Chevy TrailBlazer, TrailBlazer SS and GMC Envoy Forum banner
1 - 20 of 21 Posts

·
Registered
2006 chevy trailblazer_ls
Joined
·
115 Posts
Discussion Starter · #1 ·
I have a 2006 TB and recently I have started feeling a harder shift from first to second gear. I am just now hitting 40,000 miles and the transmission fluid is clean. I don't really tow anything and in my option I drive pretty smooth. (no hard accelerations.) It only happens occasionally and I can't seem to replicate it when I am trying to show someone else. Any suggestions? I am hoping this is not a sign of a major failure in the near future...
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,708 Posts
When it does this have you tried to turn around and go back to where you were and see if the same thing happens again? Angle of assent, throttle position, temp, and other things cause the PCM to tell the tranny when to shift. Twice in a row in the same place could be normal. Problems usually are more of a slipping tranny, not snappy.
 

·
Registered
2005 chevy trailblazer_lt
Joined
·
2,636 Posts
Jason, I recently had my PCM tuned, and after the tune, the 1-2 shift became very firm. To the point my friend asked me "is something wrong with your transmission?". Interestingly, when I had my stock tune in, I never had an issue.

I'm assuming you do not have a tune?

If you are traveling about 5mph and shift between 1st and 2nd, does the clank of the clutch plates seem loud or louder than before? Does your hard shift also accompany a noise? Does the hard shift happen under low throttle or heavy throttle?
 

·
Registered
2006 chevy trailblazer_ls
Joined
·
115 Posts
Discussion Starter · #4 ·
From what I can tell there is no noise accompanied with the "hard" shift and I do not have a tune. Mechanically my tb is pretty much stock. I have not tried to intentionally recreate the feeling in the exact same road conditions or spot, but I will be sure to try that. I have however noticed that it will do both on an incline as well as on a level surface. I might be explaining this symptom very poorly, but I can feel two distinct actions when it happens. It is almost like it goes into gear pops out for fraction of a second and goes back in, but both times are more noticeable than a normal shift. Kind of feels like when you pop the clutch on a manually twice really fast in the same gear. I guess the second feeling could be coming from something else as a result of the first. It generally is more severe under higher acceleration pressure, but it will also do it under light load too. The thing that is bugging me is I cannot find any consistency with it and everyone thinks I am nuts because I can't make it happen when they are in the vehicle. Other than this though the truck runs great and I could not be more happy with it.

I appreciate the help so far, please keep the info coming,
 

·
Registered
Joined
·
7 Posts
Same Exact Problem

Jason,

I just registered for this site. Although I don't have a trailblazer...I kinda do. I have a 2007 9-7x Saab with the 5.3L V8. I am having the EXACT same problem you are. It happens about 10% of the time and is absolutely random. I will go an entire day without it happening at all, and other days, it will happen on the first shift of the day. I called saab and they offered to put it on the scanner to see if it throws any codes, but I don't think that will work. I will also say to anyone reading this post, it is a somewhat disconcerting event. The shift from 1st to second (when it acts up), feels like the jolt you would get if you throttled the engine in neutral (standing still) to about 3000 rpm and then dropped it in gear. It isn't going to spin the wheels, but there will be an uncomfortable jolt. I am glad the car has a 5/100000 warranty on drivetrain. Perhaps if I can't figure my end out I'll worry more when i approach the end of the warranty. For now I have 2 1/2 years and 77,000 more miles to go. Maybe it will go away and fix itself...??? :undecided
 

·
Registered
2004 chevy trailblazer_ls
Joined
·
62 Posts
Hey guys and gal's. I had the same issue as you, rock hard 1-2 shift once in a while. Well about 3 months ago the trans had a hard 1-2 shift...... and never shifted again. Hope your fix is easier than mine was!
 

·
Registered
2004 chevy trailblazer_ls
Joined
·
62 Posts
So I am to assume a blown transmission on your "final" 1>2 shift?
Yes it was. Took it to a tranny shop and they said the computer was commanding it to shift but it was not shifting, there were no codes so there was a hard part broken. I found a bone yard trans with 23k miles on car-parts.com so 500.00 and a weekend later, I was back on the road.

Good Luck
 

·
Registered
2002 chevy trailblazer_lt
Joined
·
388 Posts
Usually if your traveling up hill the shift will be a lot firmer then if your traveling on level ground, ive also found that if your WOT and up at the top end of the rpm band you back off to like 85% throttle it will shift extremely firm, moreso then if you just kept it pegged and did a WOT shift, probobly because of the pressures ramping up and then not being needed
 

·
Registered
Joined
·
7 Posts
Jason ... Not yet. Called the dealer and they offered to take a look. Since it is hard to replicate, I am hoping they have someone there who is knows their stuff and doesn't just hook it up to a code Machine .... For some reason I don't think it will throw a code.. So this could be a long process... I will probably bring it in next week as my Saab dealer will give me a loaner. I will let them keep it as long as it takes. I also have noticed my cruise control sometimes works and sometimes doesn't ... I am wondering if it could be an electrical issue with one of the on board computers.. Is yours still under warranty?
 

