904 throttle pressure questions

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rod7515

rod7515

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Working with a 904 that I was told came out of a 71 duster V8 318. I had it rebuilt by a local here that does trans for lots of people and Ive never heard a complaint. Hes a racer and has been doing this for almost 20 years.
So i tell him Im going to be running it with a 408 and give him all the specs for motor, convertor and gears. I also tell him the convertor will be a 3800 stall. I let him know I plan on doing some racing so I want to have a manual valve body and a good shift kit so I can feel a harsh shift. He completed it about 3+ years ago but life has gotten in the way and I am finally getting this thing on the road and the bugs worked out.
Im not happy enough with the shift from 1st to 2nd or to drive. So I called him and he told me I needed to check throttle pressure. I put a gauge on it and I see I have around 90-95 PSI when in gear at the port. This is my first time checking this or making any adjustments to a trans in the pressure area.
So here are my questions, I want a harder shift, the builder is more worried about the comfortability of the shift. he says I could go to about 105 PSI. I ask if I could go higher if i still didnt have the shift I want and all he will say is how uncomfortable its going to be.
So how high can I turn the pressure up before it causes issues.
I need to build a bracket and some type of adjuster to make these adjustments since I dont have any kick down linkage on the car.
I noticed tonight When I checked the pressure that it did not changed with engine speed so Im guessing that once I make any adjustment it will run there at all times?
Appreciate any information and schooling you can pass my way,
Rod
 
Ask him if he used a kit or a full manual valve body?What brand is it? Is it a forward or reverse pattern valve body? Did u get a detailed bill from him? Kim
 
No i did not get a detailed invoice but it is a full manual forward valve body. Not sure of the brand.
Rod
 
Is the stub sticking up above the shift lever for the throttle pressure? If so put a lever on it and tie it back all the way. Then road test. Kim
 
Yes I put the lever on knowing I would have to adjust it. So are you saying it will do no harm to put it in the wide open, back as far as it will go. I plan on making a bracket and using a small turn buckle and pushing it back. How much pressure will that get me and will that cause any long term damage or premature wear on any internal parts such as pump?
Rod
 
It may or may not increase the pressure. When u push it back by hand is it like there is nothing there and then u cant push it anymore? Or is there resistance after about a third of the way? It may just be a dummy shaft. U may have to pull the pan to see if he used a kit or actually changed the valve body. It nag shift softer in town at lower speeds, then harder when ur getting on it. Kim
 
It's not a dummy shaft it is hooked up. Will making it full pressure create any issues in the long run.
Rod
 
You are being asked very specific questions by a transmission specialist who will use precise answers to help you.
 
Kimmer, when you say stub are you talking about the half moon of the shaft that the linkage arm goes down over and lo icks in place? If so yes and again the kick down lever is on and is in the forward position. Yes the first 1/3 of the movement is free but then you can feel it spring load as it goes back the remainder of the way. Again my question is how much pressure will moving it back create and will it do damage if it is all the way back? Once its adjusted that's where it will stay unless I would manually change it. I will be adding some type of adjusted to it this evening and trying to raise the pressure. Is there a certain pressure I should shoot for? Again it's at 90-95 psi now but arm is all the way forward.
Thanks Rod
 
The 8:28 post is asking specific questions to get information so that his answers aren't just shooting in the dark. Some manual valve bodies don't utilize the kd and shift extremely hard even when just cruising. Sometimes diagnosing a problem is a series of tests in a certain sequence. Correction; about it shifting at high rpm all the time.
 
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It is sometimes hard to guess without knowing the brand of the valve body. U can tie the lever back wide open if that’s what u want. It will shift hard all the time. U can also run the kick down setup or use a Bouchellion cable. Locar cables work but not the best. Kim
 
oldkimmer, i got to try the trans this weekend and heres what I found before I ran out of time. First I was able to fit up a turnbuckle that I bolted to the ear on the side of the trans and moved the arm all the way back. The pressure went to just over 125 PSI. I took it for a test drive and the 1st to 2nd shift was no different and i went up to about 4500 before the shift. The 2nd to 3rd feels much firmer.
First I need to correct the convertor stall from my first post. I stated it to be a 3800 but its actually a 3200 made by Dynamic.
Next, I contacted the guy that built the trans and he said the shift kit would be a Transco, the valve body is a stock with changes made to make it a manual shift. He also said that the valve body can be put back to a stock shifting on its own style so I assume not major changes were done.
The guy I had build this trans is a good guy but has different beliefs then I do. He doesnt like a trans that has a harse shift and when he races his car he just puts it in drive and lets it shift itself. He also continues to tell me that I wont get a harse shift unless I go to a reverse valve body and also since its a 904 it will be softer as well. Im not buying that but will see what your thoughts are on this.
So a few additional questions:

What affect will the convertor have on the shifting. Do I need to be above the 3200 stall of the convertor to get a solid shift?
Do you think I will need to change kits? Change valve body's?
Is it possible to get what I want to feel. Ive had 727's, 350 Turbo trans and 2004R trans that all had good shifts like im looking for and they all had higher then stack stall convertors.
Thanks for any info you can add.
Thanks Rod
 
Just shifting above the stall of the converter won't get you a firm shift; you have to COMPLETE the shift above stall. That is; the rpm has to remain above stall after the shift is over. So you would probably be shifting at 5500 to not drop below stall after the shift with a 3200 convertor.
 
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