T.A.B'S, Flaw or smart choice?

[LEVY]

If any one have an educated answer:

I know Trailing Arm Bolts are kind of "soft" for the job they do.

My question is: Is that a DMC Flaw, or were used that soft on purpose? Maybe they are intended to absorb and bent if needed to protect the more expensive frame?

If anyone have an answer please let me know.

LEVY


Just FYI, NOS TAB's are 10.9 grade M12x130mm bolts.

You can get grade 12.9 bolts through Fastenal with a variety of different coatings. I went to a Fastenal in my town and they got them in the next day. cost me less than $5 for the pair.

[Jeff K]

If any one have an educated answer:

I know Trailing Arm Bolts are kind of "soft" for the job they do.

My question is: Is that a DMC Flaw, or were used that soft on purpose? Maybe they are intended to absorb and bent if needed to protect the more expensive frame?

If anyone have an answer please let me know.

LEVY

I'm guessing they grabbed what was available. Again only a guess. I bought the 12.9 rated ones from fastenal myself.

[SS Spoiler]

Would it be possible to retro fit a heim joint on the end of the trailing arm. Then it could swivel in any direction.

[Jacko]

Would it be possible to retro fit a heim joint on the end of the trailing arm. Then it could swivel in any direction.Wouldn't that prevent the alignment of the rear wheels? I suppose spacers could be used in conjunction with a heim joint somehow.

[stevedmc]

Would it be possible to retro fit a heim joint on the end of the trailing arm. Then it could swivel in any direction.

http://sphotos-g.ak.fbcdn.net/hphotos-ak-ash4/428768_329106420467948_1497988409_n.jpg

http://sphotos-f.ak.fbcdn.net/hphotos-ak-ash4/418573_329108273801096_1337652142_n.jpg

http://sphotos-h.ak.fbcdn.net/hphotos-ak-ash4/421043_329108313801092_1785496286_n.jpg

[dmc6960]

Is that a DMC Flaw, or were used that soft on purpose? Maybe they are intended to absorb and bent if needed to protect the more expensive frame?

Soft or not, they can still bend.

I've bent a Toby TAB.

[sdg3205]

What do you "ask" for from Fastenal? Which coating?

[LEVY]

What do you "ask" for from Fastenal? Which coating?

I don't think they have more options than zinc and black oxide, I would go for zinc.


LEVY

[Nicholas R]

What do you "ask" for from Fastenal? Which coating?

I wish I could remember. I went into a store in town and the guy told me the ways they were available. I had like 3 or 4 options. I remember one was black oxide because that I did not want. I remember discussing the others with the guy then making a decision, and I cannot remember which. The originals were just zinc plated and I know they were better than that.

Also with regard to the bolts being soft. Honestly, I think that 10.9 grade bolts are certainly suitable. A grade 10.9 metric bolt is still stronger than a grade 8 SAE bolt. When the DMC-12 was in design, the math probably showed the 10.9 grade bolts to be more than adequate for the loading they would endure. 30 years later, few TABs have ever actually broken. The main issue we see is the corrosion causing a loss of bolt material, pitting, stress points, etc. and bending from creep. Typically we swap them out for better bolts for peace of mind, not necessarily because we have too.

Certainly dont confuse this with me praising the trailing arm mounting design, I dislike it as much as the next guy. I just think that given the design, the bolt used is adequate, not great, not excellent, just adequate. Also I'm curious whether better bolts were available (cost effectively) in 1980.

[sdg3205]

I'll just take an old one in and ask for a 12.9 in the same size, zinc plated. Sound about right?

[DMCMW Dave]

Honestly I think the whole problem is overblown. I've seen very few actually break on the road (one since we've been here) and it was obvious that it broke after the plating was compromised causing a rust spot that caused a weakness in the metal. I've had the broken one analyzed by fastener engineers and they had the same opinion.

This is why it's not a bad idea to change them "just because they are old" and always if they are rusted into the arm so much that they will not turn, bent or not.

