TH350 - 2004R Conversion Tips & Tricks

Discussion in 'Transmission & Driveline Topics' started by Twisted_Metal, Jun 16, 2006.

  1. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

    Feb 26, 2004
    Bloomington, MN
    This is my first draft of a write-up of the process to convert a TH350 3-speed auto LATE 2nd gen Camaro to a 2004R 4-speed Overdrive tranny.

    Parts you need: (Listed by the supplier I used.)

    2004R 4-speed OD tranny (Purchased locally in a recently rebuilt condition...$520)
    Flexplate (Stock is fine. Mine was bent and needed to be replaced.)
    Shifter cable (The stock one should work but mine needed replacing.)
    Shifter conversion kit ($80)

    Shiftworks Camaro Shifter Conversion

    The detent in the shifter is quite a bit different.

    BowTie Overdrives:
    Lock-up Converter ($175)
    Lock-up Wiring Kit ($70)
    TV Cable & conversion kit ($110)
    Speedo Gears ($60, I needed both gears.)
    Crossmember (The 75-81 crossmember is different from the 70-74 style. $175)
    Torque Converter cover ($20)
    Dipstick (Universal $30)
    Gasket & Filter
    All new hardware for everything ($30)

    B&M Super Cooler tranny cooler ($40)

    Total parts cost= Approx. $1365

    The Tranny preparation....

    Clean out pan.
    Install new speedo gears.
    Install new lock-up wiring. (Good instructions with kit.)
    Replace Throttle Valve return spring with one from TV cable kit. (Again... good instructions.)
    Replace filter.
    Install lightly greased gasket.
    Install Shiftworks conversion shift arm on tranny.
    Place the shifter cable bracket on the pan & torque pan bolts to case @ 9ft/lbs.

    The tranny is ready for installation! :D

    Shifter Preparation:

    Remove shifter from car.
    Install Shiftworks kit following the instructions.
    Reinstall shifter. (Then cuss about the lousy label they use to redo the gear indicator lettering on the plate. It is invisible at night!)

    Design new shifter indicator part and hand letter new letters with white paint ofn the back side of the plexiglass I used.
    Reinstall all shifter components.

    The newly converted shifter will still work quite well on the TH350 so this can be done ahead of the tranny install.

    Camaro Preparation:

    Install Tranny cooler. (Follow kit instructions anf use zip ties or create your own mounting configuration.)

    Disconnect downshift cable from carb and remove carburetor from intake.
    Install the TV cable conversion hardware.
    Reinstall Carb.
    (The TH350 downshift cable will need to be disconnected from the carb to allow the new hardware to fit.
    You can still drive your TH350 but you will need to downshift manually.)

    Wire the car's portion of the lock-up harness.
    (I added a lighted switch so I could see when the lock-up feature engages.)

    The car is ready! :D


    I got lazy here and paid AAMCO to watch them perform the actual tranny swap.

    Disconnect battery ground and remove distributor cap so it doesn't get cracked while you jack around on the engine and tranny.

    After getting car high enough on tall jack stands or a hoist...
    Drain pan, remove torque converter cover, and dipstick tube, disconnect driveshaft, cooling lines, detent cable, backdrive linkage, modulator vacuum line and speedo cable.
    Support tranny with a jack.
    Remove crossmember bolts.
    Remove tranny to engine block bolts and TC to Flexplate bolts.
    Remove crossmember.
    Lower tranny.

    Put fluid in new lock-up torque converter.
    Mount TC to tranny. (MAKE SURE it is fully seated in the pump tangs.)
    Raise tranny in place and align with pins on block.
    Install crossmember and bolt the tranny to the block and crossmember.
    Install dipstick/fill tube.
    Connect speedo cable.
    Connect shifter cable. (Some adjustment to Shiftworks bracket was required.)
    Connect cooling lines. (Some bending is required. The fittings are the same between the two trannys.)
    Reconnect driveshaft and backdrive linkage.
    Plug in the lock-up wiring.
    Connect TV cable to carb and tranny.
    Cap the open vacuum connection at intake.
    Fill tranny with fluid.
    Reconnect battery and install distributor cap.

    Lower car and enjoy Overdrive!

    Problems encountered:

    Shiftworks .... Poor design on shift indicator labeling. (built my own as a solution.)
    Tranny mounted bracket needed to be modified to get better geometry on the shifter arm.

    BowtieOverdrives... Crossmember interference with stock exhaust flange at the inlet to the catalytic converter.
    Cat was removed for the install but Y pipe needed to be shortened for clearance. An aftermarket cat was then welded into the exhaust system after the tranny install was completed.

    Yes... this post is a book but this is a multi-phased job, IMO. I hope it helps anyone with their decision and installaton of an OD tranny!

    I left out plenty of little details and specs just to get this done today. Ask any questions about this swap and I'll try to answer them.
    Last edited: Jan 8, 2009
  2. Qwik75LT

    Qwik75LT New Member

    Apr 1, 2006
    Middle River, MD
    I thought the 4 speed auto's were longer than the TH350, and therefore needed a shorter driveshaft?
  3. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

    Feb 26, 2004
    Bloomington, MN
    The 2004R is the same length as the TH350.
    The mount for the crossmember is approx. 6 inches further towards the rear on a 2004R. THis is why a spcial crossmember is required.

