47-55.1 TH400 transmission cross member / bracket vs TH350 for a Camaro subframe - The 1947 - Present Chevrolet & GMC Truck Message Board Network

dsraven · 09-12-2019, 05:55 PM

it looks like you were planning to bolt that to the underside of the frame, correct?
I suggest you use a ratchet strap or something (through the truck floor?) to support the trans where the cross member should be and mock up the truck so it is sitting at ride height with power train installed and with enough room under it to work. roll the truck back and forth some, at least a couple of turns of the wheels so it gets it's suspension "set". measure the rake angle of the truck with it sitting on the ground with the weight of the whole truck sitting on the suspension so you can re-create that same angle when it is on blocks. not absolutely required but it makes it easier to level things up and get the engine/trans angle correct without doing a bunch of math. if you have air bags then this step is prolly not required because you can simply set the rake angle you want by adjusting the bags later. the thing is to know the rake angle before you start so you can get the engine sitting at the angle that most oil pans/oil pick up tubes, carbs etc are made to work at. now support the engine and trans using a floor jack or some cribbing or whatever you have to support the trans end of the power train since there is no cross member right now. you can release the temporary ratchet straps from before and adjust the cribbing to get the power train angle you want. usually about 3 deg down at the rear. this is usually the angle that engines need so the carb will sit level and the oil pump will be able to pick up oil from the pan properly and the crankshaft won't be running in engine oil if the angle is extreme. some will say use whatever angle you want and that is up to you. it's just a recommendation. now that you have the power plant sitting at the right angle you should square it up with the frame. you want the engine fore to aft center line to be parallel to the frame whether it is offset to one side of the frame or whatever. the frame on your old truck may be tapered at the front so you are basically getting the power train running at the same plane as the frame is running in. you should do a few dimension checks on the frame to ensure it is square and straight before you proceed. see below link.

https://www.tersenyum.co/47-54-chevy...me-dimensions/

also check the rear axle to ensure it is 90 degrees to the frame so the engine and rear axle are also going to be at 90 degrees to each other. this is important for the driveshaft u joints to work correctly. actually, theoretically, the engine and rear axle could be at whatever angle to the frame as long as they are at 90 degrees to each other. you need the frame to be at 90 degrees to the frame so the truck will run down the road straight and the front end alignment can be done properly. you can use a plumb bob and some marks on the floor to figure this all out.
-drop a line and mark the floor at the engine pulley center and the trans output shaft center. draw a line that connects the 2 and extends out past the rear axle.
-drop a line from the rear axle at the same spot on each side, like the wheel mounting flange axle center (important to be the same place on each side and at the center of the axle center line from side to side). draw a line to connect these 2 points.
-if your power plant is centered in the frame then the dimension from the axle points to the trans output point should be the same on each side. this assumes the rear axle is not offset and is square with the frame as well. you could drop a line from the frame to check if the axle is offset and repair as required first. if the axle is offset the truck will dog track when driving-meaning the truck will go down the road slightly sideways.
-if the power plant is not centered in the frame, like offset to one side, then use some geometry skills and figure out if the axle is square to the power plant center line. measure the dimension from the axle center line to the trans output mark and make a point, on the power plant line at that same dimension, behind the axle. you can basically make 4 right angle triangles if you connect the dots between the axle dots and those 2 dots. assuming the axle is square and centered in the frame, you need to move the trans output over to make the triangles the same in front and behind the axle on each side. this means the dimension from the axle flange to the trans output dot and the other dot behind the axle should be the same dimension. if the axle is offset then this dimension will be different from left to right but should be the same per side. this can mean a bunch of marks on the floor and new lines run each time you move the trans over so a concrete floor would be nice.
-now that you have the power plant square and parallel and at the correct down angle, use some ratchet straps or blocking or whatever, from each side, to keep the trans sitting exactly in that spot side to side sitting on the cribbing so it can't move up or down. measure the dimensions and write them down on something so you can keep checking as you build a new cross member.
-install your trans mount insulator (the rubber part on the trans).
-make a flat metal pad for the mount to sit on. you could easily copy the one from the new cross member with the slots etc in the correct place and at the correct spacing etc.
-bolt that pad onto the mount and place it so that the mount is sorta in the middle of the slots to allow some adjustment later. remember that one day somebody will want to remove the trans pan for servicing so try not to make that a difficult task by making it hard to access the bolts.
-now you can use some poster board or a piece of plywood or whatever to make a pattern for a cross member that will bolt to the frame where you want it and connect to the pad you built for under the trans mount. ensure you leave some wiggle room for how much squish the mount may have with the weight of the trans etc on it. remember the trans pan will need to be accessible and you may need to leave room for the other stuff like exhaust.

