressure build up in their trans?

Hooray for random issues!

In the next week or two I'm going to order a replacement pivot shaft bearing and seal. I'm going to remove the OEM vent valve, and get some parts together to make a breather of some sort for the transmission in place of the Mazda valve. It might not be pretty, but it will prevent axle seal leaks and might cure my moody 5th and 6th gear engagement.
 
Those vents can sometimes either get stuck or plugged. I'd try a new vent first, they're usually pretty cheap.
 
Update:
Right after thanksgiving I pulled the pivot shaft assembly out. I had full intention of punching out the OEM breather, tapping it for an NPT elbow barb, and using a small carb fuel filter out to the fender. It would take up some room, but it would breathe and work well. It's a common mod on 4x4 and solid axle guys. However my damn breather did not want to come out!!!

I could have eventually punched it out of the cast pivot shaft plate, but was short on time and did not want to deform or crack it. So I went a different route that I'm actually happier with.

The OEM trans breather it's a thick rubber diaphragm/washer, a thin compressed spring, and the aluminum cap that holds it all together to a mushroom base assembly. (See attached picture).

The rubber diaphragm was actually stuck onto the base, I actually had to pry it off after I removed the aluminum retaining cap and spring. This explains why I was getting pressure build up in the transmission.

Convinced that this was my issue, I decided to punch a small hole through the rubber diaphragm (See attached picture). This would allow pressure to vent, hopefully. I put everything back together and pinched the bottom of the aluminum cap to hold it back in place.

I drove with this setup for about 500 miles, and it fixed the goofy/tempermental shifting I was getting. Shifting was easier, and could be done faster.

I decided to revisit this project last week. I used a trim tool (see attached picture) to pop off the retaining cap, no need to remove and reseal the whole pivot shaft assembly again. I removed the rubber diaphragm, and cut a small circle out of some thin aluminum sheet to replace the rubber (See attached picture). This way the aluminum circle can seal the transmission, but without the risk of sticking like the rubber. I reinstalled the cap+spring+aluminum circle, pinched the cap, and made sure it could move and rotate to prevent binding of the spring. 100 miles later and everything is still smooth!

I have no idea why the vent got stuck in the first place, but whatever the reason might have been the transmission can vent again and I don't have to worry about my axle seals eventually leaking from this.

It should be noted, that this fixed some shifting issues and prevented pressure in the trans. I did this after having bled the hydraulic clutch system, and cleaned/re-lubed the shifter and shift cables. It was while changing the trans fluid that I noticed this.

Hopefully this helps other folks in the future who may have this problem, although it does not seem to be common.
 

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Mauro_Penguin said:
Update:
Right after thanksgiving I pulled the pivot shaft assembly out. I had full intention of punching out the OEM breather, tapping it for an NPT elbow barb, and using a small carb fuel filter out to the fender. It would take up some room, but it would breathe and work well. It's a common mod on 4x4 and solid axle guys. However my damn breather did not want to come out!!!

I could have eventually punched it out of the cast pivot shaft plate, but was short on time and did not want to deform or crack it. So I went a different route that I'm actually happier with.

The OEM trans breather it's a thick rubber diaphragm/washer, a thin compressed spring, and the aluminum cap that holds it all together to a mushroom base assembly. (See attached picture).

The rubber diaphragm was actually stuck onto the base, I actually had to pry it off after I removed the aluminum retaining cap and spring. This explains why I was getting pressure build up in the transmission.

Convinced that this was my issue, I decided to punch a small hole through the rubber diaphragm (See attached picture). This would allow pressure to vent, hopefully. I put everything back together and pinched the bottom of the aluminum cap to hold it back in place.

I drove with this setup for about 500 miles, and it fixed the goofy/tempermental shifting I was getting. Shifting was easier, and could be done faster.

I decided to revisit this project last week. I used a trim tool (see attached picture) to pop off the retaining cap, no need to remove and reseal the whole pivot shaft assembly again. I removed the rubber diaphragm, and cut a small circle out of some thin aluminum sheet to replace the rubber (See attached picture). This way the aluminum circle can seal the transmission, but without the risk of sticking like the rubber. I reinstalled the cap+spring+aluminum circle, pinched the cap, and made sure it could move and rotate to prevent binding of the spring. 100 miles later and everything is still smooth!

I have no idea why the vent got stuck in the first place, but whatever the reason might have been the transmission can vent again and I don't have to worry about my axle seals eventually leaking from this.

It should be noted, that this fixed some shifting issues and prevented pressure in the trans. I did this after having bled the hydraulic clutch system, and cleaned/re-lubed the shifter and shift cables. It was while changing the trans fluid that I noticed this.

