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While it's not a TH400 I'm installing, the 700 I have doesn't have the traditional rear mount pad on the case. Instead, I have to use an extension housing that has the pad on it. This should bring the bell housing face to rear mount length to that of a TH400.
That being the case, I need a crossmember to suit as well as a means to relocate the torque arm. I'd like to keep my current torque arm which uses the OEM clamshell style mount with a poly bushing.
The Hurst and B&M crossmembers no longer have a presence on the internet. Meaning that they appear to be discontinued.
I've come across Spohn and UMI.
I'm liking the UMI over the Spohn in that it looks like the UMI is adaptable to the factory style "clamshell" torque arm mount. Seeing as I have the UMI adjustable torque arm, it's a more economical route in that the purchase of another torque arm isn't required.
Are there any other swap products out there?
Traditional case with pad and holes for rear mount.
Vette case with no mounting pad or holes. Shown with the standard extension housing installed.
Extension housing from a B-body (?) with pad and holes for rear mount.
Using this extension housing should make the 700 the same installed length (bellhousing to rear mount) as a TH400.
I used spohn but it does not leave alot of clearance around trans subframes and xmember for exhaust. With longtubes you gotta go under and around the trans subframe
Can be abit low clearance for street driving depending on car ride height and suspension travel
Yeah. The deal breaker here is the clearance for the exhaust.
When the current exhaust was designed (Hedman mid-length headers, 2 1/2" y-pipe to a Flowmaster cat back 3"), I modified the factory crossmember to provide every bit of ground clearance that I could manage. Even with the car on dropped springs, there's still about 3" from the lowest point on the y-pipe to the ground. Not a lot but enough as contact has been minimal (although some parking lot speed bumps are problematic).
I'm definitely not looking to modify this exhaust as the future plans are to replace in it's entirety, headers to tailpipe, and keep that aside as a workable assembly.
So far, the only aftermarket piece I've found is the Hooker part posted above. I've talked with Toddoky (from Holley/Hooker) and while there are no guarantees it'll work, it is a TH400 swap crossmember with provisions for the torque arm and what looks to be plenty of clearance for the exhaust.
Still working on a decision....
It's not a TH400 going in but rather a 4L60 from a Corvette. As such there is no provision for the rear transmission mount on the case (That was a surprise to both the transmission rebuilder and myself. Unfortunately I don't have much room for recourse with the rebuilder due to our geography).
Instead, I need to use an extension housing from a late 80's/early 90's B-body that has the rear mount provision. With that, the overall bell housing to mount distance is the same (as nearly so) as that of a TH400.
Parts I'm trying to source are based around that.
That said, the only interference I anticipate is around the exhaust. The tunnel clearance and that around the crossmember I hope will be OK.
I would weld a bar on the 700r4 style crossmember and make the new extended housing pad bolt to that lol. Thats a weird swap. Why not use a proper trans rebuilt for your application?
There a few complications with that approach. The extension housing that I need, while it has the rear trans mount pad, doesn't have provisions for the torque arm. It's better to have it off the transmission anyway but this forces me into that. There's also nearly 5" in the difference between the two mounting locations with the new location being further rearward. That said, I can't simply adapt my existing crossmember. It gets messy in a hurry.
The Hooker crossmember (post #2) looks to remedy all of that. I hope.
As for the transmission: a guy that was local to me before I moved across the country has proven to be competent in his building a high performance automatic. I had discussed my specs with him and one thing I asked was for an up to date core to use. He sourced a case from a 91 Vette. He didn't see this issue with the rear mount. Whether he should have known or not is another question. I transported the thing home also not seeing this issue until I was ready to install it. At 2500 miles distance, there's little I can do to replace it. If I were still local I have no doubt that he would step up and replace the case. He'd still do it but getting it to him is beyond the realm of what's reasonable. Or practical.
So, here I am trying to gather the right mix of parts that will allow me to install it properly. Right now I have a home made bracket that adapts the extension case bolt holes to the crossmember. Not the best and certainly something that's likely to fail. The car will be mobile and definitely driveable but from a racing point of view, not the best idea. The bolt holes not only carry the weight of the transmission but they also transmit the motion of the torque arm. Those bolts are only screwed into cast aluminium.
Well you could do a trak pack style torque arm mount which is a bar that goes between the subframes. A short trq arm basically. And then beable to mod the current crossmember. But sounds like the hooker style might work for you better
Funny you should mention the trak pack. Redneckjoe out of Florida just sent me PM about one he picked up 150 bucks. I've thought about those too.
I live in the wrong country as far as being a car guy is concerned. $1.36 CDN for one US buck. And everything has to be shipped. As soon as the border is involved, prices escalate.
could TIG weld some aluminum bar stock to your existing tailhousing or find the b-body one.
BMR makes a th400 crossmember. maybe you can get some ideas from the design? http://www.bmrsuspension.com/?page=p...415&superpro=0
I've considered the welded approach. I'n not sure of there's sufficient material to weld to or enough depth to add a couple of threaded holes. Still, if none of my other attempts pan out (like sourcing the correct b-body part), that may be an option.
I've seen the BMR crossmember. It's very similar to UMI. Problem is, neither offer any room for my existing exhaust . That's something I don't care to change at the moment.
The Hooker part looks to have everything I need. From the part description, it says " to accomplish an LT1/LT4 T56 transmission swap behind a Gen 1 SBC engine ". All that remains is to determine how much difference there is between the early model T56 and my converted 700.
I really miss the old hot rod shop I helped manage. We could build anything. And we did.
02-18-2017, 12:06 PM
