Anyone had these symptoms with a 904?

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TylerW

TylerW

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Hey guys:

The 904 in my '68 SL6 Valiant is acting up. I've been into one of these already and am pretty familiar with how they work but I'd like to get some feedback to help me decide if I want to repair this original unit or find another one with part-throttle downshift, etc. Here's what's up:

Field-find car. Sat for who knows how long. Trans full, no leaks, fluid dull red, "kickdown rod" adjusted per FSM.

First dozen test miles shifted soft between 1-2, but on time. 2-3 normal and on time. Third day of driving had long, slushy 1-2 shift, then acted fine ever after with a nice firm 1-2 shift, on time.

Drove several ~50 mile road trips during week, things degraded. Began having an audible "shwuup" noise immediately before 1-2 shift, every time. When it is COLD, it will sometimes start in second, sometimes start in 1st and shift directly to third, sometimes will stay in 1st until it warms up, skip 2nd when it finally shifts, then shift normally.

When it is HOT, it randomly shifts 1-3, or it shifts 1-2-3 and stacks 2-3. Today it shifted once from 1-2 at about 4mph. Otherwise it shifts on time and feels good except for that noise at the 1-2 shift.

I haven't lost any gears, 1st, 2nd, and 3rd do not slip under heavy acceleration, reverse feels good and I have engine braking in manual low. All of this bad behavior is amplified when the transmission is cold, but it still possesses the capability to act strange when hot.

Your thoughts are appreciated.
 
I'd drop the pan and change the filter before I wrote it off . Mine did strange things like not wanting to go into reverse when cold and was cured with new fluid and filter.Lasted 10 years after that and was still ok when I pulled it and put in a 4 speed
 
I think you have a governor problem so a fluid and filter change might be a good idea. But I would check the return of the kickdown; maybe put a return spring on it.
 
If I understand you correctly this trans is original, not rebuilt that you know of. Any 50 year old trans most likely needs rebuilt due to seals being dried out and not sealing properly IMO
 
Purt near any time you have intermittent issues like that, it is almost always seal related. SOmetimes they seal, sometimes they don't. I do agree however, with doing the fluid change and also I would add some Lucas transmission conditioner as well. What have you got to lose? If it works, oh happy day! Right?
 
If its a sealing issue,ATP at-205 is a great product. The most expensive choice but it works.
That is, if seals are stiff and not sealing. Otherwise mechanical repair will be necessary.
As mentioned, the govenor could be sticking or the kickdown isnt properly connected.
 
Thanks for the suggestions. This culminated in a sudden loud whine, followed by a bad 2-3 flare and 3-second reverse engagement delay...lol. Something came apart in there. It sounds very similar to the noise a 4L60E made when the sun shell cracked apart. Probably will toss another one in there, gets a little expensive when hard parts break and send fragments through everything.
 
Well if you do that, it would be nice to know what ails this one.
But before you rip it out, I would do either an oil pressure test if you have gauges, or at least an air-pressure test.
IIRC you can transfer valve bodies between 67 up to something like 73/74 Or the PT KD item can also be swapped onto older VBs.
Too high a fluid level can do strange things too.
The whine is probably a planetary; but don't know about the sudden-onset.
 
Tooljunkie said:
If its a sealing issue,ATP at-205 is a great product. The most expensive choice but it works.
That is, if seals are stiff and not sealing. Otherwise mechanical repair will be necessary.
As mentioned, the govenor could be sticking or the kickdown isnt properly connected.
Click to expand...
These types of so called products are at best a temporary fix. They will soften and swell the seals for sure, but so will an old trick used by less than honest used car lots and car flippers. A spoonful of brake fluid swells and soften seals. Different product, same result.
 
Drop the pan and check the filter. Whining sounds like pump cavitation. Restricted filter will do that. I had 71 Demon slant 6 years ago that was given to me with a bad transmission. It would shift through all gears for about 1/8th mile then loose all forward gears. Reverse still worked. I dropped the pan and sludge and gunk were in the pan. Dipstick looked red. The trans would shift fine until the gunk was pulled up against the filter then it would loose line pressure. Clean pan, new filter, new fluid. I drove it over 200 miles the next day.
 
A 2-3 flare accompanied by a delayed reverse engagement means worn direct clutch. It's the first drum behind the pump. This is an easy fix. Pull out the pump and drop out the two front drums and front band. Put the pump in a vise and put the direct drum on it with new clutches with around .040 to .080 clearance and air check it to test the seals and rings. If they're good; leave them; at least leave the seals, changing rings isn't too hard. Same deal with the forward clutch. And if the front band is black or worn down replace that too. Put it back together with a new front seal, large o-ring and gasket. I wouldn't recommend changing the seals if they pass the pressure test because they do take some finesse and are easy to mess up.
 
A bad filter will cause a whingeing type noise as the pump is cavitating and is starving the trans for fluid. I would start there.
 
