I Hate My 904

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bobscuda67

bobscuda67

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Last year I had a flare up problem on my rebuilt 904. Flared up bad between 1/2-2/3 gear changes. Adjusted the throttle rod back and forth, cranked up the pressure relief valve, adjusted the bands. Still did it. Took it out and it had a burned up kickdown band, after 20 miles of driving. It had a Trans Go SC-TF kit when I bought it, so I called them for advise. The tech told me I needed a TF-2 kit since I went from 273 to a 340 engine.

Over the winter I installed the TF-2 kit and a new A500 kickdown band. I also installed Alto Red Eagle clutches and Kolene steels with an extra one in the foreward and the direct drum. Set the foreward clutch pack at .025 and the direct at .073. Set the pressure relief valve to the TF-2 lowest setting. Put it together and air tested it. All was well.

Installed it this spring and it still flares between gear changes, but not as bad as before. Adjusted the throttle pressure rod back and forth, still flares but shift points do change. The harder I get on it the bigger the flare.

When it was rebuilt before I had the 2;74 gear set installed and a newer input shaft. I wonder if the pump should have been changed or if there is a mismatch of hard parts causing a pressure leak. I guess the next step would be to test the servo and line pressure.
How would I do a pressure test and what should the readings be.

This thing has me pulling my hair out. Thank's guys for any help.
 
Bob your front clutch clearance is pretty tight IMO. I generally like to see them have at least .010" per clutch plate or they may drag. The rear clutch pack can be somewhat tighter since it's engaged in all forward gears. That's not related to the problem though since flare up is the problem.

Question 1, did you go through the front pump and check clearances because it sounds like low pressure. Either a sloppy front pump or regulator valve in the valve body problem. A mismatch is also possible since you say the input shaft was changed but if you pressure tested it that should have showed up. Question 2, did you verify all parts in the valve body are assembled correctly?

To test the line pressure install a gauge into the middle port located on the passenger side right behind the front servo. I don't know how much the Trans-go kit steps up the pressure to but stock it should be 55-60 with the trans warmed up to normal opp temp, wheels off the ground (car secured properly with jack stands), transmission in 3rd gear and the engine at 1000 rpm. My guess is your going to find low pressure by your description.

Also on the throttle pressure adjustment you say you adjusted it back and forth. Loosening it will only make flare up worse and soften the shift in every situation. You want it set so the lever on the trans. where the linkage is hooked pushed all the way rearward or close to all the way when the throttle is wide open. That gives maximum throttle pressure for firmest shifts and less chance of flare up.
 
the flare up is caused by band not releasing fast enough...it is actually in two gears at once...

so you have 5 disc and steels in the front and rear clutches?

I set my front clutch pac at .070 and the rear around .030....it is almost as you have them backwards...
 
Tony with all due respect I think your getting overlap and flare up backwards. Overlap is when it's in 2 gears at once. Flare up is when the engine revs up between shifts.

I agree that the clearances he said seem backwards.
 
Sorry if I confused anyone, but what I meant to say is I have a 4 disc foreward [rear] and a 5 disc direct [front]. The rear set at .025 and the front set at .073. The car does not creep in neutral.

I did not take apart the pump. It functioned fine when it was behind the 273, and before the input shaft was changed. I also changed the converter when the input shaft was changed.

When I installed the TF-2 kit I went through the valve body and cleaned all the valves and double checked everything.

It has the part throttle kickdown valve on the valve body which I installed when it had the 273. I was wondering if that might have any affect on shift flare up. I could take it off as it's not needed with the 340.

Yea Fishy, I know loosing the throttle pressure linkage makes it worse, but I was in that state of mind where logic gets thrown out and you try anything.
I had it adjusted so that the carb would only go to half throttle and it still flared.

I will check the line pressure today. I'll let you know my findings.
 
bobscuda67 said:
Sorry if I confused anyone, but what I meant to say is I have a 4 disc foreward [rear] and a 5 disc direct [front]. The rear set at .025 and the front set at .073. The car does not creep in neutral.

No problem. Those clearances sound fine
Click to expand...
I did not take apart the pump. It functioned fine when it was behind the 273, and before the input shaft was changed. I also changed the converter when the input shaft was changed.

If the input shaft had the same amount of sealing rings and all the oil ports were in the same locations it should be fine.
Click to expand...
When I installed the TF-2 kit I went through the valve body and cleaned all the valves and double checked everything.

It has the part throttle kickdown valve on the valve body which I installed when it had the 273. I was wondering if that might have any affect on shift flare up. I could take it off as it's not needed with the 340.

