Reality of trailing arm bolts?

[Redsquall]

How important should replacing the tabs be when they seem slightly bent and still rotatable?
has anyone here actually had it break on them?
im looking for level headed advice as I have an auto transmission and it sound like a major job to replace.
thank you

[Michael]

A broken TAB can literally kill you if it happens at speed. It's basically like a broken ball joint on the rear wheel. I check mine every time it's in the air and you are right, it's a bear with the auto. If I ever have to drop the autobox for any reason, I'm replacing the TABs with some of Dave's offerings from DMCMW whether they need it or not.

I have seen (in pictures only) cars with broke TABs. Fortunately they were low speed and caused minor damage and the driver was unhurt. I'm sure there are a few threads with pics here on the subject.

I have never replaced my TABs but I believe you can do it on the auto just by removing the mount itself and not actually dropping the tranny altogether.

[Jonathan]

The reality of TABs?

There's never been enough specific information on failures to say definitively what will or will not happen.

It isn't consistent for the most part. The advice is to replace them if they are frozen in place, i.e. rusted in place, or they aren't frozen (like yours) but rotating them shows that they are bent.

I also have an auto and understand changing them is a pain in the butt. I don't know that from my own experience as I've never done the job. I have every single nut and bolt and replacement fastener sitting and waiting in one of my parts boxes, but it all just continues to sit there.

There are other factors that can contribute to them failing, such as they got scratched, etched, dinged or banged up in some way and this damaged portion becomes the point where the metal fatigues and fails outright. Rust can do that for you if the failure point is a rust pitted spot. Temperature will also affect the metal failing. Ambient temperature that is. If the metal is cold because it is cold outside, the materials strength is reduced and the likelihood of failure increases.

Changing them out is a good idea, sure. It is also somewhat of an insurance policy. There are a few areas on the car like this, where changing out old parts proactively may help you avoid a potential problem. Fuel lines are another major one. No guarantee that it would have failed if left alone though, there just isn't the information available and there is too much variability on each car's history to make one all encompassing rule.

And as with changing or working on fuel lines, there is a risk that you could make matters worse. Not saying brand new, properly installed replacement TABs or fuel lines are a bad idea, but getting there and the cost and work to do so needs to be evaluated. As with any kind of risk management decision like this, you weigh the likelihood of failure (probability) and the consequences of failure (severity) against the costs (real or imagined) of doing the work or doing nothing (or at least just inspecting/monitoring only).

[jmettee]

I had mine break while driving about 35 mph over a railroad crossing. The rear starts to randomly "steer" since the upper & lower control links are all that's controlling the wheel. At higher speeds, it's a good chance of complete loss of control.

If it's bent, it's weakened & in failure mode - should be replaced ASAP if a bend is seen. For mine, it wasn't bent, but the bolt was original & of poor quality surface finish....it rusted from both sides & failed in the middle of the bolt. Looking at the bolt, it's a classic fatigue failure with the bolt bending forward & rearward with the drive thrust/braking.

Bottom line: Replace them. I've done it on both auto & manual cars, it's not terrible & definitely worth doing as opposed to wrecking the car or hurting you & your passengers.

[Delorean Industries]

A trailing arm failure at speed will result in your death almost certainly. The amount of weight over the rear will over come the upper/lower rear link bushings without being tied at the forward mounting point. The wheel will climb against this new direction of travel and cause the failure side to drop and dig in.

This is why I designed a safety system for all of our builds. I now incorporate a three point hoop method of binding the arm in case of failure as done in F1 and other sanctioned motorsports. The two radius arm reinforcement points are attached to the outer most point of the TAB bolt limiting the aft travel if sheered to a minimum and giving the driver the ability to stop. This is accomplished with a high tensile strength cable arrangement. Not to be confused with brand X ground trap updates by the transmission as many have though they were on our cars.

[content22207_2]

A trailing arm failure at speed will result in your death almost certainly.

A tad dramatic.