The biggest advantage to Toby's is that they were made of inconel, which is inherently rustproof. I've actually seen a bent Toby Bolt (the owner is on the list and may choose to pipe up here) that was caused by apparently improper installation and the shims falling out. It didn't break, but then again we pull out lots of bent OE bolts that are not broken either.

Remember that the bolts are going through a rubber bushing that takes up most of the shock forces, so they really are not all that prone to breaking IF THE BOLT ITSELF IS NOT COMPROMISED.

[LEVY]

I'll just take an old one in and ask for a 12.9 in the same size, zinc plated. Sound about right?

I would say yes, but to make it easier, use Nicholas measurements: Grade 12.9, M12 x 130mm bolts. Thread does not really matters as long as you get a nylock nut grade 5 or better that matches the bolt.


LEVY

[dmc6960]

Soft or not, they can still bend.

I've bent a Toby TAB.


I've actually seen a bent Toby Bolt (the owner is on the list and may choose to pipe up here) that was caused by apparently improper installation and the shims falling out. It didn't break, but then again we pull out lots of bent OE bolts that are not broken either.


I already piped up!

It should also be noted that the installation was proper when it went in. What ended up being a problem was one of the "hardened" washers sitting against either the inner bushing sleeve or or the trailing arm crushed inward. This loosened the joint. I dont remember missing any shims that day, but perhaps my memory is faulty. I was missing shims a year prior on the original TABs which prompted immediate replacement with a perfectly timed 1st release of the Toby TABs.

[Kevin]

My question is: Is that a DMC Flaw, or were used that soft on purpose? Maybe they are intended to absorb and bent if needed to protect the more expensive frame?

Back to the original question, Stephen Wynne once said he thought the latter and that the suspension was engineered for soft TABs. He's not a fan of the harder TABs because the original TABs were supposed to absorb shock or pressure and be flexible. With harder TABs, something unintended may be damaged if the TAB doesn't take the blow. He thinks replacing the TABs is just part of regular maintenance.

Not necessarily my views, I'm not sure what to think, just passing it along as I've heard it.

[DMCMW Dave]

because the original TABs were supposed to absorb shock or pressure and be flexible. .

Not to argue with him but IMO the "give" is all in the rubber bushings which are infinetely softer than the TAB.

[LEVY]

Back to the original question, Stephen Wynne once said he thought the latter and that the suspension was engineered for soft TABs. He's not a fan of the harder TABs because the original TABs were supposed to absorb shock or pressure and be flexible. With harder TABs, something unintended may be damaged if the TAB doesn't take the blow. He thinks replacing the TABs is just part of regular maintenance.

Not necessarily my views, I'm not sure what to think, just passing it along as I've heard it.

I think there is some truth to that.



Not to argue with him but IMO the "give" is all in the rubber bushings which are infinetely softer than the TAB.

I'm just looking for answers, definitively rubber is softer than metal but, if you apply a lot of force to that bushing, something will have to "give", I believe the TAB will ultimately bend before the rubber compress more than 1/8", specially if the bushing is in new condition.

LEVY

[stevedmc]

This is why it's not a bad idea to change them "just because they are old" and always if they are rusted into the arm so much that they will not turn, bent or not.

Steve Rice changed his TABs because he wasn't single at the time. He didn't want to risk having to listen to her parrents fuss should she die in the Delorean.

[Bitsyncmaster]

I already piped up!

It should also be noted that the installation was proper when it went in. What ended up being a problem was one of the "hardened" washers sitting against either the inner bushing sleeve or or the trailing arm crushed inward. This loosened the joint. I dont remember missing any shims that day, but perhaps my memory is faulty. I was missing shims a year prior on the original TABs which prompted immediate replacement with a perfectly timed 1st release of the Toby TABs.

That's what I found on mine.

