wierd transmission problem

Starting at 85,000 miles, my '99 Blazer began this strange behavior. The trans is fine for about 30 minutes, and then suddenly shifts extremely hard between all gears. If I stop for gas, or let it sit a few minutes, it will go another 30 minutes before shifting hard again. This has been going on for the last 20,000 miles. The engine light remains on all the time. Any ideas on what's going on?

You might have an active transmission code. Have a tech pull it or I heard that you can rent the scanners from places like AutoZone. I understand that electronic solenoids in the transmissions act up or jam up from contaminates in the fluid. This act sometimes log a code(s). I only know cause I borrowed a Chevy Shop Manual stumbled on the information. Good luck!

auto zone will scan for free hard shift after warm up in my case was transmission valve body known problem had mine rebuilt for 400.00 while on a trip to north carolina (aamco burlington nc ) took 4 hrs of highway driving to set code 1870 after repair gass milage went up 3-4 mpg on highway tranny was slipping worn valve body gives hard 1-2 shift

Starting at 85,000 miles, my '99 Blazer began this strange behavior. The trans is fine for about 30 minutes, and then suddenly shifts extremely hard between all gears. If I stop for gas, or let it sit a few minutes, it will go another 30 minutes before shifting hard again. This has been going on for the last 20,000 miles. The engine light remains on all the time. Any ideas on what's going on?


my 98 LT did the same thing, your engine code will be for transmission component slipping! The valve body on mine went at 84,000 miles, it ended up needing a new vavle body, cost about $300! Mine was worse though not only the hot slamming when shifting (only hot or sitting for a few minutes) but it also needed all new clutches and torque converter. A common problem, the tranny's are JUNK! That is for sure your problem, I guarantee it! :-) good luck, let me know how you make out!

had same prob with our 99 blazer, needed a PWM TCC solenoid(pulse width modulated tourque converter control solenoid) i also changed the kick down solenoid, fluid and filter. the pwm tcc was about 25.00 . and easy to change

My 98 Blazer is doing the same thing (hard 1-2 shifts and p1870 code). It did it last summer, so I flushed/changed the transmission fluid and filter, and it went away until now. Now, I clear the code, and it goes back to shifting normally (since the control module is what is causing the hard shifting to prevent damage from the "slipping"). Whenever it sets the code, I clear it each time, and it goes back to normal for about a week. What is the cheapest permanent fix? I'm a student, and I can't afford an overhaul/rebuild. I found this info (http://forums.pickuptruck.com/showflat.php?Cat=&Board=UBB24&Number=262973&Forum=UBB24&Words=p1870&Match=Entire%20Phrase&Searchpage=0&Limit=25&Old=allposts&Main=258250&Search=true#Post262973) online about it. The TBI they refer to is a technial bulletin from GM that states that the transmission needs to be rebuilt with a newly-designed valve body (expensive tear-down and rebuild).

99church, did your Blazer set the 1870 code? If it did, maybe I can just change out the PWM TCC solenoid...

Yes it did, common problem with 4L60e transmission,

ordered tcc pwm solenoid from bulkpart.com,,,,27.75 shipping included, located in dallas, tx, makco dist.

Yes it did, common problem with 4L60e transmission,

ordered tcc pwm solenoid from bulkpart.com,,,,27.75 shipping included, located in dallas, tx, makco dist.

Also, in the valve body. The bore wears for the TCC regulator valve, which leaks oil pressure for the TCC apply valve. So the torque converter slips, causing code 1870. Harsh shifts because of failsafe mode.

Pull valve body, use reamer on TCC regulator bore. And oversize valve.

Thats, if the solenoid don't fix.

Well, the parts alone (reamer and spring, etc.) to fix the valve are about 200 bucks with shipping, and my local AAMCO says they fix them all the time for $275 total. I think I'll let them take a chance on screwing it up before I screw it up worse than they can. :lol:

Very good call on letting the pros handle it. It doesn't make sence to buy all that tooling for one job.

It is fairly routine. There are some other bores that can wear also.