Leaky CV boot - will a sealant work?

[ '87 Porsche 944 ]

I am wondering if I can put a specific sealant around the outer ends of my replacement CV boots to keep grease in and keep the elements out. I thought of a non-hardening oil-resistant sealant (Permatex has one). I think this might end up clogging the CV joint if drawn inside, and might not resist grease anyways. I am stumped. Searching the internet suggests nobody cares about this.

more detail: my CV axle boots leaked grease so much there was a nasty cakey coating on my control arms EDIT the boots were not ripped, the grease squeezed out between the joint and boot metal rim - they were torqued pretty tight. one of the axles actually had rust underneath the boot. There are no clamps on either end of the original boot. the original cv axle itself appears to have had an epoxy coating on it. aftermarket kits have pinch clamps for the rubber end, but the metal end around the joint - where all the grease comes out - still seems not to have anything there except the six bolts squeezing the metal boot rim and joint onto the spindle. …I can hear someone asking already : yes I could get a new axle assy but the problem still stands about sealant.

leaky CV boot - will a sealant work?


You already probably have dirt and crud in the CV joint and it is likely compromised already

Time to replace them

Leaking (torn) CV boots need to be replaced. Sealants will not work in a “greasy” environment so that idea is out. If grease can get out then dirt can get in and when that happens the CV joints wear out. Sorry I couldn’t have better news.

@SteveCBT @missleman The question is about the replacements. I have taken them apart already and am getting new. The question is about installing the new boots with a sealant that resists grease or not - it seems people just install them without regard to any sealant, the sealant going on either end of the boot.

Yes you can use a sealant. The only sealant to use is one called “The Right Stuff” by permatex. Unbolt the flange (ring), slide it and the boot back to clean the flat surface of the boot and the mating edge of the CV joint. Add more grease if needed and clean the mating surfaces again. Then add a bead of "The Right Stuff to the mating surface of the boot. Then assemble and bolt into place. Give the assembly about 4 hours to cure.

@keith I’ll check that out.

The problem I think is the metal-to-metal interface of flange-to-joint.

Perhaps a tape will help… the way Teflon tape helps with metal-to-metal fittings in air/water plumbing applications.

Doesn’t the boot have a lip on it that goes between the flange and the joint and acts like a gasket? BTW, I believe that the “epoxy” is not an epoxy, but a two part rubber “potting compound”. You can use "The Right Stuff’ in its place on thin film applications like this.

@keith the old and new boot flanges are flat metal… unless the old one’s gasket totally disappeared before the grease shower. The joint is flat. No gaskets… there might be a groove around the joint, but I thought it was just a machining artifact… I just happened to read that some aftermarket versions have a cork gasket - might see about this. Interesting about the potting compound - how is the right stuff different from ultra black?


I’ve replaced several CV boots over the years . . . without any sealer

So far, so good

Take the axles out, clean everything good, use new boots, clamps and grease, and you’ll be fine

The right stuff is a rubber compound, not silicone. It is more resistant to oil and grease. Most silicones will loose any adhesion they have when exposed to oil. In a gasket situation where the silicone is held captive, it is OK. The silicone does not otherwise break down. The Right Stuff maintains adhesion when exposed to oil.

I thought there should have been a gasket between the flange and the CV joint, but if there is a groove machined into the flange, it is probably there for a sealant of some kind. Ultra Black might work since it would be held captive by the groove and the bolts, but given a choice, I’d use The Right Stuff. Use a really thin bead.

Did you use the clamps on the outside of the flange? Without those, the bolts might not be providing enough clamping force.

I just tried the Right Stuff - looks OK in a test run. thanks @keith.

I also recently learned that Porsche uses a different shaped plate on either end of the axle - the plates on the wheel are longer as if to pinch the boot down more effectively.

I’m not visualizing this at all. Guess I’ll have to take a peek under my 924S to see what you’re talking about, and to see if mine has the same problem.

@NYBo good idea - but you can also check the PET for your model and year - the '85-88 944 PET has the diagram on illustration 501-10, under the section “Main Group 5: Rear Axle: 502: vibration damper, stabiliser”. part no. 7 is shaped more closely to match the edge of a circle than part no.5.

It is also easy to imagine how, when in haste, these plates might get mixed up upon reassembly.

an update to this for those interested :

I recently had a new CV axle shipped from Germany. it was pre-greased, and a cap was installed over the joint, secured using masking tape on the OD of the joint. There were signs of grease weeping (wet looking only, no globs) on the cardboard box area surrounding the joint. there was minor if any leakage past the masking tape from what I could tell - the tape was still secure. the largest amount of leaking seemed to be from the bolt holes, also evidenced by wet grease around them.

back when I removed the joints from the car, all the bolts actually were very greasy. I was alarmed by how greasy they were.

I conclude that the CV joint holes are a major contributor to leaking. I imagine grease gets packed around the bolt and forces its way out the hole and boot. I also think some goes between the joint-spindle interface. so I’m going to consider putting Right Stuff down in the joint hole to some depth, if not just around it… and as I write this, suppose I ought to put some between the joint and spindle too…