The importance of replacing one-time-use bolts

[tdi_allan]

Unlike a lot of my fellow TDI Clubbers, I farm out work that I can't do due to time/space restrictions. One of those jobs is CV axle removal/rebuilding/replacing. I had the OE axles rebuilt for a second time and installed in late January. All was well, did the winter Lemons Rally in February, and then started commutting ~30 miles round trip per day to a new job.

Fast forward to Friday July 7 - normal acceleration from a stop produced a SNAP and no forward motion. AAA towed me home, and after jacking the car up the passenger wheel spun very freely while the car was in gear. While my fears of transmission or clutch failure were alleviated, it was pretty obvious what happened. Towed back to the shop where I had the axles installed, and this is what they found:

It is likely that these bolts have never been replaced as per Bentley:

All 12 bolts were replaced and the car is operating normally again. Needless to say, I'll be double-checking these as soon as I get a chance (the lift at the shop I share with my racing team is currently occupied by an almost-finished race car...)

 

[Lightflyer1]

It is their fault as they are supposed to find and use the correct info. Anyone who has dealt with these cars knows these kinds of fasteners are used in the vehicle. The owner should not have to tell them these kinds of details. That is what they are getting paid for.

 

[Ol'Rattler]

Your preaching to the choir. There are a lot of folks that think they know better than the manufacturer. Some other car brands use TTY bolts as well.

I did reuse some engine mount bolts once but didn't yield them a second time. What I did was torqued them and IIRC only went 1/8 turn instead of 1/4 turn and with 72K since I installed them, all is good. I would not recommend that but I was in a pinch. I would always wait for new TTY bolt on anything that rotates.

There is a thread titled something like "why you shouldn't take your car to the dealers" and in regards to T/B jobs, cars would come into his shop after a dealer T/B job running like crap and every once in a while with broken MM bolts with the engine fallen down on the T/B side.

Talking to a parts guy at a local dealer, he took a lot of pride in the fact that they never replaced TTY bolts.

 

[gaddman]

Maybe I'm just lucky, but I've re-used axle bolts on my own cars and never had a problem. I had one occurrence where my son did not get them tight enough and a couple of them sheared off like that. I wonder if they just did not get them tight enough...(easy to do if you don't lock the wheel to keep the axle from turning) or torqued them too tight? If that's the case, even using new bolts would not have prevented this. I'm not advocating re-using TTY bolts.

 

[Ol'Rattler]

Baloney. New TTY bolts installed per Bentleys will never give you a problem.

 

[gaddman]

True that...but what I said was if they under or over torqued them, even with new bolts there could be a problem. Of course new TTY bolts installed per Bentley is the way to go.

 

[jimbote]

Allan... the bentley entry you posted is NOT referring to the axle flange bolts but is referring to the axle NUT that holds the outer CV to the hub... the axle bolts you pictured are not one time use and are probably the victim of improper torquing

 

[Mark]

Allan... the bentley entry you posted is NOT referring to the axle flange bolts but is referring to the axle NUT that holds the outer CV to the hub... the axle bolts you pictured are not one time use and are probably the victim of improper torquing

I was waiting for someone to notice that. Axle "nut", "self locking". The items pictured are neither a nut, nor are they self locking.

And yes, that big honkin' nut under your center cap should be replaced every time.

 

[tdi_allan]

Follow up

Mark and Jim, you are both correct. I have edited the post to reflect the non-issue of the axle nut. As noted above, I'll be checking these bolts again soon to see if they were properly tightened. Thanks for calling out my error.

 

[Tdijarhead]

I thought the axle bolts were reusable also, I just put a new engine in my car and have already checked those bolts twice just to be sure.

 

[Ol'Rattler]

I thought my memory was messing with me, but per Bentley's the drive axle flange bolts are not TTY and are reusable.

Don't do like Guber did and put red Lock Tite on them. IIRC I didn't use Lock Tite of any kind and they have not sheared or loosened in 130K miles since I did the clutch. A torque wrench is your friend..........

 

[jimbote]

I thought my memory was messing with me, but per Bentley's the drive axle flange bolts are not TTY and are reusable.

Don't do like Guber did and put red Lock Tite on them. IIRC I didn't use Lock Tite of any kind and they have not sheared or loosened in 130K miles since I did the clutch. A torque wrench is your friend..........

yep, never seen these bolts come loose when torqued to spec ... the 8mm flange bolt spec is 30 ft lb ! and that is dang tight for an 8mm bolt!

