700r4 swap questions.

[Awann99]

I recently picked up a used 87 700r4 to swap in place of the th350 in my 1969 1500. I wanted to get a little better gas milage and help quiet the engine down on my commute. I have a 3:08 rear end in the truck currently and I will be swapping that to a spare 3:73 5 lug 72 read end I have so the 700r4 will drive better. I’ve already swapped to disk brakes using 72 stuff so I will just have to swap the rotors from 6 to 5 on the front. I’m not sure how to set up the lock up harness on the trans. The guy I bought to from had just cut it at the base. Any suggestions to a kit to use and how to hook it up? I also wasn’t sure which torque converter I should go with. The trans came with one but I’m not sure how to identify it. I’m running a 235r75r15 and will have a 3:73 rear end. I know I will need to get the drive shaft shortened as well.
Thanks guys.

[tim_mc]

There are some threads on here that discuss the electric solenoid for 700R4s and how to wire a power through a newer brake light switch that has cruise control contacts to kill the lock-up on the converter when braking. I believe you just need a 12v source and ground to click the solenoid into lock-up.

I just installed a 700R4 with 3.08 gears, but my lock-up is done hydraulically with a shift kit and an older valve body. I have a spare rear end I was going to build, but so far I really like it with the 3.08s. It doesn't lug like many have mentioned. For short trips where I don't want it to hit OD, I just put it in "3". With some recent carb changes I'm OK leaving it in OD all the time. As for the converter, make sure it's a lock-up one. Hopefully there's a part number on it to let you know if it's a standard stall. Mine is a DGM35-3.

The big thing to get correct is the cable geometry. You'll want to get a bracket that corrects the pull for the TV cable since it controls pressure relative to the throttle position. Here's a pic of mine with the Edelbrock 8026 TV cable adapter and 8036 adjustable cable bracket. I tried to keep the TV cable parallel with the throttle cable.

[Awann99]

How does the 3:08 handle when pulling anything. I wanted to stay with the 308 but I feel like it would solely become a cruiser. Plus 5 lug steelies are much easier to come by. Any idea where to get a cable bracket adapter for a quadrajet?

[tim_mc]

I don't tow with my C10 and specifically wanted to cruise, so I can't answer that. If you plan on towing often then a gear swap may be what you need. I suggest installing the 700R4 and see if the 3.08s can handle it for occasional towing - if not, then you can swap to the 3.73s.

Here's a link to a Q-jet/700R4 thread...you may want to Google some others.
https://ck5.com/forums/threads/calli...-700r4.255404/

[Awann99]

Thanks. I found a thread over the brake switch lock switch you mentioned. Monster transmission has a kit for it. What kind of mpg do you get with your truck now that you swapped?

[tim_mc]

Originally Posted by Awann99

Thanks. I found a thread over the brake switch lock switch you mentioned. Monster transmission has a kit for it. What kind of mpg do you get with your truck now that you swapped?

I just did the swap a week or so ago and am still playing around with the jetting on the new carb. It will probably be a while before I start tracking mileage. I'm just glad to have it back on the road.

[notsolo]

As stated the 308 rear gears are decent, scoots pretty good IMO.....would be best to calculate the speedo gears before you install it also, I came up with 39-18.. for me with 29" tall tires. Correct carb linkage is most important......I think Summit has carb bracket.

[Indyuke]

I wired the TC lockup to the 4th gear (OD) pressure switch. Anytime the the transmission went into 4th, the TC would lock up. I didn't bother wiring the lockup through a brake switch or engine load switch, because anytime the transmission wasn't in 4th the TC would be unlocked.

Some people wire the TC lockup through the 3rd and 4th pressure switches. Just comes down to minor details on what times you want your TC to be locked up.

Edit: just realized this is an older thread.

[ubtripn]

I wired it to a rocker switch on my dash, I hit it when I am over 55 mph then shut it off manually when going slower. Not a big deal for me, I drove it for 5 years without it wired, and it didn't overheat or anything but I wanted to extra 3000rpm gain at highway speeds.

[Steeveedee]

To the OP- I had a 700 in my '68 Skylark behind a SBC. When it went south, I had a 350 put in, and I did not have to change the driveshaft length. It was done in '06, so I don't remember if the yoke had to be changed. Maybe look at which tail shaft length you have?

[Claudman]

I have been using the B&M Converter Lock-up control and like the way it works. You can dial in the speed that the lockup can become active so that it only locks up on the highway. Part Number is 70244.

You have to place a sensor for the speed behind the speedometer, but it's not a big deal.

[Big Kev-O]

I like the idea of the B&M lockup because it works similar to GMs design but the paying and additional $200+ to install an outdated transmission doesnt seem smart. I assume the OP is using the 700R4 because it was affordable. My truck was wired for switch operated lockup when I bought it. A lockup relay is wired to switched power that is disconnected when the brake pedal is depressed. I can lock it in 3rd & 4th by flipping the switch and it unlocks while the brake is being pressed. I believe this is what is in my truck. Can be peiced together for about $25.

https://www.bowtieoverdrives.com/cat...php?ITEMID=334

I just switched from 4:11s to 3:73 with 265/70/16 tires. Of course it towed like a beast with 4.11 but the 3.73 cruise much better on the highway and still has some low end tow power. I would never conside anyting less than 3.55 for towing with a SBC mated to a 700r4.

[hevy_chevy67]

Not the cheapest option, but I really like Bowler's lockup kit. Only goes into lockup in O/D, and will wait 8 seconds after shifting before going in.

[GMCJOE]

3.08’s are low for running with a overdrive transmission, and could cause it fail from overheating. 3.42 gears in my opinion are as low as you want to go. 3.73 are good overall gears for the 700r4. I have the factory 4.11’s and runs out great with my 700r4.

As for lockup, plenty of material out there to read on how to hook it up and different options for it. I personally when with a non lockup torque converter for my 700r4. I also have about 2k into my transmission from getting it built by a reputable shop. Only thing I sacrificed is a few 100 rpm’s, about 1-2 mpg, and it’ll run just few degrees higher on temp for the trans.

[gmc684x4]

Old threads keep going op has not replied since may he proubly has his tranny wired up

[Sparky dave]

I have 3.73s and don't do much highway driving and would prob have gone with 4.11s of I ever change. But I am on 22s at the moment. Building a v671 blower so going to see how it feels with a bit of extra torques first

[siggyfreud]

Originally Posted by GMCJOE

3.08’s are low for running with a overdrive transmission, and could cause it fail from overheating. 3.42 gears in my opinion are as low as you want to go. 3.73 are good overall gears for the 700r4. I have the factory 4.11’s and runs out great with my 700r4.

As for lockup, plenty of material out there to read on how to hook it up and different options for it. I personally when with a non lockup torque converter for my 700r4. I also have about 2k into my transmission from getting it built by a reputable shop. Only thing I sacrificed is a few 100 rpm’s, about 1-2 mpg, and it’ll run just few degrees higher on temp for the trans.

There were plenty of cars (C4 Corvette's for example) that came from the factory with 3.07 rears and a 700R4. My college roommate drove an 85 with that combo and it was great due to the low first gear.

Using converter lockup in overdrive will help reduce heat since the TC doesn't have to slip.

I had a 4.11 and 700R4 in my 66 GMC and it was too short for the street IMO. I couldn't maximize acceleration due to traction issues. Would have been better with different suspension, but I think a 4.11 with 700R4's 1st gear is overdoing it for most situations.