Struggling with my 700R4

[legend57]

K. Here is what I have.

Truck:
1976 K20 in process of full restoration. Truck is running with steering and brakes, so its able to move under its own power. Most sheetmetal is at the body shop preparing for the full repaint, so it isn't driveable on the street.

Drivetrain:
Level 3 700R4 from Gearstar.
NP203 with part-time kit (rebuilt by Gearstar (incorrectly), and then rebuilt again locally to correct the issue. Gearstar is great, this was an anomaly)
400 Engine - rebuilt. Tuned and runs great.
Stock front and rear axles

TV set up:
Used the Bowtie Overdrives kit to connect TV cable to the QJet.
Line pressures (psi) at idle:
Park: 80
(I checked to make sure the pressure rises instantly when the throttle is moved)
Reverse: 125
Neutral: 80
Drive: 80
D3: 80
D2: 180
D1: (haven't been able to test yet. Shifter needs adjustment)
I haven't checked the line pressure at full cable extension in each gear yet. I need a helper.

Issue: (at idle with the Transfer Case in 2WD H)
When I shift from Park to reverse, I get a solid, but not harsh, shift. Feels right. If I let off the brake, the truck wants to roll.

When I shift from Neutral to Drive, it is less solid. It isn't delayed, or imperceivable, but just different than reverse. If I let off the brake, the truck barely wants to roll. I have to touch the gas to get it to roll. It almost feels like the brake is parking brake is engaged. I just rebuilt the rear brakes and they are adjusted to have very little drag, so I'm pretty sure it isn't that. I have tried to back down the driveway and then drive forward, but it just doesn't seem like it wants to go. If I give it throttle, it will go, but again just doesn't seem right. Maybe I don't have enough fluid in it? It has been hard to check the level since I haven't been able to get it to temperature yet.

The line pressures seem OK, but I am weary about trying to drive it up and down the block to test it out. I don't want to burn anything up. Anything else I can check before hand?

I'm thinking either something in the transmission or transfer case isn't quite right. My confidence in the T-case isn't high. Is there a way to check it?
Ideas on how to diagnose.

 

[NickTransmissions]

OK. Here is what I have.

Truck: 1976 K20 in process of full restoration. Truck is running with steering and brakes, so its able to move under its own power. Most sheetmetal is at the body shop preparing for the full repaint, so it isn't driveable on the street.

Drivetrain:
Level 3 700R4 from Gearstar.
NP203 with part time kit (rebuilt by Gearstar (incorrectly), and then rebuilt again locally to correct the issue)
400 Engine - rebuilt. Tuned and runs great.
Stock front and rear axles

TV set up:
Used the Bowtie Overdrives kit to connect TV cable to the QJet.
Line pressures (psi) at idle:
Park: 80
(I checked to make sure the pressure rises instantly when the throttle is moved)
Reverse: 125
Neutral: 80
Drive: 80
3rd: 80
2nd: 180
1st: (haven't been able to test yet. Shifter needs adjustment)

Issue: (at idle with the Transfer Case in 2WD H)
When I shift from Park to reverse, I get a solid, but not harsh, shift. Feels right. If I let off the brake, the truck wants to roll.

When I shift from Neutral to Drive, it is less solid. If I let off the brake, the truck barely wants to roll. I have to touch the gas to get it to roll. It almost feels like the brake is parking brake is engaged. I just rebuilt the rear brakes and they are adjusted to have very little drag.

The line pressures seem OK, but I am weary about trying to drive it up and down the block to test it out. I don't want to burn anything up. Anything else I can check before hand?

I'm thinking either something in the transmission or transfer case isn't quite right. Ideas on how to diagnose?

Your pressures at idle are a little on the higher side but that's to be expected as Gearstar likely installed larger ratio boost/reverse boost valves as well as a stiffer/longer TV boost spring in the valve body. That said, what are your pressures at full TV? If you didn't do a test to see how the unit would react to throttle position, I'd do that first before taking it for a test drive.

 

[Matt69olds]

To expand on nicks advice, watch the pressure while you move the throttle. The line pressure needs to increase with throttle opening.

I’m curious what tv cable kit you bought from Bow tie. Since these trucks came with 700 transmissions, and you are using a Q-Jet, you shouldn’t NEED a kit. At most, you would need to cut off the tv cable linkage and the throttle shaft, and transfer and weld to your current Q-Jet and run a factory tv cable bracket. That would duplicate the factory tv cable setup.

 

[Chevy 88]

All I see is problems with the 700R4.

If I ever get another old school automatic - I'm going with the T350.

They have problems too, at least they either work or they don't - with the exception of the vacuum line.

 

[legend57]

All I see is problems with the 700R4.

If I ever get another old school automatic - I'm going with the T350.

They have problems too, at at least they either work or they don't - with the exception of the vacuum line.

Yea, I probably should have gone with a 4L60E (early 1 piece case model). I'm not 100% sure it is the trans. Could be something odd with the T-case. I'm going to do the line pressure testing and I'll report back.

 

[Matt69olds]

All I see is problems with the 700R4.

If I ever get another old school automatic - I'm going with the T350.

They have problems too, at least they either work or they don't - with the exception of the vacuum line.

The majority of problems are caused by people that don’t understand them, or know just enough to get into trouble.

People think the can cobble together the tv cable brackets/linkage, and think as long as the cable is tight at WOT, all is good. And if all you did is drive at WOT, that would be true. Unfortunately, it’s the other 90% of throttle opening that will destroy the transmission.

The 700 is a good light duty transmission. With some upgrades, it’s a great medium duty transmission, assuming it’s installed correctly. If you plan on lots of power, or beating on the truck like it owes you money, then bite the bullet and go 4L80.

 

[Broken85]

They even put 700R4s in some of the K20’s and Almost all of the suburban. I have plowed snow with one for the past 40 years. Granted it’s low mileage but we just finally had to rebuild the transmission last year for the first time since new. And that is hooked to a 350hp small block. If you don’t pressure test them before you drive them for correct TV cable position you will burn it up in five miles. If you think you got it close without pressure testing it, you will probably burn it up in 5 years. The gen1 and gen 2 of these transmissions were a problematic for sure, but around the early 90’s the geek squad finally dialed these things in and made them decent trannies for light duty trucks.

 

[Matt69olds]

Agreed. The first generation (82-84) definitely had some flaws. In typical GM fashion, they kept improving it until it was just about perfected, then started over with a new model.

 

[peats]

All I see is problems with the 700R4.

If I ever get another old school automatic - I'm going with the T350.

They have problems too, at least they either work or they don't - with the exception of the vacuum line.

I have a couple with no problems. Maybe the problem is you.

 

[Scruffy49]

I have a couple with no problems. Maybe the problem is you.

In my case, definitely
.
1979 block/heads. Unknown year redrilled tbi mid-rise manifold. Everything else is stock 1992 parts on the engine. Have to use the “universal” (fits -nothing- correctly) tv cable. And like clockwork, every 8 months lunches reverse and 4th, snaps the flexplate, and gets a lift home on a rollback… OBS body, Squarebody heart transplant.

Switching to a 4wd version 350 or 400, Qjet and normal 1979 distributor. Truck gets the stuffing beat out of it doing local natural disaster recovery. 700r4 plus 32” tires and 3.42s equals a ticking time bomb.

My 85 C10 is staying Qjet 262-6 and Th400.