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TH350 to 700R4 swap questions

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TH350 to 700R4 swap questions Empty TH350 to 700R4 swap questions

Post by Dinomyte on Wed Aug 22, 2018 9:37 am

I think I've read just about everything here and elsewhere on the internet about this swap. I've still got questions, so I'm posting here where I know the answers will be good. . . .

1- will I need to modify the floor pan for the 700r4 to fit?
2- do I need to use the lockup feature on the transmission?
3- should I be looking to remove the TV cable and brackets from the donor auto a TBI350 from a 1989 Suburban?
4- what stall should I be looking at, (so what factors influence the choice?)
5- do the TH350 cables and brackets for colum / floor shifter work correctly? I know I won't be able to get into 1st gear manually, anything other than that?

A little background:
Discovered I've got a leak that is likely the front seal, so a rebuild is needed and well this is a better choice.
I do some highway driving but the car is a big toy and I'm not concerned with fuel economy, but drive-ability is important to me.

Why the 700r4:
no electronics
lower first gear
good overdrive gear
it's available localy

What I know I need to do:

support the back of the engine
remove the old TH350
move the transmission cross-member back (don't know how far but can figure it out from the extra length of the 700r4)
insert the 700r4 and bolt it up
transmission cooler lines should need a little massaging but will thread right in.
get the drive shaft shortened (3" I believe) and back in.
get a TV cable & bracket? Donor auto is a TBI350 from a 1989 Suburban, will this engine's TV cable / brackets etc setup work?
add fluids etc, and get the TV cable setup adjusted.
connect cables etc,
go for a test drive

Thanks for the info and sorry for the essay . . .
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Post by Joe73 on Wed Aug 22, 2018 10:23 am

No floor.mods. stall will be dependent on your cam and rear gears. I recommend 3.73 with the overdrive. Great all around gear and still good on the highway. There is a company that makes a new detent selector for your factory shifter which will allow you to access all the gears and look stock. Google it but I think the company is shiftworks.
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Post by Joe73 on Wed Aug 22, 2018 10:25 am

I believe the 200r4 will bolt in With no driveshaft mod.
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Post by Dinomyte on Wed Aug 22, 2018 12:50 pm

Thanks Joe - go do know the floor doesn't need modifications

I know about the 2004r but I'm thinking the lower 1st gear would be nice.

As for the stall speed what information from the cam and what kind of formula is there for that?

thanks
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Post by thatfnthing on Wed Aug 22, 2018 12:56 pm

200-4R will bolt in with no major mods other than moving the crossmember back to the TH400 holes on the frame.  No drive shaft mods, better OD gear.  Might have to modify cooler lines, though, can't remember.

With that said, these apply to both units:

2. You do not need to use it.  However, it's advisable, as the lockup function can lower your RPMs further as much as 200 to save fuel.  It also helps the trans run cooler, as there is no slippage.  There are a number of ways to have the lockup trigger automatically.  Not using it to a degree defeats the purpose of having an OD trans.

3. The TV cable is very sensitive to improper adjustment, so it doesn't matter which one you use, as long as it's adjusted the correct way.  IIRC the critical factor is to make sure that at WOT the TV cable is pulled out all the way -- if it isn't, you will burn up the transmission.  (It's been quite a while since I did mine, so I will have to double-check.)  I use an aftermarket Lokar cable with a special spring loaded throttle connector so it pulls out all the way before I hit WOT.

4. Always a matter of opinion -- depends on your planned use for the car.  I kept mine a tad over stock (2000 RPM) because I don't do any drag racing and I didn't want to have to wind it to the moon to get moving from a stop light.

5. Expect the stock shift cable to not work.  It more than likely will be the wrong length.  I wound up having a custom one made.  If you have a floor shift, you will not need to make any changes to the column per se, but you will need an additional detent for the shifter.  You can get a new detent plate from a number of places like Camaro Central, or you can get a steel plate and grind your own like I did.  As for the dash indicator, this will be out of whack too due to the additional detent.  I believe there are replacements with the correct OD markings aftermarket, but I never explored those -- I'm currently running it without an indicator, and am planning eventually to use a Lokar aftermarket one. You should be able to get into 1st manually. I can, and I've never heard of anyone not being able to.

Joe's on the money for 3.73 being the best for all around performance.  3.42 will get you better mileage (but do NOT go any lower than that) and 4.10 will get you better launches with less mileage.

Additional food for thought: if you move the crossmember, expect to have to redo your e-brake cables as well.
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Post by Joe73 on Wed Aug 22, 2018 4:00 pm

These guys have detent plates that will allow you to access all your gears of the overdrive trans. Column or floor shifter. You can also google and find ways to modify what you have to work. Id talk to these guys and see what they offer.

https://shiftworks.com/collections/components-accessories/products/1968-72-chevelle-3-speed-shifter-detent-1

https://shiftworks.com/collections/components-accessories/products/1973-78-camaro-console-lens-indicator-adapter

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Post by g3chevy on Wed Aug 22, 2018 4:46 pm

I did a 200-4R swap back in 1989 on my 1976 Laguna. As I recall I had to open up the mounting holes on the shifter cable bracket that bolts to the transmission to get it to line up properly. Obviously mine was a floor shift car. And yes, I did have to move the crossmember back to the holes furthest from the front of the vehicle. The other thing was manipulating the cooling lines to have them line up to the tranny properly. I used the TV cable bracket from the donor car and set the WOT as per the manual I had for that mid 80's vehicle it came from. The only thing I that I never messed with is the shifter detent plate inside the console which kept me from shifting down into 1st. But it looks like they have kits for our vehicles to correct this. Here's a couple links of possible solutions on this topic. The NPD link below is showing in their catalog as a direct fit to 73-77 Chevelle, Monte Carlo, Malibu and El Camino. Hope this helps.

