Mounting transmission crossmember

[Zandoz]

I have bolt-in round tube transmission crossmember mounts like these...


They are made for 3/8" mounting bolts. The transmission that will be mounted is a 700R4...the engine a light weight V6, weighing around 200 lbs less than a SBC. The crossmember will float inside the cups, so there will be no torquing or pulling forces on the brackets...only weight support. My question is would 3/8" Nutserts be sufficient for fastening these mounts to the frame rails?

 

[old round fart]

Nutserts held a sway bar in a Mustang road race car I had once but I don't think I would trust it here. Drill through the frame and put threaded slugs in it.

 

[fletcherson]

I have bolt-in round tube transmission crossmember mounts like these...

View attachment 10789
They are made for 3/8" mounting bolts. The transmission that will be mounted is a 700R4...the engine a light weight V6, weighing around 200 lbs less than a SBC. The crossmember will float inside the cups, so there will be no torquing or pulling forces on the brackets...only weight support. My question is would 3/8" Nutserts be sufficient for fastening these mounts to the frame rails?

You are going to be dealing with vibration and some torsion between the frame rails in addition to the weight. I would through bolt them to be sure. Are you going to weld the mounts to the cross member tube? I would.

 

[Golly]

Personally I prefer weld in trans cross members, as it adds a lot of strength to the chassis, and if the trans needs to come out , it's just as easy to pull the motor & trans out together.

 

[bobs66440]

You can flush weld 3/8 nuts into the frame if you wanted it removable. Otherwise I would weld the whole thing in.

 

[2old2fast]

As an example , the TP kits used self tapping bolts to hold in crossmembers & the upper rear coilover mounts.... my guess would be that properly installed nutserts would work fine.... the fasteners would be in shear, not in tension... I'd strongly advise that the ends be welded to the crossmember.... my $.02
dave

 

[Zandoz]

Nutserts held a sway bar in a Mustang road race car I had once but I don't think I would trust it here. Drill through the frame and put threaded slugs in it.

The reason I'm looking at the Nutserts at all is that I'm trying to cut down on the amount of welding needed on the frame post construction. Around here welding by someone who really knows what they are doing is expensive. I'm already at 10 crush prevention tubes, 2 link brackets, 2 air spring pockets, 2 motor mount platforms, and 2 shock mounts. Those alone will likely run more than what the frame itself will run.

 

[Zandoz]

You are going to be dealing with vibration and some torsion between the frame rails in addition to the weight. I would through bolt them to be sure. Are you going to weld the mounts to the cross member tube? I would.

I plan on leaving the crossmember float in the bracket pockets...in part to eliminate that torsion issue you mentioned. Also to allow adjustment to the engine angle to parallel the pinion angle. Welding of the ends is only recommended for racing and off road applications...and then they suggest bolts through the pockets and crossmember as an alternative to welding. That I could do any time down the road.

 

[Zandoz]

Personally I prefer weld in trans cross members, as it adds a lot of strength to the chassis, and if the trans needs to come out , it's just as easy to pull the motor & trans out together.

Actually, removability is low on the priority list. The main reason I'm going with this configuration is the ability of the crossmember to rotate in the mount cups, so I can play with the engine/pinion angles to minimize vibration. There will be a welded in 2" x 3" x .120" wall rectangular tubing crossmember for structural purposes not far behind the transmission crossmember.

 

[Zandoz]

As an example , the TP kits used self tapping bolts to hold in crossmembers & the upper rear coilover mounts.... my guess would be that properly installed nutserts would work fine.... the fasteners would be in shear, not in tension... I'd strongly advise that the ends be welded to the crossmember.... my $.02
dave

I'd thought about tapping the frame rails for the mounts, but to me only 3/16" of threads would not be sufficient.