This is the first thing I'd suspect now that you say your pump functioned fine before. Try removing it and putting the stock cover back on and see what happens. A long time ago (several yrs.) I thought about adding the part throttle kickdown to a unit I had and found some info and I think I remember it saying you had to do some other mod to make it work right. But again that's been so long ago I just don't remember for sure
Click to expand...
Yea Fishy, I know loosing the throttle pressure linkage makes it worse, but I was in that state of mind where logic gets thrown out and you try anything.
I had it adjusted so that the carb would only go to half throttle and it still flared.

Gotcha. I know how that is
Click to expand...
I will check the line pressure today. I'll let you know my findings.
Click to expand...

....
 
Well, I did some pressure test and have some resilts;

Line pressure at idle, throttle rod all the way foreward, foot on brake in drive-80 psi
Same as above but at 1000 rpm in 3 rd gear-85 psi
Line pressure at idle, throttle rod back to it's rest point, not all the way back,foot on brake in drive- 90 psi
Line pressure in 3rd gear at 1000 rpm,rod back on it's rest-95 psi
I think if the throttle rod was all the way to it's stop it would be well over 100 psi.

Front servo test;
Car in drive, throttle rod back on it's rest.
1st to 2nd gear shift-1-2 psi. Not a misprint.
2nd to 3rd-90psi.

Ok, now I know what the problem is. Could the part throttle kickdown cause this? Thank's, Bob
 
Bob those pressures are close to what my manual says they should be. Earlier I failed to mention that the line pressure I quoted was with the throttle rod all the way forward. With it pulled back it should be approx. 90 psi on a stock trans. Since you have a TF-2 kit in it the pressure will be more so I think your ok. The only test port on the front servo is on the release side so that's why the pressures seem backwards on it.

You mentioned you did air pressure tests while assembling it. Did you just test each clutch pack individually or also do a final test after the assy. was installed but before the valve body was bolted on? I do a final test after the assy. is assembled right before I install the valve body to make sure something didn't happen during assy.

If you did test it after everything was assembled using the ports where the valve body bolts too and everything tested ok and your sure all valves are installed correctly in the valve body the only thing left is the part throttle kickdown module. If you only tested clutch packs before assy. drop the valve body and test things again at the ports on the case where the valve bolts too. If everything is ok eliminate the part throttle kd module.

In case you don't have a chart that shows where to inject air in the case here's a scan from the manual. You'll see it down on the lower left side of the page. It's a 727 but the ports are the same. Use 25-30 psi of air for tests.

p.s. Sorry the picture is so small. This board won't let you load anything big.

727 Air test ports.jpg
 
OK, let me ask, does it flare on both upshifts or just one? Also does it down shift OK? And one final question just to satisfy my curiousity does it do the same flare if you shift it manually or are we talking about leaving it in drive or both ways?

What year is the transmission?
How many seal rings are on the input shaft?
Are the rear clutch drum, pump and reaction shaft from the same trans?
What about the 5 disc front clutch, how did you accomplish that, with a factory 5 disc front clutch drum or a thinner reaction plate and piston in an older style 4 clutch drum?
 
Guitar Jones said:
OK, let me ask, does it flare on both upshifts or just one? Also does it down shift OK? And one final question just to satisfy my curiousity does it do the same flare if you shift it manually or are we talking about leaving it in drive or both ways?

What year is the transmission?
How many seal rings are on the input shaft?
Are the rear clutch drum, pump and reaction shaft from the same trans?
What about the 5 disc front clutch, how did you accomplish that, with a factory 5 disc front clutch drum or a thinner reaction plate and piston in an older style 4 clutch drum?
Click to expand...

It flares on the 1/2 2/3 upshift when left in drive. If I take it easy it flares just slightly. The harder it's pressed the worst the flare. I don't drive it hard, so I don't burn up the front band again.

One input shaft ring.

Rear clutch and reaction shaft were changed along with the low gear set and front and rear planets. The pump is the same one. I had a local shop do the hard parts change as it was over my head.

I put 5 clutches in a 4 clutch drum. I had a .217 thick pressure plate step cut for the clearance.
Thanks, Bob
 
fishy68 said:
Bob those pressures are close to what my manual says they should be. Earlier I failed to mention that the line pressure I quoted was with the throttle rod all the way forward. With it pulled back it should be approx. 90 psi on a stock trans. Since you have a TF-2 kit in it the pressure will be more so I think your ok. The only test port on the front servo is on the release side so that's why the pressures seem backwards on it.

You mentioned you did air pressure tests while assembling it. Did you just test each clutch pack individually or also do a final test after the assy. was installed but before the valve body was bolted on? I do a final test after the assy. is assembled right before I install the valve body to make sure something didn't happen during assy.

