Weight savings by using and aluminum cross member on early car?

[Fixer]

Anyone know the exact weight savings doing this? Tried Search function.

[juanbenae]

would the A arm hardware be the same? meaning where it mates with the body & engages the torsion bars?

[Puma]

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[proffighter]

Without starting a discussion about bicycles, I have never ever heard of an aluminum crossmember fail, so there is no risk for this application.

[pksystems]

Depends what you mean by early car. The SWB cars have completely different suspension up front. If you swap it all out to the later car parts, the aluminum crossmember is interchangeable. It's not the best place for weight savings tho. Lowest point on the car, and the front end. You want to remove weight up high, and from the back of the car.

[Shaun @ Tru6]

I'll weigh each today Matt.

[Fixer]

Originally Posted by Shaun @ Tru6

I'll weigh each today Matt.

Cool, thanks Shaun.

A local guy has a complete front suspension from a Carrera for sale. I've never weighed the difference and interested in saving weight in any place i can. I'd be swapping the assembly.

Happy Birthday America !

[Shaun @ Tru6]

As a certified weight freak with an all steel 2174lb car with a hot 3.2, I understand well the chase for weight savings. Other than overall weight though, this is probably the least bang for buck in terms of grams lost, being low in the car and in the front.

I cut up a 928 on Saturday. The roof section with sunroof must have been close to 100lb, a good place to reduce weight on any car. Someone should be making carbon fiber skins for 928s if they aren't already.

[Shaun @ Tru6]

Using my postage scale, Al crossmember weighs in at 3lb, 14.9oz. Using the shipping scale for the steel one, I get 9.5lb so it can be anywhere from 9,8 to 9,15.

6lb is nice to lose.

[kent olsen]

I went thru the same steps with my 72 911 cpe. Up front I replaced the hood with a fiberglass unit. Then I removed the driver's side battery and replaced the pax side one with a gel battery. Then in an attempt to get more air to my right fender oil cooler I cut out the battery box and moved the battery to the smugglers box.

More weigh reductions in the rear, which is more productive, and I weigh 2200lbs with a half tank of gas.

[Fixer]

Originally Posted by Shaun @ Tru6

Using my postage scale, Al crossmember weighs in at 3lb, 14.9oz. Using the shipping scale for the steel one, I get 9.5lb so it can be anywhere from 9,8 to 9,15.

6lb is nice to lose.

Thank you Shaun. This is good data to have in search. 6 lbs is a decent reduction and the anti dive geometry of the front end is also a benefit.

Originally Posted by kent olsen

I went thru the same steps with my 72 911 cpe. Up front I replaced the hood with a fiberglass unit. Then I removed the driver's side battery and replaced the pax side one with a gel battery. Then in an attempt to get more air to my right fender oil cooler I cut out the battery box and moved the battery to the smugglers box.

More weigh reductions in the rear, which is more productive, and I weigh 2200lbs with a half tank of gas.

Nice work Kent,

I agree with all comments made regarding focusing on rear weight reduction. This '68 912 I'm building is about 200 lbs lighter out back with 150 - 160 HP Type 4 engine. The engine is shorter so the weight is more forward too which you all know. I'm already using lightweight engine lid, lexan rear glass, R taillights, R rear bumper spoiler so I figure i can lighten the front end as much as i want and still be OK.

The Type 4 engine makes really good torque [designed for it] so I want to make this old girl as competitive as i can by adding lightness.

Thanks again Shaun, -Matt

[proffighter]

You may be interested in what I've done for weight saving so far, even it's a turbo. Unfortunately you have to go through the whole thread as it's about the rebuilt of my car:

Another rust combat

[Flieger]

Originally Posted by Fixer

Thank you Shaun. This is good data to have in search. 6 lbs is a decent reduction and the anti dive geometry of the front end is also a benefit.




Nice work Kent,

I agree with all comments made regarding focusing on rear weight reduction. This '68 912 I'm building is about 200 lbs lighter out back with 150 - 160 HP Type 4 engine. The engine is shorter so the weight is more forward too which you all know. I'm already using lightweight engine lid, lexan rear glass, R taillights, R rear bumper spoiler so I figure i can lighten the front end as much as i want and still be OK.

The Type 4 engine makes really good torque [designed for it] so I want to make this old girl as competitive as i can by adding lightness.

Thanks again Shaun, -Matt

Aluminum crossmember does not do anything for anti-dive.

[Fixer]

Originally Posted by Flieger

Aluminum crossmember does not do anything for anti-dive.

I know, I would use the whole assembly.

[Fixer]

Originally Posted by proffighter

You may be interested in what I've done for weight saving so far, even it's a turbo. Unfortunately you have to go through the whole thread as it's about the rebuilt of my car:

Another rust combat

I'll read it in the morning, thank you. -Matt

[joefrantz]

One of the issues that I encountered when doing the aluminum cross member replacement was the weight of the pan that covers the cross member and protects the master cylinder and front mounted fuel pump(if you have one).

The pans are different. The pan for the aluminum cross member is much heavier gauge steel than the one for the steel cross member. The differences in pan weights negated most of the weight savings, and as I remember, you couldn't use the original light gauge steel pan with the aluminum cross member.

I ended up making my own custom pan from aluminum sheet, which weighs about the same as the original thin steel pan.

I'm wondering what others have done.

By the way, replacing the front suspension with the later version was the late Grady Clay's number one recommendation for SWB cars. He had seen many failures in the original A-arm/ball joint fixture.

[Evan Fullerton]

The aluminum front cross member is far less stiff then the steel one. I don't like them for that reason as they do not locate the steering rack as well. The torsion bar ride height adjuster bolts also can have their retension slot broken out of the aluminum crossmember much more easily. If you have a steel one that isn't super rusty, I wouldn't replace it.

[KTL]

Is the overall stiffness of the aluminum cross member really an issue? What I mean by that is, the point where the rear pivot of the A-arm acts on the cross member is so close to where the cross member mounts to the chassis. So the A-arm doesn't have much leverage to put a large moment on the cross member because the lever arm is so short?

Just an observation/question on my part. I haven't calculated anything to argue the stiffness between the two.

I completely agree with Evan that the aluminum member is prone to damage where the adjuster screw passes thru the slot. I too have seen quite a few aluminum members with that slot broken away.

[Tyson Schmidt]

The aluminum crossmember lacks stiffness in the fore-aft range.

Since the tie-rods are angled rearward pretty significantly, steering loads will cause it to flex. This leads to toe change.

I've seen many of these bent due to accident or off-track excursion.

Although it does act as a nice fuse in the system to prevent other damage.

But it's the last place to save weight, ideally, and like Evan said it's not as stiff in all directions as the steel tube design of the early one.

[KTL]

Good to know. Thanks for explaining that. The fore-aft stiffness would also explain why it's important to retain the flat braces that join the cross member to the chassis?

Speaking of stiffness since i've got your ear, have you seen lack of stiffness in the steering arm itself? I've seen JRZ-modified Boge struts with gusseting (flat steel plate welded alongside) along the length of the steering arm. I hadn't considered that the arm itself had much flex it it since it's pretty beefy in cross section. However it is rather long and the load that the steering arm feels under hard cornering with sticky tires must be pretty big.