    The TH350 driveshaft fit perfectly in the 2004R.
    The installer at AAMCO had to measure to convince himself. He thought the 2004r was longer than the TH350 too.
  4. Mountaineer

    Mountaineer Veteran Member

    An excellent description, my hat is off to you, Twisted. I've been waiting for this post. How does it drive? What is your diff ratio? RPMs at 65 MPH? Why did you have to use a different shifting bracket on the tranny? Wouldn't the one on the 200-4R work? Sorry for the questions but I'm about to do this swap in my '81.
  5. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

    Feb 26, 2004
    Bloomington, MN
    I didn't mention was the torque converter specs... It is a 1800-2200 stall converter and I'm not thrilled with the way it behaves. It seems sluggish compared to the stock converter in my TH350. Particularly when it starts up cold. Once it is warmed up from driving a few miles, it acts the way I expected it would.

    The tranny itself seems to drive just fine if you don't mind high MPH shifting.
    0-25 = 1st gear
    25-40 = 2nd gear (PITA in town. :( )
    40-60 = 3rd gear
    60-? = OD

    It doesn't want to go into 3rd (Drive) until it hits 38-40 MPH. I fear gettin pulled over just because I was tyring to find 3rd gear.

    It will NOT shift UP before these speeds but once it does shift, it will stay in Drive down to 30MPH and OD down to 45 MPH, with a light foot.

    The 2004R shifting is controlled only by RPM (governor)and the TV cable position (TV valve). There is no vacuum modulator so it does act differently from the TH350 that I had been driving for 27 years. There IS a learning curve to driving efficiently with this tranny, IMO.

    On the highway it feels like flying when you hit OD @ 60 MPH and the RPM's drop to 1500. I have only crept it up to 80 in OD but the engine wasn't even @ 2000 RPM! (I could hear the Q-jet secondaries starting to open at 75MPH.)

    My rear gearing is a 2.73 open rear. Acceleration is for 2nd & 3rd gear, OD is for maintaining cruising speed or a very slow speed increase if you ease into the pedal. IMO, a 3.42 or 3.73 rear would be PERFECT with this particular tranny. Keep in mind, the way any tranny is built will give it some characteristics that may or may not work well with a certain gearing, governor or torque converter selection. It is hard to tell until you've bolted it to a particular engine.

    Downshifts feel perfect! :D

    Nail the pedal anywhere between 30 and 60 MPH and it drops to 2nd gear, it shifts to Drive at 60 and pops into OD whenever you let off the gas. Cruising altitude is easy to maintain and a heavy foot on the pedal will slip it back to drive very smoothly.

    I feel it is off a bit on the gearing to get to a take-off accelaration level equal to my old TH350. I think most of that is due to the higher stall TC but I'm not sure if this is the sole reason or if I am getting some slippage in the tranny itself.

    Anyone familiar with conversion to a higher stall TC is welcome to leave some input here. PLEASE!

    RPMs at 65MPH = 2400 in Drive or 1600 in OD.

    The 2004R I bought did not have a cable bracket on the tranny and the tranny shifter arm had linkage for a column shift but no connection for a floor shift.
    I used the shifter arm and the cable bracket from the Shiftworks kit. They seem to be designed well to work together. The shifter arm connected to the tranny, backdrive linkage and shifter cable with no problems. (Actually seems to fit BETTER than the stock TH350 arm and has less slop in the backdrive linkage.)
    However, the geometry of the shifter cable bracket caused the cable to bind when shifting from 1st to 2nd manually. The bracket was "persuaded" to fit closer to the tranny case (Bent UPWARDS) to give a more direct line of motion to the shifter arm. The cable bracket from the TH350 was considered but did not have holes to match the 2004R pan.

    Good Luck with your swap Rick!
    Last edited: Jan 8, 2009
  6. Mountaineer

    Mountaineer Veteran Member

    Twisted, it sounds like your main problem is your rear gearing, maybe this should be next on your list of things-to-do. I was advised by my tranny builder that my 3.42 gears should be the lowest numerically to go with this tranny. Thanks again for the great post. Keep us all informed of any changes.
  7. Firechicken

    Firechicken Veteran Member

    Dec 22, 2005
    It sounds like you have too much TV. If you take out some TV you can have it shift sooner as it is supposed to. Press the button and move the cable towards the throttle arm by a click or two and it will behave nicely.
  8. Twisted_Metal

    Twisted_Metal Administrator Staff Member Lifetime Gold Member

    Feb 26, 2004
    Bloomington, MN
    Thanks Firechicken!
    It shouldn't hurt anything to give it a try.
    There is an adjustment on the linkage attached to the throttle bracket that I haven't attempted to adjust. I should probably try that too.

    The torque converter definitely feels looser before it warms up. Is that normal?
  9. tdknop

    tdknop Member

    Jun 8, 2006
    King George, VA
    I was reading this with great interest as I have a TH350 and was thinking about the overdrive conversion. Its probably a lot out of my skill set but good reading anyway.
    Twisted I saw you have a 2.73 gear in the back. I don't know what open rear is so if you could enlighten me that would be great. Also I thought that higher gears were a bit better if you had a few more ponies under the hood than stock? I have a 3.08 Posi and someone told me I should be looking into the 4's for the rear end.
    I'm only going to build my 73 to about 400hp or a little more. I want to keep out of race fuel, also because I want to drive it :).
    Anyway, any help would be cool.
  10. manicmechanic

    manicmechanic Veteran Member Lifetime Gold Member

    Oct 24, 2000
    Tulsa, Oklahoma
    An open rear means that the rear end only drives one axle as compared to both in a "posi" "Locker" or "Limited Slip" type of rear end. The benefit to the open rear is slightly better mileage since energy is not wasted driving both axles all the time. As far as your gearing goes, I wouldn't go over 3:73.1 for a street driven/Daily car unless you have the overdrive. I have 3:42.1's that run about 3400 RPM @ 65-70 Mph and at todays gas prices is not good! My 2004R goes in over July 4th weekend!
    Last edited: Jun 26, 2006

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