·
Registered
2005 chevy trailblazer_lt
Joined
·
2,636 Posts
Jason ... Not yet. Called the dealer and they offered to take a look. Since it is hard to replicate, I am hoping they have someone there who is knows their stuff and doesn't just hook it up to a code Machine .... For some reason I don't think it will throw a code.. So this could be a long process... I will probably bring it in next week as my Saab dealer will give me a loaner. I will let them keep it as long as it takes. I also have noticed my cruise control sometimes works and sometimes doesn't ... I am wondering if it could be an electrical issue with one of the on board computers.. Is yours still under warranty?
The PCM can turn off your cruise control as a warning to you to get your vehicle looked at. It could be a problem that doesn't throw a code, but is enough for the PCM to notice. I don't know the details, but I know its a sign that you should have it looked at.
 

·
Registered
2003 chevy trailblazer_ls
Joined
·
1,236 Posts
A hard 1-2 shift without a tune or other performance parts typically means wear in one of the bores of the valve body.

There is a Sonnax part designed to fix this issue:
http://transmissioncenter.net/PinHole.htm

Vehicles with a 200-4R, 700-R4 or 4L60E transmission can experience 1-2 light throttle abrupt or "bang" shifts, especially when using the Corvette or larger 2nd apply servo pistons. The current industry solution is to make the servo piston apply diameter smaller. This, however, limits the 2-4 band life. This shift problem commonly occurs when the accumulator valve is too large for the application, resulting in too much pressure on the 2-4 band. This valve train has 7 different OEM size variations: B, A, N, M, L, K, and F. They range from the largest valve diameter giving the firmest shift (B) to the smallest valve diameter giving the softest shift (F), respectively. The size variations are clearly stamped with the letter on the aluminum sleeve. Most vehicles, depending upon the transmission / engine combination, can use either the M, L, or K version. However, these are not available unless scavenged from other valve bodies. Each kit contains three springs of varying spring rates. Cost $42.00
 

·
Registered
2006 chevy trailblazer_ls
Joined
·
115 Posts
Discussion Starter · #15 ·
nratlantic,
Unfortunately, no my warranty expired earlier this year, but the dealer agreed to take a look at it, but they were "unable to replicate the problem."

I have had problems with the worn valve bodies on this transmission in other vehicles before, and installing the Sonnax kid did take care of it, but this does not feel like that.
 

·
Registered
Joined
·
7 Posts
At the shop today

Ok, So it is at the dealer as we speak. Have a nice loaner car and they will be giving it a thorough lookover. I have written down all the problems we have discussed and I have told them that even if it can't be replicated, there IS A PROBLEM. So i have high hopes!:thumbsup:

I also noticed that my gas mileage was about 2-3 mpg off. Felt like it wasn't shifting into O/D, therefore not allowing the AFM to engage. We'll see. The more problems that seem to be cropping up, the more I feel that this could be electrical. I'll advise their findings.
 

·
Registered
Joined
·
7 Posts
Report From Dealership on Fixed (hoping) 2007 9-7x

Jason and All reading..

As promised, I am posting my EXACT report on my service printout.

This was their findings on my issue as well as their exact methodology in searching for the problem.

THE REPORT reads as follow:

TECH CHECKED FLUID LEVEL WITH HOT TRANSMISSION. CHECKED OK. TECH CHECKED CODES. FOUND U0073 (TRANSMISSION CONTROL MODULE COMMUNICATION BUS A OFF), U0100 (LOST COMMUINCATION WITH ENGINE ECM) U0101 (LOST COMMUINICATION WITH TCM) AND P0700 (TCM REQUEST CEL). TECH FOUND AND CORRECTED WORN WIRING AT DATA LINK CONNECTION. TECH FOUND IT WAS WEARING THROUGH BECAUSE IT WAS HITTING ADJUSTABLE PEDALS. TECH RE-REROUTED AND SECURED. TECH ROAD TESTED AFTER CLEARING CODES. RECHECKED. OK NOW.

Remember this is a Saab 9-7 and although our cars are cousins...it is possible the codes might read differently. I doubt it, but keep it in mind. So that seems to be it in a nutshell. I am hoping it is that simple. I have driven it three times already and the cruise control has worked every time and the tranmission hasnt shifted hard again. So..... I will keep my fingers crossed :worried:. Ultimately Jason, it appears that it may be an electrical issue. I know its hard to believe, but I am thinking it may be the case for you as well. Lets keep this thread going for a month or so and if for any reason my car acts up again, i will be the first to post?

Thanks for the input everyone... Jason....Let me know how it turns out?

have a fantastic 4th everyone. Lets remember why we celebrate it.....
 
1 - 20 of 21 Posts
Top