Rough Engine Braking in Overdrive

I just bought a 2002 Tacoma V6 4wd Auto, and am new to Tacomas (had a Frontier). It has 140,000 miles and runs great other than one thing (that I didn't notice on the test drive) - when in 4th gear, the engine braking during deceleration isn't smooth. From what I've read, the Tacoma does more engine braking that the Frontier, but I'm worried there is something wrong. The engine runs fine when I'm accelerating and the transmission shifts fine too. If I turn off Overdrive, it decelerates with Engine braking more smoothly. Can someone tell me if this is normal or if this is an indication of something wrong? Any direction would be greatly appreciated.

 

That does not sound normal. I have the same truck as you. Overdrive OFF, I definately "feel" the engine braking compared to overdrive ON. With it ON, it is very smooth and rolls a long way, very little engine braking in fact.

What exactly are you feeling? Could it actually be driveline vibrations? Do you have a lift?

 

No lift. It feels like vibrations toward the front of the truck. Now that you mention it, it may make sense that it is something in the driveline. While "coasting" in 4th gear, there is less "pull" or "tension" on the driveline than in 3rd. When I give it gas, the vibrations go away. I'm going to get under it and see if I can feel a loose u-joint. Any other ideas?

 

Ok. I felt a little play in the front u-joint when moving it with my hand, but not much. I took it for a drive and put it into 4H and tried coasting down a hill and the there were no vibrations. Back to 2H and the vibrations resume. Do you think that is a valid test that points to the U-Joint(s) in the front driveline?

 

I don't think engaging 4hi effects anything in the rear besides the t-case. It does seem indicate your vibes are in the front.

It still could be u-joints but the likelyhood is much lower. To be certain, I would grease all 8 fittings on both drive shafts. btw: there should not be any side to side play in u-joints.

There are a lot of threads on here about vibes happening on 2nd gens after lifting. Many times that has been an indicator of a bearing issue in the front diff. But the 1st gen front diff has proven to be more durable. Usually, vibes in the front of 1st gens are wheel balance or wheel bearing or worn cv axle joints.

The vibe you feel is definitely on coasting right? You don't feel it on acceleration, right?

 

Thanks for your input! I'll grease the U-Joints and see if that helps. The vibration is definitely only on coasting -- most noticeably coasting down a hill or at high speeds. Once I hit the gas, the vibrations go away.

Originally, I thought it was only in higher gears as it is most noticeable when driving down the interstate at 60-70mph. But some test driving last night proved that the vibrations also occur when coasting down a hill even at 20-40mph.

The small amount of movement when I try to move the front u-joint is not even 1/4 inch of movement, but i wonder if that becomes worse at higher revolutions.

If it were the CV Joints or wheel bearings, would I feel the vibrations during acceleration as well?

 

Yeah, I think you would as long as 4hi wasn't engaged.

 

After greasing all the u-joints in the driveline, both front and rear, the vibration still exists. Some additional findings (along with the original):

1. Vibration only occurs when decelerating and not when decelerating uphill.
2. Vibration only occurs in 2wd.
3. Vibration only occurs in drive, stops in neutral.
4. On deceleration, Vibration begins around 1500 rpm (continues as rpms decrease) and accompanies a slight wiggle in the RPM gauge needle.
5. Vibration doesn't happen every time even when other factors are at play (about 75% of the time).

Does this add up to something? I'm going to check the front and rear diff fluids tomorrow.

 

I had a similar vibration behavior. It turned out to be the driveline support bearing. Your vibe seems to be noticeably upfront. the support is aft, so perhaps a non starter.