I know there a few threads on ZF6 swaps out there by now. Mine is slightly unusual because of the use of a Spec Super Twin clutch, hybrid Ram/Spec hydraulic throw out bearing and custom flywheel. I bought these parts from a member over a year ago.

While doing the 6 speed swap, also installed a D44 and grabbed the correct length driveshaft and D44 c-beam

One of the unusual parts of this swap was the requirement of a bellhousing spacer plate to allow enough room for the hydraulic throw out bearing to operate.

The instructions I was given stated I may need to use as thick as a 0.40" spacer plate. From my measurements 0.125" seemed to work fine, plus I was worried about C-beam fitment issues so I wanted to use the thinnest spacer possible.
​​​
I suspect a correctly machined flywheel would have been a better way to go, but since I already have these parts I am going to try to make it work. My Corvette has already been apart for over a year now while I addressed other issues, so I really want to get this thing driving again.

As you can see in the picture here, I am just about half a hole off with a D44 c-beam. I am assuming my best option would be to drill the D36 c-beam, factoring in the spacer plate thickness.



One thing I have not tried yet is loosening up the D44 to see if I can get the bolt hole closer to lining up. I had to install the rear to transport the car so it was snugged up without any other driveline components. I don't think that will be enough movement though, and I can't bring the trans up any higher without getting too close to the floor.

If anyone has some better ideas I am all ears. I thought about slotting the holes in the D44 beam, especially since I am using c-beam plates from ZF-Doc, but it still sounds sketchy and it would be messed up to modify an already scarce part.

The best part of this swap is that I am using an unknown condition ZF6 and D44, so it very well could be coming back out again.

 

Interesting... Is your driveshaft bottomed out? Front C beam bolts loose? Engine mount loose (this can provide perhaps ~0.050)? Bat wing bolts loose (this can give you another ~0.040) ? Same misalignment at the top?

I've done the swap on a 1986 but I used a single mass Fidanza flywheel, Spec clutch friction plate with damper springs, and the Valeo type pull style clutch. That 0.125 is certainly not helping.

 

I still have a decent amount of room on the slip yoke of the driveshaft, and the front c beam bolts are loose.

I think I'll try to loosen up the batwing next and maybe lift the trans just a little bit more and see what happens. As much as it sucked to put the c beam in, it wasn't as bad as I expected, so no big deal if I have to take it back apart again.

Is your 86 a 1 piece RMS or 2? I know that was part of the issue with my setup, bolting the trans up to a two piece RMS engine. I am sure by now someone makes a flywheel that will work, but I think the guy who put this kit together had to have something custom done at the time.

This is also my first time messing with a stick shift, so it has been a slight learning curve figuring out the clearance needed for the hydraulic TOB. I kept double checking to see why I would need 0.40" of spacer and it didn't make sense, even factoring in wear tolerance.

I was also told I needed to cut the input shaft guide tube to allow the splines to fully engage with the twin disc clutch, but I left it alone. I think there is plenty of clearance between the clutch disc and the guide tube but I guess I'll find out soon enough.

 

I have the one piece rear main seal... seems like you're off by the thick spacer plate. ZFDOC would be my go-to for helping to sort it out, he's helpful with proper setup of the push type clutch, proper flywheel, other modifications, etc.

 

Loosening up the batwing and using a tapered pin punch to line up the holes was enough to get the bolts in. It didn't take excessive force so I should be okay. I had a long day yesterday and really put zero effort into trying to get the holes lined up.

Just glad it worked out. Now to get the clutch hydraulics done and get the car ready to fire so I can find out of it is all coming back apart or not

 

Hello ACMX92, quick question, what year is your car? Which rims do you have on your car, thank you.

 

My car is a 1985 and I have 18x9.5 Rays Gram Lights 57CR wheels. They are 18x9.5, 5x120mm bolt pattern and +38 offset. These wheels are actually meant to fit an FK8 Civic Type R but the specs work out almost perfect for 84-87 C4 Corvettes. Some do not agree with running 5x120mm wheels on a 5x4.75" hub but I am okay with it myself.

 

I'm having a hard time finding a fitting to adapt the stock style clutch master cylinder to -3 braided line going to the TOB. I tried an m12-1.0 to -3 90* and it would bottom out on the hex of the fitting before sealing. Next I tried an Earls Uniflare adapter and that bottoms at the flare before the sealing washer makes contact with the master.
​​​
I ordered one more adapter fitting to see if I can make this work. I realize the original setup was tubing with metric fittings and a bubble flare at the end, I just figured I could adapt the master directly to AN without having to use tubing in between.
​​​
I have a Tilton 75-812 master cylinder with 13/16" bore but I wanted to try a stock setup first. I have an adapter plate for the Tilton but I need to machine it a bit to get it to work. I also would need to cut the stock pushrod and cut threads into it so that I can make it work with the Tilton. I wish I just bought the After Dark Speed setup from the beginning. After the hassle of trying to piece this together the $400 price tag is starting to sound like a deal.

I was able to bleed the TOB enough to disengage the clutch, which is a relief because I was half expecting to be pulling the trans back out at this point. Once the clutch fitting is figured out I can get the car ready to start and run it through the gears while it is up on jackstands.

 

Took the car out for a test drive yesterday, it fired right up after being in a million pieces for almost 2 years.

I can't believe this clutch and transmission work but it seems like I was able to go in every gear without issue. I was expecting the clutch to be worse but it's not too bad. I guess I must be a wuss because I have just the right amount of travel and pedal effort with the stock master cylinder. I see no reason to go with the 13/16s Tilton in my application. I have the clutch master spaced out so that the clutch and brake pedal are even, and I added an After Dark Speed pedal stop so that I don't over extend the hydraulic TOB.

This car is a million times more fun with the 6 speed and I can't wait to get it all put back together.