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Old 04-25-2004, 10:20 PM
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Default I tested the towing limits of my 4.7L 3.55

I posted a week or so ago about swapping out my 3.55 rearend for a 3.92 in order to 'up' my towing capacity. Well, this weekend I decided to see what my current setup could do - thought I'd take a second and share.

THE BEAST: 4.7L SLT 3.55 one-wheel peel, class III hitch...vehicle rated for 4650lbs

THE BOAT: 24' center console w/ 250hp OB, 50 gals of fuel (1.2 tank)...5200-5500lbs.

4 adults total and some moderate gear (I mean beer), we set out for Port Orange, FL (about an hour and 15 mins of mostly highway driving). The Durango pulled the boat fine, accelerated fine and I didn't notice much sliding on the highway even with some moderate wind gusts. I kept it around 65 (2500 RPM) with OD off and it did pretty well for the first hour until the transmission decided to downshift into 3rd. RPM was about 3500 and it would NOT go back into 4th. I decided to pull over, completely stop and then start back up. As I accelerated it ran fine moving up through 1st, 2nd, 3rd, hickuped a little and roughly slid back into 4th. No more problems after that.

We put in the intercoastal and stayed out a few hours.

To my surprise, pulling the boat back out of the water was a piece of cake, it didn't even seem like there was boat back there! I had no slippage and it was obvious that most of my 295lb ft of torque on the low end. On the ride home I kept it at 60 and didn't have ANY problems (went right into 4th and stayed there). We did fine. All in all, I was pretty impressed by the performance considering I was about 500-700lbs over my tow rating.

I think for the long term though, I definitely need to get some 3.92's to be on the safe side.
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Old 04-26-2004, 07:51 AM
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It probably down shifted because the trans fluid was too hot!! Better go change it.
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Old 04-26-2004, 07:08 PM
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Why would increased transmission fluid temp cause it to downshift?
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Old 04-26-2004, 07:21 PM
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MoparMarcIdaho MoparMarcIdaho is offline
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Arrow change it

and then install large heavy duty trans cooler.
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Old 04-26-2004, 09:35 PM
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It has a temp protection circuit built in.
I think it is 280 degrees when it shifts down to let things cool. This is trans fluid temp.
Keep OD off when towing that much load or put bigger/more coolers on!! Temps fail a lot of tranmissions.
I am glad you got the power that you need.
I drive a Cummins with 400 hp and 800 torque. Love it. Trans is built to hold it.
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Old 04-26-2004, 09:55 PM
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So what are my options for tranny cooler? Is this something that would cost ultra $$ or would it be in the neighborhood of new gears?

What would be the smarter move...replace the rearend with 3.92 ($500-$700 installed) or should I look into a tranny cooler?
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Old 04-27-2004, 12:59 AM
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Arrow if your broke like me

just go to the boneyard and get an old A/C condensor,they will work as good as anything out there,just make good connections that wont blow out and run quality oil.
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