Automatic transmission newbie asking basic questions

[mibars]

I'm new to automatic transmission, especially of a mechanically controlled type. I have a 700R4 and I wonder how idiot-proof it is.

While I was cruising in OD at I think around 35 mph and passed a tiny hill the trans downshifted to 3rd, then it did what if felt like couple of times shifting between 4th and 3rd, so I've manually downshifted it to D. Once I gained some speed I found that by pulling the shifter I can make the arrow point at OD without the click, the transmission staying in D as the mechanism is a bit spongy. I decided not to shift to avoid overshooting past the D. This make me wonder what would happen in the following scenarios:

1) Can I safely shift from Neutral back to Drive/Overdrive at speed without the risk that it will shift to 1st gear before upshifting to correct gear?
2) Is it possible to engage Reverse while driving and will it end up in a big mess?
3) Will the transmission eventually upshift when left in "1" or "2" or will I hit a rev limiter?
4) Is it possible to force shift to 2 or 1 while at highway speed, or will it shift to the lowest gear that would not overrev the engine?

 

[PrairieDrifter]

1- shifting from neutral to any forward gear is fine at the correct speed. It should go back to 2nd or 3rd gear depending on gear selection and speed.
2-it will not engage reverse unless maybe below 10mph, avoid at all costs, although if your quick enough it wont hurt the trans if you realize instantly before it starts making noises. It'll generally make a clicking grinding sound(trying to engage), if it engages reverse while rolling forward it WILL slam into reverse.
3- trans will not upshift if you select 1 or 2, if you select D it will upshift. Your truck most likely doesn't have a limiter so it'll over rev.
4- yes the trans will down shift at highway speed into whatever gear you shift to, and it will over rev, and lock up the rear end. Basically like money shifting a manual.

 

[PrairieDrifter]

The 700r4 throttle valve cable typically doesn't play nice with newbies. But other than that it's a gm trans.

 

[75gmck25]

The 700R4 depends on proper adjustment of the TV cable (it runs parallel to the throttle cable at the carburetor), along with transmission fluid pressures, to determine how it shifts. A mis-adjusted cable can lead to eventual transmission failure.

If you are going to use a 700R4 for towing or hauling heavy loads it is best to leave it in drive and not use overdrive. You also want a separate transmission cooler to keep the fluid in good condition. At certain engine speeds (and pressures) under load you may also find the transmission “hunting” between 3 and 4. This may cause you to use Drive under those conditions instead of overdrive.

It sounds like yours is generally working correctly, but I have no experience with the 700r4 cable adjustment. My TH350 uses a simpler kickdown cable. It does not hurt a GM automatic to manually shift back and forth between drive and neutral at any road speed, unless you rev up the engine and then drop it into drive. Even then the torque converter is a fluid coupling (replaces the clutch) and it can take quite a bit of abuse from sudden engagement.

 

[mibars]

Thanks a lot, however the fact that a computer controlled engine could have no rev limiter is also a new thing to me! I'm considering adding a tachometer and learning what's the no-go zone for a stock truck 350 TBI.

I've read a lot about the TV cable and based on the overall feel vs it appears to be adjusted correctly, it has no slack and moves freely. However I can see a broken strand in that cable...

The important takeaway I hvae is that this transmission is not idiot-proof and I'll not hang my ignition key lanyard on the shifter anymore!

 

[PrairieDrifter]

You didn't say tbi. But that said, I've never hit a rev limiter in a tbi either. If there is one, it's wayyy high in the rpm.

 

[mibars]

Ah, yes, it's TBI, forgot that important bit

 

[PrairieDrifter]

It's the least idiot proof of gm transmissions of that era.

 

[squaredeal91]

I'm not 100% sure of my memory but one time in an 87 safari van. 4.3 tbi, I was pulling a small grade in cruise control and was cresting the hill but still some good load and for fun/ experiment I put it in Neutral and cruise stayed on I'm sure she reved and bounced a couple times while I was scrambling to cancel the cruise and calm her down lol.

 

[Frankenchevy]

Your truck’s rev limiter is valve float. Also, a rev limiter won’t do anything to protect the engine from over revving if you down shift/select the wrong gear going too fast. If you pull first on the freeway, it’ll hit 10k on its way to exploding.

 

[Matt69olds]

This is the correct way to set a TV cable. You will need a helper.

Remove the air cleaner. Have a helper floor the gas pedal while you look down the throttle body. Make the the throttle opens completely. Sometimes the floor mat holds the throttle from opening, linkage flex, whatever. Bend the throttle cable bracket until the throttle opens completely with the gas pedal floored.

Next, find the lock button on the tv cable. Push the button in, slide the inner cable casing all the way back into the outer cable. Release the lock button.

Now, floor the gas pedal. You should hear the cable rachet out. Reinstall the air cleaner. Take the truck for a drive, paying close attention to the shift points. If you feel the transmission slip or slide into gear, stop immediately!

If the transmission “hangs” a bit before shifting, loosen the cable a click or 2. If it slides into gear, repeat the adjustment.

Don’t try to make major changes to the shift points by adjusting the tv cable. When in doubt, it’s always preferred to have the cable slightly too tight thsn the other way. With the cable too tight, all you will get is slightly firmer and later shifts. Too loose, the trans will slip, and burn up.

As for towing in overdrive, as long as the engine has the torque to pull without the trans constantly downshifting or upshifting, the trans won’t care. Probably 80% of the heat in a transmission comes from the torque converter. Heavy throttle will cause the transmission to unlock the converter, creating heat. The constant shifting creates more heat.

Which brings up the next topic: if you plan to tow or work the truck pretty hard, invest in a hood transmission cooler.

If you accidentally shift to reverse while driving, as long as you’re not on the throttle the engine will just shut off. If you’re on the throttle, bad things can happen. Ask any car guy who has had a rental car.

 

[squaredeal91]

In high-school one of my friends had 3 or 4 rigs that he killed reverse in lol. I'm pretty sure each Time it happened was on the highway, or at least the times that killed it were

 

[mibars]

Valve float limiter What's the max safe rpm for a stock 350 TBI? 4000 - 4500 ?

 

[PrairieDrifter]

Valve float limiter What's the max safe rpm for a stock 350 TBI? 4000 - 4500 ?

Right in that range.

 

[mibars]

I'm worried that my TC seems to lock and unlock too much. Sometimes at steady driving it seems to randomly unlock and lock couple of times. At first I thought it was cruise control playing with throttle, but with windows up I can hear revs going up and down a tiny bit. I believe it is triggered by slight uphills, like the ones you'd normally barely notice and then continues once it is back to flat. Playing a bith with throttle makes it calm down.

I've adjusted TV cable according to the procedure which moved shift points a little up and made the shifts a bit firmer, fotunately the change is not to dramating, so I assume it was just a tiny bit too loose.

I'm worried because as with any clutch it has a limited life, so if I can make to avoid that unnecesary cycling it would be great.