"CV" Boot Repair

[Knottscott]

Hello BT3 brain trust. Gotta car repair question for you. My mechanic tells that me that our car has a slight crack on one of the CV boots....he said it's not leaking grease yet, but will eventually need to be replaced....it's probably easiest to replace the whole axle assembly.

My question is whether or not I can extend the life that cracked boot by spraying it with spray rubberizer or silicone caulk? Anyone tried it? Other ideas? Comments?

TIA!

[jseklund]

I don't think you will get much extra life out of any type of spray - the CV boot is constantly twisting, expanding and contracting. Any additional life would be minimal. If it's not leaking yet, then you are in good shape.

I'm not sure what type of car it is, but the half axles are normally $100-250 and should be able to be installed in under 2 hours EASILY, if everything goes as planned.

A new CV boot probably costs $20 and should be about the same time or maybe another hour to install, depending on your preferred method of install. You really just have to get the knuckle off the end of the axle and remove/reinstall the new boot and pack it with grease. The packing with grease part is usually messy and why many people prefer to replace the entire axle.

Also, if the joint goes bad, then the axle assembly may make more sense. If no grease is leaking, however, your joint should be fine and you can just replace the rubber boot.

As you let it go, grease will start to leak out, and eventually you will start hearing a click, click, click when the tire rotates - usually when making turns. The clicking will get worse and worse until it's almost constant in many situations...

[Knottscott]

Thanks much for the excellent detailed and helpful info.

[Daryl]

I have replaced them before with a two part boot. This eliminates the need to remove the axle. When you remove the old one check the grease for grit, remove as much of the old grease as possible and just shoot the supplied grease into the joint. If there is grit you have to do a good cleaning job and may wish to go ahead and dissassemble the joint. Any way, just glue the two halves together. Be careful not to get grease on the mating surfaces. I think there was a new band for the ends.

[woodturner]

My question is whether or not I can extend the life that cracked boot by spraying it with spray rubberizer or silicone caulk? Anyone tried it?

Yes, I have done it.

Any idea how long it has been cracked? If it's relatively fresh, you are more likely to be successful with this method.

Clean any dirt you can find from the area around the crack, and use a pick or something to scrape out any dirt that has gotten into the boot. Use a grease gun to put some grease into the boot via the split. CLEAN the outside of the boot as best you can around the crack - wipe off any grease, then clean with a compatible solvent. Apply silicode liberally to the crack - you want to seal out dirt and water, but keep it less than 1/16" thick or so to enable it to flex (CV joint boots do need to flex a little). Let it cure overnight, and you should be good.

I did this to a car around 40K miles, when I was sure the joint was OK and the boot was just split at the bottom of one of the folds. The CV joint and boot were still fine when I sold the car years later with something like 320K miles on it.

Having said all that, however, half-shafts ("axles") are relatively inexpensive for most cars - around $50 to $60 at Autozone with a lifetime guarantee. While you can get a split boot CV repair kit for around $20, they don't work well from what I have heard. To replace the boot with a single piece boot requires removal of the axle - and for $30 to $40 more, it's better to replace the half-shaft as your mechanic suggested.

Replacing the half-shaft is not terribly difficult, on most cars. If you look online, you can probably find a youtube video showing how to do it on your car, to get a better sense of difficulty. The worst part is usually getting the shaft out of the transmission, due to the c-clip, but a slide hammer puller will usually make quick work of that and is available as a free loaner tool at the auto parts places.

[cabinetman]

Here's some info about using split boots.

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[Knottscott]

Thanks guys....I knew I could count on you for great info!

The car is a 2007 Hyundai Elantra with 85K miles on it.......I do a lot of the of the "fair weather" repairs and routine maintenance, but don't usually bother in severe weather, so he sees the car a couple times a year for winter oil changes and inspection. I doubt the crack is very old or he would have noticed it sooner. He does excellent work and I believe he's honest, but he wouldn't miss an opportunity for more work! (but that's really one of the reason I go to him...)

