Towing Issues: Trans Fluid Temp & Brakes

I have a 2008 Suburban 1/2 Ton 4x4 LTZ.

I think my boat weighs about 5,500 lbs (incl. trailer, gear, and gas).

I bought the Suburban because I'd always read what a GREAT tow vehicle they were. So far I haven't been so impressed:


Transmission Fluid Temp

On my first long distance tow from Portland to Lake Shasta, I noticed that when I go up long uphill grades that the transmission fluid gets really hot. The manual says that 160 - 200 is the normal operating temperature. I've seen it spike as high as 230 degrees.

RPMs going up the hill get to 3,500 - 4,000. All this just to stay above 45mph.

Is this normal?

Is it okay for temp to get that hot?

Am I at any immediate risk of transmission damage?

What about long term damage?


Once you get going downhill, the temp slowly comes back down below 200. But then you come across another problem...


Brake Wobble

Okay, now I'm going down the backside of the mountain pass and I notice that the Sub wobbles when I lightly tap the brakes... I'm simply trying to keep the speed below 60mph. Mind you, I am not riding the brakes all the way down... just pumping them as needed.

There is nothing more nerve racking than coming down a long, windy mountain with a big boat behind you and a Sub full of your family wondering if your brakes are going to work.

What's causing the brake wobble? Heat?

Are the Sub's brakes up to this kind of towing?



I'm sorry if these are stupid questions... Thanks for your help.

Whoa I'd get that thing to the dealer asap. Sounds like you have some issues. Did you have it in Tow/Haul mode it really helps the gear shifting issues. That is pretty hot for the tranny, hot tranny equals issues in the long run. That sub is more than capable of that towing weight.

As far as the brake issue goes it sounds like you're describing warped rotors. Shouldn't be so on your new/newer truck. I'd take it to the dealer and have them look it over.

Yes, I always use Tow/Haul mode.

Always tow in 3. In the mountains, 3 will also engage the overrun clutch to provide engine braking, but D will not. Warped rotors are caused by heat.

http://www.wakeworld.com/MB/Discus/messages/3183/720889.html?1249144377

I have never been a fan of the teeny tiny rotors that GM puts on their SUV's. I figure it is a good service income for them. Besides, how many customers outside of the sportscar market research that part of an SUV.

ON the flip side, my 4-runner's rotors are huge and completely fill the 17" wheels, not like the 332's on my AUDI, but not too shabby.

One more thing, you'll have a hard time getting the rotors replaced under warranty. They are considered a wear item. My sister-in-law's warped within 20k mi (TX car - no towing, no mtns) and was told to pound sand by a local dealer with a good reputation.

Do you have an external (to the radiator) transmission cooler installed? I would recommend it if you don't. That one modification by itself will help enormously. I would recommend changing that transmission fluid now that it has been so hot as well.

On the brakes, it sounds like your rotors are warped. Get the rotors turned to true them back up (obviously replace them if out of spec but there should be enough material since they are so new). Once you have eliminated the shimmy, be careful not to warp them again. Things like running through water or spraying water on hot rotors can warp them. Also uneven lugnut torque can contribute to warping.

I agree about locking out OD when towing in the hills. If your transmission is downshifting a lot you should have OD locked out.

Thats interesting. Im surprised to hear you are having issues with such a new vehicle to begin with.
It needs to be in tow/haul and out of overdrive while towing, especially with a half ton. I think the worst thing GM ever did was go to the 5.3 V8. My 97 Z71 had the 5.7 and I towed my boat many many times over the grapvine without issues. I wasnt flying up grades but for a half ton it did very well. Not to mention it was doing it with well over 100,000 miles on it. I didnt have a tranny guage on it but like others have said that is too hot for your tranny and you need to figure out why it is happening.
Take your time on grades and dont be afraid to downshift manually into second gear and run your engine at 3,000-3,500 to pull a steep grade at 40-45mph. Biggest advise I have is not to lug your vehicle. The engine can turn rpm's and it is better to run them higher "freely" than to bog them down at lower rpm and dump tons of fuel into them.
That sub shouldnt have any problem slowing that boat down unless you are driving too fast, but I dont think you are. Use your engine by keeping it in a lower gear to hold you back as well.
Good luck, keep us posted.

A couple of follow-up questions...

1) I don't think it's common for trucks to have trans fluid temp gauges. Is 200+ considered high? The manual says yes, but without a gauge, how do you all know you aren't running just as high?

2) If my rotors are warped (hard to believe after just 15k miles), wouldn't I notice the wobbling in day-to-day driving? It only happens going down hill while towing. And even then, it's not right away... it comes after I'm maybe half way down the long grade. This is why I suspected heat.

First make sure your Boat Trailer is level when hooked up to your truck. When I used too much drop on my hitch I noticed the trailer moving the truck a bit. When I got it level with a higher hitch I didn't feel the trailer anymore.

