55.2-59 Need help with 55 Pickup V8 and 700R4 Swap

[lpmorgan]

I have a 2nd Gen 55' 3200 pickup and am trying to swap in a 350 and 700R4.

The specific question I have is should the trans clear the original crossmember ordo I need to cut it out? I hate the idea of cutting it out because its right where the rear of the leaf springs mount to the frame and I'm concerned about giving up that strength.
Pics of anyones setup would be greatly appreciated. Thanks

[dennislbrooks]

You will get varied responses on this as it has been kicked around before. Here is one thread.

https://67-72chevytrucks.com/vboard/...d.php?t=830279

Engine mounts will vary also.

Here is one but I also fabricate.

https://67-72chevytrucks.com/vboard/...d.php?t=831444

[Hcb3200]

What he said.
For some reason I read the rear leaf spring mount the first time and not the front leaf spring rear mount.

[dsraven]

if you cut the original trans crossmember out then it allows the frame to flex and that is not good for the cab mounts, door opening and closing consistently well, paint around the door (if you have tight gaps especially)
I have suggested this before, to support the frame with something else that simulates the crossmember in width and will hold the frame at the correct width, then cut the cross member out below the frame so it can have tabs welded on to allow the old cross member to be installed with bolts after the engine has been placed. back in the day, as a heavy duty mechanic, some medium and large trucks did this, a removeable crossmember to allow servicing of major drivelne parts. when done the temporary crossmember can be removed. then build exhuast around the crossmember after the bolt in but think about that part when building the bolt in plates or tabs. the crossmember can be lowered a little to accomodate a low set engine ot a trans pan etc

[1project2many]

The specific question I have is should the trans clear the original crossmember ordo I need to cut it out?

The engine and transmission can be installed so there is room for the transmission above the crossmember. These trucks were available with an automatic transmission. Factory installation placed the front of the block just behind the rear of the front crossmember.




If you install the engine farther back it is very likely that you will not have enough clearance to install a factory dust cover and that the transmission pan will be challenging to remove if you need to service the transmission.

as a heavy duty mechanic, some medium and large trucks did this, a removeable crossmember to allow servicing of major drivelne parts.

Yes! I feel like some of the square body C60s were like this. Careful work with a sawzall would allow the crossmember to be cut out so flat plates could be welded at each cut. Four 1/2" bolts would be more than enough to tie everything together. The removed section of crossmember could be re-used, installed below the transmission flex plate cover.

As an alternative a person might be able to locate a transmission from a 4X4 truck. These units use the flexplate cover as part of the engine / transmission mounting and use six M10 bolts to retain the cover. Maybe it wouldn't be too hard to fabricate mounts to connect this transmission to the OE crossmember.

[57tailgater]

I was thinking the hydramatic mounting consisted of a 3 piece crossmember to allow for servicing. Basically the same as the 1 piece but with the middle section removable for transmission servicing. Was looking for a picture but haven't found one. I agree with raven to not remove the crossmember totally as there's too many things mounted in that area of the frame rail. 1project's suggestion would be good.

[qbeanie]

My truck was an original automatic model. There is a factory diagram that shows the support with fasteners. I can’t locate but it’s out there. I have a 700r installed. The support requires notching to allow the 700r dust cover to fit .

[57tailgater]

Found a picture from the factory assembly manual for the 3 piece crossmember. Found on page RPO 314, sheet 7.00.

[dsraven]

wow, that took some digging. never seen that one before but good to see it and how they bolt together

[mr48chev]

I had to read this a couple of times. It is the norm to remove the crossmember that goes under the bellhousing when doing a late model automatic trans swap.

The main issue with AD or TF trucks is that when you do eventually the weight of the cab will push down on the outrigger cab mount brackets and twist the frame rails until the cab settles on the frame rail. That causes the hood and nose to not fit right and other issues. Either boxing the frame or even affixing a mount pad on top of the frame rail to keep the cab from settling should handle that.

[dsraven]

if you plan to cut the crossmember ans fab up a system like the original in the diagram, make sure to brace the frame nearby with a temp crossmember of sorts first, otherwise the frame may spring and your new fab job may not be made to fit the orignal frame width and may also ja, your zip disc or recip saw blade.
will you ve using an IFS front suspension? since their crossmember is also helping keep the frame from twisting, because it is a little further back than the front crossmember is originally, you will want to do some corner to corner frame checking (for squareness), a check for straightness and a check for frame sag BEFORE you do anything else.
personally I like the idea of the removeable crossmember using the original frame mounts and possibly a fabbed new center section or a modified original center section. it does it's job as intended but can be removed if needed.

[57tailgater]

Originally Posted by dsraven

wow, that took some digging. never seen that one before but good to see it and how they bolt together

Yeah I knew it had to be in there somewhere! They had them on AD's too and I actually had an AD one at one time I was going to use for a transmission mount but it was too narrow for what I needed.