904 slow 2-3 shift, should I be worried?

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MopaR&D

MopaR&D

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I've had a 904 in my Duster for years that's worked great. A few years ago the valve body cracked and I replaced it along with doing some zero-buck shift mods thanks to some members here (everything else seemed fine when I pulled the pan). It really firmed up the shifts especially 1st-2nd and all was good until I moved to lower altitude and picked up a good bit of HP and torque thanks to the denser air (runs mid-12s now in the 1/4). Now the 2nd-3rd shift is relatively soft and slow if I'm really getting on it. I'm paranoid I'll roast the forward(?) clutch pack if I keep doing that so I let off a bit before shifting into 3rd. The fluid is still good, has a deep pan and big aux cooler. I want to pull the pan and take a look, if it's not full of trash I'm thinking of putting in a proper Transgo TF-2 shift kit and sending it, rather not pull the trans and do a rebuild as I don't have the space currently and want to save money for manual swap. Does it sound like I just don't have enough pressure for applying the 3rd gear clutch pack for its current power level or is it toast?? I have no other issues with how it runs.
 
I had a 727 have a "soft" almost slip from 2-3 gear. Mine turned out to be a weak pump.
 
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I'm sure you know, there's really no special tools needed to rebuild one of these. And the rebuild kit is usually just over a $100 for a good one, and I've done it on a piece of 2 foot by 4 foot plywood on the back of 2 chairs when I didn't have room...
 
I totally agree about the adjustment. What's happening is a common problem in these transmissions. The slow 2-3 shift is actually the transmission trying to engage 2 and 3 at the same time. A lot of times it's because the 2nd gear band is adjusted too tightly and is still a little applied on the 2-3 shift. The TF2 kit has a corrective orifice that you knock in one of the passages in the transmission that slows the fluid flow and allows the 2nd gear band time to release fully. Usually adjusting the band a little on the loose side will cure it. Usually.
 
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I think it is re-build time, BUT to be sure, adjust the KD band first to see if it corrects the problem.

A shift kit will not fix a worn out trans & could make the problem worse.
 
Thanks for the replies, good to know rebuild kits are cheap at least and I do have a set of sturdy plastic hobby horses I could lay a piece of plywood over. I did adjust the KD band back when I put in the 'new' valve body. I'm familiar with the 2-3 overlap issue as the 727 in my truck does that, feels like the brakes are being tapped sometimes when it does that shift. This feels more like the opposite if anything. Sounds like I won't know until I drop the pan and take a look though. I did buy Tom Hand's Torqueflite book last year and have been reading through that to understand how it works. I'd like to think the transmission didn't suddenly kick the bucket because it wasn't shifting like this before I moved from Colorado and picked up an instant ~90 HP thanks to going from 5000+ feet elevation to basically sea level.
 
MopaR&D said:
Thanks for the replies, good to know rebuild kits are cheap at least and I do have a set of sturdy plastic hobby horses I could lay a piece of plywood over. I did adjust the KD band back when I put in the 'new' valve body. I'm familiar with the 2-3 overlap issue as the 727 in my truck does that, feels like the brakes are being tapped sometimes when it does that shift. This feels more like the opposite if anything. Sounds like I won't know until I drop the pan and take a look though. I did buy Tom Hand's Torqueflite book last year and have been reading through that to understand how it works. I'd like to think the transmission didn't suddenly kick the bucket because it wasn't shifting like this before I moved from Colorado and picked up an instant ~90 HP thanks to going from 5000+ feet elevation to basically sea level.
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Everything works great till it doesn't... :( ...
 
Here's a video I took of the car going down the strip a few weeks ago so y'all can hear it shifting through all the gears at WOT:

 
Sounded like a chirp 1 to 2 but 2 to 3 sounded fine to my untrained ear!

How has your transition from CO to GA been?
 
MopaR&D said:
Here's a video I took of the car going down the strip a few weeks ago so y'all can hear it shifting through all the gears at WOT:

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Sounds pretty good from here. I don't hear any shift flare like it's slipping.
 
