Tremec TKX 5-Speed Conversion

[CoronetDarter]

As much as I enjoy driving the Coronet, whenever we take long trips, like to the Mopar Spring Fling in Van Nuys, I take the Dart because it has an ancient Keisler Engineering Tremec 5-speed and I can cruise at 65 and 2,100 rpm. I've been mulling over converting to the Tremec for years but there always seemed to be something else that took precedence.
And then one night it just happened. The wife and I were on the couch on a Friday night watching a Mecum auction on TV. I started ruminating again about swapping out the auto when Maria turned to me and said to just do it now because later on I'm not going to do it. What she was referring to was my earlier decision to retire in early 2024, and knowing that once I'm on a fixed income the Tremec will most likely be out of reach. So who am I to argue with my wife? The next day I got on the phone with SST and ordered the kit.
That was back in May. It's been sitting on the garage floor ever since. Summer set in and next thing we're busy most every weekend, taking camping trips and hanging with family and friends. We got back from our Yellowstone vacation the Labor Day weekend, squeezed in one more camping trip and now I'm ready to dig into the project.

There have been several threads on this subject, with Greg Kern's swap into his Charger being the Go To reference thread. But I'm sure I'll run into my own set of issues that will bring some uniqueness to the conversation. So here we go.

 

[1 Wild R/T]

Do you have a lift? It make those kind of jobs sooooo much easier...

 

[CoronetDarter]

First a short background on the car. It's a 69 Coronet 500, from the factory with a 318 2V, 3 spd auto on the tree with a 3.23 geared, 489 8 3/4". Somewhere along the way a PO swapped in the 440. I bought the car on an Ebay auction back in Sept 2013. I'd already had the Dart and was "just looking at B-bodies". The wife was away for the weekend with her girlfriends, leaving me to my own devices (so it's partly her fault). The car was in Texas with a reserve, so I threw in a figure. Reserve Not Met. Added another $1,000; RNM. I started getting curious, bumping up my bid in $500 increments wondering where this thing would land. Well, I found out; $13,000. Sunday afternoon Maria walks in finding me and two of my car-buddies huddled around my computer screen. Asking what's up, Steve turns to her and says "your husband's about to buy another car". Sure enough, timer went to 0 and I was the only one to bid!
Long story short, I drove the car for about a month and had an accident - the left front tire decided to chart its own course and left the Coronet with a crumpled fender. After a 2 1/2 year resto project, it's now been on the road for about seven years. The link below is to my resto thread:

My 69 Coronet project

I'm a long timer lurker, 8 month member with my 69 Coronet 500. The car wasn't bought as a resto project, instead I was planning on driving and enjoying it while making periodic upgrades. The Coronet was originally a T7 Dark Bronze, 383 2V with a 727 on the column, bench with a buddy seat...

www.forbbodiesonly.com

 

[CoronetDarter]

Do you have a lift? It make those kind of jobs sooooo much easier...

Great question. I'll get to that shortly...

 

[CoronetDarter]

Fast forward to present day. The car is modeled after an R/T, but I wouldn't call it a clone. I didn't like the 500's chrome moldings so pulled them off, welded up the holes and painted it 2013 Challenger Toxic Orange (orange is the wife's favorite color, go figure). The engine was rebuilt by a local machinist that knows Mopars. It has a Hughes Engines valvetrain with a hyd FT cam; Icon pistons at about 10.1:1 compression, 440 Source aluminum heads, Eddy aluminum intake, 800 cfm AVS carb and Doug's headers. The 727 was rebuilt by a local shop and has a Frank Lupo Dynamics 3,000 stall converter. The 3.55's were swapped out of the Dart (it got 4.10s). Over the years I added the fiberglass hood and R/T stripe.
It makes for a real nice cruiser, but with the 3.55's the engine's at 4,000 rpm just keeping up with traffic. Honestly, over the years I've been debating whether to sell the car or get the 5 spd because I don't drive it at all out of town.

 

[CoronetDarter]

As said earlier, the kit came from Silver Sport Transmissions. American Powertrain is the other well known dealer. I've bought from both over years, getting parts for the Dart's Tremec. I just seemed to have a better experience with SST; nothing against AP at all. But you have to pick one, and SST got the call.
It's the new TKX model, close ratio with 2.87 1.89 1.28 1.00 .68 gears. After the tranny is installed and broken-in I'm swapping out the rear gears for 3.91's.
The kit comes with everything you need for the swap: bellhousing, clutch, flywheel, pilot bearing, trans mount, pedals, speedo cable, fluids, and various odds and ends. I upgraded to the hydraulic clutch and pistol grip shifter. It's not a cheap decision; all in it was $6,800 with shipping. It'll be installed with just a shifter boot, no console.
With the 2.87 first gear and 3.91's the car will be a beast off the line, and the OD will be such a pleasure to drive on the freeway. I am so ready to fall in love with this car again.
First order of business is to strip the interior.

 

[Kern Dog]

Do you have a lift? It make those kind of jobs sooooo much easier...

Heh heh heh.....I know a guy.

He has a little experience with the swap too.

 

[1 Wild R/T]

Heh heh heh.....I know a guy.

View attachment 1531570

He has a little experience with the swap too.

DO IT!!!!

 

[Kern Dog]

 

[1 Wild R/T]

Greg, have you finished the Borgeson swap?? Sounds like it's trans swap time....

