Super Hard Shift between 1-2 after getting off the highway

[66GalaxieStL]

1999 GMC Safari RWD 113K

So I bought this van about 4 months ago and when I'm on the highway towing a trailer(Even without a trailer, I tow though all the time) when I get off the highway I have a super hard nasty shift from 1-2 and sometimes 2-3. This usually happens after I've been driving 65+ MPH. When I shut the car off and restart it the problem goes away.

The CEL went off when I took my trailer off. I drive with a trailer 95% of the time. The code it threw was a P1870- Funny thing is I hooked the trailer back up and the light turned off. Seems the van runs and shifts better with a big load. The van drove great all week and with no problems. Last night I was driving around 70-75 mph for about 30 min. I got off the highway and it started back up again! The light is also back on.

Any Ideas to what this could be?

[Phantom]

This GM service bullitin

TSB # 01-07-30-023A
Harsh 1-2 Upshift, SES, MIL, or CEL Illuminated, DTC P1870 Set (Replace Valve Body)
1996 Buick Roadmaster
1996 Cadillac Fleetwood
1999-2000 Cadillac Escalade
1996-2000 Chevrolet Camaro, Corvette
1996-2000 Pontiac Firebird
1996-2000 Chevrolet and GMC Light Duty Truck Models
1996-2000 Oldsmobile Bravada
with 4L60-E Automatic Transmission (RPO M30)
Built Prior to January 15, 1999 (Julian Date 9015)
This bulletin is being revised to update the Parts Information.

Please discard Corporate Bulletin Number 01-07-30-023 (Section 07 -- Transmission/Transaxle).
Condition
Some customers may comment on a harsh 1-2 upshift and the Check Engine Light or Service Engine Soon indicator is illuminated.
Diagnosis
Typically, these vehicles will have been driven more than 32,000 km (20,000 mi) before this condition occurs.
The scan tool may show a DTC P1870 set as a history code.
A harsh 1-2 shift or DTC P1870, caused by wear in the control valve body, may be difficult to duplicate when the transmission temperature is below 93°C (200°F).
Cause
The condition may be due to wear in the control valve body. This wear occurs in the bore that contains the TCC isolator and regulator valves, and results in poor, or no, TCC apply.

Important
DTC P1870 is a type B code. The conditions for setting the P1870 DTC must occur on TWO CONSECUTIVE TRIPS (ignition cycles, with a drive cycle) before setting a P1870 history code.
When the conditions for setting DTC P1870 are met (first trip), the PCM commands maximum line pressure and harsh 1-2 shifts are the result.
This may result in a harsh 1-2 shift with no history code if the conditions for setting the DTC required for the second trip are not met, on two consecutive trips (Ignition cycles, with a drive cycle).

When the conditions for setting the DTC are met, on the second consecutive trip, a DTC P1870 is stored as a history code.
When the P1870 code is stored, the PCM will turn on the Service Engine Soon (SES), Check Engine Light (CEL), or Malfunction Indicator Lamp (MIL).
Correction
Install a control valve body with the revised TCC regulator and isolator valves. These valves are used in all transmissions produced after January 15, 1999 (Julian Date 9015), and all of the service parts currently available through GMSPO contain revised TCC regulator and isolator valves.


If all of the following conditions are true, it is not necessary to rebuild the transmission or to replace additional transmission components beyond the control valve body.
Transmission operation is normal before the transmission reaches operating temperature, or before DTC P1870 is set (no slips, flares, or missing gears).
The torque converter is not blue or overheated.
The transmission fluid is not burned or has no burned odor.
The transmission fluid pan contains no abnormal debris (clutch material, bronze, brass, or metal fragments

[66GalaxieStL]

Is this a job someone that is mechanically inclined can do?

[Phantom]

Yes it should be , drop the pan and you should be able to access everything you need , the valve body is just above the pan

[66GalaxieStL]

Lol I I dropped my van off and in 20 min they called and said it was going to be 2500. I called another guy up and told him what's going on and said that it needed the valve body upgraded which would run me $250! He said its very common.

[Phantom]

Lol I I dropped my van off and in 20 min they called and said it was going to be 2500. I called another guy up and told him what's going on and said that it needed the valve body upgraded which would run me $250! He said its very common.

2500!! run Forest run ! get outa there fast

LOL yea it is common , that is why GM made a Technical Service Bulletin ,,250 don't sound bad

Item 740 in the pic is the valve body

['cudapaul]

Check your trans fluid first. If it is blackish/dark, or has a "smokey" smell to it you have worn some clutch or more likely, some TCC lining.

Repairing the valve body is the correct fix, but if you have the above condition, you have shortened the life of your trans, and may want to consider rebuilding it. If the fluid looks and smells good, then get the valve body fix done since you may have caught it early enough.

Check with whoever is doing the repair work and ask them how they are fixing it. The correct fix is to ream out the TCC cyclinder in the valve body and install a sleeve and new valve. If they are going to fix it that way, then go for it.

And make SURE that they guarrantee that will fix the problem.........

[drmmhmd]

Check your trans fluid first. If it is blackish/dark, or has a "smokey" smell to it you have worn some clutch or more likely, some TCC lining.

Repairing the valve body is the correct fix, but if you have the above condition, you have shortened the life of your trans, and may want to consider rebuilding it. If the fluid looks and smells good, then get the valve body fix done since you may have caught it early enough.

Check with whoever is doing the repair work and ask them how they are fixing it. The correct fix is to ream out the TCC cyclinder in the valve body and install a sleeve and new valve. If they are going to fix it that way, then go for it.

And make SURE that they guarrantee that will fix the problem.........

most shops now use an aftermarket shift improver kit that has a new valve that fits into the old worn out hole. slick really, or you can use the Sonnax kit,
Part Number: 77805E-K
TCC Apply Valve, Aluminum with Teflon Seal (4L60-E, PWM only)

cudapaul is correct that reaming the hole and replacing the spool is a good option, these valve bodies are problematic and there is a whole bunch of fix it kits. I know Superior makes a kit also. there is even a Sonnax universal fix all valve body kit has lots of reamers and parts. personally, the price is great. and if you keep driving it you will hammer your transmission into garbage. when we rebuild these transmissions we often buy after market new valve bodies that "fix" all the GM weakpoints and throw the valve bodies that come out into rubbermaid containers as it is more efficient to sit down and do 10 than have a man do one.