When going down hills use your gears to control your speed. I rarely have to use my breaks when descending a long grade.

200+ is high but I wouldn't worry unless the fluid stays over 200 for an extended period. IF you are going to do a lot of towing than a true external trans cooler will be needed.

GM brakes are on the small side and towing can warp a set within 10 miles. If you notice brake pulse at higher speeds, not towing, then your rotors are warped and need to be replaced.

If only they'd put 3/4 ton running gear and a diesel in the sub.... What a great vehicle that'd be.

You're definitely pushing the limits of what that truck will do, especially if you have the 5.3 motor. Just take it slow. Let that motor turn a lot of rpm's. 4-5k wont hurt a thing on that small motor. Down shift to 3rd on the descents to keep the brakes cool.

I towed with my 5.3 equipped Tahoe for thousands of miles. It was a slug on the hills, but never had any problem. You just have to be more conscious with them both climbing and descending.

After changing over to a 3/4 ton diesel I've never looked back. It'll pull the same grades at 70+ turning 2k rpms that my Tahoe did at 45mph and 5k rpms. It's much more relaxing.

Good luck... They're great trucks for general use, but a bit lightweight for a long haul with your whole family and a weeks worth of supplies.

Could it be the trailer brakes transferring vibration back through the truck? I question only b/c you don't experience it other than downhill grades with trailer in tow. Do you have any noticeable vibration in the pedal or is it just a general vehicle vibration under braking? Can you see any light/dark spots on the burban or trailer discs?

There really is no such thing as a "warped" brake disc. Vibration under braking is almost always caused by uneven pad transfer across the disc face. When you get this type of vibration it will generally continue to get worse as the transfer layer builds up in the same spots. Turning or replacing the discs is usually still required and will remedy the issue for a short time, but it will likely return until the pads are replaced with a better set and a proper bed-in procedure is followed.

Here is a good tech paper on the subject:
http://www.stoptech.com/tech_info/wp_warped_brakedisk.shtml

I would first change your driving style and use the truck to engine/trans brake on steep grades like suggested above. I would also try to determine which system is causing the vibration and look into upgrading the pads.

This is why I've always owned 3/4 ton Suburbans.
Bigger brakes, big block engine, bigger cooling system, heavier axles, rear leaf springs, lower geared rear ends.
All adds up to a much more competent tow vehicle.

Great feedback.... some responses/thoughts:

On the trans fluid, I can't decide if a flush is necessary or not. I have only been on two long towing trips where the temp has exceeded 200 degrees. Even then it was only on uphill grades... and quickly came back down in temp on the way back down the hill.

GM offered a "Heavy Duty Trailering Package" which includes external transmission oil cooler and external engine oil cooler. My Sub dose NOT have this... I picked it off the lot and assumed it had everything I needed to tow (tow bar, tow mode, autoride suspension, 7,000 rating, etc.). I wonder if I can get this package installed at the dealer? Do you think it would help keep the trans fluid temp. down?

On the brakes, I am starting to wonder if it's the trailer, not the Suburban. Afterall, this only happens when I tow, and even then, only down hill after some heat has built up (i.e. only on long downhill grades... about half way down). I will have both brake systems inspected.

Chris, I looked at the 3/4 ton Suburban but they do not offer it in LTZ trim. So it's missing a lot of the creature comforts of the 1/2 ton LTZ. It was as tough call, but I figured that 95% of the time we are NOT towing and it has to serve the purpose of luxury family hauler. For the other 5% of the time when I tow, I figured the 7,000+ tow rating would be plenty to tow the boat. I wish GM wouldn't have made that decision so hard.

I also wish they'd make a 3/4 ton diesel Suburban. I'd buy it as long as I could get it in LTZ trim.

know anyone with a different trailer you could lug up and down a hill? might be the easiest way to find out if its the trailer or not.

as i sit here in my work truck, a 06 3/4 gas chevy, the trans temp gauge goes to 300, with the red area starting at 270, i believe my duramax with the allison is the same and its been around 230 before when its 100 degrees pulling up the hills in eastern wa.

Good point on the trailer - surge brakse can be a problem on long descents. A lot of people that tow in the mountains install a switch on the dash to engage the reverse lockout solenoid on the trailer to keep the brakes from overheating.

Yes, the HD trailering package is an external trans cooler and engine oil cooler, which you need and will definitely help.

If the fluid is clear and red, flush probably isn't necessary.

