[JC455]

I grabbed on of these for my 64 Tempest.

https://www.holley.com/products/engi...ts/71222008HKR

It says it's for an LS swap, but with all the adjustment holes on the mounting rails, I'm sure it will work for my Pontiac V8/5 speed swap.
I went with this design because of all the adjustability, and the fact that it bolts to the side and bottom of the factory frame, so it should help stiffen the wiggle in that section.
I'll mount the trans on a rubber piece, so it'll retain the factory movement-ability.

[JSchmitz]

Originally Posted by JC455

I grabbed on of these for my 64 Tempest.

https://www.holley.com/products/engi...ts/71222008HKR

It says it's for an LS swap, but with all the adjustment holes on the mounting rails, I'm sure it will work for my Pontiac V8/5 speed swap.
I went with this design because of all the adjustability, and the fact that it bolts to the side and bottom of the factory frame, so it should help stiffen the wiggle in that section.
I'll mount the trans on a rubber piece, so it'll retain the factory movement-ability.

I have looked at those. A little more than I want to spend right now. But we'll see

[4zpeed]

PMD engineers most likely didn't want people chippin a tooth on a radical 1st - 2nd shift, albeit at the cost of letting the drive line flop around...

I mean, probably the main reason all the high horse power stuff like RA4's and HO models just fell apart in the street after a good beating.



Frank

[70GS455]

The 68 - 72 Buick A bodies have the same stamped cross member as the first picture

Sent from my SM-T817V using Tapatalk

[KEN CROCIE]

Could it be that Pontiac just carried over the x-member cushioned design from the full size cars? The engineering was already verified and in use.

[i82much]

Originally Posted by Formulajones

LOL it's always something isn't it?

It never stops! I think I have some of the ripple in my quarter panel that Tom was talking about in the other post. My frame is boxed, though. I don't have the four speed rear control arm braces installed yet. Now this thread has got me wondering whether a 65 with a stick shift and a boxed frame can ripple the quarter panels on street tires just from not having those rear control arm braces installed.

[4zpeed]

Originally Posted by KEN CROCIE

Could it be that Pontiac just carried over the x-member cushioned design from the full size cars? The engineering was already verified and in use.

Thanks Ken I didn't know that. Harmonics and vibration play a large role in the fatigue of components, more then some may think, over time it will actually destroy things.

Industrial type machines, large compressors, generators and the like set on springs and other isolators to dampen the effects and save on wear or combat anchor failure.

The people at PMD were not dummies, if you want something to function, but would like for it to live past a few hundred trips down the track... well, build it that way.

Originally Posted by i82much

It never stops! I think I have some of the ripple in my quarter panel that Tom was talking about in the other post. My frame is boxed, though. I don't have the four speed rear control arm braces installed yet. Now this thread has got me wondering whether a 65 with a stick shift and a boxed frame can ripple the quarter panels on street tires just from not having those rear control arm braces installed.

The braces will help with pinion angle and might reduce the rippling effect, is your rear end bushings and or body bushings worn? Street tires shouldn't be a issue.

Edit - Those braces are well wroth installing, that rear cross member has been known to flex, 'bend' under heaver loads, especially since weathered and 50 yrs old.



Frank

[Scarebird]

How much do you think these rubber isolators actually move?

I would astonished if they changed more than 75 thou in horizontal motion, that most likely in events such as speed bumps, pot holes and curbs hit.

I think Tom has the right idea; they are there for frame flexing and NVH reasons. The only thing Pontiac could have done better here to me is use clip nuts for speed of install.

[george kujanski]

^^^^^ next time I mess with mine I'm welding nuts to the top side bracket.

George

[lust4speed]

I'd say the reason that the bolted or rubber isolated cross members both work is that they do so very little. The job of the rear cross member is to simply locate the transmission in both vertical and horizontal planes and nothing more. Would be nice to remove torsional stresses from the engine and transmission cases while we are at it, and the rubber isolated mount is better.

If I want to stiffen up the chassis I don't think I would start by taking a bent piece of round tubbing with squished ends and bolting it to a 1/16" unsupported section of frame rail and believe I really accomplished much. If chassis twisting loads the crossmember, then either the thin frame rail is going to flex a little or the rubber isolator is going to absorb it. In either case, neither Pontiac or the others were thinking that their crossmembers were doing anything except supporting the rear of the trans.

