First there were brakes ... and then there were none

We took my wife's '34 on its first road trip to Tuscaloosa this week.Taking a freeway exit in Birmingham, there was a violent vibration from the front end and the right front wheel locked up as I applied the brakes. Since the ramp was long, I was able to get the car stopped safely on the shoulder. Looking under the car, I noticed the right front brake caliper hanging loose inside the wheel. So I called AAA to get a flat bed. The lady kindly informed me that I had 100 miles free towing and I was 98 miles from home. Luck was with me.

On my race car I never used anything but aircraft bolts for the suspension, brakes, and anything else I didn't want to fall off. But I wasn't as careful with the '34. This caliper bracket was held to the spindle by a 3/8" Grade 8 bolt with a lock washer and a 1/2" grade 5 bolt. The 3/8" bolt had worked itself out and then the 1/2" bolt broke.

Everything is fixable, but this car is not going on the road again until all suspension, brake, and steering hardware is replaced with either aircraft bolts for sheer applications or Grade 8 bolts and Nyloc nuts or red LokTite.

We were really lucky we didn't have a wreck or damage anything too badly. I won't make this mistake again (even though I knew better to begin with). If you have any Grade 5 stuff in high stress applications, you may want to rethink that.

 

Dodged a bullet there my friend - good reminder to think about hardware when putting a car together, thanks for that.

 

I would think Grade 8 would work fine. Are you sure that 3/8" bolt was torqued to spec?

 

I just did a brake job on the front of my 55....wilwood stuff....safety wired.....

 

That bolt looks like it's been hanging on by a thread for a long time and that lower ball joint doesn't seem right either. Is most of the tapered part up inside that stack of washers?

 

Glad there was no accident, and thanks for the safety reminder.

I would add that I have been reading the most lock nuts, like nylock, probably should be replaced each time you remove them.

 

And in a high heat area, maybe Stover lock nuts would be better than nylock nuts.

 

I've never seen a cotter pin installed like that. Is that an aircraft procedure?

 

Agree about the lower ball joint assy. looking odd.
One big problem these days is Chinese bolts, not at all sure they are kosher on strength according to specs for grade markings. And most aircraft stuff I ever saw was fine thread I think if you use name brand stuff from a US company selling US made bolts such as ARP in stressed areas you'll be safe. I'm getting leary of hardware store bolts.
Dave

 

Glad to hear that no one was injured.

I'm not familiar with your brake setup, so excuse my ignorance. Is that a custom fabbed deal?

 

That custom spindle is a good bit thinner than the stock spindles the ball joint was designed for. Once you torque the nut and get the taper to seat properly, it takes the extra washers to get the nut back up in the cotter pin area.

The two bolts in a high temp area are the brake bracket bolts, and both go into a threaded hole on the bracket or spindle. I think LocTite will be fine on the 1/2" bolt, but safety wire is a better bet on the 3/8" one. Thanks for the suggestion, I hadn't thought of that.

I agree Grade 8 is fine strength wise, but I like aircraft bolts for shear applications. Their relatively shorter threads allow you to get all of the stress points on the smooth shank instead of the threads. Of course you could accomplish the same by getting longer Grade 8 bolts, sizing them so that the smooth shaft matched the grip lenghth, but then you would need to cut them in most instances.

 

Pegasus Racing has a good supply of AN bolts. Order a catalog.

https://www.pegasusautoracing.com/home.asp

 

Yep, that's a Fat Man Mustang II setup with tubular control arms and coil spring and separate shock.

 

EEEK! I had something similar happen to our '56 Caddy convert. I'd swapped a Saginaw power steering box for the worn original, and used grade 5 bolts. The lower one backed out, leaving the top two, which sheared of when I turned the wheels to (try) to leave a car show. Like you, the Gods were smiling me that day, and I learned a valuable lesson on car building.

Brian

 

If the through bolt fell out first, even a grade 8 on the 1/2" would of broke there too.

 

A 1/2" grade 5 bolt is pretty stout. The fact that it broke was due to the grade 8 backing out. If a grade 8 was used, it may have snapped sooner. Whatever you put in, make sure its tight and has a locking feature of some sort.

Bob

 

Here is the replacement for the bolt that backed out. I don't think it is going anywhere. Thanks for jogging my memory Squirrel.

I agree the 1/2" bolt probably would not have broken if the other one had not disappeared, but I put in a Grade 8 anyway with good old red LocTite. Don't expect a repeat of this adventure.

 

Yeah, just dropped $200 at Coast Fab on nice NAS bolts for the brake bolts on the '64 Country Sedan. The calipers involved are German, but 9/16 is close enough to M14 and 5/8 close enough to M16...

 

There can be times when a grade 5 is just fine. Your brake setup is a less common application as to hardware loads. Grade 8's = very strong, but more brittle.
Grade 5's I seem to recall are softer core with more 'plastic' or stretch before they yield.

 

Is it just an optical illusion or is the broken bolt in the caliper bracket smaller in diameter than the hole in the spindle?

 

Within any grade of bolt, there is a range of minimum tensile strength. This value comes in handy when I have to calculate torque for applications at work.

Check the link below which may help some here understand the grade differences. I have used plenty of grade-5 hardware on stock cars and in general car fabrication and have never had any of them fail on me. I'm a total stickler for the correct use of washers, lock washers and nuts. Anything critical gets torqued.

http://www.fastenal.com/content/feds/pdf/Mechanical Properties of Inch Fasteners.pdf

Bob

 

Optical illusion. The bottom part of the bolt you are seeing does not include the thread and thus appears smaller in diameter.

 

Amen to that.

Interesting side note. My son, who is a long time Ford now Toyota mechanic, told me Ford and Honda had problems with brake caliper bolts vibrating out and finally had to resort to the yellow LocTite. He said it was so strong he once broke a ratchet trying to get some out.

 

I've never used the yellow (Loctite 641) before, I'm more familiar with the blue and red. The red is a bitch to break loose hardware after it sets up. We use the blue at work quite a bit for vibration-exposed hardware in military applications.

Since everything that ships gets a vibe test and has been qual-tested with a particular locking compound, we have no problems in the field.

Bob