Swervin... 700r4 follow-up

[mhorning]

Hey Mike, I talked with you last week about this 700R4 I installed in my truck.

http://67-72chevytrucks.com/vboard/s...013#post724013

I've been driving it for a few days and it seems to be shifting into all 4 gears. However, I notice that when I first start out, the truck seems to run at about 2200rpms, which I think is third gear. As the truck warms up, say after 10 minutes or so, I am noticing that it will cruise at about 1600. I am assuming that is the 4th gear kicking in. So does this sound odd to you? Is it possible that my TV cable is slightly out of adjustment or does the tranny shift differently until it warms up? It's cold up here, maybe 10-20 degrees

[swervin ervin]

I'm assuming you have the vacuum for the lockup routed throught the TVS (Thermostatic Vacuum Switch) mounted in the intake. What this does is control vacuum to related components with engine coolant temp. At around 160-170 degrees it opens and lets vacuum through. So, with stock 700R4's locking in 3rd also, this sounds about right. After it reaches operating temp, it will lockup in 4th too. Although, I'm not real sure it will lock in 3rd either if it is not up to temp.

Although, even if not locking, it should shift into 4th no matter what the engine temp, just not locking up. The way my tranny is, since I modified it, it does't lock in 3rd, only 4th. It shifts into 4th no matter what the temp, the way they are all supposed to. Then right on que, when my gauge hits around 160-170 I can feel it lock and it drops about 200 rpm.

Sounds like you have 2.73's. This would cause some low rpm numbers in lockup for sure. I cruise around 2000 (after lockup) at 70 with 3.73's.

Check this page and look at number 2. Substitute 2.73 where it has 3.73. Works out to 1605 rpm. This is also assuming 28" tire diameter. If yours is different, change this also.

http://www.73-87.com/convers_calcus/equation1.htm

[mhorning]

Mike,

I have 3.08 running on the stock rally rims- 15 inch I think. I can get it to kick into 4th like you said, but it doesn't seem to actually lock up until it gets warm. That is if I am thinking correctly about it locking up...I can feel it kick into another gear and it seems to stay there as I maintain the speed. Is that what I should be feeling?

About the vacuum, I guess I'll have to check that out. Does that line run down to the top of the tranny?

Forgive the stupid questions. I have again ventured into a new realm. The truck's been running great though, thanks to your carb advice earlier this past summer.

[mhorning]

Mike it looks like if I did my math right that I should be in 4th at 70 at 1690 rpms. Sounds about right.

[swervin ervin]

In stock trim, the vacuum hose will come from the carb to the TVS, the black one in the intake, and go to the low vac switch mounted on the firewall beside the brake booster. No vacuum goes to a 700R4 at all. This switch controls power to the lockup solenoid in the tranny. When vacuum is applied, it makes a connection and lets 12 volts go to the tranny. No vacuum breaks the connection, so the reason behind the name low vac switch. It's right not to lock up until it gets warm per the TVS. I tried to route mine without the TVS, just straight vacuum to the low vac switch. It would lock right away, cold. This seemed to me to cause bad driveability when cold. I also didn't feel this was good for gas mileage or plugs, etc,, so I put the TVS back on.

Yes, the 1690 sounds about right. What diameter is your tires?

[1FaastC10]

unhook your vac from the TVS, ad route it to an engine vac source. that should get your converter to lock as soon as possible. i think you will be better off leaving it the way you've got it hooked up now, as it is hooked up the way it was from the factory. there's got to be a reason the general did it this way.