Do the 6 speed verts have a special chassis brace that goes by the tranny like the auto does ? Google is failing me in my search

 

The stamped steel sheet metal "brace" that bridges under the M6 driveshaft in a 'vert is essentially (if not exactly) the same as for an A4. It's contribution to chassis strength is marginal, nowhere near what SFCs can provide.

 

I do have a auto brace....but I understand the manual one is different ?

 

I'm sure that the "transmission support" (what had been traditionally referred to as a "crossmember") is different between A4 and M6 cars. But that is not what I was thinking you were asking about since you referred to a "chassis brace" that is unique to the 'verts. I'm not 100% positive if this 'vert-unique "chassis brace" is different between A4 and M6 cars, but given where it bolts to the chassis, I don't see any reason why they would be designed differently. As I mentioned, they are stamped steel and don't provide much stiffening to the 'vert's chassis, nowhere near as much as SFCs. Most people toss this piece if they have to do any work that requires its removal. While its been 25+ years since I've had my KBDDSFCs installed, I believe the installer put the "chassis brace" back in (I'll have to get under my car to confirm this). But then again, I may have pulled it 10 years ago when I did my S60 & rear suspension swap.

 

My car is not a vert but I got the brace for additional structure....I also got the vert front engine crossmember cradle....It is 10x beefier than the standard crossmember ....and I do have 3 point SFCs

 

I see. Here's a pic of the chassis brace on my 'vert. As you can see its held in by 2 bolts on each side of the car, and it was removed and re-installed when my 3-pt SFCs were installed (which used the same bolt holes at the 3rd / inboard points).



As you can see, its stamped steel.

 

FWIW, that center brace pictured above looks exactly the same as the stock piece from my T-top cars.

BMR used to make a stronger one many years ago, not the driveshaft loop version but a tubular bar with welded angle mounts. I put one on my '00 car when I installed the SFCs, not sure if it made any difference on its own because the SFCs went on at the same time.

 

Interesting. Am I confusing this piece for another vert-specific piece (which may or may not still be on my car)? I had read long ago somewhere that stated that the 4th-gen f-body 'verts had "additional chassis bracing" that the coupes did not have. I had always assumed that the piece shown in my photo was it. Now I'm totally confused (not hard to do BTW).

 

FWIW, I searched around this site and found an underbody pic of what appears to be an A4 'vert which shows an "Y" shaped brace in the same area as the one I showed above (you may remember this 2023 thread that was started by a now-banned member). It was hard to tell exactly where it bolted up to making it hard to compare to the brace I showed above, but MAYBE........... there IS a difference between braces used for A4 vs. M6 cars, and maybe its (they) are braces used for both coupes and 'verts, and maybe those braces have nothing to do with the so-called "braced" 'vert body????

Regardless, I'm about as confused about this issue now as ever.

 

So here is what I can provide from my personal experience:

From what I have seen, there is no difference in that brace (I seem to recall that it's official name is a "tunnel brace") from M6 to A4 regarding the hardtop or T-top cars. I've owned (two of these from brand new) a '98 Z28, '99 Z28, '00 WS6, '02 Z28, all of them A4 trans and T-tops, and everyone one of them has had that same brace that you pictured above. Additionally, I've worked on several M6 LS1 F-bodies (specifically I'm thinking of a '99 hardtop SS and an '00 T-top Z28) that were all hardtop or T-top cars, and they have also had the same brace you have pictured above.

With that said, I've never been underneath any convertible model LS1 F-body, M6 or A4, so I don't have any first hand experience there. I've never seen (in person) the brace from the pics in that link you posted above. That's not to say that some convertibles didn't come with it (maybe the A4 ones did, as that's clearly an auto trans in that pic), I've just never had the chance to see it in person.

But I know that you bought your car new, so apparently the M6 convertibles came with the same tunnel brace that a hardtop or T-top car would have come with regardless of trans type. That doesn't really make sense if you ask me; I mean, why would the M6 convertible get less bracing than an auto? The only other explanation is that, perhaps, the earlier models (such as your '98) didn't get that more robust "Y" shaped brace regardless of trans type? But then that would also suggest that all of the earlier convertibles (meaning '97 and prior) also didn't get that Y-shaped piece.

