Thread: Developing hard-shifts / Towing / Need Opinions

I have a 2008 grand prix base model with 95,000 miles. I’ve owned the car since 30k miles and had the transmission flushed at around 50k miles. I made sure to ask if the fluid would be flushed or just the pan drop and top off – the dealer said no flush and then proceeded to flush it >:0

I have done a fair amount of trailering motorcycles and gear with the trailer and bikes probably nearing the tow max capacity of 1000lbs. I’ve estimated (on the high end) 9k miles of this type of towing.

Recently, I have noticed under light acceleration the shifts between 1 and 2 and maybe 2 and 3 have become slightly harder. Not jarring or anything but noticeable. It definitely does not happen all the time. I haven’t done a good job of noting when it happens (trans temp, outside temp, drive time etc).
I am planning to have the tranny serviced soon (not flushed!) and I’ve done some reading about potential solutions. Tranny cooler, shift kit are what I’m seeing but I wanted to see if anyone has any comments about my observations.

Do shift kits increase the heat buildup in the transmission requiring a tranny cooler? Would installing a shift kit without a cooler, and continuing to tow in the manner I have been, be a recipe for transmission failure? Would a transmission shop install a shift kit and or cooler or would they stay away from these "modifications"?

Anyone think I'm destroying my transmission? I generally run 215-225* over the long trailering trips with the highest I ever saw at about 230*.

Thanks in advance!

So I had a pan drop, filter and fluid done at the local transmission shop. He mentioned there was more material in the pan than he would like to see. He mentioned it may go 10k or 30k he doesn't really know.

I asked him if it was related to towing and he said probably, but he said "it has 90k on it too" indicating wear at this point happens (but he saw more than normal). I know that at 90k this tranmission could be in excellent condition if it were perfectly maintained and had never been towed with. Whats done is done; so where do I go from here?

I have a trans cooler in the mail and overall the car is running great. Should I jump ship and sell it, just run it with the cooler and bump the fluid changes to 25k, throw in the shift kit, or run it into a tree?

All opinions are welcome but if you can back it up with some sort of experience that's better. Thanks!

Originally Posted by Scottydoggs

if you wanted to do a shift kit, the time was when the pan was off. you may want to suck out a quart of fluid, and dump a quart of lucas trans medix in there, it will help keep it alive longer.

get a long clear plastic hose, that fits down the dip stick tube and to the ground. push it down the dip stick tube till it dont move down any more, then siphon into a empty quart bottle on the ground.

I wanted to get new fluid in asap and the shop went straight to "full rebuild" when I mentioned a shift kit. I would be open to putting in a shift kit at any time. But for $100 I couldn't have bought everything I needed to drop the pan (needed a in-lb torque wrench in addition to all supplies). I will consider the lucas.

Originally Posted by 02NavyBlue

As long as the material in the pan was just dark sludgy stuff, and there wasn't a mound of it, that's normal. If there were silver metal flakes or something, I'd be worried. The slightly harder shifts probably happen when the trans is getting to a high temp (210+), and our impala does the same. If I were you, I'd throw in a shift kit and trans cooler. The cooler is something that should have been installed before towing things around that weight for long periods of time, but still doesn't seem too late. Which trans cooler did you order?

I verified that it was mostly clutch material and he said there was a normal amount of brass(?). I notice the (ever so slight) firm shift at low speed and low throttle. I may even be making them up as this transmission probably isn't the smoothest even when I bought it. There's still a little push to the shifts (right?). I bought a hayden kit from rockauto - the the Hayden 403. I hope that's a good choice for me.

Originally Posted by matt5112

I beat the living crap out of mine for 15K after it had a 75K on it. The only real issue was an overly long 1-2 shift at WOT only. Other than that, it was very well behaved. Unfortunately, it's not a very long sample.

