Well, I found this interesting. My new ‘12 Boss does not have an axle vent. At all. The hole is plugged. That’s not normal, right??? The hole is there, but there’s a bolt/plug in it.

I noticed this because when I went to pull the fill plug and check the oil, it let air out. It was clearly pressurized.

Thoughts???

This in the hole…

It looks/feels factory. And it’s a brand new car, so I have no reason to suspect someone did this due to leaks.

It's correct. In Boss cars the vent is on the top of the diff cover. It makes seepage a little less likely. The stock GT diff cover doesn't have this feature so on those cars it's on the axle.

Aaahhhhh. sh*t, I found it.

So is that normal then for the thing to hold pressure? She’s been sitting for a few days also, thus it caught me by surprise to hear it vent when I pulled the plug.

galaxy said:

Aaahhhhh. sh*t, I found it.

So is that normal then for the thing to hold pressure? She’s been sitting for a few days also, thus it caught me by surprise to hear it vent when I pulled the plug.

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Not sure about that part. I've never experienced that myself. It could be your vent is dirty/clogged? Super cheap part so might be worth replacing as a just in case thing. Then again, it'd probably clean up easily enough if it is clogged.

I think this is the one:

If you ever plan on driving at high speeds (over 100mph), you will want a rear axle overflow catch can. JLT used to make a great one that a lot of us used 10+ years ago that was a simple catch can with a single bolt mounted bracket but I don't see one online now. Any of the short vent style ones will allow the differential fluid flow out all over your diff when you do high speeds. After a quick google, it looks like Kohr and Cortex sell fancy ones.

https://kohrmotorsports.com/product/axle-differential-vent-kit-mustang-universal-club/

https://www.cortexracing.com/shop/rab-40-1000-cortex-differential-breather-vent-catch-tank-kit-universal-1703?attribute_values=2,8,7

EDIT: This: https://jonsespeedlab.com/products/jlt-performance-rear-axle-expansion-tank-2005-14-mustang-jlt-ax05

Unfortunately JLT was bought out by S&B Filters years ago so the JonseSpeedLab link is bunk. For whatever reason, S&B Filters discontinued a lot of JLTs products. It looks like JonseSpeedLab just don't update their website when a part goes out of stock to stay relevant in search results.

That said, if anyone knows where NOS or even used JLT axle/diff expansion tanks may be, I am very interested. I don't like any of the options currently available, far too much labor involved for a simple gravity tank. IMO, if you are going to the trouble of mounting the expansion tank in your trunk you might as well go full hog and install a cooler as well.

@cholmes1 Perhaps the Bob's Machine one could work?

I installed the Bobs Machine unit years back. Works great.

BackInBlack said:

Not sure about that part. I've never experienced that myself. It could be your vent is dirty/clogged? Super cheap part so might be worth replacing as a just in case thing. Then again, it'd probably clean up easily enough if it is clogged.

I think this is the one:

https://lmr.com/item/LRS-4022A/86-04-Mustang-88-Rear-Axle-Housing-Vent

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I agree, it seems that the 8.8 is under vented, It probably wouldn't hurt to run 2 vents, in my car I picked up one of the little plastic vent valves off of another diff in a scrapyard, and use the vented cover as well. FWIW, the guys running the single vent line in the axle, have been plumbing it for a tube, and putting a spiral in the tube to slow down the "blowby" on the track

TMSBOSS said:

I installed the Bobs Machine unit years back. Works great.

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Did you make a write-up of your install?

I reached out to the company to see if they will send me the installation guide.

mwjscn said:

@cholmes1 Perhaps the Bob's Machine one could work?

Mustang 2005-14 axle reservoir “KR” style - Bob's Machine

Mustang 2005-14 axle reservoir "KR" style

bobsmachine.com

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Thank you. This looks promising. I will reach out to the company

It's pretty straight forward, the metal straps sandwich under the existing upper arm bracket bolts so the tank element sits above the diff pumpkin.

Thank you, @mwjscn - that is very helpful.

Did you take additional photos of your installation by chance. Did you see a need to upgrade any parts from their kit?

For example, in your photo, I see that it is powder coated black, but on the website it shows brushed aluminum. Was that something you did or how it arrived?

I can't claim ownership of the photo, just something from my reference stash of images that I thought would be helpful here. I believe the person who installed this one just sprayed it with some black paint.

Found this for others: https://www.svtperformance.com/thre...-bobs-auto-sports-rear-axle-reservoir.940000/

A lot of us had problems with the Bob's catch can. If I recall (it's been over 10 years), if the car is lowered you will have clanging when the axle compresses into it. Several of us tried adjusting it, bending the bracket, etc and nothing worked. Hence, switching to the JLT. I might actually still have my Bob's in a box if someone is interested - PM me.

This refreshed my memory about the issues with the Bob's:

Thank you @Champale. I read the thread and that is a concern appropriately raised by @VoodooBoss and @drano38. I also appreciate @mycroft for bringing the mod idea to my attention.

The canister itself certainly cannot be mounted to the axle as that would defeat the gravity drain back feature. I’m trying to visualize how the Bob’s could be mounted but not be struck by the diff while it’s in travel.

The shallower diff plug may be an option but the ones shown in Rick’s photos looks pretty shallow from the jump.

Anyone with experience on modding these kits?

Perhaps you could slightly shorten the brackets to remove it from the the axle’s arc path.

I will need to await sage advice before going the Bob’s route

I’ve been running the Bob’s kit since 2019. For such a simple concept, it took some trial and error to get it dialed in. The only physical mod I made to eliminate any contact with the axle was to open up the half-moon shaped cut on the one mounting arm. This is for the upper control arm to differential bolt to pass through on compression.

Getting the vent hose and fittings to my liking is where the trial and error came in. The hose needs to be long enough to allow for full suspension travel, but not too long that it kinks on compression. Regular rubber hose was much more prone to kinking, so I’ve ditched that in favor of braided motorsport grade hose with AN fittings. I still have over-the-axle exhaust, which presented one more obstacle. The ideal length hose would come in close proximity of the exhaust, and actually melted a spot on the hose. A sleeve of heat shield over the braided hose has been my final iteration and works well.

The last consideration is which port to vent from. I originally tried to vent from the hole on the axle tube where the OE vent was (GT model). Nothing but issues trying to get that port to work with the OTA exhaust. When I switched to the Cortex watts, the diff cover had a larger port available and has been the solution.

Why go through all of this? Because I hate the smell of diff fluid and didn’t want a breather can in the trunk. If you go the Bob’s route, just plan on NOT using the included fittings and hose. DYME Psi made my hose custom length with heat shield as an installed option. I’ll see if I can find the length from the order confirmation and will post here if helpful.