[dbhost]

Yes you can eke out a little bit more life by using RTV on the crack as long as it isn't leaking, and the boot is completely, and perfectly clean. Guess what's not likely to happen?

On the plus side, Half Shafts are pretty easy to replace if you can get the car off the ground with a decent enough amount of space to work... Just get a loaded half shaft instead of joints and boots. Driving a joint off a shaft is no fun in the garage...

[jseklund]

Cabinetman's link takes you to Raxles.com - which is where I buy my axles from.

I drive an Audi, and the CV joints go bad on these cars as a rule. I have gone with the "replace the axle" theory each time I've changed an axle, as I didn't want to deal with the grease and cost savings wasn't a concern at the time.

The first time I did the axle replacement, I bought a relatively inexpensive axle from an autozone-type place. It failed in 30,000 miles (about 7-8 months of driving for me). After that, I went to Raxles and have had no failures using them. I have replaced the failed axle and the original axle on the other side with Raxles and have probably 50-70K on each axle and no signs of any problems at all.

I helped a co-worker replace both axles on his car, which he bought from Autozone, and both failed within a year.

The warranty is great, if it covers boot failure, but you still have to redo the labor. The half axles on your car sound like they may be a bit less - so it may be worth just doing the entire half axle if it's less than $100 more. Just remember that you get what you pay for with these parts (at least that's my experience).

[woodturner]

The first time I did the axle replacement, I bought a relatively inexpensive axle from an autozone-type place. It failed in 30,000 miles (about 7-8 months of driving for me). After that, I went to Raxles and have had no failures using them.

Could be something unique to that car or different about the Audi axle design.

I've used the ~$50 Autozone parts with the lifetime warranty for a number of years, never had a failure or had to replace a second time, even 100K miles or more.

One caution is that many designs require rather careful handling - for example, if the axle is picked up by the joints rather than the axle shaft, the joints can be damaged. I've always wondered if commercial shops are as careful with them as the manufacturer's recommend. In any event, I've had no problem with the AZ parts, but I handle them carefully and install them "by the book".

[woodturner]

Yes you can eke out a little bit more life by using RTV on the crack as long as it isn't leaking, and the boot is completely, and perfectly clean.

The boot does need to be cleaned, but it's easy to do. Agree that he may be able to eke out a little more life - 200K miles and 10 years or so, in my experience when I did it - but it's definitely not the ideal or "right" permanent fix.

No reason not to try it, though - the joint might eventually fail anyway, but if not, he will have saved a good bit of money.

[woodturner]

The car is a 2007 Hyundai Elantra with 85K miles on it

FWIW, the top quality axles for that car are $68+core at Autozone.

[JSUPreston]

From personal experience, make sure to take care of the CV joints. When I was in HS, I lived at a childrens home here in AL. We had a Dodge Omni that the kids were allowed to drive. The maintenance crew never worked on the car unless it was dead on the side of the road. We could complain constantly, but something HAD to break before we were taken seriously. Heck, it had an automatic that for a while we had to shift manually, because it had a tendency to jump out of drive...until the #2 person at the home heard about it. Then, we were scolded for driving it that way, but it got fixed.

Anyway, I was driving the car one night to the local Wally World, and took a left turn. We'd been hearing the clicking for a long time, but it was never fixed (see above). Anyway, when I finished the turn, I couldn't straighten the wheel. I slowed the car down to a crawl and parked it nose first in the ditch on the left side of the road. I walked home and told the houseparent what happened. A bunch of us went and were able to push the car out of the ditch and get it to a parking lot.

When the CV snapped in the turn, it jammed up the steering on that side. When I "parked" it in the ditch, it knocked the broken shaft loose, which is why we were able to steer it and push it to a parking lot.

I'm just glad that when it gave, I was doing no more than 10 mph and was on a back street at night. It wouldn't have been pretty at a higher speed on a busy road.

[T...K21]

I say... just replace the whole axle. Replacing the boot would be an option if you catch it early. But trying to replace it after it has been ripped for awhile is worthless. Dirt and grim that enters inside the boot puts excessive wear on the joints and you'll end up replacing the axle anyways.