700r4 swap into 68 Chevelle

[Tony Silva]

Ok, so the other day I bought a 1989 Chevy full size truck Silverado. I needed it for the front sheet metal for my dads pick up, as it turns out it has a rebuilt 5.7 liter motor and a 700r4 tranny. So, heres my question, what parts are needed to install the 700r4 truck transmission in to a 1968 Chevelle? The Chevelle currently has a TH350. The car also has full dual flowmaster exhaust system (not a whole lot of room left underneath the car). Does the cross member have to be moved back? I'd really prefer NOT to drill any holes in the frame because this Chevelle is a convertible...and the frame has already been "worked" to be road worthy and look nice. As the car is right now...it is show worthy...driven only on weekends...

[Tony Silva]

Oh, and also, I believe the 700r4 is also referred to as a 4L60. Tranny mount location, length, slip yolk spline count. What or where can I find the specs. Id really like to have everything ready for a swap so it will only take a couple of hours. I can figure out the wires from looking at my cousins truck...he went to a 700 from a 350. I just hate lifting up this convertible. And want to do the swap to only be a two hour project.

[slingslingbinks]

The drive line yoke spline count is the same. The 4l60 is close to the same lenght at the th350. U have every thing to swap it out so go for it. Jack it up and swap it over and deal with the small stuff later. If u have to cut the driveline down then do it. Easy swap but it will take more than 2 hours, but it will b worth it. Don't forget to swap over the t.v. cable and set it all up. I set up a 4l60 in my 70 elky that had a th400 in it and the x member matched the other holes and build another drive line, Set up the t.v. cable and used a transgo shift kit to make it lockup with out any wires running to it. Left the shifter as it was and the only thing i couln't do is manualy hold it in 1st gear. Witch was no big deal, Have fun and enjoy your overdrive and lock up converter, And gas mileage

[silicon212]

The standard length TH700R4/4L60 is about 2.375" longer than a 6" shaft extension TH350, so if that's what you have in it now, you will need a driveshaft that's about 2" shorter than what's in it now. The mounting point is about 3/4" behind the point for a TH350, so you will have to modify the crossmember for it to properly fit (just extend the hole in the crossmember if there's enough steel). The 700R4 and TH350 use the same driveshaft yoke with the same spline count so you need do nothing there.

The width of the TH700R4 is the same as a TH350 so no hump mods are necessary. You will need to lose the vacuum modulator line (as the 700R4 does not use one). Proper adjustment and operation of the throttle valve (TV) cable is critical on this transmission, as this performs the same functions as the detent cable on the TH350, with the added functionality of the vacuum line modulator which it replaced. If this is not properly adjusted, it could be the end of the transmission in short order.

The TH700R4 is a great transmission for that car; it will improve economy and add torque in first gear for quicker launches due to it's shorter first gear ratio.

Anyways, here's the answer to your second question:

[Tony Silva]

Wow!!! Thanx for all the info. Today is July 6. I started the swap last week on July first, just doing a couple hours each day going about it nice and slow. Finally, I've completed it!!! The swap was fairly straight foward. I did have difficulty getting the TV cable dialed in-just-right, but all is good now. I did have to get a new shift indicator bezel assembly due to the 4 foward gears rather than just the three. Also I made use of an older four speed detent ratchet shifter I had had in a box for 3 years!!! Had to elongate some bolt holes...nothing major though and I also ended up having a 4x4 fab shop in Paradise,Ca build me an aluminum drive shaft. It came out really nice. On the freeway, with my buddy driving his stock vehicle next to mine.....at about 65 MPH the engine is spinning 1,750 to 1,800 rpm's. I'm running stock sized 15 inch Rallys, I've got a set of 18" Rally styled wheels with an overall rolling diameter that is greater than the 15 inchers. Does any body know the formula for figuring out speed & distance. I want to calibrate my speedo...or atleast try to calibrate it before I have to buy a kit. Any ways, Thank you guys for all the info. It was a great help.

[slingslingbinks]

Good job, Yea the t.v. cable adj. is tricky. Find a spedo shop who can calibrate the trany OR build a adaptor to speck it out to the correct speed. Also a.t.r.a. has a website that has a spedo calculator on it. Ask around your local area for a a.t.r.a. Trans shop and they might b able to help u.

[Tony Silva]

OK, thanks. I'll give a company called Transmatic here in Chico, Ca. A call some time in the next day or two. A.T.R.A. What does the letters stand for.

[slingslingbinks]

Automatic transmission rebuilders ass.

[slingslingbinks]

atra.com

[slingslingbinks]

tony check this site out
http://www.atraonline.com/SpeedGC_Simple.asp

[Tony Silva]

Quick update...this swap has been completed for a long time now. The 68 convertible Chevelle is already sold. It's been gone for quite some time. I have already rebuilt 3 other Chevelles since this time...but anyways, the swap went very well. I had an aluminum driveline out of an Aerostar minivan modified, The tranny needed the tailshaft from a th350 bolted onto it. I had to install a pressure switch and a torque converter lock-up controller. The swap was really easy. The frustrating part was adjusting the TV cable to get the shift timing correct. Had to buy a very SPECIFIC bracket to bolt onto the carb allowing the correct geometry of the tv cable movement.

[Tony Silva]

...as a side note, I never knew the tailshaft on the th350 will bolt onto the 700R4 allowing the use of the older style cable operated speedometer.

[slingslingbinks]

Hey Tony, 10-4 on the t. v, cable and the geometry. Cool to know about the output shaft's will swap. C-ya Scott