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So, I made arrangements to have a highly spec'd 700R4 built.
All the good stuff and more.
This was from a builder I'm acquainted with through a mutual racing friend. However the two of us live on opposite sides of the country. I picked the transmission up over the holidays as I was home for a visit.
Now the good part. Seems this transmission, which research tells me came from a Corvette, (hence the large letter "V" on the bell housing part of the case), has no provisions for installing the traditional OEM crossmember mount.
Returning it for the proper case and all the internals isn't even remotely practical given our geographical differences. My question to the crew here at Thirdgen is: Has anybody encountered this before and what were your remedies?
I've started plans on building a bracket that will attach to the tailshaft bolts and will provide a platform for the mount to attach to. Maybe there's an aftermarket version already in existence?
1). Traditional case with bosses and threaded holes for the transmission mount.
2). "V" case (Corvette) with no bosses or holes. There is however a common surface between the two styles of cases. (Thirdgen tailstock housing installed).
The only thing that comes to mind would be to TIG some material or a plate on there, and then drill\tap it for your mount. Or swap all of the guts into your existing case (providing it wasn't damaged - I can't recall the specifics).
This is the hardest thing for me about paying other people for work, especially over long distances. It's always such a huge letdown when something turns out to be wrong. And we all know Murphy's law visits more often than we'd like.
I really hope you're able to get it figured out without too much hassle.
Edit: It appears that the crossmember mount was cast into the tailhousing rather than the normal pad location. It also appears to be a little shorter than the tailhouse used on F-body cars, so I'm not even sure you could use a Vette tailhousing and relocate your crossmember... Which wouldn't work anyways, as you have to mount your torque arm to something.
Swapping the parts out isn't a reasonable option for a number reasons.
That leaves me with either a) adapting something to the transmission to accept the traditional mount or b) fabricate a new crossmember and use the Corvette tailshaft housing. (picture below).
I'm inclined to go with the first option.
Welding something to the case is an idea....but I think a piece of steel angle with the vertical component attaching to the tailshaft housing bolts (lower two of the four) and the horizontal component creating the surface to install the mount to.
EDIT: Yes, you make a point about the torque arm mount. Totally forgot that bit. Makes me more inclined to adapt to the case itself.
Something else that's different between the two transmissions is the length. Fortunately, the overall difference in length between the Corvette case and the regular case isn't a factor here. As it happens, my driveshaft ended up being a little too long after the swap to a Dana 44 from a BW 9 bolt. That's something I've never corrected. The shorter Corvette unit works out well in this case.
But damn....
Well, if there's a sunny side to all of this... At least it's still February. I'm not sure about Alberta, but around here it usually takes until April or May for all the salt to get washed off the roads.
Nice score on the Dana!
I'm sure someone might come up with another alternative at some point, but if it were my car, I'd be leaning towards TIG welding a plate... Or maybe even just building up a pair of bosses with a TIG... I'm not really sure what the capabilities of welding cast aluminum is. All I really have experience with is iron\steel.
Buy or fab a crossmember to get your torque arm off the trans.
Get one for the TH400 / 200-4R mount location.
Install a Caprice extension housing and regular mount.
Your picture in post 4 is a Caprice, not Corvette housing. Since you won't have the torque arm ripping upwards, you don't need stiff, noisier poly, you can go rubber.
Verify the output shaft ( Vettes are shorter) and the slip yoke have proper engagement through full suspension travel.
Done.
Hmm. The last Caprice transmission I purchased had provisions for the transmission mount cast into the case, not the extension housing. That was the unit previous to this one. My understanding is that it was from a '91 Caprice. (1st picture, post 2)
I'm not sure what to think at this point.
That's this a Vette transmission makes it 7/8" shorter from the face of the bell housing to the tip of the output shaft. That's fine as my driveshaft should be about an 1" shorter. The extension housing though using the f-body part still keeps the overall case dimensions the same so clearance at that point (housing to radius in yoke) is as it was before. Close but still OK.
I agree with moving the torque arm off of the transmission. That's a part of the OEM arrangement I never liked however that's more purchases and additional work. What's more is that my exhaust was built first and the stock cross member modified to fit around the pipes. Any changes there will be something that's organized down the road.
As a project, there are always plans moving ahead (and sometimes sideways as in this case). One of the plans is to replace the exhaust system in it's entirety. Headers, a manufactured cat-back setup like Holley's, built collector extensions to connect the two and then another crossmember built to fit around that. (Easier a crossmember than exhaust pipes for me).
I can see the new crossmember. torque arm, getting a different extension housing, making that all work together and adapting the whole thing around the exhaust is probably the way going forward. (Maybe way forward).
For now though, initial thoughts are to build something that will adapt this transmission to the current platform without ruining either. It should be compact and efficient from what I've worked out so far however, it's still an adaptation. Not that that's anything new to hotrodding.
Buy or fab a crossmember to get your torque arm off the trans.
Get one for the TH400 / 200-4R mount location.
Install a Caprice extension housing and regular mount.
