New Transmission Struggle thread

Hopefully someone else can learn from this. I am pretty frustrated with it at the moment.

I moved from a 15 year old flawlessly working 727 to a 904 last summer. Mainly to find a little more ET and help fit a trans shield to be legal without chopping up the tunnel. I used one of my Dad's transmissions that had been sitting idle for awhile, it worked, and it didn't leak but it was real soft on the 2-3 shift. We had another 904 rebuilt, and it worked good, did drag week with it, set new best ETs etc. The only thing I really didn't like about it was the 2-3 shift was kind of soft(compared to the 727) but that could have been high expectations for a stock 904(cheetah VB and A&A spring pack only mods) behind a 550-600HP 416. I freshened up the top end of the motor over the summer and was just busy and lazy so I didn't get it running until a month or two ago. When I fired it I had a transmission leak and it turns out the converter snout was cracked.

I pulled the transmission, removed the front pump to change the converter bushing and decided to keep going even though I had no trans building expirience. I pulled the high gear drum out and the clearance was in spec and nothing had been overheated, the forward clutch was way looser than spec but also showed no signs of slippage. While I had it out I had decided to use this Brand new but very old A-1 trans brake valve body. I drilled the hole in the front piston per the instructions and put 5 red clutches and Kolene steels from A&A in as well as new seals on the piston. Off the top of my head the clearance was .65-070 for that clutch pack. I did the same clutches and steels for the forward clutches, and the spec setup to A-1s instructions .045 I believe. I replaced any seal or ring I came across from a kit I bought from A&A. I adjusted the front and rear bands to spec and I felt it all went together well and I didn't have any worries. I also plugged the stock vent and moved it to the tail housing.

As posted in another thread I put it in yesterday and it ran through the gears on stands(not ideal I understand) but reverse was wonky and didn't give me a good feeling. I had a fuzzy memory when i came to how i adjusted the low reverse band so I pulled the pan and checked that, i was confident it was right so I changed the valve body back to my trusty Turbo Action Cheetah. Initially things looked good, reverse engaged, everything worked on the stands etc. Test drive time-failed! Reverse 1st and 2nd work fine, high gear is slow to engage but letting off the throttle it will go in and feels solid once its there. And its leaking out of the bell housing.......pissed!

I will pull the trans again in a few weeks but I am not certain what to look for. I used a known good converter, new pump bushing, new seal. I was extra careful to make sure I greased up the new seals on the high gear piston. Is that hole I drilled in the direct apply piston causing the problem? Is it a band adjustment deal? Reverse works just fine so the clutch pack works.

My only thought is the ancient A-1 valve body instructions told me to drill a hole in the piston for high gear. I am also using the A&A spring pack for the direct clutch and maybe those two mods don't work together? But it sure doesn't have any problem engaging reverse?

There is a race the first weekend in November that I normally do well at so I might just put my 727 back in for that event because the car clearly doesn't want a 904 lol.

My almost 6 year old boy rode around the neighborhood with me for the test drive. He obviously sensed I was frustrated and commented "I dunno Dad.....maybe you just need to change more parts?" I am sure he is right!

1/16" bleed hole in the piston - in the correct place - for transbrake use is normal along with relocating the vent. Cracking the old style converter neck in the corners is normal and fixed by using the later neck and pump gears. The multiple spring pack kit in high gear is a good idea. A leak in the bellhousing is not the fault of the trans, buy they will drop some fluid if the crack in the converter neck is allowed to get too big. .

A mistake made putting any of it together, regardless the trans used, will result in a malfunction. It's not the fault of the 904, although admittedly, there can be more maintenance needed when put behind big horsepower. They work great when done correctly. Going back to a 727 is going backwards. Fix the little trans.

Is the TA valve body transbrake? LBA? Perhaps an up to date valve body would be a good idea.

Clark, can you contact Rusty Butterworth? He is really good on those 904's.

I learned somthing interesting about TA valve bodies the other day....They are typically only set at 120psi of pressure while many of the others are set at 200psi.....Also, when I ran a 904, it would always burn high gear due to lack of oil....You have to run a nice deep pan with one of those to live.....My 2-cents worth.

So I finally got off of my rear and worked on this thing, member DusterW2 sent me some good info as well as some posts I found on here. I had set the kick down band to stock settings per the instructions for the A-1 valve body I was going to try. That setting was slightly different than the instructions for the turbo action valve body. I reset the band, replaced the pump assembly with another one I had, new converter bushing, and new seal and put it all in. The trans works great now, I didn't get to beat on it too hard but I got one good wide open 2-3 shift in and it was nice and crisp with no flare. However it still leaks out of the bellhousing. The only common denominator is the converter because I used a totally different pump assembly.

I have a converter out getting the snout changed to the A500 style so I am going to wait until that gets back before I dig into the leak any further.

not sure if this will help. we never had any trouble with front pump seal leaks until we went with stroker motors.then after we would freshen trans always had a seap/slight leak. buddy went with pro trans vb and we had a little problem with it,so called pro trans and he helped us with vb. also asked him at that time about seal seal. i have been doing these since 1971 but thought i maybe last my touch. he said to look at front seal for overheating witness marks and if found conv hub is burning seal causing leak. we found he was correct and ended up spacing trans away from eng using mid plate of approx .090 thickness. look real close at seal. might be heating up. just a thought.good luck

At one time the hot tip was to use a Turbo 400 front bushing in place of the narrower torqueflite bushing. The theory was that the wider bushing when fit to the torqueflite convertor supported it better

I wondered about something like that, there is almost room for two bushings in there. I also noticed one of my pumps had the bushing installed from the engine side of the pump and one from the trans side.

The seal I took out didn't look damaged or burned up at all but it was sure leaking, it will go back together with a different converter just to rule one more thing out.

Have you ever pressure tested a torque converter, I have chased a few leaks in that area and most of them end up being a leak around weld on converter hub.

I had a B&M 10 inch leak around the front seal due to converter hub run out of around .003, it wouldn't leak at idle but would above 2500 RPM
That was a challenge to find

The 904 drive hub is notorious for cracks, often hard to see.

This is a converter I have never run before, but it has been used in my dads car before.

My other converter cracked the hub and that is what lead me down this rabbit hole of "i should do some upgrades to the transmission". I am going to have an A500 style hub put on it and change the pump over. This is the 3rd time I have cracked a converter hub over the years. I have been very close to putting my 15 year old rock solid 727 back in!

I've seen that problem (small radius at the corner) dealt with by drilling a 1/4" hole (2 X or more the existing radius) centered on the intersection of the vertical and horizontal notch surfaces.

But not in this application...?

I went this direction before I even put the 904 in the car.....

The converters Clark is using have this modification.

You reinstalled the correct washers under the pump bolts right?

Yes I did, I made sure i got the rubber backed washers even though my seal kit only came with regular flat washers.

When I pulled it out the first time it was obvious the leak was coming from the seal, and the vent has already been relocated to the tail shaft so we can rule that out.

Thank you for all the replies.