On the second vehicle with a 4t65e, dropped the pan 6000 miles ago, installed the transgo shift kit and filled with dex VI. It did shift quite a bit quicker. However there was a very dark coating of dark clutch material on the pan and the bottom of the transmission. Just this week I dropped the pan again to change the filter and fluid because the vehicle has 78K miles on it with zero maintenance records after 20K miles. This means the fresh fluid will do a very good job of clogging up the filter right quick. I also opted for a bottle of Lucas transfix, a cooler and Dex III. Despite all of this, the transmission shifts exactly as it does before. Which to be honest is a rather good sign, means nothing in there was going wrong that the Lucas could help out with. This time there was a very light coating on the pan and case compared to the first pan drop. Again, very short sample, but still no real issues.

If the hardest you are on the vehicle is towing, and even then, you're not trying to drive it hard, it should last for a while yet. If it does go, a back to basix build from TEP would last longer than your existing transmission has and is under $1500 to your door. Just pay a shop 400-500 for the install and you're back up and running for another 100-150K easily. The only other question is are you willing to keep your care for your car for another 100K miles. If so, it's a relatively small investment compared to getting into another used car, certified or not.

The reality of this transmission is, it will run for 200K miles and more. But there are other small issues that can develop, and take it out prematurely. There's really no way to predict if something like that will happen. Since your car has the newest valvebody style, it's least prone some of the major issues. But for example, you still have the GM short lip input seal which can cause the car to not move from a stop very suddenly and without warning. The forward band can crack and fail, leaving you only with the 1-2 manual band for forward movement.

It's very tough to say exactly how long in any state, but a properly built replacement will do a better job for longer than a factory replacement. On the flip side, a poorly built replacement might give up after a couple days. There are many horror stories out there about poorly rebuilt transmissions.

I'm hoping my trans feels exactly the same or better than before (even though I think it can only get worse when you add new fluid). I've done a fair amount of towing in hilly western WI at 60-70mph with too much shifting between 3 and 4. I am going to stick it in 3 from now on - screw the mpg's. If I could dump it for $8k+ and buy another vehicle that would certainly be an option; I paid $13k for it certified with 28,000 miles. I would be sad to see it go for sure.

The shop ballparked $2800 for a rebuild. Would that be any more or less certain than a TEP rebuild? What do you mean a proper rebuild may work better than a factory replacement - whats the diff?

Thanks to all contributors!

Originally Posted by stocker

I wanted to get new fluid in asap and the shop went straight to "full rebuild" when I mentioned a shift kit. I would be open to putting in a shift kit at any time. But for $100 I couldn't have bought everything I needed to drop the pan (needed a in-lb torque wrench in addition to all supplies). I will consider the lucas.

I refuse to torque bolts with such a low torque spec that are simply holding the pan on. Namely because I don't trust my in-lbs torque wrench. I simply thread by hand, then snug with the ratchet.

I verified that it was mostly clutch material and he said there was a normal amount of brass(?). I notice the (ever so slight) firm shift at low speed and low throttle. I may even be making them up as this transmission probably isn't the smoothest even when I bought it. There's still a little push to the shifts (right?). I bought a hayden kit from rockauto - the the Hayden 403. I hope that's a good choice for me.

Brass wouldn't be normal at all. I'm not a fan of smooth shifts as it simply means the clutches are slipping more. Quick firm shifts are what I prefer. However you normally don't get that unless there is a shift kit/bumped line pressure in the tune or the transmission has been built to do that.

I'm hoping my trans feels exactly the same or better than before (even though I think it can only get worse when you add new fluid). I've done a fair amount of towing in hilly western WI at 60-70mph with too much shifting between 3 and 4. I am going to stick it in 3 from now on - screw the mpg's. If I could dump it for $8k+ and buy another vehicle that would certainly be an option; I paid $13k for it certified with 28,000 miles. I would be sad to see it go for sure.

The point wasn't the new fluid so much as the Lucas transfix. Keeping it in one gear might be fine. Your fourth gear hub won't strip, so that's a non-issue. GM fixed that a while ago. As for the current value, it truly depends what they sell for in your area.

