Compression braking

I have to travel over a small mountain everyday and unless I put the truck in tow/haul mode I'm constantly riding the brakes due to the 14% grade. Compared to my 08 Tundra the compression braking in tow/haul is great and at times excessive but that's fine. What I do notice is that when the transmission does downshift after applying the brakes then letting off to let the engine do the work it seems to pulse as if it's getting ready to upshift then quickly decides to stay in gear. This is especially when it downshifts in third gear.
Am I correct to understand that when in cruise control and with tow/haul mode engaged the rear brakes modulate to slow down when someone gets in front of you? Is this also true that this takes place going downhill with compression braking? Is that the pulsing I'm feeling or is it just the trans hunting for gears?

 

No, the "modulating" you are feeling is brake shudder from overheated brakes.

It's pretty common knowledge that the adaptive cruise brakes too aggressively in certain driving situations. Going down a mountain pass is one of them.

I suggest you don't use adaptive cruise in that situation. Gear down manually in S-mode, and try to stay off the brakes.

 

Thanks for the reply but the truck doesn't have the chance to overheat the brakes when this happens, it's the trans as I'm not on the brakes, this is what happens...

Crest the hill, start downhill, click on tow/haul. Upon coming to curve or getting close to another vehicle in front I'll hit the brakes, trans downshifts (usually into 4th), keep going downhill-not on the brakes, get to another curve or closer to car in front hit brakes again and it downshifts into 3rd. Depending on how hard I hit the brakes it will either stay in the present gear, if I give it a touch more a little quicker it'll kick down another gear. This is all in a matter of 2/10th of a mile at the very most.
When it down shifts the second time this is when the pulse begins, again it feels like the truck wants to upshift but then decides to stay in the present gear midway through the shift (to be clear it isn't really shifting). To describe it another way it feels as if a very short rubber band is attached to the bumper, it stretches, hit's it's limit then lets go, rinse and repeat until I hit the gas to have it upshift. I'm not on the brakes and cruise control is not on.
Now the only reason I engage tow/haul is because it downshifts quicker than if not. If I'm not in tow/haul I'd be on the brakes most of the time.

So I understand what you're saying regarding the adaptive cruise but again, I'm not using cruise control so it shouldn't be the adaptive cruise control braking.

So my question is, is the transmission supplemented with the brakes in downhill situations like I described when cruise control is not on?

 

Sorry if I misunderstood, but you did mention using cruise control.

I've had the shuddering happen twice. Both times I was using the adaptive cruise going down mountain passes in moderately heavy traffic. The adaptive cruise was constantly on and off the brakes very aggressively. By the time I neared the bottom of the pass, each time the AC applied the brakes, my entire truck shuddered noticeably, especially thru the steering wheel.

Once I stopped using adaptive cruise in those situations, and started downshifting manually, I haven't experienced the shudder. Others have reported the same problem.

 

Sorry, was typing my reply and went to cook dinner, must have hit Post Reply when I walked away, finished up with what I was writing and reposted.

 

When you say others have experienced the same shudder, was that while using cruise control or was that in the same situation as mine?

 

Using adaptive cruise. Often while cruising down mountain passes with moderate traffic. But that's not the only scenario.

The system uses too much braking, instead of downshifting, IMO.

Bottom line is I think the brakes on 3rd Gens are under-engineered, and the adaptive cruise is poorly implemented. A lot of reports of guys needing brake jobs under 30K miles.

That's ridiculous, IMO

 

I agree, 30k isn't great at all. When I got my 08 I had to change the brakes out at 15k due to rotor warpage. After it happening again in another 15k I realized I needed to change my driving habits with the mountain I go over everyday. Luckily I have a great relationship with my dealership's service department and they warrantied them a second time. After towing my wheeling rig over the Rockies on the way to Moab I realized I needed better brakes so I swapped them out for Centric cryo'd slotted rotors and Hawk LTS brake pads. Huge improvement over stock, combine that with keeping it in 4th gear when towing and occasionally going into 5th on the flats I've only changed them once with 170k on 2 sets.
I'd love to swap out the 2024's brakes for something bigger, APB makes a 6 piston kit with 16" rotors and free pads for 10 years, only $3,200.https://apbbrake.com/products/2022-toyota-tundra-front