This transmission temp issue is an interesting conversation for me, as i have been experiencing something very similar lately. i have a ~4k-4,500k boat that i am pulling with a 2007 Denali (6.2liter). it has the 6speed allison transmission in it and i pulled my boat back and forth accross the Cascade mountain pass a couple of times this summer. Here is what i expereinced, i have been trying to deduce more causes, but have not been able to figure it out yet:
Note: Before i made any of my trips, i did the 36k tune up which included flushing the transmission fluid
Trip 1: Memorial Day weekend
-Outside temp: 85-95
-Tow/haul mode mostly on
-stop and go traffic up the mountian pass, and then ~70mph the rest of the ~250mi
-Virtical Climb: ranging from sealevel to 2,500ft
-Denali with 2 adults and 2 small children, plus ~300lbs of stuff
-Boat with full tank of gas (yes, i know this was stupid) and probably 500lbs of gear (having 2 kids seems to mean that i have to move my house every time i go anywhere)
-Transmission temp running 180 to 212

Note: before this trip, i had the trailer serviced which included repacking all the bearings (tandem axle trailer) and bleeding/refilling the brakefluid (disc brakes)
Trip 2: Fathers Day weekend
-Outside temp: 90-100
-Tow/haul mode on and off (on when required to climb)
-average speed of 70-75mph for 250-300mi
-Virtical Climb: ranging from sealevel to 2,500ft
-Denali with 2 adults and 2 small children, plus ~400lbs of stuff
-Boat with half tank of gas and probably 100lbs of gear
-Transmission temp running 163 to 183

Trip 3: This past weekend (August 1st)
-Outside temp: 85-95
-Tow/haul mode on and off (on when required to climb)
-average speed of 70-75mph for 250-300mi
-Virtical Climb: ranging from sealevel to 2,500ft
-Denali with 2 adults and 2 small children, plus ~200lbs of stuff
-Boat with full tank of gas and no additional gear
-Transmission temp running 193 to 230

Trip 3.5 (return trip - August 8th):
-Outside temp: 75-80
-Tow/haul mode on and off (on when required to climb)
-average speed of 70-75mph for 250-300mi
-Virtical Climb: ranging from sealevel to 2,500ft
-Denali with 2 adults and 2 small children, plus ~200lbs of stuff
-Boat with half tank of gas and no additional gear
-Transmission temp running 163 to 185

It seems to me that the most critical factor in the transmission temp is the outside temperature, where i am getting ~2-2.5 degree increase in the transmission temp for every ~1-1.5 degree increase in the outside temp.

I did call 2 GMC dealers, and BOTH told me that i am ok running up to 250 degrees, but i agree with folks that anything above 200 (especially for extended durations) is hard on the vehical.

Anyone have any thoughts or analysis that i may have missed on why the transmission temp would fluxuate so much?

Sorry, not trying to hijack the thread. just wanted to add some additional similar information/experiences to see if there is any commonality

Your Transmissions will be fine. You guys are never going to tow enough or tow heavy enough stuff to cause problems. At my old dealership besides the diesels, we had an Durango (V8), 1500 Suburban (5.3), and 04 Tahoe Z71 (5.3) The Durango made it to 260,000 (about 200,000 towing.) The Suburban made it to 175,000 until the trans needed a rebuild (it was slipping a lot, like a bad clutch) less than $1k and ran like new until we sold it over 200,000k. We sold the Tahoe at 165,000 with no issues. None of these vehicles had transmission temp sensors. The smallest boats they towed were 4,500 lbs and the biggest were about 7,500 lbs.

This is what diesels are for.... 32,000 lbs. I towed this rig from Richmond, VA to Merced, CA and back in 6 days. 5,596 miles.

Nice.... That's the way to do it. Ha, ha, ha.

I too, have never had a problem with a transmission when serviced properly. My vehicles have always towed. I sold my Sub with 145k on it and the trans was just starting to do a few strange things. Who knows how much longer it would have gone.

Oil temps (both trans and engine) go up a ton on high ambient temp days. It makes a huge difference. 10 degrees of air temp can make 50 degrees of oil temp.

Oh, and yes, a trans cooler can be added after the fact and it will make a huge difference if you tow a lot.

We put one on my Dad's diesel Mercedes that we used for towing the boat for almost 20 years. When my brother finaly ran it out of oil it had 420k on the original motor and trans without any issues.

(Message edited by guido on August 11, 2009)

David, I had same problems and concerns with my avalanche. You bought plenty of truck. Tranny is fine, just back off it for a bit and the temp will come down. I can usually run 55 up short grades, 45-50 up longer grades (always in second gear uphill, otherwise in third gear). My guess is you're pushing it just a little too hard. On the brakes, it is warped rotors. Been there many times. And agree with the downhill engine braking technique. One trick I've learned... If I have to use my brakes, I punch the accelerator before coasting again to be sure the trailer brakes disengage. Good luck.

(Message edited by Phenom_1819 on August 11, 2009)

Are your trailer brakes engaging on the downhills?

Our trailer has no brakes at all, when we get over about 90kph (around 60 mph) on a steepish hill it will sometimes get a sway on that pushes the truck around. Instead of tapping the brakes, tap the gas, that should straighten it out.

(Message edited by jtnz on August 12, 2009)