TH350 to 700r4 swap

[74 Shortbed]

I know I'm late to this party but I'll put this up. If it's accurate, and I have no reason to believe it isn't it'll be a big help to whoever find this thread. It also has measurements to the center of the trans mounts from the face of the bellhousings.

It is accurate I measured a few and it matched..

 

[Camar068]

Good info for us guys that don't have access to them to measure, thanks

 

[R8rPhan]

I know I'm late to this party but I'll put this up. If it's accurate, and I have no reason to believe it isn't it'll be a big help to whoever find this thread. It also has measurements to the center of the trans mounts from the face of the bellhousings.

Awesome...

Just went under and measured my existing tail housing.. It's about eight and a half inches long...

According to your diagram, a 700r4 with 6" tail housing is 30" long.. My trans now, with the 9" tail housing (8 1/2" measured) should also be 30" long.. It has about 2" of yoke shaft sticking out before the U joint part...

So does this mean, that once I get the 6" housing and output shaft for the 700r4 that I won't need to modify my drive shaft at all??? If so, that's one less headache...

 

[R8rPhan]

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So, I got the numbers on the trans I'm gonna get...

9TXM007H

So according to this chart, it's an 89... This is a good thing...
Would like to know what the 'TX' indicates (the 'M' means it's a 700r4, evidently)...

Also, since it is coming off of a 4x4, it won't have a tail housing or correct output shaft with speedo gears...

My existing TH350 has what appears to be a long tail housing... Apparently, the tail housing for the 700r4 only comes in one size, 6" (according to the lengths diagram posted previously)

Are tail housings and output shafts available to just 'buy' or will I have to get them from a scrapyard? Or???

When shopping for one, what questions do I need to ask? What do I need to look out for?

 

[R8rPhan]

The swap is going into a 79 cab w 79 1 Ton frame...

I got a tilt steering column and shift linkage off of a donor 88 suburban.. The suburban had an OD tranny, so swapping that with my existing 79 column should take care of linkage/shifting, right? They appear to be identical in as far as mounting in the truck.. Are they?

So, besides the tail housing, output shaft (with speedo gears), what else will I need to have ready before the swap?

I guess I'll need a TV cable and bracket (are these sold as a kit, if not what all parts do I need to get to put it all together?), a nice large aftermarket tranny cooler, a torque converter if this one doesn't come with one (probably does) and what else?

Is that everything?

Are there any electrics involved, or other cables?

Will the TH350 dipstick tube I already have work on the 700r4?

Should I mess with replacing the pump/seals while it's out? Is that something I can do myself, or does a tranny shop/tech need to do it?

 

[HotRodPC]

Awesome...

Just went under and measured my existing tail housing.. It's about eight and a half inches long...

According to your diagram, a 700r4 with 6" tail housing is 30" long.. My trans now, with the 9" tail housing (8 1/2" measured) should also be 30" long.. It has about 2" of yoke shaft sticking out before the U joint part...

So does this mean, that once I get the 6" housing and output shaft for the 700r4 that I won't need to modify my drive shaft at all??? If so, that's one less headache...

Yes, for the most part, the Squarebody Th350 which is what's called the intermediate output shaft, but most call it long shaft cuz they're aren't aware there is a 12in output shaft used on wagons and vans in the olden days. But a Squarebody 6in tailshaft Th350 can be an even swap with the 700r4, same driveshaft, same detent cable to TV cable linkage and all. Keep in mind, this only applies to 2wd units. Not 4x4 cuz the trans cases are different length. The difference in the case length for the 2wd is the 700r4 w/ 6in tailshaft, and the Th350 with the 9in tailshaft makes the 2 the same overall total length within a 1/2 inch or so which is easily made up in the driveshaft yoke. And Th350 and 700r4 have the same 27 spline output shaft.

 

[R8rPhan]

And Th350 and 700r4 have the same 27 spline output shaft.

Okay, there is a problem... The later model 700r4s have a 30 spline output shaft from everything I've read...

So I guess that means, I'll need a different driveshaft yoke if the TH350s have 27 spline shafts (meaning my yoke is 27 spline)...

Or can my existing tail housing and 27 spline output shaft from the TH350 be used on the 700r4? If it can, is this a bad idea (should I make sure to use all 30 spline stuff)?

My understanding, is that the earliest 700r4s with 27 spline output shafts were complete pieces of crap and should be avoided at all cost.. Is this because the shaft itself is a weak point (I'm not going to be racing, but I will be doing some towing up steep inclines and hauling firewood) or just an indicator that these are the early POS trannies (with other things making them weak)?

 

[R8rPhan]

So, in the pic below of my carb, there is the throttle cable on top, and then another cable on a bracket on the bottom.. Is this bottom cable the kick down cable or the TV cable? Or do they both do the same thing? and this cable is all I need for the 700r4?