A broken trailing arm bolt at speed would definitely be a challenge, but not necessarily fatal. I've been trained to safely steer an 80,000 lbs vehicle to the side of the road in case of a front tire blowout. Surely a broken trailing arm bolt wouldn't be world's more difficult. Like a front tire blowout, I'd stay off the brakes until control is re-established. Don't know if I'd hit the accelerator however (with a front tire blowout your first reaction is to floor the accelerator to compensate for slewing towards the blowout). I'm guessing the rear end would slew towards the broken TAB because the wheel would pivot rearward, like the back wheel of a hook & ladder. Probably need to steer into it like losing your rear end on ice.

Grade 9/Class 12 bolts only cost a couple of bucks apiece -- just replace them.

Bill Robertson
#5939

[iflights]

I found this information helpful when I was asking that same question...

http://www.dmcnews.com/Techsection/tabolts2.html

[axh174]

im looking for level headed advice as I have an auto transmission and it sound like a major job to replace.
thank you

I have an auto transmission and I replaced my original TABs with a set of Toby TABs. The best advice I can offer when replacing the TABs is to get a 75-degrees (at least) offest boxwrench. This wrench can easily fit between the transmission and the TAB head and allow you to easily get the TAB loosened.

Using the offset boxwrench, I didn't have to remove either of the transmission mounting brackets, however I do recall having to remove the TAB bushing plate and bushing in order to get enough of an angle to get the TAB completely removed because the tranny was in the way. For me, this was not that big a deal since I was replacing the TAB bushings anyway. A word of caution, though: if I recall correctly, the bushing retaining plates are bolted to the frame such that small nuts are used between the frame and the bushing housing. If a nut slips out of your hand, it can get lodged/lost in there and potentially cause reassembly problems.

As for torquing the TABs to their proper spec upon re-installation, my torque wrench was too large to fit between the TAB nuts and the fiberglass body for proper torquing, and I had to make use of a torque adapter.

[PJ Grady Inc.]

They must absolutely be replaced when bent along with the bushings. If you double nut the pivot bolt there is no need for exotic materials like the Monel Toby tab's but there is nothing wrong with overkill. That best why to keep them from loosening/bending due to the twisting movements of the suspension oer bumps and undulations.
Rob

[content22207_2]

Monel Toby tab's

Inconel. Same stuff used for bolts that hold airplane engines on (Toby Peterson worked for Boeing -- he used a Boeing supplier to make his trailing arm bolts).

Bill Robertson
#5939

[DMCVegas]

They must absolutely be replaced when bent along with the bushings. If you double nut the pivot bolt there is no need for exotic materials like the Monel Toby tab's but there is nothing wrong with overkill. That best why to keep them from loosening/bending due to the twisting movements of the suspension oer bumps and undulations.
Rob

What about the brackets that Dave Bauerle used to sell? They bolted to the frame and then the end of the bolts. Didn't provide structural support per se, but he did say that it radically cut down on the amount of vibration and protected the TABs. Which I beleive was supposed to help prevent the TABS from bending. What's your opinion/experience on those?

[content22207_2]

Bauerle Brackets don't attach to the TAB. If they did, the TAB wouldn't be able to move up and down with the rear suspension. They were intended to catch the trailing arm in case a TAB broke.

41716 41717

Bill Robertson
#5939

[content22207_2]

IMHO the best solution was Bryan Pearce's HEIM jointed trailing arms:

41718 41720

Bill Robertson
#5939

[Delorean Industries]

I'm in the process of cutting one of those up for scrap.

[David T]

I'm in the process of cutting one of those up for scrap.

If a bolt is bent it has been stressed past it's yield limit and is weakened and stretched. The shims will be loose or have fallen out. You should not drive on a known, damaged TAB. If one is bad the other is questionable too so replace in sets. Yes, it is a bit more difficult to do the left side TAB on an automatic but not impossible. You do not have to remove the transmission. Too soft a bolt and it will bend and stretch, too hard a bolt and it will be too brittle and just break. Do NOT source locally. Get a set from one of the Delorean vendors. It must also be properly installed and torqued. Too loose and it will bend, too tight and you will stretch it and collapse the spacer tube in the bushing. If the shims are missing you will need to have the rear toe reset on a 4 wheel alignment machine to spec. The TABs should be final torqued with the weight of the car on it's suspension.