 

[oilhammer]

Those bolts were all overtorqued. I reuse those all the time, not an issue. Some of them I have had out and back in several times, too.

However, some boot kits come with replacement bolts, and some folks like to use those, but I find they are generally not as good as the OEM bolts Volkswagen uses.

 

[jokila]

Those bolts were all overtorqued. I reuse those all the time, not an issue. Some of them I have had out and back in several times, too.
However, some boot kits come with replacement bolts, and some folks like to use those, but I find they are generally not as good as the OEM bolts Volkswagen uses.

The torque on the manual trans is different from the auto trans bolts. Maybe the wrong spec was used.

(M8) 30 ft. lbs
(M10) 52 ft. lbs.

 

[MadScience]

Yup, I reuse these bolts and had zero problems. I agree that a torque is your friend...for so many jobs too.

 

[oilhammer]

The torque on the manual trans is different from the auto trans bolts. Maybe the wrong spec was used.

(M8) 30 ft. lbs
(M10) 52 ft. lbs.

It is the size, not necessarily the transmission although in some cases like the ALH, the two go hand in hand. I just snug them down, but if you do not have a feel for it then get your torque wrench out. Kind of like asking a surgeon how many stitches to use and how tight to pull the silk. Or asking an orthodontist how tight to pull the wires on the braces (ask me how I know ). You just get a feel for it.

 

[mk3]

I would think the bolts were under-torqued. Lack of friction on the drive face is what let the bolts become all that held the shear. I really high grade bolt can handle 'a lot' of shear but you'd want that to be on the shank. This shear faces was in the area of the threads where there is less material and also extreme stress concentrations from the sharp geometry.

If the bolts were very tight the high friction would have held. I suppose ... extreme case they were tightened so much that they failed but then you should see the material necking down and evidence of twisting and yielding.

If you cleaned up the bolts and examine closely you might be able to determine how they failed.

oh, btw I agree with oilhammer a person can get a feel for tightening a bolt...just want to stay under the point where one can feel it starting to yield.

 

[where2]

Those bolts were all overtorqued. I reuse those all the time, not an issue. Some of them I have had out and back in several times, too.

Definitely over-torqued. When I replaced the axles on my MkIV last summer, I found one sheared like that. It was "glued" in place with RTV by the previous "mechanic" to make everything appear as if it was "A-OK" under there. It seemed really odd when one bolt was shorter than all the rest when I removed them all. While trying to put them back on, I found one would not start in a particular hole. When I took them all back out, I found one was shorter, and that little broken off end was still in the flange. When I realized what the issue was, I feared it was frozen/rusted in place. Why would some "mechanic" not fix this, if it was easy? I hit the tip of the bolt I could see on the outside of the flange with a Dremel to put a slot in it, then turned it out with a 90° angle screwdriver. To my complete astonishment, the broken segment was merely finger tight, and contrary to my original fears was easily removed! Again, why didn't the previous "mechanic" care enough to fix this correctly?

To replace it, I rooted through my collection of old metric bolts from MkI and MkII VWs and came up with a replacement from some previous car I had that may have been scrapped, or ones I collected in a junkyard to replace those you always find with half stripped triple square heads. I used my 1/4" drive HFT torque wrench to torque them per Bentley. (same torque wrench I used on all the 316 stainless 1/4-20 bolts on my solar array. 316 SS does not like being over-torqued!)

 

[UhOh]

There are torque values. Yes, one can get a feel, but it's an approximation. I get distracted, I get tired, and angles can often be awkward. I cannot always trust my senses, in which case I reach for the torque wrench. If I were a professional I wouldn't want to have anything come back to me due to improper torquing; and, really, why would I look to do any different with my family members?

Yes, many folks here who do the same jobs with a lot of frequency can very well likely manage by feel.

Inspect all threads (cleaned). Only reuse if they're not single-use and all looks good. Torqued to spec and there should be ZERO reasons to look over one's shoulder.

 

[Nozzleman]

If you find one of these bolts broken off, it's a good bet that the rest of them have run loose and are micro-fractured. I would replace all on that side at minimum.

I have seen that happen on lug studs where one after another snapped off.