If I were thinking of changing things, the only logical reason would be to design something that continued to locate the trans but with less weight.

[4zpeed]

Originally Posted by lust4speed

Would be nice to remove torsional stresses from the engine and transmission cases while we are at it, and the rubber isolated mount is better.

If I want to stiffen up the chassis I don't think I would start by taking a bent piece of round tubbing with squished ends and bolting it to a 1/16" unsupported section of frame rail and believe I really accomplished much.

Agreed, and the entire function of the rubber is to isolate, pretty nice on PMD's behalf.

Edit - Some people can start a fight in a empty room...



Frank

[JSchmitz]

Outboard rubber mount does almost nothing. Harder to install than direct bolt in design. I'd rather have something easier to install that locates, and controls, the trans more positively. Especially when a couple of degrees is miles when it comes to driveline angles. The thing is hand grenade precise when it comes to side to side location. The center rubber mount is totally sufficient to isolate vibration and secure the trans. Not counting on the crossmember completely to stiffen the chassis. Just that every little bit counts. Ever jack up the front of your car and watch watch what the frame does? Now's where someone can jump in and explain to me how the crossmember won't help that. I'll post up what I end up doing. Thanks for all of the input!

[Tom Vaught]

Originally Posted by Scarebird

How much do you think these rubber isolators actually move?

I would astonished if they changed more than 75 thou in horizontal motion, that most likely in events such as speed bumps, pot holes and curbs hit.

I think Tom has the right idea; they are there for frame flexing and NVH reasons. The only thing Pontiac could have done better here to me is use clip nuts for speed of install.

On my convertible, which I have owned longer than most of you have been alive, the rubber biscuit is a solid rubber part with a groove molded into the part. This groove is centrally located so that there is equal rubber (about 3/8" on either the top or bottom of the biscuit.

Now when you slip the metal clamp over the biscuit, the bottom of the metal clamp is about 3/16 to 1/4" ABOVE the mounting surface of the bracket welded on the side of the frame. So when you install your proper length bolts and nuts, the crossmember is compressed quite a bit and does not "flop around" as some have assumed.

So if the crossmember is trapped solidly by the biscuit, there is basically no movement unless the crossmember sees a high load trying to twist the crossmember and that is highly unlikely with the trans crossmember mount also trapping the crossmember and the trans in a "fixed" location.

So if you have biscuits that allow the crossmember to move, you bought some crappy parts. The parts, as was posted were most likely there for NVH issues and agree were most likely a similar design to the big Pontiac stuff.

But I have always used NOS stuff from Pontiac that I had on the shelf with no issues. So the comments about the biscuits allowing the crossmember to flop around is telling you that you bought some crappy repop parts.

All above being said, I did not design the parts, I have just worked with the parts for many years. To assume that I have to explain why a Pontiac engineer did stuff means that the person making that statement has little knowledge of how a Automotive Vehicle is designed and produced.

My uncle always said you had Cadillac and then Pontiac as the premium vehicles. The Buicks, the Oldsmobiles, and the Chevrolet vehicle lines were for the people who could not afford the Cadillac or the Pontiac vehicle.

To imply that the Chevrolet vehicles was equivalent to the Pontiac in terms of which were Premium vehicles, is a laugh.

Lots of misinformation in this thread, mostly made up in the last few weeks.

Tom V.

[4zpeed]

Originally Posted by JSchmitz

Ever jack up the front of your car and watch watch what the frame does? Now's where someone can jump in and explain to me how the crossmember won't help that. I'll post up what I end up doing. Thanks for all of the input!

If your talking about a bumper jack on one corner most of that flex is the junction where body meets mechanical fastened sheet metal that's bolted to the core support.

The cross member sets behind that point, where the body is solid. Now if your pulling the front tires off the ground using HP, you may need to re engineer something.

The one piece body combined with the frame actually makes for a rigid structure, everything is basically a compromise, the body gets bolted on with rubber bushings.

I get what you're talking about, as mentioned previously rubber gets old and aftermarket, well pffft..., but with some performance added you may need to upgrade.

Between juggling everything that is needed to manufacture a solid quality product and guarantee performance and comfort, I think PMD has done a pretty good job.

Edit -

Originally Posted by 4zpeed

PMD engineers most likely didn't want people chippin a tooth on a radical 1st - 2nd shift, albeit at the cost of letting the drive line flop around...

I mean, probably the main reason all the high horse power stuff like RA4's and HO models just fell apart in the street after a good beating.

