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Tranny problem on 1990 C1500 with 700-R4


ksubenny
02-15-2010, 10:54 AM
1990 Chevy C1500 pickup, 2WD, 5.7L with the 700-R4 4 speed automatic, probably around 180k miles, the odometer stopped over 5 years ago. The 1-2 shift was getting a little sloppy and I knew the tranny fluid/filter handn't been changed in over 4 years so I did it, not a big deal once I got the pan off. Changed(not flushed) fluid and filter, filled back up with Dexron III and off I went. For the first couple days the 1-2 shift was happening at a slighly elevated speed(about 25 mph instead of 18mph-ish) but it disappeared pretty quickly and I didn't think anything else of it. But yesterday about 2 weeks after the change the tranny decided it didn't want to shift into 2nd until 33-35 mph and the RPM's were up in the mid 5K range at least(no tach). Checked fluid and it was where it needed to be, it did this at every stop sign and light, once I got out of town the 2-3 shift was slightly elevated but the final shift was about where it belonged.

My garage is now back in a condition I can pull it back in and work on it, but I'd like to get some input as potential causes before blindly dropping the pan? I don't have a ton of experience on tranny's other than having a general understanding of the operation but will at least attempt to do this one myself. From what I'm seeing it appears to be isolated to the 1-2 shift, but will probably drive it to work tomorrow(12 miles one way) to see if it continues with the very delayed 1st-2nd shift and to see if it acts up in any other ways. I don't have the Helms manual for it but would consider buying the full set(105 bucks) if it would be useful.

tblake
02-15-2010, 11:30 AM
I would first take a look at the throttle boost cable that goes from the throttle body to the trans. Sometimes they break causing late (or early) shifts. Maybe it is out of adjustment.

ksubenny
02-15-2010, 08:10 PM
Well finally got the truck in the garage after spending all weekend putting the garage back together. After taking a brief look before supper it appears that the kickdown cable is attached and feels like I would expect. I still need to crawl under the truck and check the transmission end of the cable but at least from the top side it feels good. I did find a cracked line(emissions sticker calls it the purge line) off the throttle body(cracked at the hose fitting on the throttle body) to the vapor canister, but as far as I know that shouldn't impact a thing on the transmission. I'm heading back out to the garage to do a bit more investigating this evening and see if I can find anything else, otherwise I'm probably dropping the pan tomorrow after work.

2000CAYukon
02-15-2010, 09:14 PM
That is not a kickdown cable. It is called the Throttle Valve Cable and it completely controls shifts on the 700R4. See http://www.tciauto.com/Products/Instructions/instructions/gm_tv_cable_adjust.htm on how to adjust it.

When you did the filter, did you make sure the filter seal is in correctly and that you have a good seal? Did you recheck the fluid level with the engine hot?

I have a 90 K1500 with 147K miles. About 20K miles ago, I took the valve body off and found that the spacer plate was worn where the check balls hit the plate.

Transgo makes an improved Throttle Valve as I was not happy with the 1-2 shift on my truck. I ended up installing a Transgo 700R4 Kit with a new spacer plate along with a Corvette Servo and a .470 Boost Valve (.296 Reverse Boost Valve).

An example of what I installed is here https://www.700r4l60e.com/store/product.php?productid=92&cat=65&page=1

//2000CAYukon

ksubenny
02-15-2010, 09:54 PM
2000CAYukon:

Thanks a million as it appears you and tblake were dead on, I just wasn't familiar enough with this tranny, all the other vehicles I've worked on thats a kickdown cable. After looking at the adjustment instructions you linked to I went out and saw that the slider was sticking out of the mounting bracket about 3/4" to 1". Adjusted it as the instructions said and after a quick mile and back it appears to be shifting just right. I'll verify tomorrow on the way to work but at least right now it looks fixed.

Thanks again for the help!

tblake
02-18-2010, 10:17 AM
Nice Job!

tblake
02-18-2010, 10:37 AM
2000CAYukon, Does transgo make a kit like this for the 4l60e? And to install it, does the trans need to be removed?

2000CAYukon
02-18-2010, 08:08 PM
2000CAYukon, Does transgo make a kit like this for the 4l60e? And to install it, does the trans need to be removed?

I have a 4L60E car and I installed the Transgo HD2 Kit and was very happy with the results. It already had the Corvette Servo but I did change the Seals on the Servo (D-Ring style).

For your truck, I would recommend https://www.700r4l60e.com/store/product.php?productid=369&cat=64&page=1

The tranny does not need to come out to install this kit. On my car, getting the servo out was not much fun. I had to drop the cat and modify the tranny hump to get it out. A lot more room on my K1500 for the Servo.

The torque on the valve body is in inch-lbs so you do need the correct torque wrench for this job. Getting the snap ring back into the servo cover can be a little tricky. There is a special tool for that too.

//2000CAYukon

tblake
02-19-2010, 06:40 PM
sounds good, thanks!!!!!!!!

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