 

[T-Test]

As an example , the TP kits used self tapping bolts to hold in crossmembers & the upper rear coilover mounts.... my guess would be that properly installed nutserts would work fine.... the fasteners would be in shear, not in tension... I'd strongly advise that the ends be welded to the crossmember.... my $.02
dave

I use self tapping bolts on just about everything, like T/P did. Fastenal has them in bags of 100 for 1/4"==5/16"===3/8" sizes. I also used 3/16" thick frame material. No problems in 10 years.

 

[old round fart]

Have you considered a welding course at the local trade school , buying a MIG machine and charging the other guys to weld their stuff and pay for your new addiction!

 

[Zandoz]

Have you considered a welding course at the local trade school , buying a MIG machine and charging the other guys to weld their stuff and pay for your new addiction!

I have considered that possibility, but I've not found any offerings that are not part of a full blown trade curriculum. Also, it would be quite a while before I would be good enough at it to trust my work on structural/safety applications. I'd love to have someone show me the ropes of doing good tack welds, so I could at least do the configuration just how I want it, then take the pieces to a pro for final welding. At this point my only welding experience is doing a few poor self taught tack welds, and that was 30+ years ago. Back then there were several extended family professional welders near by, so there was no need for learning to do it myself. Not having learned to weld is one of my great regrets.

 

[fletcherson]

I have considered that possibility, but I've not found any offerings that are not part of a full blown trade curriculum. Also, it would be quite a while before I would be good enough at it to trust my work on structural/safety applications. I'd love to have someone show me the ropes of doing good tack welds, so I could at least do the configuration just how I want it, then take the pieces to a pro for final welding. At this point my only welding experience is doing a few poor self taught tack welds, and that was 30+ years ago. Back then there were several extended family professional welders near by, so there was no need for learning to do it myself. Not having learned to weld is one of my great regrets.

If you want to learn to weld, there is a lot of good free info on various welder manufacturer sites. The best way to learn is just buy a machine and practice. Even in school, that's what you do with some oversite. I am a self taught welder and was later state certified. I welded for years since, but I learned in my garage and read about it. The wire feed welders are pretty easy to learn. Prep is a big part. There are a lot of tutorial videos on u tube and related sites.

 

[Zandoz]

If you want to learn to weld, there is a lot of good free info on various welder manufacturer sites. The best way to learn is just buy a machine and practice. Even in school, that's what you do with some oversite. I am a self taught welder and was later state certified. I welded for years since, but I learned in my garage and read about it. The wire feed welders are pretty easy to learn. Prep is a big part. There are a lot of tutorial videos on u tube and related sites.

I've looked at the wire feed welders at Harbor Freight a couple of times...I may just go ahead and spring for one.

 

[fletcherson]

I've looked at the wire feed welders at Harbor Freight a couple of times...I may just go ahead and spring for one.

Pay attention to the duty cycle rating, that's how long you can weld before the machine needs a break. Also, get one with Aragon gas shielding, it it much cleaner welding, and get at least a 100 amp machine. You would be better off to opt for a better machine than you think you need to start with because it will weld better and make you a better welder and you won't outgrow it. Jmo. My first mig was a Clark 100 amp with Aragon. I still have it and have woked the devil out of it since 1993. It is only a 20 minute duty cycle which is ok for most body work type stuff, but aggravates me for anything significant. I since procured a 250 amp Marquette Napa branded machine that is a work horse. There are also videos available, I bet the library could help you with some material. A welder and torch are invaluable tools for building cars. It's hard for me to imagine doing without them since having them. They are very worth wile investments. You can recoup your investment later if you don't use them because guys buy them used. I would caution you to do a little investigating before buying a hf welder. I haven't used one, but I have bought several tools from them. Some are ok, some are junk.

