'72 Trailing Arm Questions

[Roger D.]

Just finished removing the old trailing arms (with a sawzall) on my '72 body off chassis restore project. I noticed two holes on the top side of the trailing arms on either side of the access hole to the leaf spring bolt (top left pic). A couple of years ago I ran across a couple of trailing arms from possible '75 or newer cars and picked them up just in case I needed them in the future. One of those arms had the same holes however slightly larger diameter (top right pic). The other one had no holes. Question: What were those holes originally placed there for and will this aspect be taken into account in futire judging if I use one or both of the newer trailing arms?

IMG_0491_R1.jpgIMG_0490_R1.jpg

Maybe more importantly, check on the condition of the original trailing arms (top left pic above) and the pic below. Does the condition of these warrant replacement? There is some fairly heavy rust/pitting issues on the originals.

IMG_0492_R1.jpg

[Dick W.]

Re: '72 Trailing Arm Questions

Holes are for rear sway bar brackets for cars so equipped

[Dan B.]

Re: '72 Trailing Arm Questions

Hard to tell exactly from your pictures, but that looks like surface rust with some minor pitting, which as long as you don't have any rust through or thin spots, would be fine to clean and refinish. Don't forget to replace the bushings while it's apart. Dan

[Joe L.]

Re: '72 Trailing Arm Questions

Just finished removing the old trailing arms (with a sawzall) on my '72 body off chassis restore project. I noticed two holes on the top side of the trailing arms on either side of the access hole to the leaf spring bolt (top left pic). A couple of years ago I ran across a couple of trailing arms from possible '75 or newer cars and picked them up just in case I needed them in the future. One of those arms had the same holes however slightly larger diameter (top right pic). The other one had no holes. Question: What were those holes originally placed there for and will this aspect be taken into account in futire judging if I use one or both of the newer trailing arms?

[ATTACH=CONFIG]48232[/ATTACH][ATTACH=CONFIG]48233[/ATTACH]

Maybe more importantly, check on the condition of the original trailing arms (top left pic above) and the pic below. Does the condition of these warrant replacement? There is some fairly heavy rust/pitting issues on the originals.

[ATTACH=CONFIG]48234[/ATTACH]

Roger-----


These arms should be considered scrap metal. Completely irreparable. Notice how the rust has gotten under the overlapping metal and caused some "separation". This renders the arms scrap. Period.

As far as the holes go, it's just as Dick mentioned; they're for the attachment system for cars with rear sway bars (i.e. 65-74 with big block and 75-82 with FE-3). Some cars without sway bars had trailing arms with no holes (my original 1969 small block is one example). Sometimes, cars without rear sway bars did have the extra holes. How can you tell which sort of arms your car had? Well, if it's a 1965-74 big block or 1975-82 with FE-3, you know what it has to have. Otherwise, if you have the original arms for the car, you can tell; if you don't, you can't.

[Patrick B.]

Re: '72 Trailing Arm Questions

I believe the only small block cars that that came with the holes in the trailing arms originally were LT-1s. Other than the sway bar, the whole rear end assembly of an LT-1 is the same as a for a big block. I used to look for the unused holes in the trailing arm as a way to spot real LT-1s before the cars got old enough for trailing arm replacements to be common. The GM over-the-counter trailing arms had the sway bar holes so cars with replacement arms began to look like LT-1s.

[Gary R.]

Re: '72 Trailing Arm Questions

As Joe mentioned, there is rust separation in the picture of the rear arm. Since these are nothing more then overlapped & welded "C" channels they rust inside out when exposed to salt, snow, and rain. Reach your fingers inside by the large side hole and check for bulging. Look up my thread on T/A's I show a few pictures of rotted arms. I would attempt to reuse those arms based on what I see, check them very close.

[Roger D.]

Re: '72 Trailing Arm Questions

Thank you all for the information. I feel like these are the original trailing arms however the only basis for that thought is that it is a 70k mile very original car that looks like nothing has ever been done to it's underside during it's life. It is by the way a 350 small block.

