pulling boat shaking it up on the hwy
 

95 4x4. Still new to the blazer. So I don't know if I am missing something obvious. I had a knock sensor code that I could not figure out until recently so I blamed everything on this. Now that the knock sensor is fixed, I need help figuring out what is going on when I pull the boat. The first time I took it out, at about 45 mph I got a shudder that felt like it was from the front area of truck and in the steering. When I slowed down it went away. I kept going and it went away shortly. I pulled the boat 50 miles to the lake with no issue. I pulled it back home and no issue. The next week same thing. The transmission fluid is full and color looks ok. I will be changing it out this weekend. When not pulling the trailer, the truck runs great. No problems, except ac vents go to the defrost under a long load every now and then. I replaced all the vacuum lines. Any thoughts? Thanks for your time.

I do not trailer my boat with these toy cars but I'll take a stab.


At around 50 MPH the Transmissions OD /locking Convertor kicks in. I'm guessing that you may need to trailer the boat with the OD turned off. There is a "1st", "2nd", "Drive" and then another "Drive".. yes?

Thanks, but I only use drive when pulling the boat. It is only a 15' bass boat. Not really heavy to pull around. I will get to the transmission fluid change this weekend and see what happens.

They are not really "toy cars" they are rated to tow up to 5900lb IIRC. Ive personally towed a 19.5ft bowrider with mine, boat alone weighed in at 3500lb + trailer weight it pulled it like a champ without the slightest hesitation on the launch ramps or going up hill.

But yes you are probably right about the torque convertor locking up, most likely it is "searching" for the right gear. You should run it in 3 or D rather than in OD. The transmission cannot find the ideal balance between drive or Overdrive based on motor speed, and vehicle speed; there are shift points programmed based on vehicle speed and engine speed. When towing the vehicle speed at an rpm is reduced due to the extra load you are towing this (ie normally at 2k rpm in OD you are moving 65mph but with the boat you may only be moving 55-60mph) this leads the computer to want to gear down to compensate for it creating a cycle of kicking it in and out of OD. This would explain why you dont notice an issue without the trailer.

On the newer blazers there is a "tow haul" button for the trans which basically all it does is change the shift points to eliminate gear searching while towing.

The Hypertech is pretty much designed for that problem isn't it? I mean, along with HP boost and all that crap.

If your going to tow with your Blazer I would strongly recommend a tranny cooler. I run the B&M SuperCooler. I bought mine from Summitracing.com. Actually I live close to their Nevada store & bought it there.

Quick update. I was attempting to do a transmission filter change when I noticed a little atf around the vacuum lines on the transfer case. I pulled the lines and they were dripping with atf. Now after reading about some issues I removed the fill hole for the transfer case and the atf was gushing out. I found that this is due to a bad input seal. Now I am reading up on how to drop the transfer case. I will keep you posted on the progress. This sounds like it could be the source of the problem.