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700r4 problems

C

Chevy1231

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I'm having some shifting problems with my 700. Shift 1-3 are good firm shifts but 4th is a little weird. If I'm getting on it pretty good it kind of falls into 4th but if I'm tAking of easy it will get up to about 45 and just hang out in 3rd until I star to back out of the throttle then it will shift into 4th and it's still not a good firm shift like I want but at least I can feel it shift. I'm wondering if it is the valve body. I just rebuilt it about 1500 to 2000 miles ago. It's got an alto 8 disc 3-4 clutch pack, borg Warner high energy band, corvette servo and .500 boost valve. Like I said I'm very happy with the 1-3 shifts but the 3-4 shift is pretty disappointing. I also notice that when I have my lockup turned on it locks up about 3 seconds after it shifts into 4th and I don't like that either.

And also if it matters for about the first 100 miles it wouldn't even shift into 4th
 
You could try and loosen the Throttle Valve cable a few clicks.

Any shift kit? Or did you block the 3-4 accumulator or at least install a stiffer spring?

Sometimes the accumulator piston PIN bore will wear and leak internally bleeding off pressure that would otherwise go to the clutch.

Some transgo kits actually block the 3-4 accumulator altogether.
 
3500GMC said:
You could try and loosen the Throttle Valve cable a few clicks.

Any shift kit? Or did you block the 3-4 accumulator or at least install a stiffer spring?

Sometimes the accumulator piston PIN bore will wear and leak internally bleeding off pressure that would otherwise go to the clutch.

Some transgo kits actually block the 3-4 accumulator altogether.
Click to expand...



I will try the cable and see what happens. I didn't block anything I just put new springs in it. I might look into a shift kit. I'd like to figure out the lock up problem. I'd hate to throw money at a shift kit and it be a problem with the valve body.
 
Lockup is done electrically (oem), unless you buy a valve kit.

Just to confirm, lockup is different than 4th gear right?
 
3500GMC said:
Lockup is done electrically (oem), unless you buy a valve kit.

Just to confirm, lockup is different than 4th gear right?
Click to expand...

Yeah it shifts to 4th then the converter locks. Ive got it wired through a toggle switch then through a brake switch then the pressure switch on the valve body and from there to the solenoid. My old transmission was one of the early 700s (1984) and it had 3 pressure switches for 2-3-4 and it locked up just like it should and I had it wired the same way
 
I also notice that when I have my lockup turned on it locks up about 3 seconds after it shifts into 4th and I don't like that either.
Click to expand...

What do you want it to do? There are several gadgets to buy for lockup control. Dials, switches, adj delay boxes etc.. You're the boss. :D
 
3500GMC said:
What do you want it to do? There are several gadgets to buy for lockup control. Dials, switches, adj delay boxes etc.. You're the boss. :D
Click to expand...

I'd like for it to shift like my old one. With the lock up turned on it would shift then i would have to get going about another 7-10 mph faster then it would lock.
 
You cannot swap VBs between Non-auxilliary VB and auxilliary VB transmissions unless you do a few mods to both VB and pump.

So if both units are aux VB then swap til your blue in the face. Likewise if both are Non-aux.

More than likely there are different springs between your two units in the shift vavles.
 
3500GMC said:
You cannot swap VBs between Non-auxilliary VB and auxilliary VB transmissions unless you do a few mods to both VB and pump.

So if both units are aux VB then swap til your blue in the face. Likewise if both are Non-aux.

More than likely there are different springs between your two units in the shift vavles.
Click to expand...

What all has to be done to be able to switch them? I read that on the older ones the tcc is done hydraulically and the newer ones are done by the ECM so I guess there's nothing wrong with mine it's just not the setup I want. So I guess that explains why I like my old one better.
 
All are using a solenoid to lock/unlock the TC clutch. The solenoid shuts the flow of fluid which in turn pressurizes the piston in the TC. No difference in the trans, just a different method to get currant to the TCC solenoid.

The switch from non aux to aux requires a passage in the pump body for the transfer tube, proper seperator plate, a passage blocked in the VB, and of course the aux VB. It's not that fun. Ya probably would be better off tuning on you current VB, TV and governor to get it where you want it.
 
I finally got around to checking my line pressures at idle in park I got 75 psi, in reverse I got 135, manual 1st was 125 if I remember right. The gauge was nice and smooth and and when I pulled out on the cable at idle it went up to 150 or 160. Going down the road in all gears it stayed right around 120 to 130.

The soft 3-4 shift is really aggravating. I tried to losin the tv cable a little and it brought the shift points down but made the 3-4 shift worse. I'm not sure what else to do I even changed the valve body last week and it didn't make a difference.

Could the accumulators be causing this? All other shifts are good and firm but the 3-4 shift
 
Could the accumulators be causing this? All other shifts are good and firm but the 3-4 shift
Click to expand...

Yes, the pistons can wear out the pin bore. I'd block the piston from moving with sleeves (no spring) to keep it out of the equation. Pistons are cheap. The only difference between 3 and 4 is the 2-4 band applies and stops the reverse input drum from spinning. So it could be a band or 4th apply piston also. A healthier .500 boost valve in the pump would help bump the pressures up a bit.
 
Chevy1231 said:
I finally got around to checking my line pressures at idle in park I got 75 psi, in reverse I got 135, manual 1st was 125 if I remember right. The gauge was nice and smooth and and when I pulled out on the cable at idle it went up to 150 or 160. Going down the road in all gears it stayed right around 120 to 130.

The soft 3-4 shift is really aggravating. I tried to losin the tv cable a little and it brought the shift points down but made the 3-4 shift worse. I'm not sure what else to do I even changed the valve body last week and it didn't make a difference.

Could the accumulators be causing this? All other shifts are good and firm but the 3-4 shift
Click to expand...

120-130 is low for having a .500 boost valve . Should be closer to 200 at full throttle. I think your problem is from to low of pressure for whatever reason. What all was done to transmission when it was out? Did it get any kind of shift kit?
 
littleboy said:
120-130 is low for having a .500 boost valve . Should be closer to 200 at full throttle. I think your problem is from to low of pressure for whatever reason. What all was done to transmission when it was out? Did it get any kind of shift kit?
Click to expand...

The 120-130 is cruising down the road barely on the throttle if I stop it it shoots up to around 180-190. When I built it I got the kit with the alto 3-4 clutch. I also put in a corvette servo, borg Warner high energy band, a new stock sunshell and the .500 boost valve
 
Yea , that is much better. Now, did you check the pressure on the 4th gear circuit? Kinda sounds like you have a leak on the 4th gear circuit .
 
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