[content22207_2]

Do NOT source locally. Get a set from one of the Delorean vendors.

Except for the Inconel bolts Dave Swingle had made, vendors are buying the same bolts you can source yourself from suppliers such as McMaster or Fastenal.

OEM bolts are Class 10.9. Exact duplicates are available from a myriad of suppliers.

Class 12.9's are difficult to find on this side of the pond with hex heads. Martin Gutkowski found some in Europe. Most over here have socket heads, such as the bolts Hervey sells. Class 10.9's are easy to find with hex heads if you want to go back with OEM strength. Note that Houston sells 10.9's, not 12.9's.

On #2508 I substituted 1/2" Grade 9 bolts from Fastenal (McMaster doesn't sell Grade 9's long enough). Tubes in the trailing arms had to be enlarged 1/32". Tubes in the bushings were fine. Alignment shims also fit 1/2" bolts no problem. Grade 9's typically have high profile hex heads (about 50% taller than Grade 8's). Makes it a little bit easier to grab the bolt through the frame.

Bill Robertson
#5939

[Bitsyncmaster]

Class 12.9's are difficult to find on this side of the pond with hex heads. Martin Gutkowski found some in Europe. Most over here have socket heads, such as the bolts Hervey sells. Class 10.9's are easy to find with hex heads if you want to go back with OEM strength. Note that Houston sells 10.9's, not 12.9's.

I think Martin also has the bolts he sells plated (forgot with what). I replaced my TABs long ago with a stock set from DMCH. I bought a set of TABs from Martin and intend to replace those stock TABs but have not done it yet.

[content22207_2]

I've long considered plating basically for protection while they're in the bin. In real world use the plating quickly wears off. Zinc plating is a perfect example -- in less than a year even bolts in gentle applications such as holding a mailbox are covered in rust. What's more important is the bolt material itself. A rusty Grade 8 fastener is still quite sound and even a nut requiring acetylene turns off without snapping the bolt, but a rusty Grade 2 fastener will actually lose material and trying to turn the nut off often snaps the bolt.

Railroad tracks are a good example of underlying metallurgy. The rails and fasteners have no protective coating whatsoever, yet stand up to decades of exposure and very demanding use no problem.

Truck frames are another good example. They come from the factory with a coat of paint, but that's basically for showroom use. After a short time in the real world that paint falls off, exposing bare metal underneath which remains structurally sound for decades thereafter.

Bill Robertson
#5939

[content22207_2]

Trailing arms rotate around their bolts, wearing off plating just like lower control arm pivot bolts. Heads may retain their plating, but the shafts will eventually have bare metal exposed.

OEM Grade 10.9 trailing arm bolts are considered high strength, almost as strong as Grade 8. For comparison OEM LCA pivot bolts are Grade 5. Bolts themselves aren't the problem -- it's their application. Bolts are being required to flex up and down very unnaturally.

By comparison LCA pivot bolts stay in one place while the LCA itself flexes.

Bill Robertson
#5939

[content22207_2]

Too soft a bolt and it will bend and stretch, too hard a bolt and it will be too brittle and just break.

I humbly disagree:

http://www.americanfastener.com/astm-sae-and-iso-grade-markings-for-steel-fasteners/

Yield strength -- the amount force before a bolt becomes permanently deformed -- of OEM Class 10.9 trailing arm bolts is nearly 50% higher than Grade 5's used in the front suspension.

Class 12.9, a common TAB upgrade, has nearly 20% more yield strength than Class 10.9.

Bill Robertson
#5939

[Bitsyncmaster]

I've long considered plating basically for protection while they're in the bin. In real world use the plating quickly wears off.

I have to agree. When I was using "AN" (aircraft nuts) bolts that were cadmium plated. One install and remove stripped the plating off the shaft if there was no oil or grease on the bolts.

[David T]

Trailing arms rotate around their bolts, wearing off plating just like lower control arm pivot bolts. Heads may retain their plating, but the shafts will eventually have bare metal exposed.

