1970 Dart 340 Swinger trans swap American Powertrain or Silver Sport Transmission?

-
T

Tripped

Member
Joined
Apr 15, 2024
Messages
7
Reaction score
15
Location
Tennessee
Looking for insight on what others have done. Has any used the 5 or 6 spd trans kits from American Powertrain or Silver Sport? My car currently has the factory 4spd in it and I want to upgrade to a 5 or 6 speed and trying to figure out which kit is the best between these two.
 
When I shopped this a few years ago, Silver Sport was super expensive and American Powertrain didn't include a bellhousing. I ended up buying the now defunct Hurst TKO kit that Holley still sells the crossmember for and they have the stuff to swap to the new TKX.
 
Silver Sport seems to be tailored to Mopar more than the other similar companies.
 
I got my kit from Silver Sport and very happy with it. I am just about finished up with the install. My car was an auto to start and so far the cutting has been minimal.
 
Doesn't Passon sell a 5 speed that is a direct replacement for your 4 speed? sounds like a lot less trouble...
 
str12-340 said:
Doesn't Passon sell a 5 speed that is a direct replacement for your 4 speed? sounds like a lot less trouble...
Click to expand...

:rofl:

Good luck getting ahold of one! And if you look at the threads on people that have gotten one, I don’t think you’d still think they’re less trouble…
 
str12-340 said:
Doesn't Passon sell a 5 speed that is a direct replacement for your 4 speed? sounds like a lot less trouble...
Click to expand...
01 A2A.JPG


Yeah.....that was a textbook case of OVERpromise and UNDERdeliver.
There are numerous stories of people waiting FIVE years for delivery, then many customers had problems with the transmissions when NO repair parts were readily available.
I've done two Tremec 5 speed swaps. The first was my own car, the second was when I helped another FABO/FBBO member with his Coronet.
Mine was the last TKO that Silver Sport had in stock, his was a TKX. Mine was done in 2021 and was complete right down to the drive shaft. I paid just shy of $6000. His was in 2023, did not have the drive shaft and way a few dollars short of $7000.
Both kits were excellent, both of us had great service with Silver Sport.
 
If yur down on torque, it's
Probably cheaper to just stroke that 340? or at least bring the pressure up?
I hear the 3.58 stroke is a good all-round cure, at 185psi, or more.lol (that's what I have.)
but seriously;
I have been running the Commando-box with 3.55s, for many years cuz this combo has;
> a dynomite Second gear of 1.92 x 3.55= 6.82, which gets me to 65=5500,
>and it has a nice 3.09x3.55=10.97 starter. I could, and have, run less gear, but then, I cannot parade, cuz the engine with the current cam, wont idle slow enough in gear. As it sits, 4mph@550 is about as slow as she goes.
>To get the Rs down at hiway speed, I run a GVod (.78) for 65=2240. I run a 230/237/110 cam on that, which seems to be OK. but maybe just barely.
At one time, I ran the Mopar A833od with the GV behind it, This too made 5-gears, but using the GVod as a splitter, I got up to 7 speeds. two of which were overdrives. With this set-up, Double od was .54, so, I could run any rear gear I wanted to. and I tried a lot of 'em.
In the end, I found the total gear spread was just too much.
If too much more than 3.55s was installed, then First was too deep.
Yet, that Double overdrive was good for 87mph @2200 with the same 3.55s, while .78od was good for 64mph. So for me, I did not need the Second overdrive.
Furthermore, the gearing from 35 to 60 did not suit my cam, in Second gear.
Furthermore, I discovered that tight gear-splits of 78 or so percent, was a lil tight on the street. I found 72% more than adequate; which is what the factory 2.66 box had.
But the starter of just 2.66x3.55= 9.44 was a lil lazy in First Gear, but worse was that there was no way to parade in 9.44; which was 4.67mph@550rpm.
That led to some math, to get down to 3.5mph or so, and the Commando/3.55s was it. Then I tacked the GVod on the end for a nice 65mph cruise, and that was that; 5 gears was enough for me. and that was like 20 years ago . I've never been unhappy with these trans gear-ratios, 3.09-1.92-1.40-1.00-.78od,
with splits of .62-.73-.71-.78, and with 3.55s
roadgears 10.97- 6.82-4.97-3.55-2.77

To spice it up, I usually shift into od after Third, and into 4od last, the splits are thus
.62-.73-.78-.71od, which is, IMO, very very nice.

But, I gotta tell ya, if I didn't already have the GVod, I wouldda just run 3.23s and dropped one cam size. for roadgears of
9.98-6.20-4.52-3.23. The cam I have in mind idles just fine at 500, so that will get me exactly 4 mph in first gear; and 65=2600 in Fourth, which was an excellent compromise. The bonus with that 7gear combo, with the 223/110 cam, was excellent hiway fuel economy.
 
Neither the American Powertrain or Silver Sport 6 speed kits include everything you truly need.

American Powertrain has the crossmember that was originally made by ToddRonn restorations, which is by far the best for those keeping their torsion bars. But it looks like they're only selling the bottom half, which is bullshit. The tunnel work needed for a T56 is substantial and you need a significant upper crossmember to retain the strength in the chassis.

The aluminum bell housings out there now are nice, but, they're much thicker than the Quicktime bell housing and require more tunnel work.

This is my list for my T56 conversion from a few years back. I'm sure some of these links are probably dead but the part description/part number may help


My installation of the T56 in my '74 Duster is here, it's a lot of work. A 5 speed would require less tunnel modification, but realistically you're still going to need everything on that list. The parts themselves may be a little different for a TKX, but you'd still need an answer for each of those parts. If you have a 4 speed in there now you can have the flywheel resurfaced, you might be able to reuse the pressure plate (check the clearance because the input shaft is thicker on the T56, and check the slave cylinder clearance). I used a C5 hydraulic clutch set up because it's easier to deal with and MUCH less expensive than what either AP or SST will sell you and it's off the shelf. The one I linked is a "fancy" one from RAM but it's literally the same part as a GM one so don't bother with RAM. Some of the lines/adaptors are for a remote bleeder, but you absolutely want that especially with a Quicktime bell.

My "new" '74 Duster- or why I need a project like a hole in the head
 
Last edited:
You must log in or register to reply here.
-

Back
Top