[keith k]

As has been discussed on this forum in the past, '70 T/As seem to have a high occurrence of being built with the Formula sized bars: 1-1/8" front and 5/8" rear rather than the advertised 1-1/4" front and 7/8" rear.

There's been no real good explanation for why this would have been, til maybe now. I've been reading Rocky's new book on second gens (which is fantastic, BTW). In the chapter on the development of the '70 T/A, there's copies of original Pontiac content letters for the T/A and quotes from Herb Adams that show that until late November 1969 (a month before the start of pilot production...) the Trans Am was planned to have the same suspension as the Formula. Including the 14" wheels and small bars. Herb had not really been involved in the development of the production suspension for the car, but just before the media preview drive event, he drove one and was hugely disappointed. So he and Dan Hardin were given a weekend to try out new parts to improve it, leading to the last minute change to 15" wheels and larger stabilizer bars.

So they changed direction only a month or two before the start of production. For the wheels and tires... that was probably containable. The tires were already in production, and the JW wheels were a "fusion" of pieces Motor Wheel was already producing (the 14" spider section, and necked down outer hoop).

But stabilizer bar production tools are "long lead". The engineers would have had a handful of bars in different sizes made off prototype tooling that they use when developing tuning specs. But for production, back in those days (I used to be a stabilizer bar engineer earlier in my career, perhaps explaining some of my curiosity about this...) the bars were hot forged with specifically sized and shaped bend dies in a custom fixture. The one that was probably ready to go for the smaller diameter bars would not work for the larger diameter bars. I would guess that even going flat out on tool design/build... it's 3-6 months to have gotten the high volume tools for the bigger bars up and running. Given that '70 was only a half model year..., oops.

Pontiac likely fitted the media cars with the big bars, and then produced as many big bars as possible using low volume methods... and whenever they were short the cars just got the Formula bars.

I got curious and went through the extensive collection of photos I've accumulated of '70 T/As over the past 20+ years to see if I could spot a "changeover point". I only looked at pictures of the rears, since those are easy to tell apart (7/8 being 40% larger than 5/8, while 1-1/4 is only ~10% bigger than 1-1/8). Out of the 123 '70 T/As I have good photos of the rear undersides for, 76 had the 5/8" bars, and 47 had the 7/8" bars. So basically 60% small bars, and only 40% big bars.

There's not really a "phase in" date evident during the model year, either. Van Nuys cars got a mix early on, then seemingly all of May/June production was small bars, then the last month or so was mostly big bars. At Norwood, it was almost the opposite... most of the early cars had small bars, then mid way through the year there were a lot of cars with big bars, then back to small at the end of the year. Perhaps the two plants were fighting over not enough big bars.

I'll note that a lot of the cars I've photographed are restored cars, and it's possible that some people "fixed the mistake" when restoring their cars by replacing the small bars with the larger ones. So I suspect the real production percentage of the small bars may be a bit higher than the 60/40 I tallied above.

[Formulabruce]

I have read this and thought about it as well. I can only add that the 1970 Z-28 had a factory F-41 suspension, and big bar in front. I do not know if they had the same issue, but the parts bins were right there, the anti sway bars in "Skid boxes". I can just see one box empty and they pull from another in Sub assembly. I always have to remind myself that there was a car every 45 seconds coming off the line. They didn't want a slow down. My cousin worked on sheet metal finish.

[keith k]

Originally Posted by Formulabruce

I have read this and thought about it as well. I can only add that the 1970 Z-28 had a factory F-41 suspension, and big bar in front. I do not know if they had the same issue, but the parts bins were right there, the anti sway bars in "Skid boxes". I can just see one box empty and they pull from another in Sub assembly. I always have to remind myself that there was a car every 45 seconds coming off the line. They didn't want a slow down. My cousin worked on sheet metal finish.

Hi Bruce,
In '70, no Camaros (Z28, F41, etc.) had bars as big as those spec'd for the Trans Am -- front or rear. The Z28 rear bar, for example, was 11/16"... only 1/16" larger than the Formula bar, and much smaller than the 7/8" spec T/A bar.

Some info on '70 Camaro bars here:
http://nastyz28.com/threads/70-l78-f...estion.315513/

I hear you on the "misbuild" thing... that definitely happened occasionally back then. But no way were they misbuilding 60+% of anything. If misbuild was the answer, there'd be a lot of '70 Formulas with the fat T/A bars on them. And I've never seen a single one of those...

[bird72]

Originally Posted by keith k

........the bars were hot forged with specifically sized and shaped bend dies in a custom fixture.

THX for your expertise and interesting read. Funny you wrote that, as just this morning I was looking at 1.25" bar on my bench I need to install on front of HOsprit. I was actually wondering how they made those honkers with bends. Was looking at the ends and also wondering whatever process was used on those, can see straight angle cut.

