strange transmission noise at boat launch

K

keakar

New member
when the truck is in drive and i let off the brake, if the truck rolls backwards a bit and i give it a little gas to stop the backwards roll the trany makes a strange grunting rumble like noise.

2006 4runner sport 4.7 v8

what is going on? is this some valve function within the trany and the noise is normal somehow? everything seems fine with the trany otherwise.

it only happens if its in the process of rolling backwards in drive but if i use the brake to stop the backwards roll first, then it doesnt make the noise

and yes i call my 4runner a truck lol

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Truck frames do truck stuff.... I call it a truck too...

Alternately, I don't call a truck with a camper a SUV.

As to your original question... no idea. Does it happen consistently? Perhaps its the torque converter. Have you checked fluid levels?
 
I've notice mine do that when offroading, pretty sure you should stop the truck first with the brake then apply throttle. I think I noticed mine make an atrac-like grinding noise just when its rolling backwards in drive, not sure it started when I applied throttle to compensate though.
 
Bumbo said:
Truck frames do truck stuff.... I call it a truck too...

Alternately, I don't call a truck with a camper a SUV.

As to your original question... no idea. Does it happen consistently? Perhaps its the torque converter. Have you checked fluid levels?
Click to expand...

toyota in their infinite wisdom, decided i dont need a dipstick for the tranny :ybrick: so there is no way to check level, all you can do on my truck is overfill it and take out the "level" plug so it drains any excess out and that means its at the right amount.

it acts like its "related" to something with the torque converter slip allowing it to roll backwards when in drive but it only makes the noise if you add pedal to pull up and stop the roll.

so i load the boat on the trailer, take it out of park and let off the gas, and as it starts to roll back 6" to a foot, i give it some gas (but not a lot) and it makes a sound like a dry windshield wiper scrunching on the windshield. that is the one and only situation it does it and it doesnt seem to "go" as it makes the noise also.

curious if i might have a friction band slipping on a drum in the tranny or something but i dont really know how our tranny is made so im just guessing based on very very old experience with a few c4 & c6 ford tranny that i have rebuilt.

i have a couple of cases of fluid and plan to do a flush and replace of all the fluid but i am hesitant to do anything just yet in case i might need a tranny rebuild. the fluid is not cheap so i dont want to waste $125 worth of tranny fluid
 
Last edited:
07V8 said:
It has absolutely NOTHING to do with the transmission. It's the ABS keeping the truck in it's place to minimize wheel spin if off-road. Call HAC: Hill-Start Ascent Control.

Toyota Global Site | Technology File
Click to expand...

That's great info and makes sense!

Here's a explanation in simpler terms explaning the concept, especially the delay in throttle response.

https://en.wikipedia.org/wiki/Hill-start_assist

"The hill-start assist is a variant of hill-holder used by some semi-automatic, clutchless transmissions as well as newer manual transmissions. The system prevents the car from rolling away when trying to pull away on an up or down gradient, simulating a "handbrake hill start" manual drivers will be familiar with. The system engages automatically when a gradient of 3% or more is detected; it then acts to hold the car stationary for two seconds after the brake is released giving the driver time to apply the throttle."
 
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