Dana67Dart said:
Sounded like a chirp 1 to 2 but 2 to 3 sounded fine to my untrained ear!

How has your transition from CO to GA been?
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It's been great! New job is great, I own a nice house and actually got engaged last month so things are definitely on an upward trend. I miss some things about CO but overall I'm very glad I made the move out here.

toolmanmike said:
Sounds pretty good from here. I don't hear any shift flare like it's slipping.
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It's the difference in 2-3 shift from 1-2 that gets me, I keep expecting it to be firm and instant but with how long it takes I just picture the clutches slipping and wearing out.

I think I'm just going to go for a TF-2 kit so I can get the pressure up (and quicker KD band release) on the 2-3 shift. Obviously if I pull the pan to install the shift kit and it's not looking good I'll prepare for a rebuild but it's sounding like that likely isn't the case, hopefully.
 
MopaR&D said:
It's been great! New job is great, I own a nice house and actually got engaged last month so things are definitely on an upward trend. I miss some things about CO but overall I'm very glad I made the move out here.



It's the difference in 2-3 shift from 1-2 that gets me, I keep expecting it to be firm and instant but with how long it takes I just picture the clutches slipping and wearing out.

I think I'm just going to go for a TF-2 kit so I can get the pressure up (and quicker KD band release) on the 2-3 shift. Obviously if I pull the pan to install the shift kit and it's not looking good I'll prepare for a rebuild but it's sounding like that likely isn't the case, hopefully.
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I am no expert but 2-3 in torqueflite is always a little soft. A gear change but just a rpm change.
Let's look at this one.
 
toolmanmike said:
I am no expert but 2-3 in torqueflite is always a little soft. A gear change but just a rpm change.
Let's look at this one.
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I've heard that too, just based off the sound in those videos though my 2-3 shift is quite a bit slower. The drop in RPM during the shift is just too slow for my liking. I can accept that it'll be slower than 1-2 shift but I still think it can be a lot quicker than it is.

I'm also looking at a Sonnax Billet Accumulator Piston as it occasionally feels like the kickdown band starts to apply when I'm driving around in 3rd gear, just the faintest sensation of touching the brakes or a gust of headwind. The current TransGo instructions say to leave the piston and springs in so that's what I'm going to do; I know it's possible to use a blocker rod but I'd rather just follow instructions for this type of thing.
 
MopaR&D said:
I've heard that too, just based off the sound in those videos though my 2-3 shift is quite a bit slower. The drop in RPM during the shift is just too slow for my liking. I can accept that it'll be slower than 1-2 shift but I still think it can be a lot quicker than it is.

I'm also looking at a Sonnax Billet Accumulator Piston as it occasionally feels like the kickdown band starts to apply when I'm driving around in 3rd gear, just the faintest sensation of touching the brakes or a gust of headwind. The current TransGo instructions say to leave the piston and springs in so that's what I'm going to do; I know it's possible to use a blocker rod but I'd rather just follow instructions for this type of thing.
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I would double check the linkage and make sure the bands are adjusted properly. How long since the pan has been off?
 
Just my 2 cents.

At the speed and the rpm you are at for the 2-3 shift I would not expect it to be a tire chirping shift.

In fact I would not want to chirp the tires at near 100 mph

But that's just me!
 
Dana67Dart said:
Just my 2 cents.

At the speed and the rpm you are at for the 2-3 shift I would not expect it to be a tire chirping shift.

In fact I would not want to chirp the tires at near 100 mph

But that's just me!
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And they won't.
 