The shop ballparked $2800 for a rebuild. Would that be any more or less certain than a TEP rebuild? What do you mean a proper rebuild may work better than a factory replacement - whats the diff?

Thanks to all contributors!

That would be $800 more than a TEP rebuild of his "back to basix' nature assuming $500 for install. Link here: New-Back to Basix

Originally Posted by 02NavyBlue

Hm brass isn't magnetic, so it wouldn't be on the magnet. These transmissions aren't meant to shift so that you can't feel them, but you also shouldn't have your head get jolted back by them either. Mine shifts pretty firm when it's cold, you can feel it pretty good but smooths out when it's warmed up. All normal. There should be just a little bit of push to the shifts.

The hayden 403 is a good size for the N/A 3800 with normal driving. The 404 probably would have been best for you, but what you bought will be much better independent than the stock setup.

I'm planning to run inline with the radiator. I only want to improve on the stock system cooling but not eliminate the ability of the radiator to warm the fluid at -20 in MN winter


MATT5112: My goal for maintaining 3rd gear is to simply to eliminate constant shifting between 3rd and 4th under towing loads at transmission temps of 215-228*. I'm guessing that made most of the clutch material.


Overall, my trans would probably feel fine to anyone. I think I'm trying to compare to the dealer test drive 3 years ago... not easy.

Trans cooler installed without any incidents.

My Dad was wondering if I need to worry about air in the system or low oil after the install. Are these valid concerns? I didn't see anything about air in the lines in any of the writeups.

I'll keep an eye on the oil level but it looked fine after the test drive.

This weekend I 2 separate 100+ mile trips with 2 motorcycles and lots of gear in the car. Outside temperatures were about 55-65 degrees so quite cool but the highest my transmission got was 186. Thats a significant improvement over the temp range I had stock 212-228*. Success!

Originally Posted by 02GPinNY

I'm curious now after reading this thread. September 13th I'll be trailering my bike down to the races 120 miles away on pretty flat roads all the way. My bike weighs 480lbs. and the trailer (Harbor Freight) weighs 180lbs. I'm looking at less than 700lbs. total. The GP runs fine and has 140K on the clock. I'm having the pan dropped and filter changed this Friday. I'm hoping it will be okay to tow such a light weight. My thinking, which I'm not sure if it's correct is that if I had four adults, all my size in the car it would be 1,000lbs. I'd be towing 300lbs less weight. Just curious about your thoughts on this? Thanks.

Originally Posted by 02GPinNY

Thanks again Scotty. As soon as I get back from the races I have another week vacation. I'll install the cooler myself at that time. It's all 95 from my house to Exit 4 and then 55 South to Millville. Shouldn't be that hard on the tranny. I'm just gonna keep it in 3rd gear and take it nice and easy.

You will make it there and back fine assuming everything is in good working order. Do you have a Heads Up Display (HUD) with a transmission temp readout? Also, I've heard that some older grand prix models do not have a "hardened 4th gear" or something to that effect. If you have the hardened 4th, then I don't think you'd have to keep it in 3rd gear unless the car starts shifting between the two gears frequently.

Originally Posted by Scottydoggs

im sure you'd make it there and back. towing is easier on the car vs hauling the weight. but a cooler seems to worth it for any of us really.

I would disagree that towing is easier on a car than hauling weight. If I were hauling 1000lbs in my trunk, the shape and aerodynamics of my car don't change. If I am towing 1000lbs in the form of an open trailer with 2 motorcycles on it, a couple tires and gas cans, I've negatively changed the aerodynamics of my car and will therefore increase the constant load on my transmission. This is more and more true as speed increases - such as highway travel.

I would argue that if I were to put this 1000lbs into my trunk I could still achieve close to or above 30mpg. While trailering with the setup mentioned above, I actually see about 21mpgs.