Weird feeling at a stop and start

when you slow there is typically a steady deceleration up to the point where you come to a stop the brakes are sliding on the brake pads generating friction.

At some point the brakes will stop sliding and just grab. Good drivers will sense the impending grab and release brake force at the proper time to avoid a strong grab.

The physics of the stop are that you have steady deceleration and steady drop in speed. Deceleration is the rate of change of velocity. On a steady stop the change is acceleration is constant so the rate of change of acceleration (a value we call "Jerk" which is the third derivative of distance) When the brakes grab the velocity suddenly drops to zero, the deceleration goes way up (large change in velocity in a small time) and the Jerk goes from zero to a large value as the deceleration becomes very large.

And what you feel is described the the aptly named ""jerk" value.

However this doesn't really account for the issue when you start.

 

Yes a sudden deceleration and knocking down that inertia would cause a "jerk." However, even with a gradual deceleration, I feel the pop right before all my momentum is exhausted just before the brakes grab like in a normal stop. I then feel it right after the brakes release and I hit the gas.

 

You're worried about the increased costs associated with using AC, but not about the costs of lifting your truck and and the associated drop in MPGs? Interesting.

But in any case, I noticed the same thing with my truck. I think mine may have been more of the leaf spring issue, as I greased my slip yoke first and still noticed the 'clunk' at start and stop. Then I bought one pair of 2 1/2" u bolts at o'reillys, clamped them on front of each pack, and clunk is gone. Certainly glad I greased slip yoke as well though, as it was pretty dry. I'd definitely try the u bolts on the leafs though at the very least.

 

same issue. Thought it was the brakes but you guys are saying new. This is my new to me 2006 dclb sport with just 70k miles. No ac and happens with empty fuel tank. I just got new leafs through the recall

 

Honestly the AC thing is moot. I use it in extreme cases. I just don't drive around all summer with it. I'm a frugal guy. Yes I know lifting it and putting 255 80r17s will take a hit in the mpg department but that's necessary for the hunting and camping I have lined up here soon. I've looked at those clams you're talking about. I'll give it a shot along with doing a bunch more greasing.

 

Doing the slip yoke was easy enough too. I just removed the rear half of the shaft by removing the 4 pinion bolts and unclamping the seal over the yoke itself. Then it drops down and slides right out. Just mark the shafts and pinion mount really well so you can line it back up just as it was before.

 

Could be low on ATF Fluid, drain and add the proper amount,mine is 3.2 and it fixed the same problem. Going strong for 9 months now. was 2 qts low when drained!

 

Don't know if it helps, but I recall reading a TSB about similar symptoms:

 

i bet it is the slip yoke.

and the AC is more economical to use on the freeway. you burn more fuel when you run with the windows down because you are affecting vehicle drag. that's how i read the magazine article at the dentist office.

and fuel savings is directly proportional with increased speed.

 

Thanks for those points. I usually commute just for work, so it's stop and go and really no highway speeds. I'm usually content with the windows down. I'm going to look into my leaf springs, because they seem to have quite a bit of play. I'm going to tear open my drive shaft and make sure that slip yoke isn't dry either. And I do need to do the ATF as well. I was thrown off. I took it to a specialized toyota place south of Denver and they told me that they don't really ever service the newer tacoma auto transmissions because they're fine till 200K. I'm just now thinking of this in retrospect.

 

Did you rest the shaft on something?

Can you reuse the boot and clamp?

 

Sounds like its the TSB that was posted above. I read about it a while back, seems to be pretty common. My truck always does the same thing... annoys the shit out of me.

 

Same here and same truck. Just got my letter for the recall. Hope the new leafs fixes it but I always thought it was between the brakes grabbing to tranny needs fluid change!

 

Doubt that, Havnt you watch the MYTHBUSTERS episode when they did the pickup truck gas mileage when having a cover on the bed or nothing with tailgate up? It didn't effect a thing in gas mileage!

 

The AC is probably on most of the winter anyway, since the AC compressor runs whenever you use the defrost setting.

 

If it's a thunk right before you come to a stop, or sometimes when you let go of the brakes to accelerate, it's your leaf springs. Both of my 99s have done it, it's called axle wrap.

 

I'm going to address all these over the next week. Already ordered ATF and a new filter. Will look at the clamps. And will probably take the drive shaft off today to look at the yoke.

 

I just had the leaf spring recall done on my 07 AC, hoping it would resolve the same issue. It didn't. The universal joints are suspect at 85000 miles. I don't think the last owner ever greased them. Gonna put new universals and carrier on the shaft and have it balanced to see what that does for the clunky stop and goes, and highway vibration.

 

subbed for updates.

 

Stumbled on this. I noticed same thing last year. Doesn't do it in cool/cold weather, only in summer. Seems more pronounced the hotter the weather is. At first thought I had a sticky caliper, but they seem fine. Doesn't seem to exhibit typical U-joint symptoms either (no vibration, no ping between reverse and drive). Thought it might be a backlash issue, I can let my truck roll forward from a stop without touching gas and it still has a light "clunk" when I press accelerator. If I didn't know better it feels like a stuck caliper releasing. Taking it in for leaf spring "inspection" in a few weeks, maybe that will shed some light on it.