Auto to 5-Speed Conversion (Silver Sport Transmission Tremec TKX) Project Plus

[MoparCarGuy]

I literally just finished an Auto-to-Manual conversion in April 2025 and thought I would share some insights and tips where possible. I did the entire project myself in my home garage without a lift so anyone considering do the same will benefit. My kit of choice was the Tremec TKX close-ratio 5-Speed from Silver Sport Transmission and their customer service was always immediate to answer my tech questions.

This may take me awhile to write-up as the project took from DEC2024 until APR2025 and was done in my "spare time".
Once I dove into it, the inevitable "project creep" happened. "If I am already doing this, then why not do _____" happened multiple times and added further scope to what could have been a much quicker completion.
Bear with me on working this thread. I will post a lot of pictures and commentary of lessons learned.
I do want to preface that I had other posts asking some specific questions and I got great answers from our forum subject-matter experts. Kudos and thanks to everyone who replied to those posts.

And to spark the thread...

How do I get the 727 Auto out and the TKX in? Answer: Wheel Cribs
I made these from 2x4's using YouTube videos for the design.

Delivery of Kit and Unboxing:

I had purchased the HURST logo pistol grip shifter handle separately.

More to come!

 

[Challenger RTA]

Auto-to-Manual conversion

If only it is as easy as making a post. Thanks form the curious ones here.

 

[rklein71]

Just did my conversion a few months back. Everything fit great.

 

[MoparCarGuy]

I had collected a ton of photos, videos, and other installation info prior to purchasing the kit. This series of 7 videos had great details.

1 71 Challenger Tremec TKX 5 Speed Manual Swap Episode 1 - YouTube
2 71 Challenger Tremec TKX 5 Speed Manual Swap Episode 2 - YouTube
3 71 Challenger Tremec TKX 5 Speed Manual Swap Episode 3 - YouTube
4 71 Challenger Tremec TKX 5 Speed Manual Swap Episode 4 - YouTube
5 71 Challenger Tremec TKX 5 Speed Manual Swap Episode 5 - YouTube
6 71 Challenger Tremec TKX 5 Speed Manual Swap Episode 6 - YouTube
7 71 Challenger Tremec TKX 5 Speed Manual Swap Episode 7 - YouTube

Wheel cribs made. Kit components on hand and then it was time to get the car in the air. Unfortunately, I did not take time to do videos. I did do a few short segments and will include those as I document further in this thread.

 

[MoparCarGuy]

I did not take pictures of the interior removal. Installing the 4-speed factory tunnel (AMD part) requires carefully cutting out the auto tunnel, avoiding the crossmember in the same area. My floorpan had the reproduction tar-like underlayment installed back in 1999. It appears that underlayment caused some nasty-looking surface rust which required some sanding and treatment. I planned to install modern damping material prior to installing the proper carpet for a manual transmission (tunnel is much larger so carpet is unique). Several of the rubber/plastic plugs needed replacement as well due to age.

Here are some photos.

 

[MoparCarGuy]

HINDSIGHT TIP: I installed the 4-speed factory tunnel without installing the transmission. That turned out to be a problem. Specifically, the TKX requires the engine/trans combo to be tilted downward which can create clearance issues at the factory 4-speed tunnel. I highly recommend that you install the transmission and mockup the new AMD tunnel first so you can determine if the new tunnel needs to be slightly raised (above the factory location). Now is the time to find that out.

During the floorpan work, I planned for the tunnel cutouts (two areas which avoid the factory crossmember) by mocking up the new AMD tunnel. Removing the console bracket for the automatic shifter was pretty straight-forward. I used a cordless 18V Ridgid cutoff tool and cutting discs. The rear console bracket is the same for automatic or manual so it remained in place.

A printed photo of the cutouts from the Internet added further confirmation of the cuts. TIP: Check everything above and below the tunnel prior to cutting so you do not have to repair anything due to making a mistake.