I personally think the cross member should be bolted to the upright part of the frame cross section (web) for strength and because holes drilled in the flange of the frame weaken the frame more than if they were in the web simply because there is less material there. there are lots of guys who drill the flange though and are trouble free.
there are also universal cross members out there which have 2 bolt on flanges with a short section of tubing welded on at a 90 degree angle and then a section that goes between them which has the mounting pad welded on. the connector part is usually too long long so it is a cut to fit thing. it can fit to your truck and then be welded where the tubes join or cab be bolted together I suppose. they come in different amounts of drop to accommodate different drive system,configurations. you are basically copying that by doing the above. don't forget to leave room for exhaust pipes and shift linkage (if cable or floor shifted), under floor brake boosters if equipped, under floor battery if equipped etc. think about where and how your fuel and brake lines will run, wiring to the rear etc.

https://www.tdotperformance.ca/trans...0aAtEUEALw_wcB

https://www.summitracing.com/int/sea.../universal/yes

here is a quick video showing the welders series universal mount. since the USD is really good compared to CAD (welders series is Canadian), these may be a cheap way to go as well. they have an online catalogue as well as some videos and have a vast array of universal fabrication gussets, brackets etc. also have other hotrod building stuff like 4 link kits, C notch kits, tubular rods and adjustable ends, urethane bushings, MII kits etc.

https://www.youtube.com/watch?v=dNXxcsyjkX8

https://welderseries.com/Parts-&-Pieces-c13305849

interesting videos on different hotrod themes

https://www.youtube.com/playlist?lis...65IXLfPvUzW8MA

welders series step notch being done by a guy in his garage on a truck like yours

https://www.youtube.com/watch?v=JZUVnCFhXIQ

another done by welders series tech

https://www.youtube.com/watch?v=7aKMV2Zivxw

**Gregski** · 09-12-2019, 06:34 PM

WOW! Thank you so much, allow me to answer you one issue at a time.

Quote:

Originally Posted by dsraven

it looks like you were planning to bolt that to the underside of the frame, correct?

No, I layed it on top of the Camaro subframe, but I think I had the cross member backwards (pointy end to the rear of the truck) because that's how it had the best chance of being closest to the existing holes in the frame, yet this left it 3 inches too much forward in order to mate with the holes in the tail shaft.

I think the proper way to install this cross member is to have it point towards the front of the truck, but if I do that it is not wide enough so I will have to extend both sides, but even then there are no pre existing holes in the camaro subframe to accommodate it this way. I don't know jack about Camaros so I don't know if the late second gens even came with the TH400s. Oh well, I enjoy the learning process.

