Slips in 4th and reverse when warm, 2001 V6 4 Door

Galaxywide · Dec 30, 2021

I have a 2001 Accord V6 with the dreaded transmission issues.

When I bought it, it was leaking horribly from what turned out to be a destroyed output bearing allowing the axle to move in the seal and oil to get past. It also had various shifting issues: lurching, not going into gear, etc.

I rebuilt the trans with a full rebuild kit (transtar 80006G) including clutches and steels, a Superior shift kit (STL-HO4-388), and new bearings. I cleaned, inspected and checked everything I could, and while it wasn’t perfect the pump checked in spec, and I flex honed the bores for all the shift shafts until they moved freely and easily (Superior BB100 brush set). I also installed an external cooler and an inline filter as well.

I did NOT set the clutch end clearance using shims, since I didn’t want to buy a pile of them at something like $16 each. I did measure it, and while I don’t recall the exact numbers I remember it being close to or in spec.

It has a new filter, new fluid (Valvoline MAX Life synth), and I have replaced both pressure sensors with non-OEM replacements.

Now the problem:
When cold, it shifts great, if a bit slowly. All gears work, no slipping, converter locks up, no issues.

However, once it gets warm, it will either not shift into 4th (it attempts several times, but then errors out) or it will shift into 4th but then slips as soon as you do anything other than drive steady speed on a level road. All other gears work great when hot, converter locks up solid in 3rd. Reverse also slips when warm as well, which leads me to suspect the 4th clutch pack…but if the clutch pack is an issue, I feel it shouldn’t work at all rather than only when cold. If the pump was bad, none of the gears should work. When it’s slipping, if you drop into 3rd everything is instantly fine, no slip, pulls hard up hills, etc.

So either the 4th clutch pack isn’t getting enough pressure when hot, or it somehow it has more end clearance when it heats up than when cold. I suspect it might be a shift solenoid, an internal spool valve sticking or perhaps a pressure sensor? All I know is that I REALLY don’t want to pull the trans again, and I just want to get it working well enough to sell and get it out of my life.

Does anyone have any ideas on what to try, or what might be causing the issue? Even if it’s internal, I’d rather know then lay awake at night wondering which of the dozens of things it might be!

If you got this far, thanks for reading my wall of text, and let me know if I'm missing any important info!

Mods, I apologize if this thread is in the wrong place, if so please move it.

BlkCurrantKord · Dec 30, 2021

Switch to the Honda ATF for one. You would need some sort of diag tool to hook up and read/see what the trans is actually doing.

Gallowlight · Jan 6, 2022

What codes if any do you get when it slips/doesn't engage?
Honda ATF for these guys is DW-1, if you haven't already switched. These transmissions are cranky at best with their fluid, and Honda genuine is the best for it. Valvoline MaxLife is good stuff, but not for these trans. Idemitsu Type H you can get at most auto parts stores if you don't go to the dealer.
I'd suggest draining the MaxLife and putting in Honda to see if that helps. It's cheaper than pulling apart the trans again. Hope this helps.

Galaxywide · Jan 6, 2022

Unfortunately I don't have a list of the codes, I saved them but have since gotten a new phone. I'll have to pull them again at some point, but I do recall them being generic things like "failed to shift" or "transmission problem". Nothing specific, as that would be far too helpful.

I'm aware of DW-1, but since it's hilariously expensive and maxlife explicitly lists it as compatible I elected to go with that over the Honda fluid. Plus now I'd have to change the oil 3 or 4 times at $40+ a pop to have a decent % of the new fluid in. Idemitsu type H is interesting, as the closest Honda dealership is about 2 hours away but I do have auto parts stores. Is it just rebranded DW-1, or something else?

It wouldn't cost me any money to pull the trans out, just time (that I'd rather use for other projects). I'm loathe to pull it again just to check things on the hope that maybe something is wrong, but if there's a high chance of a specific internal problem it might be worth it.

I forgot to note in my first post that I did the rebuild over a year ago, and it really hasn't changed over that time. This car is just our winter/local beater, so it doesn't get driven much and as annoying as no 4th gear is, it doesn't prevent the car from driving so it's been a low priority.

Thanks for the replies so far!

Gallowlight · Jan 27, 2022

Idemitsu Type H is literally Honda ATF. Most idemitsu transmission fluid is OEM, just lacking the OEM lable. I'd rather run than than the Maxlife tbh. I know it's pricey to swap in that fluid, but our whole forum chants dw-1 for a reason. Nothing against Maxlife, but it is a 'universal' ATF. It can't be everything. I can be wrong, but it's worth a shot. I know you changed phones but codes tell a story and can help diag before spending money.