Hopefully this helps other folks in the future who may have this problem, although it does not seem to be common.
Click to expand...

Do you think there is any way to take the breather out without pulling the pivot shaft assembly? Vice grips maybe?
 
Doubtful. From what I remember it took a few 2x4s, a socket, and a bfh to push it out. Dont think pulling it is going to work out well.
 
JasterMake said:
Do you think there is any way to take the breather out without pulling the pivot shaft assembly? Vice grips maybe?
Click to expand...

If you are trying to pop the whole breather assembly out including the base and press in a new one, then yes you will need to remove the whole pivot shaft assembly. If you just want to service the breather like I did, then no you do not need to remove the whole pivot shaft. All you will need is a fork trim tool like what I pictured, pop it under the aluminum breather cap and pry it off slowly while rotating it so you don't botch up the shape and be able to reuse it.

In any case removing the pivot shaft is not hard at all. You just remove the 2 shift cables, remove the 5 bolts on the tranny holding the shifter assembly, and the one guide bolt on the side of the tranny. Tools you will need are a heavy hammer to love tap the pivot shaft base loose, the same trim tool I pictured can be used to pop the shift cables off. Other stuff you will need is RTV to seal the shaft again, and some white lithium grease to lube up some of the shifter assembly again before reassembly.

Again it's not hard, just have patience and a whole lot of it.
 
Thanks. I might try it your way for temporary service. There was a shitload of pressure when I opened it up to check fluid. Pssss Shhhhhhh. POOF. I even have a little bit of “leakage” coming out of the seal. I use quotes because no visible drips just what appears to be a stain emanating from the seal.
 
JasterMake said:
Thanks. I might try it your way for temporary service. There was a shitload of pressure when I opened it up to check fluid. Pssss Shhhhhhh. POOF. I even have a little bit of “leakage” coming out of the seal. I use quotes because no visible drips just what appears to be a stain emanating from the seal.
Click to expand...

What seal had the "leakage"?

Try just removing the cap with the trim tool first, it's easier/faster.

That hissing sound when swapping trans fluid even when cold is what prompted me to try this. Good luck and post up what you find.
 
Mauro_Penguin said:
If you just want to service the breather like I did, then no you do not need to remove the whole pivot shaft. All you will need is a fork trim tool like what I pictured, pop it under the aluminum breather cap and pry it off slowly while rotating it so you don't botch up the shape and be able to reuse it.
.
Click to expand...

I did this. It worked but scared the piss outta me because the rubber seal was stuck and when I pried it off it blew out the pressure. I cleaned the rubber seal and put it back together.
 
Great write up, thanks. I noticed the same build up of pressure the last two times I had to remove the fluid and wondered why the vent wasn't working. To your point on the 4WD world, all four vents on my Land Cruiser have a hose and filter and it was my plan at some point to do the same on the car. Rather than dork around with hose, I like the idea of replacing the rubber disk with aluminum or some silicone seal.

I am curious as to why the pressure build up would cause the shifting to be less than smooth. That notion makes me want to address this tomorrow and see what I've been missing out on.
 
ibcrusn said:
Great write up, thanks. I noticed the same build up of pressure the last two times I had to remove the fluid and wondered why the vent wasn't working. To your point on the 4WD world, all four vents on my Land Cruiser have a hose and filter and it was my plan at some point to do the same on the car. Rather than dork around with hose, I like the idea of replacing the rubber disk with aluminum or some silicone seal.

I am curious as to why the pressure build up would cause the shifting to be less than smooth. That notion makes me want to address this tomorrow and see what I've been missing out on.
Click to expand...

The biggest improvement for me was highway shifting.

The pressure build up might cause the Trans fluid to reach a higher temp, which didn't make sense to me because a higher temp would thin out the gear oil. It felt to me like resistance in the trans, like using a much thicker fluid than spec and switching back to a thinner one after releasing the build up.

Post up how it goes after, I'm curious if anyone else has a similar issue and outcome.
 
I noticed a pressure release when I was checking the trans fluid after noticing a leaky shift shaft seal. Which was odd because I change my trans fluid ~25k. So it looks like it doesn’t take much for the trans breather to get gummed up. I just replaced with a new valve breather when I replaced the shift shaft plate. Figured if I can get another 100k out the new trans breather I’m be good to go.

I’d suggest if you are going to replace the trans breather rubber to aluminum and if you have to pull the shift shaft plate to either replace the shift shaft seal/ bearing or get a new plate with everything already installed. I noticed a huge improvement in shifting with the new bearing.

Now that I have an extra plate I might look into tapping the old plate and venting elsewhere as other suggested. Along with a new seal and bearing.
 
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