[jbgroby]

More goodies,

Here is the write up I did to help other members do the swap from the Hydramatic to the 700R4.

Trans Swap Tutorial

As promised, I wanted to put pen to paper (keys to computer) and outline the information I’ve learned and let others know what’s all involved with making the switch from an old Hydramatic to a 700R4 on a 305 V-6 – What a journey……

Ok, after a lot of fits & starts and Covid-19 delays we finally got to where we could all meet up and do the trans swap from the Hydramatic to the 700R.
WHAT a journey, before I get into the nitty gritty, I want first shout-out to the following members for their help, knowledge and assistance in giving me pointers and suggestions. ED SNYDER for helping me located the need OEM adaptor setup. LEWIS MACKLIN and PETE CHRONIS for their encyclopedic knowledge of the 305 and the Hydramatic. I'm highly doubtful that anyone knows more about these engines than these guys posted above! And that's no Bullcrap.

Ok, here is what I did to remove, install and modify the trans swap. Some of this will mundane, but since a little knowledge goes a long way, it can't hurt.
First, as has been repeated a few times you need to locate a complete OEM automatic transmission bolt adaptor setup, which will allow you to bolt up a later model GM automatic transmission where the manual or Hydramatic trans sits. If you cannot luck out and locate this OEM setup, you can buy the needed parts from Bendtsen's Transmission Adaptors. The adaptor comes with all the items needed including a new starter and flex plate/flywheel combo.


If you go the OEM route like I did, you will have to get the bolt adaptor, the correct flywheel (there is a major difference in the flywheel design), the flex plate and the spacer plate.


The Removal- The Hydramatic version!
First you will ABSOLUTELY need a transmission jack. The Hydramatic weighs in at about 450 lbs, (about 100 lbs heavier than a Duramax transmission) you or your buddies cannot manhandle this.


Disconnect the positive battery lead. Drain the fluid, remove the trans hump cover and the upper trans firewall cover you will need to do so in order to access the 4' 3/4" bolts that hold the bell housing to the rear of the V-6 block, there are 5 smaller bolts located on the bottom of the bell housing also. The top and bottom of the bell housing will have a 4" x 4" access plate, you simply pop them off. Once removed you will see many 3/8" bolts, these bolts hold the Torus Cover to the flywheel. (Historical note, before GM designed/invented the modern torque converter we know now, they used a fluid coupling torus adaptor), close to the same principal.


As you remove the bolts, you will need a helper to turn the crank bolt to rotate the Torus Cover to get to all the bolts. While turning it, you will find a square headed nut; you need to remove this in order to drain the fluid from the Torus assembly.

Now you can remove the gear selector rod linkage, carb bell crank shift linkage (I will also explain the new accelerator linkage and TV Cable mount you'll need to change also). Now remove the propeller shaft if you have not done so already (BTW, that’s the correct and proper name). If you are happy with you rear u-joint good, but why not put on a new unit while you have this torn down?

With the truck elevated, setup your adjustable engine stand using a large piece of wood that will span past the entire width of your oil pan bottom (we used a 4x4). We realized early on that we had to remove the muffler exhaust as well, so we did, we cut through a section past the engine (easy fix). Now lift the engine a bit to get the weight off of the rear cross brace. There are two 3/4" bolts that reach up from the underside of the cross member and bolt into the bottom of the bell housing, these bolts have lock tab washers so you bend them back and remove the bolts, make sure you remove the tube sleeve as well. Now you are ready to remove the rear motor/bell housing cross member, the 700R4 will not need that cross member but will need a new one further back. My cross member was bolted in place and we saturated the bolts (4 on each side) with Kroll oil to help ease in removal (bolts have not moved in 60 years). You will need 2 wrenches one to loosen and one to act as a holdback, you have a small area to work in. (Some cross member are said to be riveted in place, if so, you'll need to grind the heads and drive the rivets out or burn them out with a torch). Once the bolts are out, you will need to beat the cross member down and forward to remove. I'd save it as another members my need it.

Ok, now setup your trans jack, strap/chain her down TIGHT! and take up some load, remove the 5 bell housing bolts from the block and walk the trans backwards. Once loose, this is where you need a few people, because of the size of the bell housing it will have to really be worked at a very steep angle. We also secured the trans to the stand with a short piece of 12/2 Romex so the trans would not slide forward. We secured the Romex through the bottom access hole to the trans jack as well.

You need to adjust your stands till angle to the max it can go. While you have that angle let down on the stand, you may have to raise the engine a bit as well. We worked off a hydraulic vehicle lift and needed to also lift the entire truck at the same time we lifted on the motor. Once you get the trans out of the way. Sit down take a break, grab a beer and a cigar, you've earned it That part of the battle is over!


The Flywheel-
Ok, breaks over get back to work - you think this is a UNION shop. You can now unbolt the 6 flywheel bolts; you need to keep the double washer/spacers as well. Once the bolts are out, take a good hold on the 30lbs flywheel and her off the crank. Now you can access and remove the 4 bolts which hold the spacer plate to the block. While you can access the rear of the block, now is the time to check for and address any main seal leaks if you have them, I did not.






700R4 Install-
Ok, mount up the new trans on the stand, strap her down as good as the last one (because you need to go the same steep angle, also the 700 is about 4" longer depending on what tail shaft the trans has, I have the long tail model.

Now, we bolted up the OEM spacer/backing plate. The OEM flywheel has a thin spacer that has to be used between the flex plate and flywheel that all 6 crank bolts must pass though, you have to pre-check this because the tolerance is extremely tight and only fits ONE way. We mocked it up and marked it with whiteout. Then reset the new Flywheel in place with the flex plate.

While we got the trans in position and angled up, we noticed that the torsion bar bolts interfered with us getting it in position by about an inch. So, we sat back and gave this some thought and realized we could loosen the 1/2" nuts that held the torsion bar cross member on and drop it an inch. The tension is still on the bars, but the back of the rods is ONLY pushing against the cross member. We took the short bolt out and replaced it with a longer bolt so we could loosen and still have the bolt secured with a nut, BUT we also put a large C-clamp in place as additional safety measure (think belt and suspenders approach!). Once the cross member was lowered an inch the trans slid right in. We reset the cross member back in her original position and walked the trans to the block.