Crossmember size? (1 Viewer)

[Ullr]

For a crossmember/support running under the Toybox to a Toyota mini-truck t-case mount will 1" OD .120 wall DOM be strong enough?

 

[bustanutley]

no.

 

[Poser]

If you use more than one piece to form your cradle you might get away with it....


Will this only be supporting the toybox and mini case, or will it be supporting the whole rear section of drivetrain?

 

[Ullr]

Will this only be supporting the toybox and mini case, or will it be supporting the whole rear section of drivetrain?

Toybox and split case, I have the 76 bellhousing bolted up to the 85 tranny, so I was going to use the mount point under the toybox versus the one under the tranny as its closer to the split case.

How about 1.5" OD .250 wall DOM?

 

[fj40charles]

Toybox and split case, I have the 76 bellhousing bolted up to the 85 tranny, so I was going to use the mount point under the toybox versus the one under the tranny as its closer to the split case.

How about 1.5" OD .250 wall DOM?

I would lean toward 1.75" or 2" .250 wall dom or 1.75" or 2" square .250 wall tubing. Just my 2 cents.

 

[Ullr]

I would lean toward 1.75" or 2" .250 wall dom or 1.75" or 2" square .250 wall tubing. Just my 2 cents.

Holy crap, thats huge. Thats gonna be a beast to squeeze in there.

 

[Ullr]

I would lean toward 1.75" or 2" .250 wall dom or 1.75" or 2" square .250 wall tubing. Just my 2 cents.

I was looking at the Toyota mini truck t-case mount, its made out of 3/16" and has a rubber isolator. The screws in the base of it are only 1/4". Grante dthe crossmember can be stronger than the mount, but that seems like an exponential difference.

 

[Isotel]

I used Square Tubing on mine.. My Thought is that the Forces on a crossmember are mostly along parallel axis with the tube,
Mine is 1.5" 3/16 wall Square, no issues thus far, But its not Tested hard yet!

 

[rusty_tlc]

I used Square Tubing on mine.. My Thought is that the Forces on a crossmember are mostly along parallel axis with the tube,
Mine is 1.5" 3/16 wall Square, no issues thus far, But its not Tested hard yet!

Wouldn't a lot of force be rotational from torque? That would put the force purpendicular to the tube.

 

[Ullr]

I think the force is up and down, so perpendicular to the long axis of the tube. Ideally you allow a little twist for torque, hence the rubber mounts, but you want to stop the up and down play possible with the lengthened drivetrain due to the Toybox, the split case now has a lot of leverage on the last mounts, which are the engine mounts on the bell housing.

So, it occurred to me that if the tube was bent down in the middle (which is necesary to clear the t-case front output flange) then down force would get translated into some tension and up force would get translaterd into some compression (anyone who actually knows WTF they are talking about is more than welcome to interrupt me at this point...) especially if the load on the middle of the tube (the Toybox) is at the apex (low point) of the bend. Theres no more down to go so it becomes a tension load along the axis of the tube to the frame mounts, and vice versa on upwards loads?

Am I high?

 

[Ullr]

Think of it as standing in the middle a slackline. Once the slack line reaches a certain point of tension it stops moving downwards and holds you up, and a large part of the force pulling you down (gravity) is translated in to force trying to pull the two slackline anchors together.

On second thought that example might only make sense to climbers.

 

[rusty_tlc]

I think the force is up and down, so perpendicular to the long axis of the tube. Ideally you allow a little twist for torque, hence the rubber mounts, but you want to stop the up and down play possible with the lengthened drivetrain due to the Toybox, the split case now has a lot of leverage on the last mounts, which are the engine mounts on the bell housing.

So, it occurred to me that if the tube was bent down in the middle (which is necesary to clear the t-case front output flange) then down force would get translated into some tension and up force would get translaterd into some compression (anyone who actually knows WTF they are talking about is more than welcome to interrupt me at this point...) especially if the load on the middle of the tube (the Toybox) is at the apex (low point) of the bend. Theres no more down to go so it becomes a tension load along the axis of the tube to the frame mounts, and vice versa on upwards loads?

Am I high?

I was thinking of it as an inverted truss, with the t-case mount as the cross piece.
\_/ rather than /-\
Trusses work best for loads in compression or up in this case.
Maybe something like \|_|/ would help with the down loads and keep the size of the tubing down?

BTW with the additional torque from the low gearing I wouldn't discount rotational forces.

But what do I know?

 

[Ullr]

I was thinking of it as an inverted truss, with the t-case mount as the cross piece.
\_/ rather than /-\
Trusses work best for loads in compression or up in this case.
Maybe something like \|_|/ would help with the down loads and keep the size of the tubing down?

BTW with the additional torque from the low gearing I wouldn't discount rotational forces.

But what do I know?

Due to clearance on the t-case it has to be an inverted truss, like frame\___/frame. 60wag was looking at it last night and thinks the 1.5" .250 wall DOM will be plenty strong, this is after all just a brace for the tcase and toybox. The tranny is bolted to a '76 bellhousing which has its own brand new mounts.

As far as torsional forces I am not discounting them, but Uncle Ben said there should be a little (very little) room for twist. So I am using the rubber t-case mount from a toyota mini truck and I will be mounting the crossmember to the frame with spring bushings. So the whole drivetrain will be mounted to the frame with rubber paded mounts. Does that make sense?

 

[Rock Taxi]

Not quite sure exactly how you are mounting it, but on my last rig, I ran a 2x2x.125" wall square tube with bushings on both ends under the Klune foot to hold up the back of the drivetrain - but I had a torque foot off the NP205 also to prevent driveline wrap.

It had a separate skid plate under it, so it did not take rock hits, just held the back of the LT1, 700r4, Klune, NP205 up.

Ed

 

[Ullr]

It will be similar to that, ,with bushings at both ends. I was also planning on keeping the skid plate seperate for it.

 

[rusty_tlc]

Due to clearance on the t-case it has to be an inverted truss, like frame\___/frame. 60wag was looking at it last night and thinks the 1.5" .250 wall DOM will be plenty strong, this is after all just a brace for the tcase and toybox. The tranny is bolted to a '76 bellhousing which has its own brand new mounts.

As far as torsional forces I am not discounting them, but Uncle Ben said there should be a little (very little) room for twist. So I am using the rubber t-case mount from a toyota mini truck and I will be mounting the crossmember to the frame with spring bushings. So the whole drivetrain will be mounted to the frame with rubber paded mounts. Does that make sense?

Makes sense and sounds like a good design.