700r4....

I am having a problem with this tranny....When cold it works beautiful...as it warms up the convertor attemps to lock then rapidly unlocks . After it's fully warm it just doesn't even try anymore...sounds like a bad pressure switch or something....

I took it to the tranny shop and the guy said he could not access the ECM (88 chevy truck) so he talked me into this...

He said he could install a check ball in the tranny (where?) to hydraulically lock the covertor as soon as it shifts in 2nd gear....

Boy it works...But I don't like it...so I want to do my mod....just lock it when it hit overdrive ...So it's only locked when in overdrive....

Question is...where did he install that check valve so I can take it out??? I guess I could ask him but I don't want to seem picky....

Really I just don't want to pay another $ 60.00 to take it out...

Thanks.........Doc

More than likely, the check ball was installed in the lock up solenoid. There are ways to wire the lock up solenoid internally so that it will only work in 4th gear though it depends on what your wiring looks like right now because different models and model years had different pressure switches inside. There are also many different aftermarket kits that can allow you to work lock up any different ways. Hope this helps.

thanks....i need to know for sure about the check ball...

I have the diagram that shows how to wire the convertor for the 4th gear only lock-up....It requires a trip to the chevy dealer to get the right switch...

What don't you like about it? I would think lockup in 2nd, 3rd and 4th would help mpg and be pretty exciting when you hit 2nd. This is interesting to me since I seek mpg but do not have my 350/700R4 running yet. Why don't you like it?

Don Shillady
Retired Scientist/teen rodder

What I don't like about it is....

When it shifts to 2nd it's like it hitting 3rd instead....It really bogs the motor...well not bad...

The worst is when slowing down to turn or yeild...If it doesn't shift back to first it chugs until it does....

worst of all there is NO part throttle down shift with this...it's all or nothing....

If you drive easy on the peddle , like grandma, well then it's not bad except the slow down thing.... but if you like to motor from light to light fairly quick well this hinders alittle...

I have put alot of these 700R4's in non-overdrive vehicles and have always wired them myself with the overdrive-only lock up mod.....

This is the first time I have used this meathod...and I don't like it...Worst of all it doesn't unlock when you hit the brake or mash the gas.....the only way is to get back to first gear.....To the wood from a stop you don't not notice it much....

If he did something to the solenoid it will not allow fluid to pass through it if you remove it see if is restricked . If it is then do this. Remove the restriction. a 1988 700 has the solenoid grounded by the ecm . with the switches in the trans you can ground it in 4th gear only The switch with only one wire to it is the 4th gear signal . Cut and splice the ground wire on the solenoid to the 4th gear switch.Supply 12 volt to the A terminal on the trans. wire connector. This will run through the other switch [4-3 down-shift]and then to the solenoid. If he didn't restrick the solenoid I have no idea what he did.

By a new Valve body, then put a shift improver kit in it. that guy messed up your valve body and your gonna burn up your transmission. it is only supposed to lock up in 3rd and 4th. '88 truck, the ECM controls lock up, the tranny guy bipassed this by adding the check ball.

the valve body is fine it only controls tcc enable oil which comes on in 2nd which it is doing the solinoid controls the tcc apply valve wich is in the pump. To see if the computer is working properly all you have to do is find the F terminal in the aldl connector [the one scan tools are attached to] stick in a 12 volt test light with key on the light sould be dim . step on the brake the light should be bright. Bring the truck up so speed warmed up 50 mph and the light should go out.

"When it shifts to 2nd it's like it hitting 3rd instead....It really bogs the motor...well not bad..."

dr_bowtie, I have a Monster Motorsport R700 which has a hydraulic lockup on the 4th gear so there is no electrical connection at all (that's what I like about it). I am still building so I don't know how it runs yet but I have concern about your comment above. Since the R700 has a lower first gear than the TH350 or TH400 the gap to the second gear ratio is a little larger, but the rear gear may have something to do with this. I have a 3.55 rear ratio and hope that is low enough to allow for the gap from low to second gear. Sooo, can you tell me/us what your rear gear ratio is? I would guess that a 3.55 or better a 3.7 rear ratio would pretty well solve the "bog" between low and second but that a higher (stiffer) rear gear like a 3.23 might make the gap between low and second worse?

Don Shillady
Retired Scientist/teen rodder

My dad has a 700 in his street rod. It has 3.25 gears. He says that it would work much better if it had 3.90 gears. So in my opinion, I would say 3.73's, 3.90's would be the way to go.

I have a 700r4 in my T bucket with a 3.73 rear and I love it. It locks off a switch on the dash but will only lock in OD. With a 2500 stall 3.06 low gear and a 3.73 gear this thing will go really good from a light. It unlocks with a brake light switch. Tap the brakes when slowing down and it down shifts out of OD.