904 race build

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MHEAD

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I have been using 904 transmissions for about 25 years and haven't had any major issues till recently.So with the added power that my cars been making I lost the sprag last year.Then we took the guts out of it and reinstalled in another case but now it slips going into third.So I figured it maybe time to put some good parts into it.
So the main questions is how do I modify the main pump support for more flow to high gear?
 
Loose band adjustment, too much clutch clearance, Orifice in the case? Maybe try smooth thin (forward clutch) Red Eagles in the direct
 
CudaFactHackJob said:
Loose band adjustment, too much clutch clearance, Orifice in the case? Maybe try smooth thin (forward clutch) Red Eagles in the direct
Click to expand...
Band is adjusted correctly.Not sure about the clearances but going to find out when I remove trans.In the past my buddy just used a standard rebuild kit but looks like time for better parts.I have heard about changing the front drum spring to a multiple spring pack and modify pump for more pressure to third.
 
What valve body is in it?
Flow volume doesn't help, pressure does.

MHEAD said:
I have been using 904 transmissions for about 25 years and haven't had any major issues till recently.So with the added power that my cars been making I lost the sprag last year.Then we took the guts out of it and reinstalled in another case but now it slips going into third.So I figured it maybe time to put some good parts into it.
So the main questions is how do I modify the main pump support for more flow to high gear?
Click to expand...
 
TrailBeast said:
What valve body is in it?
Flow volume doesn't help, pressure does.
Click to expand...
It's the same one I bought new in 1992 that came in a tci box but had j.w. scribed on it.So I was told it was a winter's rmv.
 
MHEAD said:
It's the same one I bought new in 1992 that came in a tci box but had j.w. scribed on it.So I was told it was a winter's rmv.
Click to expand...

In that case I would be all over Google looking up those names and numbers to find out exactly what I had.
It sounds like what you want to do is up the line pressure, and doing that on a reverse manual valve body should be simple.
On any other valve body can cause a bunch of other problems.

You might talk to TCI first.
You never know, they could be bored during this whole virus thing and give you a lot of useful info.
 
TrailBeast said:
In that case I would be all over Google looking up those names and numbers to find out exactly what I had.
It sounds like what you want to do is up the line pressure, and doing that on a reverse manual valve body should be simple.
On any other valve body can cause a bunch of other problems.

You might talk to TCI first.
You never know, they could be bored during this whole virus thing and give you a lot of useful info.
Click to expand...
So removed trans this morning.Pulled vb and saw jc punched in this vb.Could this be john cope?I bought this new 28 years ago.
The reason I brought up modifications to the pump is a&a and cope either sell or list this in 904 trans they sell.Thanks

15879394340682540143162167539531.jpg
 
MHEAD said:
So removed trans this morning.Pulled vb and saw jc punched in this vb.Could this be john cope?I bought this new 28 years ago.
The reason I brought up modifications to the pump is a&a and cope either sell or list this in 904 trans they sell.Thanks

View attachment 1715517056
Click to expand...


"JC" = Joe Chrisman of TranZact of Indy. He made valve bodies for TCI as well.

If it is a Rev Manual VB, the TCI equivalent is model 121700.
 
MHEAD said:
So removed trans this morning.Pulled vb and saw jc punched in this vb.Could this be john cope?I bought this new 28 years ago.
The reason I brought up modifications to the pump is a&a and cope either sell or list this in 904 trans they sell.Thanks

View attachment 1715517056
Click to expand...


DusterW2 said:
"JC" = Joe Chrisman of TranZact of Indy. He made valve bodies for TCI as well.

If it is a Rev Manual VB, the TCI equivalent is model 121700.
Click to expand...

That's what I'm finding.
 
What rpm are you hitting third? The stock single spring starts to expand and lose pressure over 6500 I think; or it might just be weak.
 
engine size....weight of car?

i use 5 thin oem disc in the front ...along with the 25 spring kit in the front drum. Use Kevlar bands front and rear...except now I have some red line wider front bands from Tranzact that i am using.
Billet Rear Servo from MOPAR 904 500 42RH 42RE TRANSMISSION BILLET REAR SERVO KIT, DODGE, PLYMOUTH AMC | eBay
plus his band strut too.....

only problem i have had with 904s were my mistakes with the rear drum lip seal.....
cars are around 2900/3000 lbs plus or minus....they have run 6.40s in the 1/8 a few times in Vegas and always at sea level....
4 of the cars have Tranzact tranny brakes...and one has old Turbo Action Cheetah RMVB....
 
70aarcuda said:
engine size....weight of car?

i use 5 thin oem disc in the front ...along with the 25 spring kit in the front drum. Use Kevlar bands front and rear...except now I have some red line wider front bands from Tranzact that i am using.
Billet Rear Servo from MOPAR 904 500 42RH 42RE TRANSMISSION BILLET REAR SERVO KIT, DODGE, PLYMOUTH AMC | eBay
plus his band strut too.....

only problem i have had with 904s were my mistakes with the rear drum lip seal.....
cars are around 2900/3000 lbs plus or minus....they have run 6.40s in the 1/8 a few times in Vegas and always at sea level....
4 of the cars have Tranzact tranny brakes...and one has old Turbo Action Cheetah RMVB....
Click to expand...
It's a 416,12.9:1 with flat tops,molnar crank and rods,modern cnc promax heads,small bullet solid 571 lift 251@50 cam,sv intake,950 qf carb.Would love to try a bigger cam but I'm maxed out piston to valve clearance. Car weighs 2900 without me.
My local track is Mason dixon.Elevation is around 550 ft.Summer time corrected altitude can be 3500 and early spring or late fall can be minus numbers.I think when it ran those numbers it was around 1200 ft.
 
It will be interesting to see what the end play is, the direct clutch clearance, condition of the ring contact area of the direct drum, and the ring wear.
 
The multi spring for the high gear clutch is good
I have heard ATI makes a reverse wound spring that is cheaper, but I haven't used it. The front pump modification consists of cutting and slot over the high gear feed, between the sealing rings. I have the dimensions written down, don't have them off memory
 
CudaFactHackJob said:
It will be interesting to see what the end play is, the direct clutch clearance, condition of the ring contact area of the direct drum, and the ring wear.
Click to expand...
End play in input shaft is .041.I probably won't tear into trans till someone cleans this garage.
 
Sterling said:
The multi spring for the high gear clutch is good
I have heard ATI makes a reverse wound spring that is cheaper, but I haven't used it. The front pump modification consists of cutting and slot over the high gear feed, between the sealing rings. I have the dimensions written down, don't have them off memory
Click to expand...
I have a pump in front of me is this it?
 
Yes, that is the hole. Make the slot .250 wide, 1.150 long, with the hole centered, .383 deep at the center. It will help feed the high gear drum. I think A&A has them available already modified.
 
MHEAD said:
I have been using 904 transmissions for about 25 years and haven't had any major issues till recently.So with the added power that my cars been making I lost the sprag last year.Then we took the guts out of it and reinstalled in another case but now it slips going into third.So I figured it maybe time to put some good parts into it.
So the main questions is how do I modify the main pump support for more flow to high gear?
Click to expand...
What I did on my pump is, using a punch I drove the sealing ball bearing that is staked in place in the pump right out. I then enlarged the diameter of the drilled passages. Then to re-seal the passage again instead of another ball bearing, I drilled and tapped for a 1/8 pipe plug. The diameter of the fluid passage for high gear is very small in the 904. Be careful not to enlarge the passage too much or your drill will break through the two ring sealing grooves. Mine just barely did this but did not affect its operation once the drum is on. Do at your own risk lol.
 
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