[David T]

You have to understand the theory behind the use of threaded fasteners. When the bolt is installed and torqued it is supposed to be subjected to a greater tensile load under torque then it will see in actual use. That protects it from cyclic loads which will quickly fatigue it. The problem is the tube (spacer) inside the rubber bushing will compress very close to the torque spec so it is easy to overtorque the bolt and compromise the spacer. Once you do that you cannot torque the bolt enough, you just keep crushing the spacer. Now the bolt is subjected to the cyclic loading and it fatigues, stretches, and bends. The other failure mechanism is corrosion. Because it is a highly stressed fastener it is more susceptible to corrosion. Once it starts to corrode it's strength is greatly diminished and it will stretch and bend. The best advice is to inspect it occasionally. It should probably be a time-lifed item but without the proper testing there is no way we can put a TBO on it. The bolt is made to be hard so it doesn't stretch as much when it is torqued. You should probably never reuse and retorque the trailing arm bolts because of the stretch. The other fasteners under similar stress are the head bolts and the con rod bolts. The Tabs should be inspected annually and if there was any sort of an accident in the rear. Write the # of shims on the frame on each side and see if they are loose. Try turning the bolt with a wrench and see if it turns. If you have locking nuts make sure they are tight. This is a "hidden" area because of the shields but it is one of the most important underneath the car.
David Teitelbaum

[LEVY]

You are right for the most part but, head bolts and connecting rod bolts are not under similar stress at all!

Connecting Rod bolts, once torqued, will not be subject to stress variations.

Head Bolts: On older engines, head bolts can be re-used if needed, on newer engines however, some head bolts are meant to stretch and can not be re-used. On this kind of bolts, a little part of the bolt, close to the head is made of a little softer material, so this bolt can not be reused. On this bolt, manufacturer instruct you to torque this bolt to predetermined torque and then turn it a 1/4, 1/2 etc. additional turn, it is at this stage when this bolt will permanently
stretch.

Trailing Arm Bolts: On this particular application, this bolt is subject to a high range of stress variations, every time the vehicle is moving, even on a very flat road, this bolt is under high stress, no to mention when the vehicle is driven on a rought terrain or worse.

This bolt receive longwise stress as well as sidewise stress!

LEVY



You have to understand the theory behind the use of threaded fasteners. When the bolt is installed and torqued it is supposed to be subjected to a greater tensile load under torque then it will see in actual use. That protects it from cyclic loads which will quickly fatigue it. The problem is the tube (spacer) inside the rubber bushing will compress very close to the torque spec so it is easy to overtorque the bolt and compromise the spacer. Once you do that you cannot torque the bolt enough, you just keep crushing the spacer. Now the bolt is subjected to the cyclic loading and it fatigues, stretches, and bends. The other failure mechanism is corrosion. Because it is a highly stressed fastener it is more susceptible to corrosion. Once it starts to corrode it's strength is greatly diminished and it will stretch and bend. The best advice is to inspect it occasionally. It should probably be a time-lifed item but without the proper testing there is no way we can put a TBO on it. The bolt is made to be hard so it doesn't stretch as much when it is torqued. You should probably never reuse and retorque the trailing arm bolts because of the stretch. The other fasteners under similar stress are the head bolts and the con rod bolts. The Tabs should be inspected annually and if there was any sort of an accident in the rear. Write the # of shims on the frame on each side and see if they are loose. Try turning the bolt with a wrench and see if it turns. If you have locking nuts make sure they are tight. This is a "hidden" area because of the shields but it is one of the most important underneath the car.
David Teitelbaum

[Nicholas R]

I agree with you LEVY. Shear loading is another consideration. Head bolts and connecting rod bolts are never exposed to shear loading, only tensile loading. TABs have a large shear plane between the trailing arm and the frame.

[Jonathan]

A couple years ago I was working on putting together a statistical analysis of TAB failures. I never got a lot of data to work with, as like Dave mentioned, there just hasn't been a lot of catastrophic failures. I remember seeing the link to the D that supposedly flipped from a TAB failure where the trailing arm dug into the ground or something along those lines. However, just as quickly were a couple other links debunking that story as it proved not to be related to a TAB failure causing the accident. What it did add to though, was the paranoia among the community about the TABs on your car failing out of the blue and with very bad timing.