I can also vouch 7/8" bar after NO rear bar on Esprit was very noticeable driving when testing rear pitch under back and forth action. On another other car, I have upgraded Formula to TA F&R bars in past and change was not as noticeable, I suspect only under real hard sporty driving will it play in. I would leave a 70 TA with smaller bars for historic, as it still is a great handler. The 15" is half of it.

[Formulabruce]

Thanks keith k for that Camaro info and Link !. I did own a '70 ss 402, but never even looked at the bars way back then. That F-41 assumption was just too easy to make I guess...

[John V.]

In Rocky Rotella's new book, the '70 stabilizer bar dia. is discussed.

Herb Adams commented that he was disappointed that the TA was not initially developed for a better suspension. Bill Collins gave him a last minute chance to fix it, around the Nov. '69 time frame I believe. Adams says they basically got a weekend to improve it. The larger dia. bars resulted from that effort.

Rocky went on to comment that a number of '70 TA owners have reported the Formula sized stabilizer bars but says that there have not been enough to know if this occurred during a certain time frame or is simply evidence of production anomalies (errors during assembly).

Apparently Rocky has not uncovered any documentation that would explain the discrepancy.

Obviously, if all of the discrepancies were found on early production builds, one might surmise that the Herb Adams recommended TA suspension improvements did not enter into production until some point after initial production start.

Another possibility is that the Manifest programming for certain TA option combinations failed to get the stabilizer bar changes they were supposed to get while others did, resulting in the discrepancy appearing throughout the Model Year or at least until somebody noticed or complained about the glitch and it got fixed.

My own opinion is that assembly line errors were rare and random so that evidence of them is not often found. But when the same "error" shows up on numerous builds, there must have been a different explanation

Perhaps it was related to a wheel/tire option combination. Later in the year, PMD released the 15x7Rally II wheel with the F60-15 RWL tire as an option for the Formula. This was the standard wheel/tire on the TA. But the Formula was not to get the bigger TA stabilizer bars. Perhaps a coding confusion ensued and the TAs stopped getting the bigger bars at that time because of some "coupling" to the wheel/tire coding.

Regardless of the reason, there apparently is no evidence that the '70 TA was supposed to get the smaller bars. Any '70 TA that got them apparently got them due to some mistake or confusion, not necessarily the fault of the guys on the assembly line.

I also learned from Rocky's book that, curiously, the '73 TA apparently got downsized rear bars sometime around Feb '73 as a result of the optional radial tire availability. But the smaller rear bar was specified for all '73 TAs at that point with or without the radial tires. My '73 is a Jan build and I haven't checked the rear bar dia., just assume that it was the .875 and not the later .812.

[Tellyshavilli]

I’ve seen the smaller diameter rear swaybar on more than one 70 raiv Trans Am which were all built in July and possibly the first week of August.

[NOT A TA]

I replaced everything in a '70 for someone a couple years ago. Had the smaller size bars.

Note: Springs & shocks were not original.

[mlewisariz]

My 70 T/A is a Van Nuys built , 06B. It has 1.125 Front and 5/8 rear.

[SS-TA]

Despite what Rockys book says my 73 TA (July build) has a 7/8" rear bar. I did e-mail Rocky with the info a couple of weeks ago. I assume that manufacturing uses up what they have in stock, although I found it odd that this happened as late as the first week in July.

[John V.]

Originally Posted by SS-TA

Despite what Rockys book says my 73 TA (July build) has a 7/8" rear bar. I did e-mail Rocky with the info a couple of weeks ago. I assume that manufacturing uses up what they have in stock, although I found it odd that this happened as late as the first week in July.

Disposition of superseded/obsoleted inventory depended.

Sometimes the instruction was to use up, but other times, the parts were disposed of or possibly sent to the parts warehouse. Just depended on the nature of the change.

Since the change in this case was related to loads resulting from the installation of radial tires, I would say it was very unlikely that engineering would have authorized the assembly plant to use up inventory of the larger rear bar without limitation. A safety issue was involved.

Was your TA equipped with the optional radial tires?

If not, I could imagine that engineering would have approved using up inventory of the larger rear bar only on builds that did NOT have the radial tire option.

Keith, I'm not sure how or why, but I just reread your OP and realize that I failed to read it thoroughly when I first responded.

Interesting what you say about your photographic evidence regarding the '70 TA bars.

It seems that the anecdotal evidence added here by others is incomplete, either failing to note the Assembly Plant and/or the time frame with the exception of mlewisariz. whose 06B Van Nuys TA seems to conform to your own evidence.

I'm guessing there will never be enough data to conclude anything substantive about the '70 TA bars but it would be useful to gather info regarding the Time Built code, the Plant, the Tire option, and the engine option.

