Hydramatic 4spd Auto Trans Floor Shifter

[HotRodLinconSr]

Gentleman I'm new here so please be gentle. I recently purchased a 1961 GMC pick'em up 1/2 ton.it has a 305 V6 w/4spd manual trans. I want to swap out the manual trans to a auto trans. Found a 61 hydramatic with flywheel, starter and torque converter.

My question is, what aftermarket floor shifter will work "out of the box" with this
trans?

[Funky61]

Welcome to the forum HotRodLinconSr!

I like your 61 Fenderside, and looks like you have factory style wheels and hubcaps too. Would love to see more photos when you are able.

Looks like you were able to source a complete automatic unit.

I am not very familiar with those, but we do have a few members that can speak to that. I'm sure they will chime in soon enough.

Glad to see you still have the early hood as well.


*Is that spare a 17" wheel?

[HotRodLinconSr]

Funky, thank you for responding. You are correct factory 16 wheels, the spare is a 16 as well. Here are a few more pics

[jbgroby]

Hotrod,

I had a 4spd. Hydromantic in my 60, when it broke back in 2019, I opted to put in a 700R4. Do you have the cross member to hold up the transmission? The hydromantic weighs in near 400lbs., If you don't' its possible to fab one out of 2'x2" angle iron (I had to do that with my 700R4). Here are some pics of the Hydro after we took her out to clean and paint and I'll post some pics of the 700 with crossmember, you will also need the block plate for the flywheel torus cover.

BEFORE you install, are you sure she's in good working condition? There are only 2 places that work on these old transmissions, ones in California and the other is in Levonia, Michigan, I was quoted 3400 plus shipping, and I still would not have overdrive, that was the driving factor for me to convert to a 700R4.

[jbgroby]

More pics, the 4x4 inspection plate is how you reach in and bolt up the 30+ bolts to mate the torus converters to the flywheel, the small bolt is a trans fluid plug, take that out and you can drain the torus converter. The pic with both transmission in it is called the Quick and the Dead. The 700R4 is a bout 159lbs vs 432 for the trans with bell housing. When installing the hydro, make sure you use block and straps, unless you are droppin it with the body off as I did originally, then you and use an engine lift to help. IF yo have a FB page, shoot me a Freind request, I have a ton more pics. Hope these help.

[HotRodLinconSr]

Jdgorby,
What's needed to mount a 700r to the 305?
I've heard an adapter plate? What about the flywheel, which one to use?

[jbgroby]

Hotrod,

There are 2 options, finding the factory OEM setup or purchasing the aftermarket setup from Bendtsen's Transmission adaptors, they sell a complete kit, adaptor, flywheel, etc. including a start (long throw gear), the new setup with run you about 1,400. One of our members may have one they want to sell.

https://transmissioncenter.net/shop/...ion-gm1000201/

You will also need a torque converter and a HELPER, because the swap while a simple and direct bolt in requires an extra set of hand. I did the swap over 2 days and paid a friend a case of beer, paid after the swap (less I be missing a bolt . You will need to make the rean transmission support, cost you less than $10,00 made with 2"x2" angle Iron from Home Depot. Also, you will most probably need to shorten your propeller shaft (driveshaft) because the length of the 700R4 is longer. My total swap cost was less than $700. I found an oem adaptor from another trucker.

You could buy my setup for $23k but the truck comes with it

[jbgroby]

Hotrod,

In this picture you see a black sharpie line, the reason for this is to simple mark alignment, the guys at GMC back in the day were geniuses, the 6 bolt hold you see for the crank to flywheel are at a perfect match, you CANNOT mess these they only line up one way correct to put in the bolts, one hole is offset slightly, so you cannot misalign. IF you decide to put in a 700R4, you need to purchase a flexible dip stick NONE of the stiff sticks styles will fit because of the angle of the inner fender and exhaust headers.

[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.

[jbgroby]

Installing the Starter -
We had to also change starters due to the cone being too big you fit in the new backing plate mount hole. Lewis Macklin to the RESCUE, he knew the parts number of the start by memory! However, the top lip of the case interfered with the upper starter bolt, we simply had to grind off about 1/8" to pass a Allen head bolt. Good thing about an aluminum case is it’s easy to grind, bad thing about an aluminum case is it pretty much ruins a grinding stones because it clogs up the stone with soft metal. We got her bolted up to the block and called it a day!


Day 2 - Cross Member Install
Ok, remember we had to remove the transmission bell housing cross member? you will now need to ADD a new rear trans cross member to support the rear of the 700R. In all my research at the time, I discovered that no one makes a direct bolt in replacement cross member, this is because on the 60-model year and some later years, we have the 'X' frame. So, we had to make one up. Another member who did this swap already explained that all we needed to do was simply install a span of metal so the rear of the trans can bolt to. We used 2 pieces of 6" long 2" x 2" angle and bolted it up to the inside of the frame (there are two factory drilled 3/8" hold that worked perfect for us to use, we made the bottom flush with the frame, we split the distance where the mount would fall centered under the rear mount holes for the trans. Then we used another angle 2 foot long with the holes matched to the rubber Trans support. We bolted the new cross member to both the new angle mounts AND the truck frame. We could have used just 1 but why not use both. Remount the exhaust and she's done.


TV Cable and Accelerator issues -
Try as I might, I could not use the old GMC Bell Crank throttle and rod assembly due to it interfering with the new Bowtie Overdrive TV kick-down cable bracket. I had to order a Terry Cable Wire Throttle setup; I then went to the local Pick & Pull yard to locate a 2005-2009 Ford/Mercury gas pedal, as it uses a wire throttle line mount. I found this pedal better than the 3 point larger Chevy Truck pedal. The Ford/Mercury pedal uses just two screws/bolt to mount vs. the larger GM pad with a base plate shaped in a triangle. Where you need to mount the pedal has limited space, the Ford pedal assembly fits in the area perfectly and only cost me $7.00. The new aluminum billet pedals sold by most trucks' places run $99.00 and are the same generally, just fancier looking – Who looks at your gas pedal…..


After I removed the old firewall mounted gas pivot, I hand placed the new pedal to make sure I had the proper movement, using a sharpie I marked the 2 mount holes and bolted (you might need to bend the lower mount in a touch to conform with the bend in the firewall) it up with ½ long x ¼” SAE thread with lock washers and nuts. I then measured the “at idle” distance and then “full throttle” distance and WROTE this down (WRITE it down - don’t trust your memory). The full travel was 1 7/8”, you need to know this to make sure your carb throttle is not restricted and has the same full movement; the carb throttle was exactly the same.

On the engine side of the firewall (FW), I mocked up the bent in the throttle sleeve to see how sharp the bends were, and they worked out to a perfect ‘S’ curve, the cable slides as smooth as butter in the sleeve.

I then lined up and marked the spot where the throttle cable would come through the firewall and meet the gas pedal. Putting the pedal at full idle, I used a sharpie to mark the spot where I needed to drill. The Ford pedal has a slot designed in the pedal-head that works perfect with the new throttle wire head. I mounted the sleeve at the FW I threaded on the new wire and locked it down to the slot on the pedal mount.