Bob's Component Resto, Part 4: The tranny

[cruiser]

Good evening Mopar faithful. Ready to go to bed? Here's tonight's light reading to help you fall asleep. Part four this evening covers the resto of the Torqueflite A-904 three speed automatic transmission in my 1974 Gold Duster. Before I restored the tranny I wanted to be sure that this was, in fact, the original "numbers matching" transmission that came with the car from the factory. Prior to purchasing the car in the spring of 2019, I determined that the original engine was gone, but the original transmission was still there. It's quite simple to determine, as most of you know, if your trans is original. Simply look for the last eight digits of the car's VIN stamped on a raised pad on the right side of the bell housing. Mine checked out as the original, and thus I thought that it was worth restoring it. If it hadn't been the original, I probably would not have rebuilt it. Note in the photo below that the last eight of my VIN are stamped multiple times - perhaps six strikes if I'm counting correctly. Came from the factory this way. I'm not sure why the stamping guy did this. If you've seen this before, please weigh in with your comments and photos. Anyhow, step one was to pull it and disassemble it. See the accompanying photos of the aluminum case and tail shaft. They were pretty bad and covered in 46 years of oil and grime. I took both parts to a blasting shop in Minneapolis, where they first sandblasted them to remove the crud, then finished with glass bead blasting to give them a smoother, more original finish. After I got the parts home, I hit them both with three coats of Krylon #4117 Clear Chalky Matte finish. I had never used this product before, but I was extremely pleased with the very factory original looking result. I highly recommend this process if you want your tranny to look and stay nice. Three steps: Sand blast, glass bead blast, then seal with several coats of Krylon Clear Chalky Matte. I couldn't be happier with the result. I also sand blasted the oil pan, then refinished it with three coats of metal primer followed by three coats of Krylon machine gray paint. The dipstick and tube were in good shape, just needing a thorough cleanup. Next came the reassembly. A new torque converter went in, along with a new filter, a new seal kit and the correctly sized speedometer drive gear. Any worn parts were replaced, then it was reassembled and reinstalled in the Duster. The shift and kick down linkages were adjusted once the trans went in. I had previously replaced the transmission oil cooler in the radiator, along with the steel cooler lines, so she was ready to roll. A test drive proved that all functions performed perfectly, and it looks great under the car. The sealer will prevent the case from having dirt and grease embed in it, as you simply wipe off any accumulation of crud and it looks new. All three of the original transmission wiring harness clips were missing, so I found a really nice used set and installed them. It's exactly like the factory setup now, and runs flawlessly.
Driving impressions: The stink on the A-904 was that it wasn't a very good unit, nor was the 7 1/4" rear axle that went into the A bodies back then. I've never found this to be the case. Both the trans and the axle are fine for a slant six Duster, and I've never had a bit of trouble with either, probably because the engine produces so little power. So neither the transmission nor the rear axle are being taxed that much, and in my experience they run fine forever once correctly set up. The car is surprisingly quick off the line in first gear, likely due to the light weight of the engine up front and the amount of bottom end torque that the long stroke motor provides. It sort of poops out in second and third, but I'm fine with that as I never beat on the car and drive like your grandmother used to. Overall, it's a very fine drive train, and I can see how it was a most excellent grocery getter back in the day. As an aside, the car brakes REALLY well with the power discs up front and the lightweight engine. That surprised me. So that's all for now. Please feel free to add your observations and comments. Now put away the laptop, turn off the lamp, and go to bed. Night - night!

 

[B'cuda]

Dayum, dats nice!

 

[GGs66GT]

Yep the 904 is robust for the /6 and by adding 1 more clutch to the packs and a wider band the 904 became a 998 with a sm. blk. case and lock up converter that was used in the later V-8 B & J bodies and the police Diplomats behind the 360. It was also used in prior non lock up cars .
Also it takes less H.P. to operate then the 727 . Thus makes a great race trans for A bodies without the fitment problems or the exploding drum of the 727.

Yep your trans looks great .

BTW if you increase the exhaust system to 2 1/4" from the header through the muffler and through to the tail pipe it really wakes up the /6 through the mid range and top end with only a slight drop in torque at the bottom . The key is to let it breath with just the right back pressure determined by the muffler choice. It made mine more like a V-8 on the freeway and when passing.

 

[GGs66GT]

Back in the day we had a '63 Dart 270 4 dr. 225 /6 push button 904 7 1/4 rear.

Well me being a kid I liked to do neutral push button starts . I did that daily for about a year . The car had a 5 year 50,000 mile warrantee on the power train and wouldn't you know it I blew the spider gears up at 50,050 miles . So Dad had to pay for the repair .
When I was asked how it happened ... "I know nothing " I said in my best Sgt. Shults impression .

My point is the 7 1/4 can take a lot of punishment before it breaks the spider gears .
I wonder if the anti slip set would be even more robust than the peg leg ?

OK now back to the O.P.