My original plan was to MIG weld the tunnel in place but the thought of sparks flying everywhere in my interior was scary. I considered using a wool blanket and welding underneath it but switched gear and sprung for a panel-bond adhesive installation. This turned out to be an excellent method and guarantees a permanent seal underneath the seam sealer.

Panel bond prep was very easy and I used self-tapping screws around the perimeter as well. The screws were left in place and seam sealer covered them above and below. NOTE: The crankshaft pilot bearing and flywheel are installed at this point but I will cover that later in the thread.

Panel bond adhesive completed:

 

[rklein71]

I like to spend a few minutes and take a hand file and remove any sharp edges. It sure saves you from nasty cuts on your hands and makes a more detailed install. I did this on the casting flash on my TKX tranny and the newly cut floor board sheet metal. In the future I can work on my car with a little less worry.

 

[MoparCarGuy]

With the tunnel metal installed, it was time to use seam sealer, prime, paint, and install damping mat. I looked at a variety of seam sealers and determined it would be easier to just use Polyurethane Construction Adhesive and Sealant by DAP. Very easy to work with and the cost is minimal per tube (approximately $10/10 oz tube). I also replaced any of the factory sealer that was cracked or crumbling while I was at it.
You may notice I removed the instrument cluster in some of the photos. More added tasks which included a new solid-state IVR, LED bulbs, and a voltmeter to replace the ammeter.

 

[tonysrt]

So even with a stock 4 speed tunnel the tranny didn't fit. So you had to use their tunnel, silver sport, to fit it. I thought they advertise exact fit? Why do these companies lie to us, so we buy their products and now are committed to make it work.

 

[MoparCarGuy]

727 Automatic Transmission Removal: The circa-1999 TCI Streetfighter transmission has worked perfectly for 25 years. The valve body was modified back then using a B&M Manual Pak forward-pattern kit which removed the need for throttle-pressure linkage but required manual shifting using the slap-stik shifter. The 10" converter was from J&W Transmissions and provided approximately 3,500 RPM stall speed. The need for ATF lines to the radiator vaporized with the TKX swap so those were pulled as well.
First was to remove the 3" TTI exhaust setup and H-pipe. X-pipes were uncommon in 1998-1999. I removed the mid-pipes and left the Walker Dynomax Super Turbo mufflers in place. No photos of the exhaust removal (argghh).
I also removed the rear valance since banging around on the exhaust pipes could possibly damage the rear exhaust tip openings in the valance.
I also removed the Hooker 5209 Super Comp 2" headers in favor of new TTI 1-7/8" headers (TTI headers should be mandatory for spark plug and other clearances).

Next, I dropped the homemade driveshaft loop and driveshaft since I would be ordering a new driveshaft through Silver Sport and then I removed the 727.
A seriously stuck converter bolt finally came out after trying about everything from torch heat to grooving the bolt head. I did not want to cut off the SFI 8-bolt flexplate ear so I order a cheap set of bolt extractor sockets. That socket removed it instantly.

 

[MoparCarGuy]

So even with a stock 4 speed tunnel the tranny didn't fit. So you had to use their tunnel, silver sport, to fit it. I thought they advertise exact fit? Why do these companies lie to us, so we buy their products and now are committed to make it work.

Actually, the TKX fit with far >1/4" of clearance all around but was tightest at the very top (1/4") resulting in the engine/trans being tilted downward 3.45° with a supplied crossmember spacer. SST supplies spacers to raise the TKX in the SST crossmember but raising it too much will cause the case to hit at the very top. I used the new AMD tunnel in the stock location and everything worked out fine. Every car is slightly different so a test-fit of the transmission and AMD tunnel sheetmetal can eliminate any potential clearance issue AND improve your driveshaft operating angles.

My advice is to raise the AMD tunnel about 1/4"-1/2" higher (only after you mock it all up and check) so you can bring the TKX up and have a slightly better driveshaft angle.
My driveshaft and pinion angles are below.

