This really is the last problem for my (new to me) 2000 blazer 2wd. Off the line and cold the 1-2 shift is nice and smooth. At the next stop sign, however, the shifting then gets a bit rough (not bad but felt) and engine tends to take off a bit past 2000 rpm at the shift point and at no change in throttle. At that point the shifting is more like a clunk and a lurch.

Fluid is a little overfilled but nice and red.

Will check TPS when I get a chance later tomorrow. There are also plans for transmission fluid and filter change.

Should I just go ahead and get the solenoids now just to be sure it isn't them or is there a way to rule them out at the pan?

Note: Fuel pump sensor for the fuel gauge is bad, can only see correct fuel till about half a tank. Will fix when fuel pump goes out.

Work done so far after buy:
1. seafoam
2. throttle body cleaning
3. MAF cleaning
4. Fuel filter changed
5. air filter changed
6. PCV valve just as soon as I can find the darn thing

Work in progress
1. spark plugs (sneaking suspicion they aren't platinum...will get AC Delco)
2. Wire set
3. Rotor
4. Distributor Cap

 

I highly doubt that it is caused by a bad solenoid. The solenoids sound like they are working, but you may have some seal issues in the valve body that are contributing to leak by once the transmission warms up a bit. But if the TPS sensor is reading weird, it can cause a shifting problem.

 

Thanks for the insight swartlkk. I'm gonna check the TPS and rule it out. I'll post back with an update this afternoon if I can.

 

TPS is good. The valve body guess seems like a likely candidate due to it not happening till it warms up. What would be my course of action if it is? I plan on dropping the pan this or next weekend.

 

I would suggest you pick up the ATSG manual for your transmission and do some reading before dropping the pan. There is a lot that can be screwed up if you do not know what you are doing and start poking around.

Here are the causes for a harsh 1-2 shift:

 

If that's the case, I guess I'll have to start looking for some quotes. Thanks. Will keep updated.

 

How about this? Found it on Alldata. Seems parallel to what you have told me and the ATSG.



General Motors Informative
GM service bulletin about code p1870 - GM service bulliten about code P1870
Posted By: NJBOB on 2/28/2006Location: Collingswood, NJ

This GM service bulliten might apply to your vehicle:
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.
Important



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

 

That could work. It is not a simple procedure though. You will want to read up on the Sonnax P1870 kit.

 

Update on transmission:

Changed the fluid and filter/gasket and added some trans-x as I have had good results from it in the past and really wanted to get some more time with the trans before overhaul.

The fact that it gets worse when it gets hot led me to believe that the oil was worse off than I had originally thought. Turns out I was right. There was a nice fine dust at the bottom of the pan telling me that this may have been the first time it was changed. No big pieces though. The gasket was a PITA as well also an indication that it had been on there quite a while. Fluid was a nice deep red though not burnt.

Vehicle shifts Much smoother though it is still a tiny bit rough...kinda like a small thump at shift 1/2 and 2/3 (less so at 2/3). Will let the trans-x set for a day to see if it gets better.

Vehicle accelerates a lot better too though that could just be my mind. Will keep you posted.

 

First, at 170,000 miles, my tranny started sliping. A guy who has a scanner couldn't see eany message code. Took it in the tranny shop where I had done some business before. He asked me if that if I intended to keep the blazer for a while the tranny could use an overhaul. I agreed to it; $1900CAN !
Rough shifting between 1-2 gear. Took it in again, he re-adjusted some tranny valves to their limit and told me he couldn't do any better. Still got the problem. It's a though it
rpm won't go down between 1-2 gear. Feels like someone is banging on the frame with a hammer.
I am wondering if there isn't some kind of module or switch specifically for the 1-2 gear shift that would be worned out ?
Danyboy