Can't downshift into 4th above 20mph. HELP

[Antonio]

Alrighty, straight to the point. Midway returning home on the highway, I went to downshift from 5th to 4th and it wouldn't let me. It felt like there was a bar in the way, or something blocking the gear. There was no grinding, it just wouldn't go. However, i can shift normally up through the gears as I accelerate. I can sorta downshift by going 5th to 3rd, then to 4th. I can shift from 4th to 5th just fine.

At a stop, i could move all through the gears just fine without any problems, once above around 20mph, this problems occurs.

I know there are more tech savvy people than I, so opinions and ideas are much appreciated. I thought about the synchro being the problem, but this only happens while moving, not standing still. I'm stumped. I'm wondering if I should be greatly worried, or if it is alright to drive until i get to the dealer.

[JRinKY]

Synchro is still the most likely culprit. Can you double-clutch 5th to 4th ?

I can't find it now, but I remember reading something about an interlock to prevent shifting from 5th to Rev. It could be a malfunction in that interlock.

[Antonio]

Originally Posted by JRinKY

Synchro is still the most likely culprit. Can you double-clutch 5th to 4th ?

I can't find it now, but I remember reading something about an interlock to prevent shifting from 5th to Rev. It could be a malfunction in that interlock.

no, i can not double clutch from 5th to 4th.

[CJsSky]

I am having a simular problem. The difference is that I have to double clutch to down shift to third to avoid grinding. Up-shifting is fine. Synchro is out. Getting new transmission this week.

[Antonio]

well, it's been much longer than I had wanted, but the car is finally scheduled to go in this tuesday. I'll keep everyone posted what the cause was. I'm also getting a bunch of other things fixed as well, so it might be there for a while. Then......when it returns......it's tune time...(and possibly solo high flow cat. Still trying to find a good exhaust shop who welds and will take on that job)

[OlSkyDriver]

Hey...it's a truck transmission don't forget. Double clutch. If that doesn't work, and it sounds like it doesn't, either keep it out of 5th, or don't down shift until you can go to 3rd, and order a new tranny. This one is done!

[Antonio]

Originally Posted by OlSkyDriver

Hey...it's a truck transmission don't forget. Double clutch. If that doesn't work, and it sounds like it doesn't, either keep it out of 5th, or don't down shift until you can go to 3rd, and order a new tranny. This one is done!

ha, just telling my, or any, service dept i want a new tranny is easier said than done I'd prefer not to have a huge trans swap done anyhow, but rather fix what's not working properly to avoid the value of the car going down any faster. Besides, they don't want to throw around trannys all willy nilly. This is definitely a strange one, and I'll post the solution when it's found. In the meantime, I have been just downshifting from 5 to 3 then to 4 to compensate.

[Bogie]

La transmission construits en France fonctionne très bien.

[JRinKY]

There is a detent in the transmission that prevents a 5th to reverse shift. The diagram in the service manual is not very clear, but it looks like it could be keeping you from making the 5th to 4th shift if it is out of position.

It would definitely feel like a bar is in the way, because a bar is in the way.

[CJsSky]

Antonio,

Good luck on getting the repair done. If they have to replace the tranny, it may be a long wait. The pratice of late is to replace, not repair. I have been waiting for a tranny for a month now. My original failed tranny was for the third gear synchro. The sencond just locked up. The original is still at the shop, but GM sent a letter that they want the old one. They would not allow the dealer to put it back on my car to get me running until another new tranny showed. If they do force a new tranny on you, and do not have an original. Then consider going the 08 route. Then they will have to replace the rear diff and some mounting. There has to be a reason for the change. Perhaps it is a good reason.

[Antonio]

ok, a little update on the situation. It's taken a little longer than I originally anticipated, but things are moving along. My car was in my possession while they were in contact with Technical Assisstance so at least I haven't been out of a car for very long.

Just recently I had the majority of my warranty stuff taken care of. Today the new "hotter" plugs were installed under warranty.

In regards to my downshifting problem, Technical Assistance advised them to drain the tranny fluid and change, saving a small sample for "testing" and for debris, etc. Also they suggested opening the shifter housing to get a better look at what's going on. So it's official. They're going to finally open him up and peek inside to see what's going on. They gave no real time frame, but I have a rental, and I don't mind being without the car as long as work is being done.

That's about all I know at this point, and I'll keep everyone updated as I learn more.

[Antonio]

Alright, here's the lowdown.

The service manager called me up yesterday. He said that he's been in contact with Technical Assisstance over at GM about this matter for a while now. They suggested him to open the shifter housing, and also take a sample of the tranny fluid for "testing" purposes. This was a few days ago they told him this. Well, they just gave him word to pull the entire tranny intact, ship it out to them in Detroit, and they'll be shipping him/me a brand new tranny to put in my car.

So that's what's going to happen. My trans is going to be replaced completely for new, and the old one is being shipped back to GM for analysis and study. Since my dealer was told not to open it, the actual cause hasn't been determined, and quite frankly, I doubt they'll tell me or the dealer exactly went wrong when the engineers do finally open it up in Detroit.

All in all, I'm happy with how this ordeal has transpired. The Service manager was honest with me to admit my problem was strange and he needed assisstance from GM to solve it. He contacted the right people, and actions are being done to resolve my issue as quickly as possible. Sucks that I have to have the transmission replaced, but at least I'll be back on the road in no time.

Oh, and throughout this ENTIRE thing, not ONCE has my dealer asked me about my performance parts....or tried to pass blame onto them. They're all pretty cool, and know me pretty well. Everytime I come in, they ask what else i've done to the car and seemed excited about it. Heck, even my saleswoman still remembers me by name and we always strike up a conversation when I'm there. Even offers me referral bonuses to bring in friends as customers. I think after this is all said and done, I'll be sending a basket to the dealer as well as writing a letter to the owner & corporate about my good experience. I think good deeds should get just as much publicity as bad ones.

So, hopefully sometime within the next week or two, I'll be back on the road

[Skip]

Remember to rebreak in the transmission as it will be new...Skip...

[Antonio]

Originally Posted by Skip

Remember to rebreak in the transmission as it will be new...Skip...

Yep, that kinda made me a little pissed remembering that i have to take it easy the first week or two, I wanna just jump back in and take off. At least this down time has allowed me to save money for mods. High flow cat and tune here i come

[JRinKY]

Antonio : Yep, that kinda made me a little pissed remembering that i have to take it easy the first week or two, I wanna just jump back in and take off.

500 miles shouldn't take more than a weekend......

[CJsSky]

I wish you luck with your transmission replacement. My first tranny went out for just a 3rd gear synchro. It was operational, but they opted to replace the tranny. The second tranny didn't last 6oo miles before a complete lockup in 3rd gear. The 3rd tranny seems to be fine, but the jury is still out. Oh, it took a month to get the 3rd trany in. I hope you do not need to wait so long.