Yes, it's definitely always even without touching the brake pedal, always at 18mph and there is a clunk as if it's hard shifting into 1st gear but it never happens if the overdrive is off.

The vehicle is a 2000 T4R LTD V6 4WD 4-speed auto trans

Thanks!

Generally a harsh downshift is a worn low and reverse clutch drum clearance issue. It's common because it's on in 1st gear and reverse only. It's just a sign that the clutch clearance is not perfect and is from age. It can go like that for years. Eventually reverse will begin to slip a little but that can last a long time too before failure happens.

Amen to that. Very informative

This could very well be the driveshaft clunking due to the slipyoke binding. Many have reported a similar clunk. May want to check it out if you haven't already.

Slip Yoke Binding Fix

Thanks, I had looked into that initially but I don't believe that's the issue I'm experiencing. The fact that it only clunks during deceleration and always at 18mph, coupled with not doing it when OD is off (or if the vehicle didn't gain enough speed to switch to 4th gear) indicates that it might be something with the transmission...

Yeah, definitely not the slip yoke binding problem. The slip yoke unbinding occurs while coming to a stop or starting to roll from a stop. If it's happening at 18mph, that's just a harsh downshift.

Just wanted to reply with a short update regarding this issue... This weekend I did some maintenance to the truck and since I had good experience with Seafoam products in the past, I decided to try their Trans Tune product.

I crawled under the trans pan and drained 4.25QT's of fluid when it was nice and hot. Then put in a full can of Seafoam Trans Tune and topped it off with 4QT's of Toyota ATF. Checked the level and trans was a bit too full at this time but I wanted to circulate the Seafoam in the system for a bit so I drove around, parked and re-drained a bit until it was just right...

Well, I'm happy to report, somehow the harsh downshift at 18mph is so unnoticeable now that if I didn't know it actually existed I wouldn't notice it. I don't know what the Seafoam did but it's smooth as silk now. In a couple of oil changes, I'll probably drain and refill another 4QT's and see the trans fluid condition.

I bought a 2001 with 318k on it and did a flush because the fluid was horrible and the A/T light came on once while doing some light 4 wheeling. The Transmission did pretty good and started shifting much more smoothly but it totally blew up this week (336k) and I am looking at doing a tranny swap. My son has the same truck with 345k and has never changed the fluid so I might be leaning toward not changing the fluid at high mileage.

Umm no. You both should do the drain and fill every 30K.

@Cjadamsdep I'd love to see what an 18 year old 345K mile TX fluid that's never been touched looks like, please post a video or at least a pic when draining out 4QT's and maybe send for analysis...

My 4wd '01 has developed that 'whine', does it in 1st and 2nd mostly (tough to hear at all once in 3rd or OD), sometimes I don't hear it at all, sometimes only in the mornings. Shifts smooth up/down as always. I'll try draining/filling, probably overdue by 60k, sorry yet fluid is transparent red still.

I have run one of those 'magnefine' filters for most of its life. Should I replace it or just remove it entirely?

When the times comes (and we know it will) I'd like to go the rebuild route you spoke of. Too bad I'm in Austin but I'd still be willing to take it to you unless you know of a good rebuilder here?

thanks for helping everyone out here and stay safe!

If it's been 60k miles, I'd drop the pan to do your drain/fill that way you can inspect the filter (metal mesh screen) to see how it looks. My tranny whine was due to a plugged up filter. I know you said you have a magnefine filter but who knows how plugged up the tranny filter was before you added it, especially with your miles.

The magnefine filter should be changed yearly.


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My 04 4Runner 2wd A/T will only engange reverse after a few miles of driving. I've replaced the filter & renewed fluids last yr when this problem first started. Any guidance you can provide is greatly appreciated.

@Johny Octane , Where are you ?

Hasn't been on since mid 17, no response to DM's, Damn, I'm close to Shreeveport.