So I decided to keep the existing G Force X-member and modify it for correct install height and make it a true bolt in. The rigidity of this unit helped with the frame twisting that I had with my drag launches and I really like this unit for it's high HP rigidity. Unfortunately G Force does not make a T56 style member for GM's A body, but they do have one for a G body, which I studied for its differences. The existing member used with the TH 400 is shown below: To modify it, I ground off the end tabs & made some 1/4" thick 2"x 3" angle pieces 3 1/2 " wide to replace them. The new assembly with relocated angle tabs. The new ends are fastened with high strength 3/8" capscrews into tapped holes. This also facilitates the T56 magnum removal and install.
Crossmember is in and the 3 1/2" dia. driveshaft was shortened to 48 1/2" from 54 1/2 " . A local roundy round powertrain place turned it around in less than half a day including balance. I had a slight mishap with the T56 Magnum vent tube elbow that connects to the case, so I made a more robust one on the lathe from an old 90 degree fuel line fitting.
I have a potentially functioning install! Driveshaft is in, clutch safety switch is wired and the clutch hydraulics work. Initially there was still a slight issue with an airlock in the hose between the reservoir and master that caused an initially soft pedal and then it went very very hard. Once that was sorted out, the pedal could even be moved by hand and was consistent in movement. The clutch releases about an 1.5" from the floor when rotated by the driveshaft, just as it is supposed to on this setup. For now the tunnel sheet metal is only held in place (for position) by two screws and will be secured later by butt welding or screws if I decide to fab a maintenance opening for the shifter. The position of the Hurst offset lever to the steering wheel is in a nice proximity for driving. Shift and steering are close together. I installed a Prothane poly trans mount to replace the tired rubber mount. Next is more interior button up, driveline geometry final adjustment and an electronic reverse lockout module that permits reverse gear below 5 mph. Tom
This is what I chose to function my Reverse gear lockout. T56 magnums have their shift pattern setup so reverse gear is up and over to the very right. This is also close to where 5th gear resides. To prevent accidental shifting Tremec supplies a solenoid internally to lock this out, but it can be overpowered manually with very hard force. On late mode factory 6 speed cars the onboard computer enables a low speeds only override to permit an easy shift into R. For swappers some people have used the 12 vDC brake pedal signal or wired up a manual accessory switch to make this work, but Samoco has a neat standalone device that uses the electronic Vehicle Speed Sensor (VSS) output to achieve what the factory has done. What you don't want to do is have the Reverse lockout disengaged while driving and chance the possibility of going into it at speed. (Imagine what may happen, when hitting your brakes on the freeway and down shifting from 6 to 5 and going into R by mistake. ) Tom
Update on progress. I have shimmed the trans and adjusted the upper control arms longer to get the geometry to where I wanted. Trans is now 2 Deg down, Driveshaft is at .25 Deg down and rear is also 2 Deg down. A manual gear box with basically a heim/roto joint rear end should work well with these settings. I decided to leave the whole tunnel as a screwed on assembly for easier maintenance in the future. I made a billet spacer to be installed between carpet and shifter boot assembly. Carpet in pic is temporary and will be replaced with new product. A DEI thermal/noise insulation blanket will cover the tunnel under the final carpet install When wiring in the reverse backup light switch I added an amber below dash indicator light. If you ever owned a manual trans Mopar, this is what the factory did in the late 60's and 70's. Underview Also added UMI instant center relocation brackets prior to adjusting geometry.
Rookie question for you, I'm in the process of installing my Tremec 5 Speed, what size shift arm (10" 12") did you go with. I need to get one myself. Also will have bucket seats. PS. Really enjoying following this thread.
Really appreciate you sharing all this great info. Nice build/swap. As you know, A stick shift in an A body sometimes makes Em Wheel hop. Let us know how you like the LCA brackets. Does the trans not have a Backup/detent type light switch in it? Or maybe the lock out control could have activated the B/U lights as well?. Just curious?
