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Old 03-30-2021, 07:14 PM
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TheBandit TheBandit is offline
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Join Date: Jan 2006
Location: Ventura County CA
Posts: 4,654
Thank you Graham! Experience really helped on the driver's side. I hope these will prevent any long term damage to the body and give a solid foundation for suspension tuning as I get more into that.

6 Speed Manual Swap

For years and years, I've been wearing away at Mrs. TheBandit with the objective of replacing the TH400 with a manual 6 speed. The cost of a transmission swap can be as much as an engine swap, depending on how you go about things, and I knew the way I wanted to do it would have a considerable financial impact. Mrs. TheBandit has always been supportive of my car hobby and she helps keep me honest and make sure we're putting money in the right places first, like retirement, college savings, etc. We are fortunate to have good income but we don't use that as an excuse and we approach all our big purchases thoughtfully. The time finally came last summer: for my birthday she wrapped up a printout image of a transmission, giving me the green light to make one of my hotrod dreams a reality!

After the green light, researched options intensely, calling different vendors and friends before deciding on an approach. You can skip the following if you're not interested in my thought process on parts/vendor selection :)

The obvious transmission candidate was the Tremec Magnum, but a friend alerted me that the standard Magnum's rearmost shifter position was about 3" forward of where a 4th Gen F-body T56 shifter was located. He had used both transmissions in different 1st gen Camaros and was really frustrated by the forward shifter position on the Magnum. I measured from my bellhousing surface to the firewall, then from the firewall back to where the shifter would be and decided the standard Magnum shifter position was not where I wanted it. This lead to the discovery that Tremec had recently released a new variant, the Magnum-F, which had the same shift location as the 4th gen F-body T56. Compared with the standard Magnum, the disadvantages of the Magnum-F were (1) more cutting required due to the extra length and (2) no mechanical speedometer drive. The Magnum-F shifter position was much more to my liking, so I chose the Magnum-F for my swap. Furthermore, I had the choice of a wide ratio or close ratio gearset. I ran a few calculators and decided the close ratio would work best with my rear gear ratio of 3.73 and tire height of 25.4in. The problem with the wide ratio is the first gear was just too low to be useful without regearing the rear and I didn't feel like the wide spread would offer the "right" ratio selection at lower speeds for the types of autocross courses I do, even if I swapped rear gear ratios. Some conversations with other autocrossers/pro touring folks confirmed the close ratio is generally preferred. Keep in mind this was before Tremec announced the new TKX 5 speed transmission, which may have been a contender if it were available at the time I was looking. The TKX is shorter and does not have the same gear selection as the Magnums, but likely will require less or no cutting to install.

Another important choice was how to approach the clutch hydraulic system. There are a few ways to mount a clutch master in these applications. One of the most common is to use a simple bent bracket hanging off the brake master/booster studs, which will accept an OEM 4th gen F-body master or can be adapted for aftermarket masters from Tilton or Wilwood. DSE and several companies offer variants of this type of bracket. I did not like this method because it leaves a relatively open hole in the firewall and I wanted to use an aftermarket master in case I wanted to change sizes down the road. Another option is a tilting/adjustable mount. American Powertrain offers a version of this. I looked at this option seriously but it also did not have a good way to seal off the firewall. Ultimately the option I landed on is the Silver Sport Transmissions (formerly Keisler) billet mounting system for Wilwood master cylinders. I liked the design of this system because it seals off the firewall and allows use of a Wilwood master.

The next option was transmission crossmember. I looked at quite a few options. One of my friends had some issues with his transmission bouncing using a simple tube type crossmember, so my preference was to use some kind of boxed design. I really like the boxed high clearance design of the Hooker crossmember, but ultimately landed on the Silver Sport crossmember for the benefit of getting everything through one source.

Speaking of Silver Sport, one of the best decisions I made for this project was sourcing the transmission and most swap components from Silver Sport Transmissions. Their customer service is beyond stellar. Every time I had a question or issue, they were quick to answer the phone and offer solutions, parts, etc. I'll give some examples as I go along in this thread. Let's get on with the build...

First up, the "big day" arrived last August when my pallet showed up on the promised delivery date. In this stack of boxes is nearly all the hardware I needed to put the transmission into the car: the transmission, bellhousing, pedal assembly, clutch hydraulics, crossmember, bellhousing alignment fixture, and hardware. Hardware is one of those little things that can really add up, both in the cost of individual fasteners and the many trips back and forth to the hardware store. Silver Sport itemized EVERYTHING - I don't think I had to go to the hardware store once for a fastener related to this swap.

