1998 Blazer 4x4. Just completed a 1440 mile winter trip through rain, wind, sleet snow and ice with no problems. On the last leg, after pulling a long grade, I noticed hard shifting from 1st to 2nd gear. I let the car sit overnight and took it around this morning. Shifting smooth as silk when cool. No illumination of engine lights. I've researched the P1870 code and remedy recommendations for this particular issue. Was wondering if anybody has installed the sonnax kit to resolve this issue and if so, did it work? My potential remedy choices are to replace the valve body with the newer generation (or) repair the valve body with the sonnax kit. Not sure which is the least expensive. Thoughts?

 

About 3 years ago I had this problem with my Blazer, setting code P1870, and the worn solenoid. It would only have the hard 1-2 shift after the transmission was warmed up. I ended up replacing the valve body with a version that had been repaired with the upgraded solenoid. I decided to go with replacing the valve body rather than trying to ream out the spot to install the new kit. I was a lot more comfortable with just unbolting everything and replacing the whole valve body myself, and I found a good seller on eBay selling repaired valve bodies.

If you do go that route and are interested, I took a bunch of pictures when I did it. I actually wrote it all up in a thread, but the pictures got wiped out a couple of years ago and I haven't ever remembered to reload them.

 

Noted and thanks. Seems like replacing the valve body with a new gen is the simple probably the least expensive fix. I took the rig out on the freeway for awhile today and could not get it to duplicate the problem. I'm a few days away from home in my old home town and tracked down an old friend of mine who's been a trans mechanic for 25 years. He is familiar with the issue and I'm taking the rig to him in the morning to pull any stored codes. I'll post an update....thanks for the offer on the pics but I'll leave the job to the pro with the proper tools and a lift. Much appreciated.

 

I have a hard shift from 1-2 when cold. Not when it is warm.

There is also some hesitation at 70 mph but it is more noticeable on the way to work when I have been on the freeway for 5 miles or so than on the way home. It was worse when I shifted to 3 rd than in OD. The postings I read said this can be caused by the distributor, could it also be related to the shifting issue?

I have read the other listings and some say change the shift solenoids and some say change the valve body. The TPI for the valve body says it has to happen when hot, so it seams this is not my fix.

Can someone confirm that the fix is the solenoids. Thanks in advance!

1998 Blazer 4x4 with 200k miles, Transmission cooler. New plugs, cap, wires.

 

Mine only did it from first to second and that was immediately following pulling a long grade on the final leg of a 600 mile trip. The following morning, it was back to normal. It's been a couple of weeks since that has happened and I've not been able to get the car to duplicate the problem nor has it thrown a code. I tried running it hard but still no duplication of the problem. I spoke to my mechanic and outside of a general tranny service, he is not recommending we do anything at this point. When cold, it shifts as smooth as butter. I just turned 110K