One thing I was speculating, that I couldn't prove with the small amount of data, was that it might be at least partially consistent with ambient temperature. I had recently taken some training at work on strength of materials, and that day we were looking at brittle failures in metals. If a piece of metal has a defect or imperfection due to manufacturing or from rust for example, it is more susceptible to failing at that imperfection once the temperature dips. So here I was thinking I might see some trend in failures going over train tracks on cold Fall days. Not exactly. If there were more data on failures, it might be also worth looking into the manufacturing side, if it would be at all possible to trace back a set of failures to a batch of TABs produced back in the day.

[louielouie2000]

Honestly I think the whole problem is overblown. I've seen very few actually break on the road (one since we've been here) and it was obvious that it broke after the plating was compromised causing a rust spot that caused a weakness in the metal. I've had the broken one analyzed by fastener engineers and they had the same opinion.

Off the top of my head I can think of 2 owners this past decade who have had their TABs break while driving: Rich Acuti & Justin Mettee. Rich said when his snapped he was going about 40 MPH and the experience was so violent it nearly flipped his car. He felt lucky to regain control & safely pull off the road. Justin's failure was much less melodramatic... he posted that he went over some railroad tracks at a pretty low speed & he heard a tinkling noise (his shims falling to the ground) and then his wheel rubbed against the underbody & he stopped the car. Neither car was really damaged from the breakage, from what I recall (both these incidents took place several years back). It's worth noting both cars are from the Northeast. I am sure extreme temperatures & corrosion from road salt were responsible for the failures.

[Jonathan]

Off the top of my head I can think of 2 owners this past decade who have had their TABs break while driving: Rich Acuti & Justin Mettee. Rich said when his snapped he was going about 40 MPH and the experience was so violent it nearly flipped his car. He felt lucky to regain control & safely pull off the road. Justin's failure was much less melodramatic... he posted that he went over some railroad tracks at a pretty low speed & he heard a tinkling noise (his shims falling to the ground) and then his wheel rubbed against the underbody & he stopped the car. Neither car was really damaged from the breakage, from what I recall (both these incidents took place several years back). It's worth noting both cars are from the Northeast. I am sure extreme temperatures & corrosion from road salt were responsible for the failures.

This is what I had at the time I decided there just wasn't enough data out there to prove anything statistically. I think Justin's is the first one there like you mentioned. Not sure about the other two.

14348

[David T]

The Tab's are subject to shear but because of their thickness they are more than strong enough for that. To overcome the cyclic bending stress they are under high tensile stress, more than they should see in normal service. One problem to anecdotal stories is that we never know the whole history of the bolts so we can only guess at why they failed. Because failures are rather rare at this point we can't consider it a design defect, rather it has to be related to age, improper torque, corrosion, accident history, or some other cause. Regular inspection is the best insurance against catastrophic failure. Once the bolt stretches it loosens and bends. Once it bends it will stretch more. The cycle repeats until failure. The other cause is the metal sleeve. Once it collapses the bolt is subject to cyclic loads. Again it will stretch and fail. On one car I saw a while back we caught a bent, loose Tab. The shims were still there. The Tabs were replaced a long time ago with an "improved" bolt. I guess not, anyway it was way before Toby's Tabs. We replaced both bolts.
David Teitelbaum

[Rich W]

A couple years ago I was working on putting together a statistical analysis of TAB failures. I never got a lot of data to work with, as like Dave mentioned, there just hasn't been a lot of catastrophic failures. I remember seeing the link to the D that supposedly flipped from a TAB failure where the trailing arm dug into the ground or something along those lines. However, just as quickly were a couple other links debunking that story as it proved not to be related to a TAB failure causing the accident. What it did add to though, was the paranoia among the community about the TABs on your car failing out of the blue and with very bad timing.

http://www.dmcnews.com/Techsection/rollover.html

[DMCMW Dave]

http://www.dmcnews.com/Techsection/rollover.html

I agree with the "debunking" as we MUCH later dismantled that car and the TA bolts were not the cause of the accident.