OEM Grade 10.9 trailing arm bolts are considered high strength, almost as strong as Grade 8. For comparison OEM LCA pivot bolts are Grade 5. Bolts themselves aren't the problem -- it's their application. Bolts are being required to flex up and down very unnaturally.

By comparison LCA pivot bolts stay in one place while the LCA itself flexes.

Bill Robertson
#5939

Actually the bolt is not supposed to move if it is properly tightened. The bushing is what allows the movement. Once the bolt starts moving the joint will fail. The theory (and practice) of torquing the bolt is so it is under more stress than the joint must handle so the bolt never sees cyclic loading. Cyclic loading is analogous to bending a paperclip back and forth till eventually it fails. As for plating, it protects the bolt from corrosion but if it is under cyclic stress it will suffer from fretting corrosion and fail. Ordinary zinc plating is only to protect from mild corrosion due to environmental factors, not stress. There are other, better types of plating to protect against stress. To properly design a joint you must take into account all factors and what the fasteners come in contact with. Picking the wrong type of metal can actually accelerate the deterioration of the fastener. Too strong a bolt and you cannot torque it enough to have it be above the cycling stress. If you overtorque the bolt you collapse the tube in the bushing. Drilling it out to accommodate a larger bolt just makes it thinner and weaker. Corrosion is not only caused by contact with water, stress also causes corrosion and is one of the reasons the bolts get seized inside the bushings. This is a highly stressed joint with a critical, highly stressed fastener. Be careful choosing a replacement.

[content22207_2]

cadmium plated

Farrar got a "professionally" rebuilt carburetor (notice the rebuilder's stickers). Steel bits were plated with something yellow (cadmium, chromate, etc). This is how they held up in Louisiana humidity:

41721

Compare to Steve's and Drew's carburetors with painted bits.

I'm all for plating, but it only gets you so far.

Bill Robertson
#5939

[dn010]

I don't think they see much abuse at all but what about the M8 bolts that hold the TA bushing and reinforcement plate to the frame? On both of my frames, many of the welded on nuts for these were stripped like the bolt had popped out.

[content22207_2]

Cheap weld nuts. The ones that hold the swaybar bushings strip as well.

From the factory some trailing arm bushing bolts were double nutted on the other side of the weld nut. If your weld nuts are stripped just do the same.

Bill Robertson
#5939

[dn010]

Both my swaybar & TA bushing bolts I doubled + red Loctite, I even go to the extent of putting a paint line on the bolts/frame so I know I did them. Just wondering why both frames would have been bad. Thank you.


Cheap weld nuts. The ones that hold the swaybar bushings strip as well.

From the factory some trailing arm bushing bolts were double nutted on the other side of the weld nut. If your weld nuts are stripped just do the same.

Bill Robertson
#5939

[content22207_2]

Weld nuts are every bit as high quality as the rest of the frame.

Bill Robertson
#5939

[David T]

Weld nuts are every bit as high quality as the rest of the frame.

Bill Robertson
#5939

Stripped threads in the weld nuts is not a general problem. Most likely cause is someone overtightened the bolt at some point or they substituted a bolt with the wrong threads or bad threads (like trying to put an english bolt into a metric nut). Or possibly the bolt was too short and did not fully engage all of the threads. Weld nuts are not all that high a quality and are usually pretty soft. It doesn't take much to overtorque and pull the threads out. Easily repaired by chopping the old one off and welding another nut on or if it is difficult to access you can put in a thread insert. The bolts holding the bushings on are not subject to the same bending loads, only shear and are more than enough to handle that. The TAB's are subject to cyclic bending and torsion loads and that is very hard on bolts. Oftentimes what is passed off as "plating" is nothing more than paint.

[content22207_2]

Easily repaired by chopping the old one off and welding another nut on

Good luck doing that though the access hole in the frame. Double nutting them is hard enough.

Bill Robertson
#5939

[content22207_2]

Plus the frame is only sheet metal. If you're not careful the welder will burn a hole right through it.