 

[Zandoz]

Pay attention to the duty cycle rating, that's how long you can weld before the machine needs a break. Also, get one with Aragon gas shielding, it it much cleaner welding, and get at least a 100 amp machine. You would be better off to opt for a better machine than you think you need to start with because it will weld better and make you a better welder and you won't outgrow it. Jmo. My first mig was a Clark 100 amp with Aragon. I still have it and have woked the devil out of it since 1993. It is only a 20 minute duty cycle which is ok for most body work type stuff, but aggravates me for anything significant. I since procured a 250 amp Marquette Napa branded machine that is a work horse. There are also videos available, I bet the library could help you with some material. A welder and torch are invaluable tools for building cars. It's hard for me to imagine doing without them since having them. They are very worth wile investments. You can recoup your investment later if you don't use them because guys buy them used. I would caution you to do a little investigating before buying a hf welder. I haven't used one, but I have bought several tools from them. Some are ok, some are junk.

The unit I'd go for is a 90 amp 120 volt gasless one with good reviews. Any more than that would require a new breaker panel and wiring for 240v. with the 120v unit I could borrow the wife's hot tub hook-up when I need to weld.

 

[fluidfloyd]

I plan on leaving the crossmember float in the bracket pockets...in part to eliminate that torsion issue you mentioned. Also to allow adjustment to the engine angle to parallel the pinion angle. Welding of the ends is only recommended for racing and off road applications...and then they suggest bolts through the pockets and crossmember as an alternative to welding. That I could do any time down the road.

Bill.

I don't think letting that mount float is not a good idea. The rear transmission mount actually locates that engine in the fore and aft direction. If it is allowed to move around or tries to rotate it might work your front mounts pretty good. By making that cross member rigid it will add a lot of torsional stiffness to your frame. If you want to make it removable then you might consider adding a threaded doubler to that cross member flange. Make it 1/4" thick and tack it to your frame. Then run the tap into the side of the frame rail. That should give you 7/16" thread engagement. Tap it for a fine thread and you will increase the thread count engaged. Then all you have to do is put a fillet weld around your 1'4" plate to the frame rail. Might find a school shop program that will do it on the fly. Buy them a beer ...opps! make that a root beer and call it a day. Good Luck!

George

 

[fletcherson]

The unit I'd go for is a 90 amp 120 volt gasless one with good reviews. Any more than that would require a new breaker panel and wiring for 240v. with the 120v unit I could borrow the wife's hot tub hook-up when I need to weld.

The output rating isn't the power supply required to run the machine. You can run a 100 or higher amp welder from a 110 volt 20 amp outlet. The welder is basically a transformer, so you are converting volts to amps, high amps, low voltage from house current. The gas welders will also weld with flux core wire without gas, but it gives you the option to use plain mild steel wire or even aluminum, if you desire. I strongly suggest doing some research related to penetration and welder size requirements so you can be successful in your endeavor. I don't like flux core wire, I have no use for it at all personally. I prefer stick welding to it by far. I only use gas shielding on my mig, it's far superior, cleaner, better penetration, more control, better visibility while welding. The only functional downfall compared to flux core is if there is wind or air movement, it can blow the shielding gas away, but I weld inside. It's much better to have more power than required to be sure you can get penetration. It's better to weld hot than cold, cold welds fail. I'm not sure how much a 80 amp welder will penetrate, probably ok for sheet metal and mild tube steel, but for heavier plate, channel, and angle, you likely need more. I'm just sharing my experience for your benefit. A low priced machine is fine for what it is designed for, but if you have to buy a bigger one to accomplish your goals, what did you save? I hope it works out well for you.

 

[Hackerbilt]

Bill.
I don't think letting that mount float is not a good idea. The rear transmission mount actually locates that engine in the fore and aft direction. If it is allowed to move around or tries to rotate it might work your front mounts pretty good. By making that cross member rigid it will add a lot of torsional stiffness to your frame. If you want to make it removable then you might consider adding a threaded doubler to that cross member flange. Make it 1/4" thick and tack it to your frame. Then run the tap into the side of the frame rail. That should give you 7/16" thread engagement. Tap it for a fine thread and you will increase the thread count engaged. Then all you have to do is put a fillet weld around your 1'4" plate to the frame rail. Might find a school shop program that will do it on the fly. Buy them a beer ...opps! make that a root beer and call it a day. Good Luck!

George

Agree with everything you said!
Thanks for saving me all that typin' & splainin'!