 

[Kern Dog]

The trans in my car is the last of the TKO-600 series. MY ratios are similar but 5th is .64, not much different from the TKX. I have 3.55 gears in mine but when I first installed the 5 speed, I had a 28" rear tire. My RPMs dropped 36% in 5th. It is basic math...the TKX with the .68 5th gear reduces RPMs 32% so if you're pushing 3500 at 70, you'll be around 2350 with the TKX.
IT was a huge eye opener for me how much smoother the car felt at speed with the overdrive. We are all so used to the comfort of our later model cars that we forget how much easier they are to drive. The reduction in RPMs makes a huge difference in how the car feels on long trips.
I've been to the Spring Fling with a variety of arrangements. Once with a 727 and a 3.23 gear, another with a 727, GV overdrive and a 3.91 and then the Tremec and a 3.55. The last one was by far the easiest to live with. The lower RPMs advantages are more than just the sound of the engine. The spinning of the fan, the alternator, the resonance of the exhaust system, the vibrations....all are reduced.
In 2022, I got 15.1 mpg while still driving 70 mph. This is with a 493 cube mill running an 850 Demon 4 barrel and a '528 solid cam. A smaller engine at 65 could turn closer to 20 mpg.
We're not into these cars for the mileage but when we are able to defy the odds and actually make notable improvements with no downside, I call that a win. Improved mileage has a huge side benefit....longer range to a tank of gas. I used to count on 200 miles from fill ups leaving a slight safety margin.

 

[1 Wild R/T]

Damn, I thought Lincoln was further from you than it is... You guys are practically neighbors....

And FWIW I think the 3.55's are actually a pretty good gear with the TKO/TKX.... I'm afraid the 3.91's are gonna be to low mostly making 1st pretty useless...

 

[BMosely]

I have the SST TKX in the ‘68 Coronet and would do it again in a heartbeat. Few things, indexing the bell housing is critical and will most likely require offset dowels. You will need to do a mock up first and measure before you know what you need so add a week for the mailman to your schedule, lift time.
The Wylwood slave cylinder is far superior to the OCB(sp?) chinesium crap. I do not know why SST would include that junk in such an expensive package. If they sent that one, change it to or you will be back underneath when it fails internally. There are actually 2 choices on the slave throw. .750” and .625”. They do not give you a choice but they should. The .750” gives a much shorter throw but delivers a heavy pedal. I have run both and kept the .750” in place. It depends on your driving style but for slamming gears I want it short and to feel the pedal. You will need to make a pedal stop that is not included in the kit. You can blow out the slave cylinder if you do not do this. It also lets you customize your engagement/release point to your liking.
If on install,it will not close on that last 1/2”, do not force it. The splines are not lined up. I think the original alignment tool that they were sending out was just a hair small(now corrected). I had to get the clutch engaged to get it installed. Much easier said than done on your back with an uninstalled transmission hanging in the air.
I am sure that Kerndog can add a few inputs to keep you from making some of the stupid mistakes that we fought thru.

 

[Darter6]

This statement has been going around allot lately,
"Buy it today. It's only gonna cost more tomorrow".
Prices go up on a daily basis ..

 

[Darter6]

I think the 3.55's are actually a pretty good gear with the TKO/TKX....

Way back when I did my Duster we installed 3.55's. It was the Keisler/TKO.
It was ok but needed to be over 60 mph when in 5th. Engine lugged because of the cam I was running under those speeds.Tire height too played a part . My 2 cents.. Always wanted to swap in 3.73 but never did.

 

[CoronetDarter]

Heh heh heh.....I know a guy.

View attachment 1531570

He has a little experience with the swap too.

Really? Can you give me his name?

Actually, I left out a critical detail in Post #1. Back to the night we were watching TV and Maria practically begged me to get the Tremec, I texted Kern and asked him if I could use his lift for the project. He immediately replied in the affirmative. Otherwise I might not have pulled the trigger.

 

[CoronetDarter]

Way back when I did my Duster we installed 3.55's. It was the Keisler/TKO.
It was ok but needed to be over 60 mph when in 5th. Engine lugged because of the cam I was running under those speeds.Tire height too played a part . My 2 cents.. Always wanted to swap in 3.73 but never did.

That's exactly why I went with the 4.10s'. The Dart has the 360/380 hp crate engine with a radical cam and with the 3.55's the 5th gear bogged down on the freeway.

 

[CoronetDarter]

DO IT!!!!

View attachment 1531571

Ok, I will. But only because of peer pressure.

 

[1 Wild R/T]

When does the install begin?

 

[CoronetDarter]

Damn, I thought Lincoln was further from you than it is... You guys are practically neighbors....

And FWIW I think the 3.55's are actually a pretty good gear with the TKO/TKX.... I'm afraid the 3.91's are gonna be to low mostly making 1st pretty useless...

Yep, we're about 20 minutes apart.
I hear what you're saying about the gearing. The Dart's the same way with the 4.10's; at 30 mph its in 2nd gear.
When I was assembling parts for the 440 build back in 2014 I spoke at length with Dave Hughes. The hyd FT cam I chose is relatively mild: 232/236 with 110° LSA. But it has decent lift at .535/.546 @ 1.5 rocker ratio. Dave recommended 3.73 or higher (numerically) gearing. When the Coronet first got back on the road with the 3.23's and the 3,000 stall converter, it was a turd off the line. When it came time to upgrade, I took the cheapy way out and used the 3.55's from the Dart. The 3.91's will be tight in traffic. But on the freeway they're knocked down to 2.65's.
The other consideration is if I want to step up a cam size or two in the future, the gearing will already be there.