Bill Robertson
#5939

[DMCVegas]

I've long considered plating basically for protection while they're in the bin. In real world use the plating quickly wears off. Zinc plating is a perfect example -- in less than a year even bolts in gentle applications such as holding a mailbox are covered in rust. What's more important is the bolt material itself. A rusty Grade 8 fastener is still quite sound and even a nut requiring acetylene turns off without snapping the bolt, but a rusty Grade 2 fastener will actually lose material and trying to turn the nut off often snaps the bolt.

Railroad tracks are a good example of underlying metallurgy. The rails and fasteners have no protective coating whatsoever, yet stand up to decades of exposure and very demanding use no problem.

Truck frames are another good example. They come from the factory with a coat of paint, but that's basically for showroom use. After a short time in the real world that paint falls off, exposing bare metal underneath which remains structurally sound for decades thereafter.

Bill Robertson
#5939

I'll agree with that to a point. In both dry and even humid climates, chassis paint does flake off and you get surface oxidation resulting in simple cosmetic rust which doesn't compromise the structural integrity of the chassis. It also is demonstrated rather well with how in both the dry climates of the western deserts and the humid areas of the south, TABs are so much easier to remove from cars than ones from up north. Particularly in the rust belt. And that's the thing: Water itself isn't nearly as much of a problem as corrosion is from road salt.

Unlike up in the rust belt where salt is used, out west and down south it's mainly just sand that's used for traction instead when roads ice over since the ice never lasts nearly as long. I beleive it was Chrysler many years ago who decided to cut corners by removing the Dust Shields from the Caravan's front brake rotors. In the rest of the country they were fine, but in the top northern states and Canada, the road salt exposure was just eating rotors while still on the cars.

Using the railroad track analogy, you're right on that too. But again it's not as though they salt railroad tracks either. So when it comes to corrosion, while the coating on TABs seems almost pointless given that it'll just be rubbed off, it is necessary for other parts that get exposed to corrosive environments.

[content22207_2]

If you think electroplating will stand up to road salt you are crazier than I am.

My Blue Truck spent the first 16 years of its life in Morristown, New Jersey. Let me make you a list of the things that haven't been replaced due to road salt -- it will be a shorter list.

Bill Robertson
#5939

[Drive Stainless]

If you think electroplating will stand up to road salt you are crazier than I am.

My Blue Truck spent the first 16 years of its life in Morristown, New Jersey. Let me make you a list of the things that haven't been replaced due to road salt -- it will be a shorter list.

Bill Robertson
#5939

I can tell you from firsthand experience that West Virginia/Ohio road salt will also rust the stainless steel Borgeson steering linkages that many owners now have installed. It's likely grade 303, but it still demonstrates the corrosiveness of road salts.

[content22207_2]

Borgeson stainless components aren't magnetic at all (steel spiders and end caps of course are), so I don't think they are 400 grade.

I went to a DMA event at Ocean City MD once. Salt spray from the ocean made all sorts of brown stains on my stainless body panels. By the time I got around to removing them they were virtually permanent. Had to Scotch Brite the whole car.

Bill Robertson
#5939

[David T]

Borgeson stainless components aren't magnetic at all (steel spiders and end caps of course are), so I don't think they are 400 grade.

I went to a DMA event at Ocean City MD once. Salt spray from the ocean made all sorts of brown stains on my stainless body panels. By the time I got around to removing them they were virtually permanent. Had to Scotch Brite the whole car.

Bill Robertson
#5939


There are many different alloys of stainless steel, each with different properties and varying degrees of corrosion rates to different things. It is important to select the appropriate alloy with the properties you need. I used to supply all kinds of metal doors. We had a customer order S/S doors. He wanted something that wouldn't rust like an ordinary cold rolled steel door. We made him the doors and a year later they were all rotten. When he told us they were used for an indoor pool we told him if we knew what he wanted we would have specified a different alloy, one that was not susceptible to Chlorine. As for steel, there are alloys that will rust and provide a sacrificial coating which protects the steel from further rusting. Used a lot on bridges, that's why you see the brown staining on the piers.

[content22207_2]

It's really not our place to tell Borgeson what to make their components out of.

Borgeson's been in the U Joint business for 102 years -- I have full faith and confidence they know better how to make their products than I do.

Bill Robertson
#5939