 

[R8rPhan]

Also, can Tranny shops 'bench test' a Tranny and Torque Converter to see what it's condition is? Or does it have to be in the vehicle to do that?

 

[HotRodPC]

Okay, there is a problem... The later model 700r4s have a 30 spline output shaft from everything I've read...

So I guess that means, I'll need a different driveshaft yoke if the TH350s have 27 spline shafts (meaning my yoke is 27 spline)...

Or can my existing tail housing and 27 spline output shaft from the TH350 be used on the 700r4? If it can, is this a bad idea (should I make sure to use all 30 spline stuff)?

My understanding, is that the earliest 700r4s with 27 spline output shafts were complete pieces of crap and should be avoided at all cost.. Is this because the shaft itself is a weak point (I'm not going to be racing, but I will be doing some towing up steep inclines and hauling firewood) or just an indicator that these are the early POS trannies (with other things making them weak)?

Nope Nope Nope, Close but no cigar grasshoppa. Your INPUT shafts is what was upgraded. Not the OUTPUT shafts. The 82-84 units do have less splines, then upgraded for 85 and up models. Carry on with your plans.

There were many bug fixes in the 82-84 models, most of them can be upgraded with backwards compatible models with parts from 85-86 models. The 87 and up models have aux valve bodies which changes things so many parts from 87 up are NOT backwards compatible to the 82-86 models but this all a total different ball of wax that will just confuse you when all we're concerned about here is that you have a complete working 700r4 ready to bolt in, but yes there were more weaknesses on the 82-84 than just the input shaft.

 

[HotRodPC]

So, in the pic below of my carb, there is the throttle cable on top, and then another cable on a bracket on the bottom.. Is this bottom cable the kick down cable or the TV cable? Or do they both do the same thing? and this cable is all I need for the 700r4?

We're gonna get you all fixed up and educated. KICKDOWN cable or rod is FORD thing. Yes, the bottom cable is your DETENT cable that measures throttle pressure to the transmission and helps determine shift points, AS WELL AS, does control kickdown or passing gear. In a 700r4, it's called a TV Cable as in Throttle Valve, and it to measures throttle pressure to determine shifts, kickdown for passing gear, AND most importantly, regulates fluid pressure so you don't burn up the transmission. Make sure you get that cable adjusted RIGHT with the correct geometry, which you have since you're set up for Th350 there or you'll cook that 700r4 in less than 100 miles or so. Th350 doesn't matter how you adjust it, it'll just have ****** shift points if you don't hook it up or adjust it right, but a 700r4, is very very dependent on that cable being in working order and adjusted properly or it'll die a miserable death of burning up starting with the 3/4 clutch pack.

 

[HotRodPC]

Also, can Tranny shops 'bench test' a Tranny and Torque Converter to see what it's condition is? Or does it have to be in the vehicle to do that?

Some transmission shops MIGHT have that capability if they have a dyno test machine that looks like a big lathe that they hook the transmission up into then they can run tests to see if it's all in working order. I'd say it'll be hard to find one that does though.

 

[R8rPhan]

Nope Nope Nope, Close but no cigar grasshoppa. Your INPUT shafts is what was upgraded. Not the OUTPUT shafts. The 82-84 units do have less splines, then upgraded for 85 and up models. Carry on with your plans.

There were many bug fixes in the 82-84 models, most of them can be upgraded with backwards compatible models with parts from 85-86 models. The 87 and up models have aux valve bodies which changes things so many parts from 87 up are NOT backwards compatible to the 82-86 models but this all a total different ball of wax that will just confuse you when all we're concerned about here is that you have a complete working 700r4 ready to bolt in, but yes there were more weaknesses on the 82-84 than just the input shaft.

So what does this mean, then? I'm assuming that I have to get a 2wd tail housing for a 700r4, which is 6 inches in length and once bolted on, my tranny will be the right length, and so will my drive shaft... I will have to move the cross member (I'm told the holes should already be there, but I have not verified this yet one way or the other)..

But what about the output shaft? Do all have 27 splines? Will all work with my drive shaft yoke?

I was just looking on eBay and see many 700r4 tail housings for sale.. Some come with output shafts... Is it safe to assume that they will all work with the 700r4 I am getting?

Are there differences regarding speedo outputs? If so, what do I look for? I don't really care about speedo gear rations as my speedo gauge will calibrate to any of them...

 

[R8rPhan]

Make sure you get that cable adjusted RIGHT with the correct geometry, which you have since you're set up for Th350

To be clear, you're saying I already have the brackets/cable I need, but just have to make sure it is adjusted properly once the new tranny is in?

 

[R8rPhan]

Curious.. Will my existing 3 speed column and linkage work with a 700r4? I don't care about the shift indicator on the column.. I've already yanked that out anyways...

Or is the total shift linkage travel amount different for the 2 transmissions and the linkage/column will need to be changed to allow that?