Trans swap from a Hydramatic to a 700R4

[jbgroby]

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 engine than these guys posted above! And that's no Bullcrap.


Ok, here 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 trans. bolt adaptor setup, which will allow you to bolt up a later model automatic where the manual or Hydramatic trans sits. If you cannot luck out and locate this OEM setup, you can buy the needed parts from Bendtsens 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 (their 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 trans) 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 so in order to access the4 3/4" bolts that hold the bellhouseing to the bloc, there are 5 smaller bolts located on the bottom of the bellhousing 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 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, thats the corrct andproper 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 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 crossmember 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 crossmember but will need a new one futher back. My crossmember 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 bolts 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 lose, the 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 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 are 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 (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.

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 RESQUE, he knew the parts number of the start be 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 its easy to grind, bad thing about an aluminum case is it pretty much ruins a graning 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-
Ok, remember we had to remove the trans/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, 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 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 botton flush witht eh 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 mount AND the truck frame. We could have use 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 find this pedal better than the 3 point Chevy truck pedal, the 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 perfect 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 them 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 (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 bend 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.

[jbgroby]

more pictures

[PGSigns]

So what is the plan for convertor lockup and the TV cable?
Jimmy

[jbgroby]

Once I get the driveshaft and shift linkage mounted, and the trans cooler set up the truck will be brought back to the trans shop for them to spec in.

I know what I don't know and trying to set up shifting is SOMETHING I don't know. Glad to pay the shop fee......

[AussieinNC]

Originally Posted by jbgroby

Once I get the driveshaft and shift linkage mounted, and the trans cooler set up the truck will be brought back to the trans shop for them to spec in.

I know what I don't know and trying to set up shifting is SOMETHING I don't know. Glad to pay the shop fee......

Strongly suggest that you do not drive the truck without the TV cable installed and at least a minimal setting ....driving a 700R4 without a TV cable connected spells certain death to the trans...even a short run will hurt it....

Talk to trans shop and ask for initial TV setting procedure...

[jbgroby]

I should have also added I'm not driving it, I'm having a flat bed bring it to the shop.

[sweetk30]

Originally Posted by jbgroby

I should have also added I'm not driving it, I'm having a flat bed bring it to the shop.

and nice old truck still living and making it more fun to drive . the lower 1st and the o.d. will make this truck a whole new ride for you with the power of the old 305 v6

[jbgroby]

Thank you, once the trans shop is finished my wife is going to drop me off and I'll run her home. here are teh accelerator install pics.

[PGSigns]

When they do the hook up ask them to give you a copy of the pressures they got when they set it up. Those will tell you how close they got to getting it right.
Jimmy

[Gls]

Thank you for emailing me the link. I dont get on the site much but look forward to the reports of how big a difference it made and cruising speed abilities. Might try this with a ‘67 351
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[truckdude239]

that is the wiredest looking torque conevtor and flywheel ive ever seen!

[jbgroby]

Originally Posted by truckdude239

that is the wiredest looking torque conevtor and flywheel ive ever seen!

The new torque converter is a standard model. If you're talking about the older Hydramatic torus unit, it was a fluid coupling set up. Back in the day, the flywheel was seperate from the flex plate. Noa they combine the two into one.

[jbgroby]

Hooked up the replacement throttle cable and connected the TV cable.

[Rick Bollinger]

I see you went with bowtie overdrives tv set up. Set your cam in the middle of the adjustment give it full throttle and cable should be set. It really is a great set up. What lock up method are you using? I went with the B&M and really like it.

[jbgroby]

Rick, because I do t know what the heck I'm doing and learning as I go. So I'm having the truck towed to the transmission shop in the 12th. to have everything set. I've never don't this before and I do t want to screw it up. Also I learned from Lewis MACKLIN that having a 790R mated to the 395, the idle speed from should be around 650 rpm. I'll need to raise my idle speed next Thursday. (Leaving for vacation early Saturday).

[Rick Bollinger]

You will love the 700r4 and great write up.

[jbgroby]

Rick, because I don't know what the heck I'm doing and learning as I go. I'm having the truck towed to the transmission shop on the 12th. to have everything set. I've never done this before and I don't want to screw it up. Also I learned from Lewis MACKLIN that having a 700R mated to the 305, the idle speed for the combo should be around 650 rpm. I'll need to raise my idle speed next Thursday. (Leaving for vacation early Saturday).

[jbgroby]

Got the new shift rod installed, I added 2 cotter pins as a safety backup.