Morning racers!

Last year I took the Duster racing and after upgrading the headers and tweaking made an additional 70+ hp. This made the transmission angry and you can hear the 2-3 flare towards the end of the day.

13.08 pass:



The plan this month is to fortify the transmission and replace the 3.55's with 3.90's and the car should be flying into the 12's.

The transmission is a 904 based 42RH which has been upgraded with a billet servo piston, Trans-go shift kit, 4.2 kickdown lever and 44RE front drum which holds 5 clutches.

The transmission is sort of a science project as I wanted to run the "lighter duty" 42/44RH rather than the 727 based 518RH. If guys can make 904's live behind Hemi's then I should have no problem keeping a 42/44RH behind a fairly mild 5.9.

My train of though is to replace the following pieces to improve the 2-3 shift.

1) Replace wavy front drum snap ring with solid.
2) Replace clutches and steels with Alto Red/Kolene steels.
3) Change kickdown ratio back to 3.2 ratio from current 4.2
4) Possible drill drum to increase venting of fluid.
5) Increase line pressure slightly, currently at 105 psi. I can't go too much higher or it will cause the governor to hang up. I had this problem when it was at 130 psi.
6) Change fluid from ATF+4 to Type F

I'm going to take apart the valve body today to see what the orifice sizes are in the separator plate. I know per the Trans-Go instructions I made them larger but don't recall what size I opened them too. I'll post later today after I checked.

Thanks!

Gary

P.S. There looks to be no restrictior in the case, it all looks to be in the valve body.

anyone?

Yeah I<m a big fan of the 904 myself.....

My 67 cuda runs 10.50 regular with lot less goodies than that

spring pack
kick down lever
5 disc clutch from an a 998

that s it....

still looking for ways to improve it....you have good suggestions

Dan

Also considering adding another clutch disc if possible.

Gary I would leave the 4.2 lever, if you go down then go to a 3.8 , 3.2 is too low to me. Your flare is the front clutch slipping while applying.

You don't really need the kolene seals, but use them if you want. Solid front RED band, no kevlar on the front band.

Definitely get rid of the wavy front washer, but it's not going to fix a 2-3. Solid has less chance of breaking.

As you know the 2-3 is a timing relationship between the front band releasing and the front clutch applying, if you don't have overlap then definitely leave the 4.2 for the leverage advantage of holding the band around the front drum. adding another clutch and changing the lever is going to mess up timing , if it's good now leave it and put fresh clutches and steels. I'm not sure where you are going to add that vent hole but it may not be a good idea.

I see your biggest issue ... ATF+4 , get that garbage out of there. It has friction modifiers to allow the clutch inside the lockup converter to SLIP when applying to control shudder, it has no business in a race trans. I ran over 180k miles with Dex 3 in my 2000 Cummins ram making 1000 ft/lbs , it's not the HP that makes it slip, it's the torque.

A 904 behind a hemi is SS is a 5k plus trans

So what oil do you recommend . TYPE F OR DEX3

Dan

Yes and if I delay the band releasing (by changing the arm ratio) will this not give the clutch more time to apply fully?



I think they come as or sold as a package from Alto, cheap insurance I was thinking.



Already there (red band)



Did not think it would, just me being through.



1) The transmission had fairly low miles on it, just replacing the clutches and steels will have me right back where I am in very short order.

2) I want to change the timing slightly. I need second to release a touch slower or for third to lock up faster.

3) I'll post a picture of the drum as soon as I find one, give me a few minutes...



I agree 100%

Like I said this was somewhat a science project, hell people told me I could not even install the trans in an a-body without cutting out the floorpan. Guess what? No cutting of the floorpan. Some judicious work with a ball-peen hammer was all that was required.

Starting out with the Mopar recommend fill was just a baseline. Type F is my go to choice in every 904, 727 I build and what the Reliant uses in its 413 transaxle.



True but I'm making far less hp than a race Hemi, around 375 to the wheels if my calculations are correct.

I run +4 in my upgraded 47re, as well as my race 727....

fluid type isn't going to be a miracle cure in this case.

For some reason I can't find the actual picture I saw so did a quick photoshop which took far less time.

There is a series of holes that allow the fluid to be pushed out the drum when the clutches are applied.

Correct, just one facet.

I believe if you are going to attack a problem leave no stone unturned. One item in particular may or may not be the issue but if you make one area 15% better and another area 5% better.. pretty soon you are on to something and the problem is resolved.

Are those holes in the thick part of the drum?
And in each one?

I can't find the original picture at the moment.

Edit: Found it!

I'm just pointing out that someone stated..."your biggest issue". That said, I'm not a torqueflight guru by any means, but I've been known to muddle my way around them. Am I +4 flag waver? No, but I work at a dealer, and I can buy it in bulk for pretty cheap. Now would I run it in a race transmission just because it's cheap? No...but I asked a very good trans guy (I turned to him to resolve what I felt was too much rpm between shifts...another story) and he said the +4 would be just fine. I respect his opinion as he puts together some of the finest record holding torqueflights on the planet so I'll continue doing what I do.

I used to run the "advanced" version of that drum you posted.... the theory behind that mod, or so I'm told, was to get the fluid from the drum to cut down on weight/inertia of the trapped fluid.

From what I was reading the theory that was advanced was it gives the fluid a path to quickly evacuate the area of the clutches and steels when applied.. Which makes sense since the only way out is around the rear drum. The question is how much fluid are we really talking?

I'm still operating under the "every little bit helps" school of thought which is why I'm considering this. The chance of weakening the drum and having an issue is fairly low with a 904 sized drum.

John I have been giving this some thought and it occurred to me- How much can the shift timing be influenced by the band adjustment? I know there is some wiggle room there.

Adding another disc solved my problem. Talk to John Cope ( CRT ). He sent me the necessary stuff to solve that problem. I'm running a 4.2 lever also.

Valve body plate picture uploaded- Looking over my notes you can see the one opening I did not enlarge. The instructions which usually are more informative state "snow plow or off road racing only" with no further information. I may call or just simply trace out the flow path to see what its purpose is before blindly drilling it out.

Speaking of which, I'm going to look into making a line pressure adjusting port in the side of the case so I can tinker without having to pull the pan off and on. I have a drain plug in the bottom of the case but it still gets old.

the "did not touch" hole.... we'd open that up on 46RE and 47RE transmissions for snow plow applications (IIRC we removed the ball under it too). Sped up the timing on going from L to R to L repeatedly..... that I remember in my snow country days. Learned that from a tech that definitely could make them live. They would "bang" pretty good after than mod, and people would often complain, but like he said..."you killed it when it was soft, now it's my turn!"

*it would "bang" pretty good coming out of park, just to clarify.

The original intent of drilling the front drum was to allow the trapped fluid to escape as a means of lowering the parasitic drag. Since, in 1st gear, the released front clutches travel at 180% of input shaft speed in the opposite direction, allowing the fluid an escape path lowers the parasitic drag of the trapped fluid.

Since the kickdown band is still partially applied at the moment of front clutch engagement, very little trapped fluid is evacuated during clutch application....but a little is better than none.