I'm leaning towards replacement of the trailing arms given the metal separation. I was hoping ya'll would make it easier to decide by a unanimous vote.

So assuming that I choose to use the two later year trailing arms will it be a judging issue if one arm has the holes and one doesn't? Also, if I chose to re-use the originals I assume that there would be a point deduction for condition?

Thanks again for your comments.

Roger

[Gary R.]

Re: '72 Trailing Arm Questions

FYI
New (USA made) arms do not come with the holes, just in case you decide to go that route. If you use originals then be sure to blast them inside/out and use a quality treatment on them. I always etch,POR15 and then top coat them.

[Kurt G.]

Re: '72 Trailing Arm Questions

Roger, Gary is, in my opinion right on this. Check for bulging, and if there is none get them blasted and then coat inside and out with POR15 before you paint them. They should make it another 70K.

[Gary R.]

Re: '72 Trailing Arm Questions

I see a typo in my response, I would NOT use those arms based on what I see.

[Joe L.]

Re: '72 Trailing Arm Questions

I see a typo in my response, I would NOT use those arms based on what I see.

Gary-----


I figured that's what you meant to say.

Once the corrosion gets between the "overlapping" metal, it's virtually impossible to blast it clean. Then, the corrosion in that area proceeds inexorably. In this case, it looks like some of the metal has actually been thinned by corrosion.

Another issue: if these arms are blasted clean of corrosion, they are going to be heavily and deeply "pock-marked". Paint will not cover that up, so these arms will appear quite "ugly". In fact, in the case of these assemblies, I think the bearing supports are going to be heavily and deeply pitted, too. Of course, they'll still be re-usable but they'll be "ugly".

[Jim T.]

Re: '72 Trailing Arm Questions

Patrick my original owner 1970 has the holes in its original trailing arms to mount a sway bar. My 1970 came from the factory with a 350/300 and turbo 400 transmission. I even have the original optional suspension rear sway bar and brackets to attach to my 70's trailing arms.

[Patrick B.]

Re: '72 Trailing Arm Questions

Patrick my original owner 1970 has the holes in its original trailing arms to mount a sway bar. My 1970 came from the factory with a 350/300 and turbo 400 transmission. I even have the original optional suspension rear sway bar and brackets to attach to my 70's trailing arms.

Jim: I must admit I never looked at any Turbo 400 cars when trying to tell if LT-1s were original. I wonder if Turbo 400 cars also used the big block rear setup with cap-type rear end yokes, the shot peened half-shafts, and the heavy duty rear spindles that LT-1s came with.

[Terry M.]

Re: '72 Trailing Arm Questions

Jim: I must admit I never looked at any Turbo 400 cars when trying to tell if LT-1s were original. I wonder if Turbo 400 cars also used the big block rear setup with cap-type rear end yokes, the shot peened half-shafts, and the heavy duty rear spindles that LT-1s came with.

Yes Pat, SB TH400, and all other 1968-1972 (probably more than 1972, but I know nothing about that) TH400 have the so called BB rear set up -- cap-type rear end yokes, the shot peened half-shafts, and the heavy duty rear spindles, but NO sway bar. I kind of get a chuckle out of people using these features to determine if the car was originally a BB because I am pretty sure there were more TH400s built over the years than BBs.

BTW: We had a 1971 Bowtie car at the Deep South Regional that demonstrated this situation (SB & TH400) and I pointed out these items to the assembled multitude.

[Bob J.]

Re: '72 Trailing Arm Questions

Yes Pat, SB TH400, and all other 1968-1972 (probably more than 1972, but I know nothing about that) TH400 have the so called BB rear set up -- cap-type rear end yokes, the shot peened half-shafts, and the heavy duty rear spindles, but NO sway bar. I kind of get a chuckle out of people using these features to determine if the car was originally a BB because I am pretty sure there were more TH400s built over the years than BBs.

BTW: We had a 1971 Bowtie car at the Deep South Regional that demonstrated this situation (SB & TH400) and I pointed out these items to the assembled multitude.

Terry, how does a person know HD rear spindles by sight?
Thanks, Bob