If you did test it after everything was assembled using the ports where the valve body bolts too and everything tested ok and your sure all valves are installed correctly in the valve body the only thing left is the part throttle kickdown module. If you only tested clutch packs before assy. drop the valve body and test things again at the ports on the case where the valve bolts too. If everything is ok eliminate the part throttle kd module.

In case you don't have a chart that shows where to inject air in the case here's a scan from the manual. You'll see it down on the lower left side of the page. It's a 727 but the ports are the same. Use 25-30 psi of air for tests.

p.s. Sorry the picture is so small. This board won't let you load anything big.
Click to expand...

I did air test the trans just before I bolted on the valve body. At 35 psi the front and rear servos applied crisply. The direct clutch thunked and the rear clutch did not make a very load noise but you could feel it if you put your hand on it. I heard no air leaks inside the trans.

I did take the valve body out today, I'll air test it again Sunday.

I did replace the governer with a higher rpm piece, if that makes any differance.

Looking at the part throttle kickdown module I don't understand how it would affect the 1/2 upshift as it just has a passage in it, the same as the old cover. It has a small piston on the 2/3 shift valve.

That makes sense that the front servo tap is on the release side. It had me scratching my head.
Thanks again!
 
OK, this may be your problem. The rear clutch drums and reaction shafts for factory 5 disc clutch drums are different. The seal ring on the front of the rear clutch drum where it goes into the reaction shaft is larger in the trans that came with 5 discs. In order to properly use this combination you need a non lock up 2 ring input shaft as the one ring shaft is smaller in diameter. It will go together but it won't be right. If you cut down the reaction plate to install the 5th disc then you can use the older one ring input/reaction shaft and early rear clutch drum but you can't use the early rear drum and one ring input shaft in a later 2 ring reaction shaft.

I think if you'll check these out you'll find there is a mismatch.
 
Ok, so I got my trans out today and have it tore down. I really don't see a problem with parts mismatch. The trans is a 1967 904.

It has a 3 clutch foreward with a 27 spline input with 1 sealing ring. The foreward drum has 1 sealing ring too. The direct clutch hub measures 1 1/8 inches. Looks like a 68-77 piece.

The pump only has room inside for a single ring input shaft. It has two sealing rings on the outside. The only number on is 2538410 so it might be the original pump and never was changed.

The direct drum is a 4 clutch and measures 6 inches at the lugs.
I had the flare up problem before I fit the extra clutches in the drums. I thought the TF-2 kit would fix it. It helped, but didn't fix it.

Thanks guys.
 
Bob my only guess is it must be a problem in the valve body somewhere since it sounds like all the mechanical parts are right. I haven't done enough 904's to know the diff. between their different flavors but it sounds like Guitar knows them real good. Maybe he'll have another idea. Sorry I couldn't be more help.
 
OK, check the kick down (2nd gear) or front band servo bore very closely. That case may be old enough to where it's worn down the servo bore to some sand holes. I've seen that before and since it doesn't use a lip seal it needs to be in good shape.

It could be taking longer to engage causing the 1/2 flare and releasing early causing the 2/3 flare.

Also check the inner lip seal of the front drum piston. Sometimes the groove is just too deep and the lip of the seal doesn't stick out past the hub. Take the piston out and run your finger up and down the hub across the seal in the direction of the piston apply. If you can't feel the seal you need a new drum.

Another problem I've seen is the rear clutch drum hub, the part that splines into the front drum may not be long enough to accommodate 5 discs. Check the front discs very carefully, if the teeth look a little bent (not quite flat anymore) then they have rolled off the hub and the hub isn't long enough.

Do any of the discs look overheated or burnt?
How about the band, does it look overheated or burnt?

Any dark spots on any of them or blueing of the drum or steels?
 
fishy68 said:
Bob my only guess is it must be a problem in the valve body somewhere since it sounds like all the mechanical parts are right. I haven't done enough 904's to know the diff. between their different flavors but it sounds like Guitar knows them real good. Maybe he'll have another idea. Sorry I couldn't be more help.
Click to expand...

Thanks Fishy, I did air test the clutch packs in the pump out of the case and it looks like there funtioning fine. I'm still leaning toward a valve body problem, maybe it has a crack or the case does. If it does, I might never find the cause. Thanks again!
 
Guitar Jones said:
OK, check the kick down (2nd gear) or front band servo bore very closely. That case may be old enough to where it's worn down the servo bore to some sand holes. I've seen that before and since it doesn't use a lip seal it needs to be in good shape.

It could be taking longer to engage causing the 1/2 flare and releasing early causing the 2/3 flare.