This is the mind set of someone who doesn't understand compromise.




Frank

[JSchmitz]

Originally Posted by 4zpeed

If your talking about a bumper jack on one corner most of that flex is the junction where body meets mechanical fastened sheet metal that's bolted to the core support.

The cross member sets behind that point, where the body is solid. Now if your pulling the front tires off the ground using HP, you may need to re engineer something.

The one piece body combined with the frame actually makes for a rigid structure, everything is basically a compromise, the body gets bolted on with rubber bushings.

I get what you're talking about, as mentioned previously rubber gets old and aftermarket, well pffft..., but with some performance added you may need to upgrade.

Between juggling everything that is needed to manufacture a solid quality product and guarantee performance and comfort, I think PMD has done a pretty good job.




Frank

Was eluding to the fact that the factory frame is like a noodle. That every bit of strengthening helps. The fact that this section of the frame is not boxed and flexible supports the argument to rigidly tie it to the other side not the opposite. Kinda like polyurethane suspension bushings. Rubber isolates vibration better. Poly controls better. What do you want to achieve? Engineering is almost always a trade. VERY seldom no compromise to be made.

[4zpeed]

Originally Posted by JSchmitz

Was eluding to the fact that the factory frame is like a noodle. That every bit of strengthening helps. The fact that this section of the frame is not boxed and flexible supports the argument to rigidly tie it to the other side not the opposite. Kinda like polyurethane suspension bushings. Rubber isolates vibration better. Poly controls better. What do you want to achieve? Engineering is almost always a trade. VERY seldom no compromise to be made.

I feel there is always a compromise, rigidity or comfort, performance or mileage, compression or longevity, seems ground must be given to produce quality/performance.




Frank

[JSchmitz]

I guess I should try and find a Cadillac crossmember. That way I'm not implying that Pontiac is inferior. Surely the Cadillac design is better since it's a luxury car. Give me a break. I thought we were ALLOWED to have our opinion. But if someone's opinion doesn't match ours it's "misinformation" and we just don't understand because we're not automotive engineers.

I'm trying to improve on the factory design. We all do it. That's Hot Rodding. That's why I started this thread. If you want to get your panties in a bunch, because I question almighty Pontiac and engineers, go right ahead. Take a look at EVERY transmission crossmember you can find. See any rubber booties where they bolt to the frame? I guess the Pontiac engineers 50+ years ago were the only ones that understood driveline vibration (NVH, ooh an acronym!). Sometimes, just sometimes, things get OVER-engineered. Adding cost and complexity to something with little or no gain.

I think I may just fabricate a crossmember from scratch. Possibly box the frame where it intersects. Make it a three piece design for ease of removal and installation. Old Chevy trucks had a wishbone crossmember in some manual trans trucks that was riveted to the frame. Very beefy. If I remember correctly, it tied into the bellhousing. Converted one to automatic. Was a mother to get that crossmember out of there.

[4zpeed]

Did you post to get some opinions or just state your view point? Just because you don't like it doesn't make it a bad design.

You're allowed any opinion you wish, you know what they say... In the original post you said you never cared for the design.

"My '65 Chevelle had a tubular design that I like much better" Nothing wrong with that, grab one from a Chevy...




Frank

[JSchmitz]

Originally Posted by 4zpeed

Did you post to get some opinions or just state your view point? Just because you don't like it doesn't make it a bad design.

You're allowed any opinion you wish, you know what they say... In the original post you said you never cared for the design.

"My '65 Chevelle had a tubular design that I like much better" Nothing wrong with that, grab one from a Chevy...




Frank

I posted to see what other designs were out there. I wasn't, and still am not, interested in keeping the original design. This has turned into a debate about how great the factory design is. I'm sorry that this hasn't stayed more matter of fact. Egos and personal feelings have prevailed over facts (If there are any present). I'm guilty as well. This has gone way too for for a simple topic. I'm done.

[4zpeed]

Originally Posted by JSchmitz

I posted to see what other designs were out there. I agree that the design isn't all bad. I'm sorry that this hasn't stayed more matter of fact. Egos and personal feelings have prevailed over facts (If there are any present). I'm guilty as well. This has gone way too for for a simple topic. I'm done.

Well beyond the bar room brawls I thought it was a great topic, thanks for the thread.

I apologize if my post seemed sarcastic, we're all Pontiac people here, much love brother.



Frank