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700R4 Overdrive

D

digitalepiphany

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I bought my blazer last August, and the guy told me that overdrive is out and that putting it in OD would lock up the transmission, so I should only put it in D. He said something about a solenoid being out.

Since I've owned it, I haven't had any problems, but I've never put it into OD. This hasn't been a problem, as I've only ever driven it around town. I'm now at the point where I want to get this fixed.

So, what can you guys tell me about this? I'm unfamiliar with transmissions, but a "solenoid" seems fishy to me.
 
digitalepiphany said:
I bought my blazer last August, and the guy told me that overdrive is out and that putting it in OD would lock up the transmission, so I should only put it in D. He said something about a solenoid being out.

Since I've owned it, I haven't had any problems, but I've never put it into OD. This hasn't been a problem, as I've only ever driven it around town. I'm now at the point where I want to get this fixed.

So, what can you guys tell me about this? I'm unfamiliar with transmissions, but a "solenoid" seems fishy to me.
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It's a bit fishy, because as far as I know, a 700R4 uses servos and not solenoids to shift. The only solenoid is to lock up the torque converter

If he's telling you that putting it in OD will cause the transmission to "lock up", either he doesn't know what he's talking about, or the OD has a serious problem that replacing "solenoids" isn't going to fix. Replacing servos or solenoids only fixes shifting problems. I've never heard of a bad OD locking up the whole transmission, sounds a little extreme. Maybe someone else has heard of such a thing.

Overdrives aren't very strong, it is possible to break them if you attempt to tow heavy in OD, hammer on them, or are running tires too big without gearing down. Before you do anything, check your TV cable for proper adjustment. You won't know what's going on with it until you try, and there may very well be a shifting related problem with the servos, valve body, accumulators, etc, but if there is mechanical damage, be prepared for a rebuild or replacement, or get used to driving around with no OD.

Here's a transmission diagram that gives you an idea of what you're working with:

http://www.transmissioncenter.org/700R4_4L60E_Parts_Blow_Up_Diagram.htm
 
Could you have misunderstood? on many 700's the torque converter clutch is wired to engage in 4th gear, hence, lockup in overdrive? Have you tried it?
 
It wasn't a misunderstanding on my part. He specifically said it was a bad solenoid, and that the transmission would lock up if put in OD. Kain was with me when I bought it, so maybe he'll chime in, but I'm positive that's what he said.

I haven't tried it in OD because I don't have the money right now for transmission work.
 
The solenoid controls the converter clutch only, fourth gear is hydraulically applied just like any other gear. I understand your reluctance to try overdrive after the warning you received, I just cant believe it would lock up the trans.:dunno:
 
It's possible he meant "lock up the torque converter", as in no slip in the converter, but you interpreted it as "lock up the drivetrain", like your tires lock and skid the truck.

There is an old trick for when your solenoid is bad or you're too lazy to figure out the truck wiring. You put a little ball bearing in the TCC solenoid, which is like having it always engaged. So that might be what he was talking about. There is also a valve in the valve body that enables lockup, so the clutch isn't engaged all the time, but it will be when you're in 4th gear. The TCC solenoid normally vents this hydraulic pressure to the pan. When you put current to it, it closes and the pressure now goes into the converter to apply the TCC. Having the TCC "locked up" all the time in 4th gear is better than not getting it to engage at all. The 700 will run too hot in 4th not locked up.

It's hard to imagine what bad thing could happen by moving the manual valve from 3 to OD. Best case is that the servo applies the band, you go into 4th gear and happily save gas. Possibly you would have to manually downshift to pass or whatever, as it might lug the engine instead of unlocking like it should. I would expect the worst case to be that nothing happens and you're still in 3rd, but how can anyone be sure?

Does the converter ever lock in 3rd gear?
 
Sorry, I didn't get an email notification for your replies. Just noticed them here.

He told me that the transmission would lock up if put in OD, due to a bad solenoid. That's all he said.

@Blue - I don't know what you mean by "Does the converter ever lock in 3rd gear?". Please explain?
 
digitalepiphany said:
@Blue - I don't know what you mean by "Does the converter ever lock in 3rd gear?". Please explain?
Click to expand...

As you know, the torque converter allows slip between the engine and the transmission. To save gas, there is a clutch inside the converter that can be locked during cruise to eliminate the slip. You may notice what almost feels like another small shift after it goes into 3rd. A good test is to cruise down the highway at light throttle, then without letting off the gas, tap the brake pedal just a little. There is a switch on the brake pedal to disengage the TCC, so you should notice the RPMs go up 100rpm or so, then lock back in after you let off the brake.

Or if you have a tach, just stay at a steady speed (like cruise control) and see if the RPM changes as you go up and down grades.
 
After looking into this some more, the only solenoid I could find is a TCC solenoid. Could that be what the guy was referring to? If so, would that present any problem with putting it into OD?
 
That would make sense that he would be referring to that solenoid. It can lockup the converter (normal) when the trans shifts to overdrive but cannot lock the trans up, no worry.
 
Perhaps the torque converter failed to unlock when the previous owner had the truck,and it stalled out at a stop sign ,like a manual tranny will if you didn't push in the clutch...and that is why he says it will "lock up" if you use overdrive..??..
 
diesel4me said:
Perhaps the torque converter failed to unlock when the previous owner had the truck,and it stalled out at a stop sign ,like a manual tranny will if you didn't push in the clutch...and that is why he says it will "lock up" if you use overdrive..??..
Click to expand...

That is a possibility, good thinking!
 
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