Thanks guys. Steve-The shift lever I'm using is a 10" stick with a 1.3" offset toward the driver. Hurst# 4106. AOOOA- I've used the instant center relocation of the bottom bars before and they seem to worked well with the auto. When I went pro touring and lowered the car and put new heim end bars and a direct body mounted sway bar, I took off the old SSM kit. Subsequently the car cornered real well but never did hit hard for traction. Of course there were many factors involved like different tires, spring rates, shock settings etc. The ideal instant center relationship to the antisquat point on the car was probably off after the changes. I'm trying to get something that will do it all and with a manual trans it is even more challenging. So the new style UMI brackets with 3 different positions is going to be an interesting try. With respect to the back up light switch, and to clear any confusion, there are 3 electrical connections to the T56 Magnum. The lockout solenoid (+/-12Vdc), the electrical VSS ( pulse signal) and a separate reverse gear detent switch. The lockout module only uses the first two connections. The 3rd is a specific detent switch designed is for the backup lights when the trans is actually in reverse gear. With the way the above standalone lockout module works, any time the car is moving less than 5 mph or stopped, regardless of gear lever position, it would send out an energized signal. This would have the backup lights on in any shifter position at low speed or at a stop light even if is was not in reverse. Tom
Awesome work, really appreciate the time you took to share this part of the journey with us. I will be installing an SST Tremec Magnum kit this summer and I am sure I'll refer to your thread for insights!
I took a chance with a new ACC 2door auto Chevelle carpet kit, knowing that the modified tunnel might not fit. ACC manufactures their products with some excess material so with the Tin Man tunnel kit, that was made for a console A body car, there may be a chance of it working out. With some patience, cutting, trimming and a heat gun it came out as follows: Shifter in 1st gear position
The Sick Speed swap is essentially finished. Just waiting for our winter snow to disappear to test drive it. A few misc items: Since the location of the mechanical speedo cable on the Tremec Magnum is further back than a stock TH 400 your speedo cable may not reach it. Your options are to replace with a longer cable or use an extension. I used a GM female to GM male extension. Rear end UMI relocation brackets are in. Don't forget your triangular bracing brackets with any stick car. These old Edlebrocks are not made anymore but other manufacturers as well as 4 speed stockers are around. Another pic of the billet spacer/adaptor for the floor shift boot that allowed me to use the smaller Hurst boot with the raised Tremec shifter stub. Here are the two different types of pilot locators that I experimented with. As you know I used the bronze one but there was enough material on the roller style one also to accurately machine it to fit this particular crank. Of the 5 big block cranks I had only, one old core was factory machined to fit a chevy pilot bearing/ bushing as it came out of the box. Even the service block with it's crank was smaller.
Man, that looks glorious! On the frame braces, UMI is a good source for those parts these days. I'm very happy with all the UMI suspension pieces I've installed on my Skylark.
Here's a pic of the reverse shifter position with the lit amber light indicating it's actually in reverse gear. Even though it's way over to the right, I still prefer to get a glimpse of an indicator. The lockout works well and is an easy shift as intended at low speed.
First ride today. The snow up here is finally gone so I was able to open the garage door to the downstairs machine shop and take it for a trial run. What a difference! It's not the same car anymore. Even with the 308S cam, its very streetable and the transmission ratio spread (1-4) seems great. Shifts are smooth and easy to control Love the hydraulic twin disc clutch No vibration from the American Powertrain 455 flywheel No noises from trans or shift stick interference No driveline vibration. Haven't had a chance to get into 5& 6 yet Very very easy to get into the cam 's powerband. I need to take it easy for the clutch break in First impression of the relocation brackets functionality is good. More testing with different tires on a better surface will tell The only hangup was the neutral safety switch. I needed to push the clutch very deep into the floor to start after the carpet & floor mat install. For now I bypassed it Initially it was going to be an around the block ride. An hour later I convinced myself to continue it later on better condition streets with a full tank of gas. Tom
Took the car out for some more break in driving. With the 308S cam, 26" tire and 3.73's and my tuning I can go to a low of 2100 without any surge, so no cruising below 2000rpm. The beauty of the Tremec Magnum, is you can drive it easy one moment and beat on it the next due to the strength and it takes it. Unlike other transmissions that are top or side loading the Magnum is an end loader with a very solid case, big gears, heavy duty shafts, and double and triple syncros in addition to just two overdrives. I like this transmission a lot. Finally got it into overdrive during some highway cruising At 60mph in 5th it revs 2300rpm At 75mph in 6th it also revs 2300 Some recent pics after the swap. Tom