thanks again for all your words, I am still digesting the rest of them

09-12-2019, 05:55 PM	#1
dsraven Registered User Join Date: Nov 2010 Location: calgary alberta Posts: 8,501	Re: TH400 transmission cross member / bracket vs TH350 for a Camaro subframe it looks like you were planning to bolt that to the underside of the frame, correct? I suggest you use a ratchet strap or something (through the truck floor?) to support the trans where the cross member should be and mock up the truck so it is sitting at ride height with power train installed and with enough room under it to work. roll the truck back and forth some, at least a couple of turns of the wheels so it gets it's suspension "set". measure the rake angle of the truck with it sitting on the ground with the weight of the whole truck sitting on the suspension so you can re-create that same angle when it is on blocks. not absolutely required but it makes it easier to level things up and get the engine/trans angle correct without doing a bunch of math. if you have air bags then this step is prolly not required because you can simply set the rake angle you want by adjusting the bags later. the thing is to know the rake angle before you start so you can get the engine sitting at the angle that most oil pans/oil pick up tubes, carbs etc are made to work at. now support the engine and trans using a floor jack or some cribbing or whatever you have to support the trans end of the power train since there is no cross member right now. you can release the temporary ratchet straps from before and adjust the cribbing to get the power train angle you want. usually about 3 deg down at the rear. this is usually the angle that engines need so the carb will sit level and the oil pump will be able to pick up oil from the pan properly and the crankshaft won't be running in engine oil if the angle is extreme. some will say use whatever angle you want and that is up to you. it's just a recommendation. now that you have the power plant sitting at the right angle you should square it up with the frame. you want the engine fore to aft center line to be parallel to the frame whether it is offset to one side of the frame or whatever. the frame on your old truck may be tapered at the front so you are basically getting the power train running at the same plane as the frame is running in. you should do a few dimension checks on the frame to ensure it is square and straight before you proceed. see below link. https://www.tersenyum.co/47-54-chevy...me-dimensions/ also check the rear axle to ensure it is 90 degrees to the frame so the engine and rear axle are also going to be at 90 degrees to each other. this is important for the driveshaft u joints to work correctly. actually, theoretically, the engine and rear axle could be at whatever angle to the frame as long as they are at 90 degrees to each other. you need the frame to be at 90 degrees to the frame so the truck will run down the road straight and the front end alignment can be done properly. you can use a plumb bob and some marks on the floor to figure this all out. -drop a line and mark the floor at the engine pulley center and the trans output shaft center. draw a line that connects the 2 and extends out past the rear axle. -drop a line from the rear axle at the same spot on each side, like the wheel mounting flange axle center (important to be the same place on each side and at the center of the axle center line from side to side). draw a line to connect these 2 points. -if your power plant is centered in the frame then the dimension from the axle points to the trans output point should be the same on each side. this assumes the rear axle is not offset and is square with the frame as well. you could drop a line from the frame to check if the axle is offset and repair as required first. if the axle is offset the truck will dog track when driving-meaning the truck will go down the road slightly sideways. -if the power plant is not centered in the frame, like offset to one side, then use some geometry skills and figure out if the axle is square to the power plant center line. measure the dimension from the axle center line to the trans output mark and make a point, on the power plant line at that same dimension, behind the axle. you can basically make 4 right angle triangles if you connect the dots between the axle dots and those 2 dots. assuming the axle is square and centered in the frame, you need to move the trans output over to make the triangles the same in front and behind the axle on each side. this means the dimension from the axle flange to the trans output dot and the other dot behind the axle should be the same dimension. if the axle is offset then this dimension will be different from left to right but should be the same per side. this can mean a bunch of marks on the floor and new lines run each time you move the trans over so a concrete floor would be nice. -now that you have the power plant square and parallel and at the correct down angle, use some ratchet straps or blocking or whatever, from each side, to keep the trans sitting exactly in that spot side to side sitting on the cribbing so it can't move up or down. measure the dimensions and write them down on something so you can keep checking as you build a new cross member. -install your trans mount insulator (the rubber part on the trans). -make a flat metal pad for the mount to sit on. you could easily copy the one from the new cross member with the slots etc in the correct place and at the correct spacing etc. -bolt that pad onto the mount and place it so that the mount is sorta in the middle of the slots to allow some adjustment later. remember that one day somebody will want to remove the trans pan for servicing so try not to make that a difficult task by making it hard to access the bolts. -now you can use some poster board or a piece of plywood or whatever to make a pattern for a cross member that will bolt to the frame where you want it and connect to the pad you built for under the trans mount. ensure you leave some wiggle room for how much squish the mount may have with the weight of the trans etc on it. remember the trans pan will need to be accessible and you may need to leave room for the other stuff like exhaust. I personally think the cross member should be bolted to the upright part of the frame cross section (web) for strength and because holes drilled in the flange of the frame weaken the frame more than if they were in the web simply because there is less material there. there are lots of guys who drill the flange though and are trouble free. there are also universal cross members out there which have 2 bolt on flanges with a short section of tubing welded on at a 90 degree angle and then a section that goes between them which has the mounting pad welded on. the connector part is usually too long long so it is a cut to fit thing. it can fit to your truck and then be welded where the tubes join or cab be bolted together I suppose. they come in different amounts of drop to accommodate different drive system,configurations. you are basically copying that by doing the above. don't forget to leave room for exhaust pipes and shift linkage (if cable or floor shifted), under floor brake boosters if equipped, under floor battery if equipped etc. think about where and how your fuel and brake lines will run, wiring to the rear etc. https://www.tdotperformance.ca/trans...0aAtEUEALw_wcB https://www.summitracing.com/int/sea.../universal/yes here is a quick video showing the welders series universal mount. since the USD is really good compared to CAD (welders series is Canadian), these may be a cheap way to go as well. they have an online catalogue as well as some videos and have a vast array of universal fabrication gussets, brackets etc. also have other hotrod building stuff like 4 link kits, C notch kits, tubular rods and adjustable ends, urethane bushings, MII kits etc. https://www.youtube.com/watch?v=dNXxcsyjkX8 https://welderseries.com/Parts-&-Pieces-c13305849 interesting videos on different hotrod themes https://www.youtube.com/playlist?lis...65IXLfPvUzW8MA welders series step notch being done by a guy in his garage on a truck like yours https://www.youtube.com/watch?v=JZUVnCFhXIQ another done by welders series tech https://www.youtube.com/watch?v=7aKMV2Zivxw



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