87 700r4 trans shifts up and down alot

[Kapote]

I have an 87 350TBI with the 700r4 trans i picked up recently, yes it is well used but drives great. the onlything is that when you are crusing between 55-65, it shifts in and out of overdrive alot, ive never had an auto trans in a squarebody before, anyone know of how to adjust or help this?

[RUN GMC]

I own a 87 GMC 350 tbi/700r4 and when I first got it I had the same problem over drive riding out longer than it should and disengaging at about the same as yours.....what I found out was the trans fluid was low but read ok on the stick because it foaming and causing torque convertor shudder......to tell this is when you pull your trans stick check after driving it for any bubbles no matter how few they are and if so add an 1/8 of a quart of trans fluid.....keep doing this and you should feel improvement in the driving and the shift and lock up....mine locks up at about 50 mph and disengages at 45 mph......I did this over a period of 3 days mostly highway driving before mine stopped at the later stage moveed to the more normal range......hopes this helps just look at your trans dip stick closely you will see a difference in the fluid coating it......

[mattybilt79]

You didn't mention what vehicle its in? That's the speed range for the od gear split. A very very common complaint I have seen for years about 700r4's. Blazers with 3.08 gears are terrible about gear hunting especially with taller tires. Honestly a lower gear ratio will solve the problem. From owning an 84 k5 with said issue its advised to leave trans shifted to 3rd if your stuck at that 55-60 speed limit gas mileage will suffer slightly but won't constantly have up down shift and rpm change either. As a comparison my wife and I both had 95 TBI vehicles me a burb with a big block 4l80e and 4.10s her Tahoe small block 4l60e 3.73 ratio both had 285/75/16s . Driving the same stretch of highway the Tahoe constantly downshifts to maintain 75 mph where the burb never down shifted due to the lower gear ratio an higher tourqe rating of the motor.

[Cabnchassis]

The national speed limit was supposed to be 55 basically during the years of the square body. It was changed in 74 and then changed back in the late 80s so that gearing probably drove just right for the time. That is if it was in one of the dozen or so states that actually cared to comply with the law. If you don't know your rear gear ratio it'll be on the paper in the glove box if you can still read it or it's even still there.