700R4 Lock-up question

[Ole Greenie]

Hey All...I have a question about lock-up on a 700R4 tranny. I have the later version (post 86) of the transmission and I need a bit of knowlegde/wisdom about lock-up. My issue stems from the converter locking in 4th gear under slower speed conditions causing my motor to lug. Now I have a 3.07 rear gear and was wondering if this lugging was attributable to the long gear set or due to some switch or pressure valve within the trans. Should the transmission be going into 4th gear in slow speeds at all? It is about 5 years old with only about 10000 miles since bought from Bowtie Transmissions. TV cable is adjusted correctly.

Is there an adjustment that would keep it in 3rd until a certain speed or will I need to swap out gears? What is the "Normal" gear set for someone with a BB and a 700R4?

Thanks for your help!

[cdowns]

change the rear gears to 373 and it will b fine

[6772owner]

I have heard of people putting a switch into the lock-up circuit so that they can manually disengage the lock up, this would help some with the lugging as it will raise your RPM's. Which method are you using to control the lock-up? I have a 90' 700R4 and used the Jet Performance kit and have not had any problems, but I believe that I have 4.10 gears, so that may be why. Let me know if I can help in any way.

[Ole Greenie]

Hey guys...Thanks for the insight and suggestions. Like you all, I'm guessing the 700R4 was not designed for gears as long as the 3.07 I have.

Anyone have a set of 3.73 gears????? Suggestions on a vendor?

[VetteVet]

Here is a bookmarked site I found that talks about TCC lockup. It is somewhat technical but what I gathered from it is that there are kits that control lockup with an adjustable vacuum switch. The 373 rear gear ratio seems to be the preferred option but it depends on the weight of the vehicle,tire size, engine torque,shift preference, and many other variables. I suggest you contact Bowtie or TCI transmissions and give them all your specs.

http://www.rowand.net/Shop/Tech/LockupTCCWiring.htm

[Ole Greenie]

Ok...I received confirmation. I need to run a 3.73 gear set. Problem is I'm in Iraq and I don't know which rear end I have. It is out of a 71-72 5X5 lug truck.

So those of you who know, which size do I have? 10 bolt 8.5"?

Your help is much appreciated!

[Indyuke]

If you have friends or family that has access to the truck, have them take a pic of the rear gear cover, and then post it on here. We will be able to tell you what you have.

My impression was that the stock setup in these trucks was the 12 bolt rear, unless the SPID said something different. Someone will correct me if I'm wrong.

My truck came with 3.73 gearing, and it shifts into overdrive at about 30mph while coasting down a hill. Under heavy throttle it will wait until about 60-65mph to shift into overdrive.

[Wrenchbender Ret]

I have 3:08 gears in mine with 700R4 & it drives wonderful. I use a vacuum switch hooked into ported vacuum & pressure switch in 4th gear test out let. It only locks up in 4th & releases at closed throttle & heavy throttle.

[leddzepp]

I have a 700 R4 with 3.07 gears and I love it. I keep it out of overdrive around town to prevent it from shifting into 4th gear.

[rsavage]

First Ole Greenie - thank you for your service to this country.
I have a 200 4R in my burb with 3.07 gears. It will shift into 4th (OD) and lock up the converter at about 45, which lugs somewhat as I am only at about 1200 rpms. When not on the highway, I run it in 3rd (1:1) and have a manual switch that will manually lock up the converter in 2nd and 3rd. When using it this way, I have to remember to flip the switch when coming to a stop to unlock the TC. Perhaps you might want to do a similar set up as it would save you from changing out the rear gears. I got my wiring kits from Bow Tie OD's.

[Ole Greenie]

Originally Posted by Wrenchbender Ret

I have 3:08 gears in mine with 700R4 & it drives wonderful. I use a vacuum switch hooked into ported vacuum & pressure switch in 4th gear test out let. It only locks up in 4th & releases at closed throttle & heavy throttle.

Can you help me out a little more hear? How do you instal lthe vacuum switch? Thanks

[Wrenchbender Ret]

I get the vacuum switch from a late 80's van. It is on the fire wall outside & has a green & a blue wires going to it. Get the connector also. You can mount it any where on your truck & hook a vacuum hose to a ported vacuum outlet on the carb. Wire it in to the connector to the trans. Most of these trans. have pipe plug outlets on the right hand side. I get a choke oil pressure switch used on late 70's GM's. & put it in the 4th speed outlet. & wire it in the circuit.