[KirbyInc.]

This is my first post on this forum, so hello everyone!

My 1998 Sienna LE with approximately 221,000 miles on it has been intermittently bumping when going into reverse. This bumping is a lot worse if I don't let the car warm up first. If this car is fully warmed up, it isn't that bad or sometimes I don't feel the bumping at all. 95% percent of the time, I warm up the car before driving it - but on the rare occasion that I don't have time, I always dread the bump.

It's been doing this for quite a long time now (I don't think it's gotten any worse or better since I acquired it), and I'd like to know if anyone else has encountered this issue, and whether they got it fixed.

Other than the bumping, the car is in spotless condition and drives perfectly and quietly.

This car was passed down to me by my parents about 4 years ago (I grew up with this car lol) and I've been taking extremely good care of it since then. I believe my parents kept up with regular maintenance too, ever since they bought it second-hand in 2001.

I'm also exceptionally attached to this car, and don't mind spending money on it.

Thanks in advance!

 

[pjksr02]

Is this coming from the engine/transmission, or from the suspension? Is it just a bump, once, when you shift?

After checking the ATF level, check out the motor mounts. See if the engine "jumps" when you shift.

 

[KirbyInc.]

Is this coming from the engine/transmission, or from the suspension? Is it just a bump, once, when you shift?

After checking the ATF level, check out the motor mounts. See if the engine "jumps" when you shift.

Is this coming from the engine/transmission, or from the suspension? Is it just a bump, once, when you shift?

After checking the ATF level, check out the motor mounts. See if the engine "jumps" when you shift.

Thank you so much for getting back to me!

The ATF level looks fine and is red in color.

I think it's coming from the engine - though it could be coming from the transmission too. According to my mechanic (who I know personally and I get under-the-table mechanical work done), all the engine mounts have been replaced. I can't remember off the top of my head whether the transmission mounts have been replaced - but if I had to guess, I'd say they haven't. I really hope this is a mount problem and not a sign the transmission is going. Everything else with the transmission is perfect.

This is a video of me putting the car from Park to Reverse to Park to Reverse to Drive and back to Park. I noticed there's a bit of a knock when going from Reverse to Drive, but it's not very noticeable. The bump when going into reverse IS noticeable from inside the car though.

VID_20210216_210508.mp4

drive.google.com

 

[pjksr02]

Good idea to make a video.

I'm not an expert on mounts, but it looks like there's a little play in your "dogbone" mount (left side of the engine compartment. That one is easy to inspect (and replace if needed); see if the rubber is cracked.

Hopefully someone else will chime in here.

 

[KirbyInc.]

I suppose you're right, there is a little play... The problem is, I don't know what's normal and what's a bad mount! I inspected the rubber on the dogbone mount a couple days ago and it looked fine. As it should, because I replaced it about 2 years ago because it was cracked and thought it could be the cause of the bumping! The mechanic who replaced it (the mechanic I use when I'm in Mexico) showed me the old dogbone mount, and sure enough, it was in terrible condition. Unfortunately, it didn't fix the bumping...

 

[BabyToyoda]

What's strange is the fact that it happens when cold. Must have something to do with the higher revs it idles at when cold, which put more of a jolt on the drive train when going into reverse or drive. Since it only happens at higher idle RPM and only in one direction, I would make double sure none of the mounts are going out or developing play.

 

[KirbyInc.]

What's strange is the fact that it happens when cold. Must have something to do with the higher revs it idles at when cold, which put more of a jolt on the drive train when going into reverse or drive. Since it only happens at higher idle RPM and only in one direction, I would make double sure none of the mounts are going out or developing play.

You raise a good point. To me, it does feel like something in the drivetrain. I'm a little skeptical about the mounts being the issue.

The reason I say this is because, first, it's important to note that the car does jolt sometimes when going into reverse, even when the engine is fully warmed up.

Second, I've noticed the jolt very rarely happens when going from Reverse to Park to Reverse to Park. You could keep doing that forever and never feel a jolt - but as soon as you go into Drive to Reverse or vise versa, you can feel it. The bump is happens pretty frequently when going from Drive to Reverse, but on the rare occasion, there might be a slight jump going from Reverse to Drive.

That being said, it could be the mounts. I don't know. The whole situation confuses me greatly.

I'd love to hear anybody's thoughts on this, as I'm very interested in people's opinions - however, I'll eventually be taking the car to my mechanic to inspect this problem exclusively. He's passionate, trustworthy, and cheap so maybe I can get a good answer that I can share here for documentation purposes! Hopefully I won't need a rebuilt transmission haha..

 

[pjksr02]

It's probably not the case, but are you sure the correct ATF is in the transmission? It should be dexron/mercon 3 (MD-3). Also, the fluid level is checked with the van idling, warmed up, and in Park.

 

[KirbyInc.]

It's probably not the case, but are you sure the correct ATF is in the transmission? It should be dexron/mercon 3 (MD-3). Also, the fluid level is checked with the van idling, warmed up, and in Park.

I'm pretty sure the fluid is correct but now I'm paranoid haha

I will recheck the fluid as you described after work today and get back to you

 

[BabyToyoda]

Valvoline Maxlife, Multi-Vehicle (full synthetic) works great in these vans, but I would assume there would be other issues with shifting other than going between park and reverse if ATF was the issue either by amount or by wrong type.

After watching your vid again, the engine clearly bounces up a bit once that clunk hits. I would suspect tranny mount is worn and allowing metal to hit metal, or rubber to pull apart.

The dogbone mount is pretty soft, and is not actually designed to handle much of the load of the engine bucking around. It handles as more of a vibration damper, at least from what I have read about why it is there. There's no way it could ever handle the torque of the engine. But they can clunk a bit if completely broken from the rubber inside the dog bone.

Maybe have someone rock the van back and forth on flat smooth ground while in park and try to video record the mounts to see if any look like they are popping around.

 

[Micah202]

I went through a mounts issue a while back. It's pretty amazing the array of symptoms that can pop up for the mounts being dud. It's aspecially worthwhile haveing the trans mount checked.