Your picture in post 4 is a Caprice, not Corvette housing. Since you won't have the torque arm ripping upwards, you don't need stiff, noisier poly, you can go rubber.
Verify the output shaft ( Vettes are shorter) and the slip yoke have proper engagement through full suspension travel.
Done.
Follow up:
It seems the Caprice transmission has provisions for the mount on the case and the extension housing. That bit of information from the racing friend who has been the middle man on several transmission projects for me.
For now, I've fabricated an adapter that should allow me to install the transmission and keep the rest of the infrastructure the same.
My only concern is that I've re-engineered the attachment points and may be putting too much stress on the extension housing bolts. As they were, they transfer the upward energy of the torque arm movement to the crossmember. This new adaptation will do the same thing, just in a different way.
After this season is through (and hopefully the car will still intact until October), I'm incorporate the changes mentioned above. That is certainly the best fitment of the torque arm, having it connected directly to the crossmember. The tough part is, one thing is connected to another and then another so any changes will be very involved. Probably to the point of a new exhaust to go along with the crossmember, trans mount and torque arm.
I hope to have the transmission back in the car for a test fit today and will make the final few cuts on the adapter.
Buy or fab a crossmember to get your torque arm off the trans.
Get one for the TH400 / 200-4R mount location.
Install a Caprice extension housing and regular mount.
.
That raises a question.
Seeing as the 700R4 is the longest (in overall length) of the automatics, wouldn't putting the transmission mount of the tail housing make if even longer? Longer as in the position of the mount itself relative to the car. So much so, that any crossmember will have to fabricated rather than bought? It looks like from the pictures posted here, that the Caprice housing will set the mount rearward another 6" or so. The TH400 and 200-4R, although their mounts are built into the tail (as I understand anyway), would be shorter from bell housing to mount.
It's going to be a lot of work any way you look it.
The B-body had the 200-4R before it got the 700-R4.
So it made sense to reduce the number of crossmembers in production to one that worked for every Caddy, BOP, and Chevy.
The length of the transmission is a separate issue I already addressed: Vette output and tail housing are shorter, so check yoke engagement. The Th400/ 200-4R/ B-body mount location will be served by an aftermarket crossmember.
Your bracket looks pretty good. 3 thoughts: triangulate when you can instead of letting the L take all weight. about the 2-bolt mounting: 4 would be cool. And if you're worried about stress to those bolts but you're talking about not removing the tq. arm from the tail that adds stress, you're not that worried?
I'll have to look further into what's available for crossmembers although, due to the exhaust, nothing off the shelf is bound to fit. When I'm referring to length, I'm talking about from the face of the bell housing to the centre of the rear support. It seems to me that if the B-body tailshaft housing with integral support is added to the 700, then that really stretches things. Is that going to make it longer than a TH400, bellhousing to mount? I'm going to go to my transmission chart to see what the differences in dimensions amount to.
To answer one of your points, yes, I've addressed the driveshaft yoke engagement and spline to spline, there is about 7/16" less than the original. That would be the overall difference in tailshaft length between the regular 700 and the Vette. It's 7/8" actually however the Vette shaft is cut off clean at the splines whereas the more typical shaft has a bullnose which adds 7/8" of length but only half of that is splined (is that confusing enough?)
As for the bracket and overall installation. If I had a welder (or any of the other shop equipment that I had prior to moving cross country) I'd have approached it differently. As it is, what you see was done with an angle grinder and a cordless drill. With the fully equipped shop I would have gone straight ahead with a suitable crossmember and tail shaft support.
My thoughts really are that the whole thing is a compromise. As discussed, the perfect arrangement will incorporate your suggestions. For now, this new adapter is ready to go having been test fitted (looks pretty good under the car) and painted yesterday.
I'd be interested to know at what power levels and under what circumstances the extension housing mounted torque arm experiences failure. In all of my years with these cars and here at Thirdgen, I've never come across an example of a broken installation despite knowing that this is a weak point in the design.
A quick follow up:
I see now how moving the rear transmission mount to the extension housing of a 700 would make it very close to or maybe exactly the same length as the TH400 or TH200-4R. Interesting.
If I can source a crossmember for a thirdgen f-body TH400 swap, perhaps it can be fitted with a minimal amount of modification. Something to look in to.
The 700 is shown with the rear mount in the case. If it's relocated to the extension housing (as in a B-body?) then that might make up the 4 15/16" difference.
There's not a lot room available for adaptation. Certainly, the y-pipe would have to modified.
Your picture in post 4 is a Caprice, not Corvette housing.
That bit of information surprised me.
This just came across my computer screen.
Thanks for the heads up. (And I did end sourcing a Caprice extension housing)
Vette on the left (a C4 I think) and a traditional 700 on the right. (Caprice not shown)
Resurrecting this long dead thread as there were some very insightful comments on a remedy.
After having test fitted the Holley crossmember just the other day (progress has been slow to put it mildly although expensive!) things have cascaded into several different fitment issues.
For anyone still around and interested, the link to the new thread is:
02-14-2017, 10:52 AM
