E46 M3 half shaft failures

[PCarroll]

We've just had the second identical half shaft failure on my wife's 2005 E46 M3. The left inner boot rips and lost all the grease. Luckily I discovered it in time this time. The CV joint still feels okay. The second failure was identical and after only one track weekend.

The car is set up for the track with very stiff suspension and a very low ride height (800/900lb springs). The half shafts on this car are different lengths. The driver side seems to be slightly shorter. This means the left shaft operates at a slightly greater angle than the right. On the track, this side is much more loaded.

The only thing I can think is the ride height is too low? This could cause the CV joint to bind and produce a lot of heat. Problem with this theory is I checked the play with the car on the ground and the shaft moved in and out smoothly. So no binding I could detect.

We had similar problems on my E36 when lowered too much (way beyond what the stock bodywork will allow). In that case it was the outer joint that failed. But there was static binding that was easy to detect.

I'm having it repacked and am going to try raising the rear 1/4" or so.

Has anyone out there had a similar experience on a E46 M3?

Thanks
Peter

[flink]

Those boots can swell up like a balloon at high speeds and rub against things you wouldn't expect them to rub against. The vette guys have problems with this with some aftermarket boots, particularly. This fix is to .... put a zip tie around them!

[CP Louie]

The only issue I had was the driver side on the diff gets hotter than the others and the grease ran out when I took the diff out. Not really a failure. Turner makes a kit that allows for the repacking and boot replacement on the wheel side. The diff sides can be done as is. Chris

[PCarroll]

We're using a boot/repack kit I found on the Internet locally for $26 ($140 from BMW). Has the same manufacturer's mark on it. GSK I think? Nice mark up.

BTW, the car has a conventional LSD rather than the fancy E46 M3 thing - if that matters.

I thought I saw Turner or someone had a special way of venting the boot with a tiny brass tube. Mentioned something about World Challenge cars. But I could never find it again. Anyone know where that went?

[sped here]

Those boots can swell up like a balloon at high speeds and rub against things you wouldn't expect them to rub against. The vette guys have problems with this with some aftermarket boots, particularly. This fix is to .... put a zip tie around them!

Also - they blow up due to heat and grease gassing. I have seen Porsche race cars that use a straw (like the kind that comes with WD-40) inserted along the axle under the band clamp to vent them along with the zip tie to keep everything in check. DSS racing axles come with vents formed right in the boots for their higher end stuff too.

[scottbm3]

Back in the day when I was working in CART and building axles and uprights we used to put tiny vent tubes between the axle and boot. Unless you've ever used Krytox grease you'll never know what real CV grease is like !!



-Scott B.

[robjohnson]

Remember to 'burp' the boots several times, and use a precisely measured portion of grease. Get all the air out that you can to lessen expansion and ballooning during operation. I've seen factory boots over packed and pop the retaining clips off dumping the grease under the car.

[CP Louie]

Venting means just add a small diameter tube 1-2 mm between the shaft and the boot on the shaft side. It vents the boot and is too small for any real grease to come out. Use Teflon tube. Chris

[PCarroll]

Just back form Mosport... Kept failing. Eventually it seemed to stop after raising the rear end substantially. The inner boot was blown up like a balloon. And grease blew out the outer end and sprayed all over place. I wonder if the shop we jobbed it out too put shitty grease?

I'm surprised that you can lower the E46 far enough to boil the grease. Certainly we never had this problem with the stock fendered E36s.

I've probably abused these used ones enough to replace them preventatively. I swear I saw one of the usual online BMW suppliers selling a racing version that had the vents already installed. I think it was just modified OEM. Not custom. But I can't for the life of me find it now.

Anyone know where it was?

[TOOLEAN]

Peter, I am trying to follow along... What exactly did you try before Mosport? Just the venting?

[PCarroll]

We had two driver side inner boot failures in rapid succession. On this car I believe the driver side shaft is a bit shorter. I think I caught it in time so I sent it out for repacking and new boots.

So... In addition to that, before Mosport we raised the rear of the car about 1/2". My wife and I were sharing the car so it saw a lot of back to back runs. It's also extremely well setup, so it gets a lot of full throttle time at Mosport. The boot was still inflating like a balloon. So much so that it blew a bunch of grease out of the outer boot. Pretty messy back there now.

So I raised the rear spring perches another 2 turns. So maybe another 3/8" higher? It seemed to be better but I'm not sure how much grease is left in there. It looked still a little inflated. But nothing like before.

The shaft was already back in the car before I started this thread. So I'm just investigating solutions.

So far I am assuming the failures are due to the very low ride height. We had similar failures on some E36 race cars that were extremely low - 3 sets in one weekend on my E36. I never expected it to be an issue with a street compatible car.

Even at the original low ride height, the shaft had good play and was not binding. On the E36 you could feel it binding with no play. So I'm surprised it generated that much heat. The car is a 05 M3 with Motons and 900lb rear springs (not coilover). So I can't see the shaft flexing hardly at all under load. It's only using 265 Michelin PSCs so maybe that is allowing us to lower too much? We have tons of fender clearance.