Tellyshavilli's comments about the RAIV cars is interesting. The RAIV builds were all late. Did the late decision to complete these orders have any bearing on the bars (my own comments about the coding for certain TA option combinations playing a role perhaps?) or was this a function of their build timing and Assembly Plant mirroring what you have seen? Without knowing whether these were Van Nuys or Norwood builds limits interpretation.

Would be useful to have more detailed data regarding the '70 TAs that have the smaller bars.

[eaglesan13]

Keith,

What's on your blue/sandlewood car? Just curious, since I seem to recall that your car was built fairly close to my old blue/sandlewood car (04B Van Nuys car), which has the large bars on it.

[Norwood]

My 07C has a small rear bar

[A Schab]

My O3C LA built car has the large rear bar.

[keith k]

Originally Posted by eaglesan13

Keith,

What's on your blue/sandlewood car? Just curious, since I seem to recall that your car was built fairly close to my old blue/sandlewood car (04B Van Nuys car), which has the large bars on it.

Hey Chris,
My current T/A (04B Van Nuys like yours was, but about 30 units ahead of it, by VIN) is a small bar car. The one built 50 units (again, going by VIN, and also an 04B body...) after yours also got the big bar, but the one another 10 after that (L10400X, and 04C) was back to the small bar. That's the way it seemed to go with the first few months of production at Van Nuys...

My previous '70 T/A, an 06D Norwood car, had the small bars on both front and rear.

Originally Posted by John V.

Keith, I'm not sure how or why, but I just reread your OP and realize that I failed to read it thoroughly when I first responded.

Interesting what you say about your photographic evidence regarding the '70 TA bars.

It seems that the anecdotal evidence added here by others is incomplete, either failing to note the Assembly Plant and/or the time frame with the exception of mlewisariz. whose 06B Van Nuys TA seems to conform to your own evidence.

I'm guessing there will never be enough data to conclude anything substantive about the '70 TA bars but it would be useful to gather info regarding the Time Built code, the Plant, the Tire option, and the engine option.

Tellyshavilli's comments about the RAIV cars is interesting. The RAIV builds were all late. Did the late decision to complete these orders have any bearing on the bars (my own comments about the coding for certain TA option combinations playing a role perhaps?) or was this a function of their build timing and Assembly Plant mirroring what you have seen? Without knowing whether these were Van Nuys or Norwood builds limits interpretation.

Would be useful to have more detailed data regarding the '70 TAs that have the smaller bars.

John, for all of the 123 cars I mentioned having photos of, I also have the VIN (and therefore assembly plant and general build date), original drivetrain, etc. info. I tabulated it all, but there's really no "pattern" that emerges, so I simply summarized it as I did.

[3tas4me]

My 02C built '70 has the large front bar. Rear bar may still be on the car or may be missing but I would think It came with the large rear bar if it has the large front bar.

[poncho-mike]

I have seen a number of different sway bars on the rear, but I think all have been equipped with the 1.25" on the front.

I parted out a mid-July build 70 T/A automatic with a/c many years ago. I remember it had a small rear sway bar, which confused me because I thought it should have the 7/8" bar.

The dismantled 1970 T/A Ram III aut (early July build) had a large rear sway bar. Dates for the engine were all around early to mid-C dates.

I have parted several other 70s, and I have seen both on those cars. I know one was an early car, and it had a large rear bar. Most all of my cars were late cars built in Norwood.

[RAJ7395]

Pretty scary when you think of it.

The front and rear bars are designed to work together to produce the desired anti-roll performance characteristics. If the bars are mis-matched, they will yield sub-optimal anti-roll performance.

Back in the 80's, I found a 1.25" TA bar in the local junk yard and installed it in my 73 camaro (no rear bar). In a hard turn the outside front tire took all the load, broke loose and pushed/plowed. It was really bad in the rain. Once I added the matching rear bar, the car was balanced and shot through the corners like it was on rails.

[mlewisariz]

An additional note on my 06B Van Nuys. I checked my build sheet,and on the lower section it shows *F41 SPC PERF SUSP. I wonder if the asterick has any meaning in relation to available bar sizes or a missed cue for assembler.
I would think the proliferation of smaller bars might indicate a shortage of larger dia. parts in Van Nuys.

[Formulabruce]

Originally Posted by mlewisariz

An additional note on my 06B Van Nuys. I checked my build sheet,and on the lower section it shows *F41 SPC PERF SUSP. I wonder if the asterick has any meaning in relation to available bar sizes or a missed cue for assembler.
I would think the proliferation of smaller bars might indicate a shortage of larger dia. parts in Van Nuys.

This is what brought about my mentioning the F-41 in a early post on this thread.