Of course I had to open things up and play racecar simulator right away!

My TH400 was so excited it peed itself. It was nice to see the fluid drained clear and it will be ready for a new home.

Out with the old.

With the old transmission and flex plate out of the way, I got to work installing the flywheel and bellhousing so I could check alignment. I also installed the pilot bearing and posted this photo to my Instagram account.

See something wrong? No? Did you look really closely at the photo? I sure didn't. But Jeff Kaufman at Silver Sport Transmissions apparently did, because soon after I posted this photo he reached out to let me know my pilot bearing was installed backwards! There is a radius entry on one side that is supposed to face the transmission to help with shaft alignment during installation. No worries - I got the right tool for removing the pilot bearing and popped a new one in the right direction. Important note: there is a press-in plug in the back of the LS crank that can get dislodged if you try to use the bread trick to remove the pilot bearing. If that happens you can have a nasty oil leak that will get all over your clutch, so borrow or buy the right tool if you can.

Checking bellhousing alignment is a very important step. Any kind of side load on the input shaft can cause poor/difficult shifting and premature wear. Using the gauge plate provided by Silver Sport, I found my runout was out of spec: the total indicated runout was 0.015in, meaning the center of the transmission was offset by 0.0075in.

To correct this, I bought a set of 0.007in offset dowel pins from RobbMc Performance. This guy was very friendly on the phone and got the pins out to me quickly. Important note: to install these dowel pins for use with a cast aluminum bellhousing, you must cut down the length so they do not bottom into the bellhousing.

The LSx dowel pins install in open holes in the bellhousing. I tried a hammer from the backside to pop them out, but they didn't budge. So I got to work making a tool to pop them out. I welded a bolt onto the foot of a c-clamp and put a socket over the dowel so I could press the old dowel pin out of the block.

Unfortunately that did not go so well on the first attempt.

I grabbed another c-clamp and welded some reinforcement onto it for another try.

This time it worked perfectly and I was able to get both original dowel pins out of the block.

With the new offset dowels installed, the total runout measured less than 0.001in, meaning the bellhousing has less than 0.0005in centerline offset. To be honest that is probably well within the noise of what can be measured effectively with a gauge plate. Time to install the infinitely variable torque converter:

Clutch selection was tough, because there are tons of options and always lovers and haters of every brand and type. After driving a friend's high powered turbo LS Camaro with a Magnum and Monster twin disc setup, I was really tempted to put a twin disc in my Nova, because the pedal feel was so light and easy. But I don't have the power to warrant the cost of a twin disc setup. I also considered the LS7 clutch setup which is a very popular candidate, but didn't like the idea of the weight or the self adjusting system it has which apparently causes issues for some (not many!) people. Ultimately I concluded that you can't go terribly wrong with any of the major clutch manufacturers. I decided on a Monster Stage 2 with a 28lb flywheel, because it was rated to my torque requirements and generally had positive reviews. Having driven the car now, I am happy with my choice - pedal feel is only moderately stiffer than stock application clutches I've used in other cars and it has a good transition.

The next important measurement to check was the clearance between the throwout bearing and the clutch fingers. This is a critical measurement, because if this clearance is too great, the clutch may not fully release. If it's too tight, the clutch may not fully clamp. Either situation is bad. Silver Sport provided shims to get the spacing just right. I used straight edges to measure and ended up with a clearance of 1/8" which is in specification.

Now we get to the REAL FUN - open heart surgery on the floorpan! This big ol' 6 speed transmission most certainly would not fit without making some room. Another advantage of working with Silver Sport is they have a library of cutting templates for many car and transmission applications, some involving just minor cuts here and there, others requiring a bit more space. In my case I used a template intended for a standard Magnum transmission, as a starting point for my longer Magnum-F. I started by establishing a centerline for the template, measuring from the A and B pillar areas to find the center of the tunnel and extending that line using a laser level.

Then I taped the template down and marked out my cut area

My choice of surgical instrument was my trusty angle grinder and cutoff wheel. Minutes later, here's Johnny!

Once the bulk of the cut was made, I took a few additional measurements from the bellhousing and transmission and extended the cut back a little bit to make room for the longer Magnum-F. This meant cutting directly through one of the integrated floor crossmembers, but don't worry - I will show you how that is addressed later on. I will also mention at this point that I later extended this cut even further back to make room to transition the tunnel... but for now this is about the minimum cutting needed to fit the Magnum-F into my car.

It was time...

That's as much as I have time to write-up for today. I will continue the update soon.

Ongoing 70 Nova build:
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