I have not tried adding vents yet. I thought I saw them as an option on shafts somewhere. I thought it was Turner but I can't find them now. I've been using used shafts. So maybe it's time for some new ones anyway.

Strangely, Raven had built plenty of race cars both E36 and E46. All of them use stock OEM half shafts without vents. Only two of the widebody cars had problems and that was due to excessively low ride height. Once we raised them up they were fine.

[SmallJ92]

I had my right side inner boot tear after a track event a couple of months ago creating a huge mess of grease. I think the left side boot may have developed a small tear recently also, so I need to check it tomorrow. I'm curious to see what you find with regards to these ticking time bombs.

[PCarroll]

Based on the picture of your car in your signature, I suspect yours is also caused by the ride height. It's even lower in the back than ours was. We never had a problem with the right side (it's longer than the left shaft so it operates at a slightly lesser angle). But I suspect if we did lower it, it would do it too.

Next time you come off a long/hot session on the track, immediately look under the back of the car to see if the boot is inflated. It does go down quickly after a few minutes.

Inflation seems to be the byproduct. The real problem is the excess heat being generated by operating them at an extreme angle.

Below is the car before making changes. I've since raised the rear about 3/4". Seems to have controlled it. I'm going to take fender measurements from some of the Raven race cars since they are not having the problem. Because thay are running much larger tires, I suspect they are not lowered as much as this. The narrower 265 tires on this car seem to encourage too much lowering. We'll find out at O'Fest...


More at: http://www.driversmeeting.com/pcarroll/albums/128

[albrazzi]

I'm a pump guy and over the years I have seen fluid pumps that were no more than a modified CV joint and angle is everything, I suspect under load one side is inflating and the other side is under vacuum, that along with the thermal expansion of everything especially he lubricant and there you go. Venting will manage the heat but not the pumping. I have had one go out but it was just fatigue, age and heat from the exhaust and you have all that covered already.

[99MPower]

what kind of CV grease is the shop rebuilding them using?

[PCarroll]

That's a good point. The driver side inner boot is very close to the exhaust. On the track, that heat will definitely be a factor. Though still probably not the primary cause...

The grease was the standard GKN stuff that came with the rebuild kit. Since the OEM shafts generally worked, I figure that was good enough. The race cars are using OEM. So they are missing the source that I am experiencing.

We also flashed the DME recently with better software mapped to 94 fuel. The car makes considerably more power now. That shows up as heat. It was enough to tax a tired fuel pump into failure. Also runs a little hot even with the oversized rad now. Time to look at airflow through the rad...

[99MPower]

thought about running a better synthetic CV grease?

Whenever I rebuild an E36 half shaft, I'm using Redline CV2 synthetic grease. Not the best stuff out there (i've seen CV grease going for $200+ a tube), but from my experience, better than the OEM GKN stuff.

[NeilM]

thought about running a better synthetic CV grease?

Whenever I rebuild an E36 half shaft, I'm using Redline CV2 synthetic grease. Not the best stuff out there (i've seen CV grease going for $200+ a tube), but from my experience, better than the OEM GKN stuff.

Earlier this year when instructing at a PCA event I was in the garage next to a guy with a Porsche Super Cup car — 480 hp, sequential shift, the whole bit — and his mechanic. The mechanic told me they'd recently blown a CV joint and had to replace the halfshaft ($2300 each, ouch!) because of failure to use the correct Porsche spec CV joint grease. And yes, it's $200+ a tube!

So Peter, it could be worse...

Neil

[albrazzi]

That's a good point. The driver side inner boot is very close to the exhaust. On the track, that heat will definitely be a factor. Though still probably not the primary cause...

The grease was the standard GKN stuff that came with the rebuild kit. Since the OEM shafts generally worked, I figure that was good enough. The race cars are using OEM. So they are missing the source that I am experiencing.

We also flashed the DME recently with better software mapped to 94 fuel. The car makes considerably more power now. That shows up as heat. It was enough to tax a tired fuel pump into failure. Also runs a little hot even with the oversized rad now. Time to look at airflow through the rad...

This year I wrapped the crossover pipe with heat tape like the Bikers use for burn protection, I guess it is a good move, I didnt want some kind of home made heat sheild that might fall off on Track. But then I'm not making the heat you are.

[raamaudio]

Did you check the suspension geometry with the car lowered that much? Excessive lowering can really mess up the roll center, roll couple, etc besides just causing CV failures. I have gained 1.5 seconds a lap on my ex TT car with just a 1/4" raise to where I knew it should of been but wanted to try it a little lower.

Most cars handle better if not to low, just do not look as fast

Rick

[PCarroll]

Actually you could feel it get a little worse after raising it back up. It's still a rocket. But lower was even better. Same for my E36. Front may be a different story... I only raised the rear. Funny thing was the shaft play was still fine set really low.

[albrazzi]

You mean play/float sitting still, I cant imagine that relating too much to the stresses under load.
Who was it who said "You first need to finish the race to win it" reliability is everything.