Also check the inner lip seal of the front drum piston. Sometimes the groove is just too deep and the lip of the seal doesn't stick out past the hub. Take the piston out and run your finger up and down the hub across the seal in the direction of the piston apply. If you can't feel the seal you need a new drum.

Another problem I've seen is the rear clutch drum hub, the part that splines into the front drum may not be long enough to accommodate 5 discs. Check the front discs very carefully, if the teeth look a little bent (not quite flat anymore) then they have rolled off the hub and the hub isn't long enough.

Do any of the discs look overheated or burnt?
How about the band, does it look overheated or burnt?

Any dark spots on any of them or blueing of the drum or steels?
Click to expand...

Ok, I checked the front servo bore and I see no imperfections. The bore is shiny were the sealing ring seats. I checked to make sure the bores are round, they are. Also looked for cracks in the piston.

The disc look good, no bent teeth or burn marks. I will double check the engagement into the rear clutch drum. The kickdown band is like new and there are no blued hot spot marks on the front drum or steels.

I took the pump, front and rear drums and valve body to a trans shop today and told them to look everything over and make sure it was right. I thought another pair of eyes on it couldn't hurt.

I will tell them to check the direct drum seal when they call me.
Thanks Guitar for you help.
 
This is going to be tough to diagnose without being able to touch it or see it so let's see if we can do a little process of elimination.

Has it always done this before the rebuild or just after the rebuild or was it a trans you purchased as a core and had it rebuilt?
 
Guitar Jones said:
This is going to be tough to diagnose without being able to touch it or see it so let's see if we can do a little process of elimination.

Has it always done this before the rebuild or just after the rebuild or was it a trans you purchased as a core and had it rebuilt?
Click to expand...

The trans worked perfectly, nice short shifts when it was behind my 273. It had a Trans Go SC-TF kit in it.
Three years ago I bought a 340 block to build so I took the trans to a shop to build up.
I had them put the low gear set in it, they replaced the output shaft. I had them replace the input shaft so I could get a converter easier.
They also did some valve body mods to help the flow. They blocked off the accumulator and shimed the rear servo.
When they were done I put a part throttle kickdown module on the valve body. I installed a 5200 rpm governor on it too.
Installed it last year and the thing flared badly. Worked on it about all summer,finally it burned up the kickdown band and was undrivable.

Pulled it out again last fall. I installed the TF-2 kit and added an extra clutch in the direct and the foreward drums. Also installed an A-500 kickdown performance band. It shifts better, at a light cruise it doesn't flare. At half throttle it still flares.
I have the valve body pressure relief valve set at it lowest setting per the Trans Go kit.
 
you stated that you installed a different governor which will affect the shift as it is related to work with (against) line pressure and throttle pressure, I use John Cope at Cope Racing Transmission call him and he can tell you whats possibly wrong, also what apply lever ratio you using and how many springs in the front drum? this will affect 2-3 shift some, i say lose the valve body and go with a manual low band apply valve body
 
bobscuda67 said:
They also did some valve body mods to help the flow. They blocked off the accumulator and shimed the rear servo.
When they were done I put a part throttle kickdown module on the valve body. I installed a 5200 rpm governor on it too.
Click to expand...

If it worked correctly before they did the valve body mods I bet they screwed up something in the valve body. Maybe drilled something wrong. Back when I was a kid I took my car to a guy that was supposed to know what he was doing to have him install a shift kit. He drilled a passage wrong and trashed 3rd gear. The other mods you mention are standard mods so I doubt there's a problem there.
 
CHEATHAM said:
you stated that you installed a different governor which will affect the shift as it is related to work with (against) line pressure and throttle pressure, I use John Cope at Cope Racing Transmission call him and he can tell you whats possibly wrong, also what apply lever ratio you using and how many springs in the front drum? this will affect 2-3 shift some, i say lose the valve body and go with a manual low band apply valve body
Click to expand...

The governor does work in conjunction with the throttle pressure but there's no way it can cause this problem. John Cope is a real good fellow.
 
Update to my problem.
Took the clutch packs, pump and valve body to a shop and had them look at it. They air tested it and it was fine, but had them replace the front drum piston seal with an updated one, with a lip, anyways. The pump was withen specs. The TF-2 kit was installed corectly per Trans Go's instructions.

I removed the part throttle kickdown module and set the pressure at four full turns from flush. I tightend the kickdown band to just under 2 turns.
When it's driven at cruise speeds, it shifts perfect. The 1-2 and 2-3 are short and crisp. When at 3/4 to full throttle the 1-2 shift feels like it has a slight overlap, the car slows down between shifts. The 2-3 shift is very firm and short. Overall an improvement from before, but still not where I want it to be.
 
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