https://www.npdlink.com/product/shifter-conversion-kit-powerglide-2sat-th350-or/115220/10272

https://www.ebay.com/itm/1976-1977-1978-Camaro-Shiftworks-4-Speed-Overdrive-Conversion-Kit-SC2261-IN-STK/123051593383?hash=item1ca6724ea7:g:jH0AAOSw~rpZRENW

https://www.ebay.com/itm/1973-1974-1975-1976-1977-Cutlass-Shiftworks-Overdrive-Conversion-Kit-SC2352/142747908045?hash=item213c7037cd:g:5IkAAOSw1Rdax6n4
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Post by bigredlaguna on Wed Aug 22, 2018 9:23 pm

The TV cable is the most important part of the swap. The stud the cable attaches to on the carburetor needs to be in the proper location relative to the shaft. The stud for a th350 kickdown cable is in the wrong position and is likely why many overdrives are killed in short order.

Adjusting the TV "properly" on a linkage designed for a th350 will not give you the proper starting point from idle. The TV cable needs to move the instant the throttle blades move because there is little pressure form the pump at idle. This is why all good trans suppliers/rebuilders etc. want you to verify pressure rise with a gauge on the trans and that you get the pressure instantly upon moving the throttle.


There are adapter kits for most carburetors, but you may have to source a base plate for a Q-jet that has the proper linkage point.
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Post by thatfnthing on Thu Aug 23, 2018 9:41 am

Wow, it's all coming back to me now.

The TV cable should be at its full extension from the trans when at WOT, and conversely should be fully retracted into the trans when at idle.  However, the WOT extension is priority #1.

The issue with using a combo that wasn't paired by the factory is that the length the cable will extend from the trans is usually not equal to the amount of 'throw' that the throttle will have.  For example, my TPI throttle has slightly more throw than the cable will extend, but instead of doing the geometry math to relocate the stud, I simply added a spring extension to the throttle body end of the cable.  This way the cable is fully retracted at idle and fully extended just prior to WOT (which is okay), but still has that little extra play for me to mash the throttle all the way without breaking anything.

It worked for me because the two were close enough already.  A severe imbalance will need to have the throttle stud relocated.  So in the end it doesn't matter which TV cable gets used, as long as it meets the two requirements above.
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Post by Dinomyte on Thu Aug 23, 2018 3:36 pm

Thanks for all the information everyone. Turns out the truck and transmission are "on the farm" about an hour away so going to try and get there on the weekend. Anything special I should look for ?
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Post by Hs1973 on Fri Aug 24, 2018 9:51 am

Im about to put a 700r4 im my chevelle as we speak. I Found out that the early 700r4 has a 27 spline converter that after 84 was changed to a 30 spline due to tha 27 Being to weak. So keep an eye open for the number of splines, you naturally dont want a 27 spline one. As far as my research looks like the 27 spline is a model with alot of problems. So keep away from 82-84 year trannies. Also look for blown out pump seals wich im told is a commen problem.

Summit has both a adjusteble tv cable plus bracket sets for different model carbs. Also the shifter inside the car needs to be rebuild to be abel to go in all gears. Or Else you wont be abel to use the 1 gear setting. Since the shifter cannot shift Down that low in its original form. There is a kit for rebuilding it, but it is rather Pricey. Also summit has different kits to control the lock up, they ringe from 100 dollars and up. Please post your experience with getting it going.
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Post by Dinomyte on Fri Aug 24, 2018 11:08 am

thanks Hs1973 - I haven't even bought the things yet just trying to figure out if it's what I wanted. SO that being said IT IS WHAT I WANT. So long as the transmission is in reasonable shape it will be bought this weekend. It will likely be rebuilt. Thanks again for the info.
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Post by 73ss on Fri Aug 24, 2018 1:27 pm

shiftworks makes all the parts to do the job right. I used one of their kits in my swap. They also make a shifter cable that is adjustable on both ends allowing you to get the shifter detents lined up perfectly with the tranny detents. I was able to retain the "slap stick" function of my original shifter with one of their kits.

One of the biggest gripes with a 700 is the big spread between first & second gears. Too much of a rpm drop when going from first to second. this was done to get the low HP, heavy cars up and moving back in the day.
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Post by Hs1973 on Sat Aug 25, 2018 10:28 am

You are welcome. Im deep in the swapping, almost ready to pull the engine and trans out to clean up the engine and mount the new trans. So far it has not been that difficult.
My trans is a stage 2 build by mad dog transmissions, and has alot of upgrades and is supposed to handle 500 hp. I have been looking at the shiftworks slapstick kit with new shifter and all, its Pricey but looks Real Nice. I have the horseshoe shifter out of a 71 montecarlo wich shiftworks also have a kit for. I look forward to see how my car behaves with this trans in it, should be faster also since the 1 gear is lower than the 350 trans.
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Post by Dinomyte on Sun Aug 26, 2018 9:09 pm

Picked up the Trans yesterday, looks like its in good shape, got some questions about it though

2CAM284A

2- 1992 year
CA - application (what it originally came in)
M - 700R4
284 - day of 1992 it was produced (October 11th 1992)
A - first shift

Big K on the side - Truck transmission (typically 4x4)

Have I got the deciphering right?  What is model designation CA?

TH350 to 700R4 swap questions 20180810
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