So, I suppose, it's either trans specific [but] ONLY when it's a convertible, or it's a model year thing?

 

Thanks, that's some solid testimony. I'll take some solstice in the fact that the factory did what it did when it did and all we can do as owner / hobbyists is to make whatever the factory provided better. While this is an intriguing puzzle from a historical perspective, I'm not going to loose sleep over it.

My advice to the OP is since they already have 3-pt SFCs to not worry about any marginal improvement that these stamped factory braces might provide. But if they can fit it in like was done on mine, more icing on the cake. It certainly can't hurt.

EDIT: Now that I think about how the floor pan may flex when stressed in a rebound situation (think bottoming out all 4 corners of the suspension), I suspect that the floor pan will flex primarily along an axis parallel to the (relatively weak) trans / driveshaft tunnel (which conversely stiffens the floor pan front-to-back more than side-to-side). This type of flex would put a brace like this that straddles across the tunnel into tension, which a simple stamped steel brace would be relatively strong in resisting. So maybe there is more to this brace than I had previously given it credit for.

 

I agree; I like to learn about these interesting factory oddities or rare optional features that could only be had under specific circumstances. It's fun trivia (and also sometimes quite useful) when you are an enthusiast of a related platform.

I agree with retaining the brace (whichever one you have) if at all possible. I did so as well, as it fit just fine with the SLP 3-point SFCs that I installed on mine 20+ years ago. I'm not sure that the "Y" shaped version would be usable with 3-point SFCs though.

As a point of reference, I was able to find that upgraded BMR tunnel brace that I bought for my '00 WS6 ~25 years ago. Here's a link to it: https://www.bmrsuspension.com/product/252

Interestingly, it specifically says in that link "non-convertible only", which would imply that at least some convertibles, under some conditions, must have had some differences that make this part incompatible (such as that larger "Y" shaped piece). What I can tell you from personal experience is that the BMR piece linked above fit just fine in place of the stock stamped steel brace pictured on your M6 convertible, which was the same as the brace on my A4 T-top car. And I was able to reuse it with the 3-point SFCs as well (though I recall having to trim the mounting bracket just a bit to clear the SFC mounting bracket).

So maybe the Y-brace is something that wasn't introduced on the convertibles until later in the LS1 years, or maybe there really is a bracing difference between trans types with the convertibles for ALL years. We'd need more examples/data to know for sure.

 

I'll try to get an underneath photo since my car is stock outside of replacement parts, like shocks, etc...I was looking and looking for existing photos but couldn't find one.

** OK, update. I went out in the garage but it's really tough for me to see underneath the car. I took some so-so photos of the area but I'm not sure I even saw what you guys are talking about. If the photos have any value at all, great, but I probably missed. RPM WS6 feel free to delete this post if no value. Pleas excuse the dirty underside as I haven't washed underneath since the Fall. The car just isn't driven much in the winter.

 

Thanks for the pics NC01TA!

From what I can tell in this picture:



...It appears that your car has that "Y" shaped brace that can be seen in the thread linked earlier by JohnnyB here: https://ls1tech.com/forums/suspensio...l#post20516602 . It's tough to tell for sure based on that angle, but yours appears to be more similar to the Y-shaped one than the wavy stamped steel one that's on my A4 T-top cars and Johnny's M6 convertible.

Assuming you DO have the larger brace, we're still left to wonder if it's because yours is a later model year (2001) convertible, or because it's an auto trans convertible. I guess what we'd really need to see is a picture of the stock brace for either a later M6 convertible or an early A4 convertible.

 

I am unsure as to the level of flex F bod uni bodys have around the transmission area is....but my thought in getting the vert brace is....it cant hurt !!!

I am tempted to dissect the front crossmember to see what kind of bracing is in it

 

Concur w/ RPM's assessment.

Speaking of which, your mention above of the 'vert's front crossmember being stronger (let alone different) than what is used in coupes is the first that I've heard that. Strength forward of the firewall is not something that suffers much (if at all) when the top is chopped, so it doesn't make a lot of sense to strengthen the 'vert in that area. Do you have any further insight to this claim?

 

it is substantially braced inside....and braced with rods outside .....pics to follow soon

 

 

 

on the top and bottom outside there are notches where the inside member is welded