MopaR&D said:
I've had a 904 in my Duster for years that's worked great. A few years ago the valve body cracked and I replaced it along with doing some zero-buck shift mods thanks to some members here (everything else seemed fine when I pulled the pan). It really firmed up the shifts especially 1st-2nd and all was good until I moved to lower altitude and picked up a good bit of HP and torque thanks to the denser air (runs mid-12s now in the 1/4). Now the 2nd-3rd shift is relatively soft and slow if I'm really getting on it. I'm paranoid I'll roast the forward(?) clutch pack if I keep doing that so I let off a bit before shifting into 3rd. The fluid is still good, has a deep pan and big aux cooler. I want to pull the pan and take a look, if it's not full of trash I'm thinking of putting in a proper Transgo TF-2 shift kit and sending it, rather not pull the trans and do a rebuild as I don't have the space currently and want to save money for manual swap. Does it sound like I just don't have enough pressure for applying the 3rd gear clutch pack for its current power level or is it toast?? I have no other issues with how it runs.
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Here's a good thread. Check out post#10. 727 2nd to 3rd flare up Do you have a manual valve body? I would guess no if it's a street car..
 
If I remember correctly the last time I had the pan off was 3 years ago.

THANK YOU for that thread link btw, I knew there had to be a past thread with that kind of info I was looking for but didn't know what keywords to use in the search tool. I do not have a manual VB, it's a stock late-'70s (non-lockup) unit I modified by drilling out some of the holes in the separator plate and omitting some check balls per @CudaFactHackJob (who sadly seems to no longer be here...??)

I think at bare minimum the pressure regulator on the side of the VB needs to be increased and I could probably reduce the number of turns out for the front band adjustment. I don't remember adjusting the hydraulic pressure screw, if I did mess with it I just made sure it was at factory spec when the VB was out. But since I need to drop the pan to do the pressure adjustment I might as well do an air pressure test on the front clutch and if that checks out then install a proper shift kit, a TF-2 is pretty cheap anyway.
 
Update time... I ended up just ordering a TF-2 kit, it arrived last week. I dropped the pan today and it looks pretty good so I guess everything was fine after all but I'm still going to install the shift kit because I want that 2-3 shift to be firmer.

The weirdness that looks like brown oil or water in the right half of the pan is just the reflection of my house lol.

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Question, there's a section in the TF-2 instructions that says to drill 2 holes in the valve body where the lockup valve is if it's a 1977 or later unit. Mine is a 1977 but it's non-lockup, it has the valve in there but it's held in place by a spring and I assume does nothing. Do I still need to drill the holes or can I leave it alone?
 
I re-read the instructions and it's clear those 2 holes should only be drilled if the trans has a lockup converter so I left it alone.

Next question, how important is it to replace the low/reverse servo spring with the one that comes in the kit? In the Transgo instructions it says to reuse the stock one in a 904 if the spring in the kit doesn't fit right, makes me think it's not super important? I only ask because after watching some videos it seems like a pain in the butt to replace that spring in the car by yourself and get the servo piston back in and reinstall the low/reverse band strut.

EDIT: Just went out and took a peek inside the trans for the first time, looks like someone's been in here before. Pics inbound...
 
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I see some goodies in here... Red lining on the kickdown band, double-wrap low/reverse band and a purple low/reverse servo spring. That servo spring isn't stock right? I'm guessing I should just leave that in...

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Well it's all back together, runs great and I'm much happier with the shift quality. 2-3 is quick and firm at WOT just the way I wanted it. I elected not to install the low/reverse servo spring that came in the TF-2 kit and it seems fine with whatever one was already in there, shifts into 1st and Reverse just fine; if anything a tad less harsh than before I installed the shift kit and when the valve body only had some holes drilled out in the separator plate from the last time it was apart. The only issue I noticed is there's still what seems to be a slight cross-leak causing a barely-noticeable occasional dragging feeling when coasting or maintaining speed on flat ground in 3rd gear. Hopefully it's not enough to burn anything up. It's the kind of thing I bet 99% of people wouldn't even notice but I do because I'm hypersensitive to how my car drives lol.

I did notice looking closer at the low/reverse band, looks like one part of it is a bit discolored and warped like it overheated, could that be causing the issue?
 
If you end up rebuilding it, a good trick for a super hard engagement of the trans is to scuff the surface area under where the band engages with some 80 grit. I did this to 904 on my D100 truck, and man when it shifted, it hit so hard it hurt. Heh.
 
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