I wouldn't even bother with the fluid and filter; just a waste of money. $4 a quart plus filter and gasket all for nothing. When the filter clogs you lose all movement; both forward and reverse. And what clogged it? Your clutch fiber material. Even a stack of old used clutches would be an improvement; as long as the clearance was right.
 
yeah when it comes to 904s, mine have accepted a lot of cobbleing over the years. I reconditioned my first one in 76,on the dining room table,in an apartment, that my new bride and I had just moved into. It was a core, a spare, and I didn't need it until several years later. It is still with me, having outlived several A-bodies.
Ya know and that's another thing; that trans was out of a 71 Demon 318, and was the best shifting trans I had ever had. I built a couple of clones, and I think I still have one or two of those in the back shed. 1971 was a good year for 904s
 
Please post a pic of the look on her face when she walked in on a transmission all over her dining room table. Did she throw your ring back at you? :wtf:
 
CudaFactHackJob said:
I wouldn't even bother with the fluid and filter; just a waste of money. $4 a quart plus filter and gasket all for nothing. When the filter clogs you lose all movement; both forward and reverse. And what clogged it? Your clutch fiber material. Even a stack of old used clutches would be an improvement; as long as the clearance was right.
Click to expand...

I would agree with at least checking the filter due to the explanations of noises and function from it, as pretty much everything mentioned could be caused by a loss or restriction of fluid pressure.
Fluid pressure losses or aeration can even cause skipped shifts and wild variations in shift points.
Usually a plugging filter will cause the loss of reverse first, since reverse uses more fluid to engage than the forward gears and also has more places in the circuit to loose fluid around sealing rings and the reverse servo seals.

That said, you are probably correct in your statement that the trans is in worse condition than what a plugged up filter would cause.
 
On the one that I had with a plugged transfilter, it wasn’t clutch material. It almost looked liked old leaves and trash in the pan. Reverse does operate at a higher pressure. I am not sure why I lost all forward gears and not reverse. Funny story relating to that. On the Demon that I eventually owned. Before I owned it, it belonged to a friend who LOVED beer. I would be on my way to her house and I would see her driving down the road in reverse coming back from the beer store lol. I can assure you reverse worked well. Prior to the filter change she would drive it everywhere in reverse. Oh to be young and dumb again.
 
I don’t usually sell parts being a hoarder but, I have 2 spares and I’m down the road. PM me if ya need one. Craig
 
Thanks Craig, I very well may need to holler at you.

Past that, just another update:

Yesterday, I went for another drive down the street and back just to see whether or not letting it sit a few days "fixed" it, lol. It did not.

In fact, things went from bad to much worse in the space of a mile. I turned around half a mile out, started back. It hung in 1st again, then went directly to third. However, this time third started slipping. I eased it back home and by the time I got down my driveway, it no longer pulled in any forward range, either in drive or selecting manually. Reverse was sort of there but slipped. I went inside, came back out a few hours later, tried again and it dropped into gear just fine. So, I lost everything when it got hot, then got everything back when it cooled off.

In all seriousness, I know this might be pretty bad and I'm just documenting stuff for fun because I've NEVER seen a transmission develop so many symptoms, so severely, so rapidly. What the heck? Behind a slant six? I'm definitely going to pull the pan and look for a filter problem. The only problem with that angle is if the filter is stopped up...what with? Pieces of the kickdown band? That's my guess based on the noise I kept hearing. I'll update when i get it cracked open.
 
TylerW said:
Hey guys:

The 904 in my '68 SL6 Valiant is acting up. I've been into one of these already and am pretty familiar with how they work but I'd like to get some feedback to help me decide if I want to repair this original unit or find another one with part-throttle downshift, etc. Here's what's up:

Field-find car. Sat for who knows how long. Trans full, no leaks, fluid dull red, "kickdown rod" adjusted per FSM.

First dozen test miles shifted soft between 1-2, but on time. 2-3 normal and on time. Third day of driving had long, slushy 1-2 shift, then acted fine ever after with a nice firm 1-2 shift, on time.

Drove several ~50 mile road trips during week, things degraded. Began having an audible "shwuup" noise immediately before 1-2 shift, every time. When it is COLD, it will sometimes start in second, sometimes start in 1st and shift directly to third, sometimes will stay in 1st until it warms up, skip 2nd when it finally shifts, then shift normally.

When it is HOT, it randomly shifts 1-3, or it shifts 1-2-3 and stacks 2-3. Today it shifted once from 1-2 at about 4mph. Otherwise it shifts on time and feels good except for that noise at the 1-2 shift.

I haven't lost any gears, 1st, 2nd, and 3rd do not slip under heavy acceleration, reverse feels good and I have engine braking in manual low. All of this bad behavior is amplified when the transmission is cold, but it still possesses the capability to act strange when hot.

Your thoughts are appreciated.
Click to expand...
Try flushing the transmission. I get a lot of people coming through where I work with problems like that. The flush usually fixes it
 
I have a feeling a few parts need to be refreshed.
I would expect to find bits and pieces in the pan.
Getting worse as it heats up tells me running it more just causes more damage.
 
Hey guys:

Here is the final installment of this saga. I pulled the pan and the pictures should tell the story, pretty much. The gunk on my finger looks black but it is mostly metal paste. Open to ideas what caused this. Thanks.

20190521_180343.jpg


20190521_180421.jpg
 
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