 

[MoparCarGuy]

The next step was to remove the factory crank pilot bushing, clean the recess, and install the supplied pilot bearing. A bushing extractor tool removed it with ease and the new pilot bearing was installed as per the instructions.
Next, the flywheel was thoroughly cleaned with brake cleaner and installed to proper torque spec. The McLeod SFI-spec flywheel is 10-1/2" and 130T (teeth) and SST supplied new flywheel bolts.
NOTE: The centerlink has been removed along with the Hooker headers.

 

[MoparCarGuy]

The setup of the bellhousing runout to index the crank register and bellhousing to within 0.005" was a learning experience. Not complicated but needs to be done correctly. Once you run through the process a few times it is not too bad. You will benefit (on big-blocks) with a flywheel turning tool since the big-block inspection cover is removable and allows for easy turning of the flywheel from below the vehicle versus turning the crankshaft with a socket from the front.

Modern transmissions are very sensitive to input shaft misalignment issues so do it right the first time and protect your investment and warranty.
My final runout was 0.00145" which is almost 3-1/2 times better than the allowable 0.005".

I used RobbMC Performance alignment dowels (PN 1019 .021" offset ) to correct the alignment after correctly determining which dowels were needed.

One of the STOCK DOWEL PINS before and after removal using a pair of visegrips and a small hammer to tap it out:

NEW 0.021" Offset Dowel Pins Installed and oriented to 2 o'clock for my required correction (concentricity):
NOTE: I locked down each dowel's center set screw after setting them using my digital angle finder on the dowel "flat" at approximately 30.50°-30.75°. That is a 1/4° of accuracy.

 

[MoparCarGuy]

Next was to install the clutch and pressure plate with the bellhousing. I painted the bellhousing and inspection cover the normal street hemi orange. The setup of the hydraulic Mantric Clutch Slave Cylinder (CSC acting as a throwout bearing) is part of the bellhousing installation, too. The CSC must be set up to provide a cushion with no air gap when the clutch is fully released. Clutch wear is "taken up" by the CSC since it has enough travel to compensate for the wear.

I found this process to be very straightforward and logical. My installation required three (3) 1/4" spacers. The kit came with two (2) 1/4" spacers. A call to SST and they had a spacer shipped immediately to me for free. Two days later, I got the spacer. There were plenty of other items I was doing to fill the time so no delay in the project at all. Thanks, SST!

WARNING: It was at this point that I re-installed the mini-starter and mistakenly put it in the outer position for an 11" clutch. The bellhousing has provisions for the upper stud and lower bolt for either 11" or 10-1/2" clutch. I did not find out until start-up day. LOL. Starter engaged and freewheeled but I figured it out immediately and made the correction in about 20 minutes thanks to the phenomenal fitment of the TTI headers to starter clearance.

 

[MoparCarGuy]

Obviously, I am not going over all of the basic mechanical for aligning a clutch/pressure plate in order to install the transmission but here a few of the photos I took.
The transmission went in fairly easily up until the last inch or so. SST is rightly adamant about not using the transmission bolts to "pull" the transmission into place. Broken ears and a nightmare were not in my plan and I was pleasantly surprised that the transmission went all the way in with just arm-strength. The angle of the transmission jack was super critical for this as I am working under the car with minimal leverage. A lift would make this so much easier!
Anyway, the results were great.

 

[Mopar Nut]

The setup of the bellhousing runout to index the crank register and bellhousing to within 0.005" was a learning experience.

Did you use Silver Sport Transmission‘s YouTube video for that?

Great write up.

 

[MoparCarGuy]

Did you use Silver Sport Transmission‘s YouTube video for that?

Great write up.

I did watch the SST video and quite a few other videos for checking the runout. It is not that difficult once you run through the process.

 

[Mopar Nut]

I did watch the SST video and quite a few other videos for checking the runout. It is not that difficult once you run through the process.

The video made it look easy.

 

[R4Sedan]

Very nice, great looking car as well.