Full Race 904 D/2 Problems

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slant six

slant six

Do More With Less
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Hi Guys,

I am trying to sort out a problem I am having with a fresh build.
I have a TF3 valvebody in a 904 - Have used it for years with no problems. Kickdown Wired Back as per Transgo and Mr. Shifts' instructions.


I recently Rebuilt the trans with all aluminum Drums and Full Roller Kit.

Now when I Shift into D/ High Gear it "hunts around" and will randomly downshift to 2nd - This should not happen with a full manual Valve body.

I adjusted and Verified shifter cable position - that is correct.

This one has me stumped - Any Help would be appreciated.


Greg
 
Did you air pressure test the drums when you rebuilt it? I always bench test them stacked on the front pump then again test them as an assembly once installed in the case. The front drum is responsible for high gear. If the seals in it aren't sealing good or the stator rings broke or folded when installing the pump you won't have high gear.
 
fishy68 said:
Did you air pressure test the drums when you rebuilt it? I always bench test them stacked on the front pump then again test them as an assembly once installed in the case. The front drum is responsible for high gear. If the seals in it aren't sealing good or the stator rings broke or folded when installing the pump you won't have high gear.
Click to expand...


Hello, I did not air pressure test anything, I am not quite sure about how to implement this technique.
FOr this build I did not have the pump apart except of course the input shaft was out of the center of the pump.

I have High Gear, It just does not consistently stay there.


Greg
 
rmchrgr said:
Click the link here, read through it, see if it makes sense.
Click to expand...

It seems that he had a similar problem..


Maybe my issues are just in the Valvebody?

I could slap a stock one on there and see what happens - I think with the TF3 kit I have 2 ports in the case blocked or restricted. - I am not sure how that plays with the stock valvebody for this test. - I also have no governor any more - it's replaced by an aluminum spacer.

I suppose I could have not fully tightned something or the VB got some crud or something in there making it malfunction?

Thank you,

Greg
 
slant six said:
I also have no governor any more - it's replaced by an aluminum spacer.
Click to expand...

To me, your issue DOES sound governor related since the governor is sort of like a mechanical road speed sensor. If it's 'hunting' like you say, perhaps it's not seeing what it's supposed to see in terms of pressure to make the shift. Did you eliminate the governor before you rebuilt the trans or after?

If you have no governor, I'm not sure if/how it would affect the line pressure but we would probably presume that it does. Maybe Tracy or someone with a little more knowledge can answer that.

So then, with the VB modified to reroute said governor pressure to provide constant full line pressure... well, I think your answer might be in there somewhere. Whether it's directly related to those parts or not is the question. There may be an adjustment somewhere or some sort of provision you need to add to handle or compensate for the modifications. Maybe you need a check ball or plug somewhere, different manual valve... something.

Read what Kunkel says in the reply about how the TF3 is modified. Also, did you see the part about the plug in the case? Do you have that plug?

"...The way the TF-3 makes the valve body full manual is to reroute the governor circuits so that the governor pressure circuit always has full line pressure, this way the trans will shift to the selected gear regardless of car speed. If the port in the back of the case that leads to the governor is left open, the governor pressure can bleed off through it. See the diagram below, the governor pressure port is where the soft plug is supposed to be installed.

Because the fluid routing for the gears is the same as stock, the rear band will apply in 1st and should supply compression braking; reverse pattern manual VB's usually don't apply the rear band so there is no compression braking, it just freewheels when throttling back in 1st.."
 
..............U may also have a problem with an input shaft sealing ring or a pump sealing ring..............kim.........
 
slant six said:
Hello, I did not air pressure test anything, I am not quite sure about how to implement this technique.
FOr this build I did not have the pump apart except of course the input shaft was out of the center of the pump.

I have High Gear, It just does not consistently stay there.


Greg
Click to expand...

If it's a leak but not one to lose 3rd completely it can hunt back and forth.
If you pull the valve body down you can apply air pressure to the ports where the valve body meets the case front and back.
Those holes are where the fluid flows through to get to where it needs to go, and hitting specific holes with air pressure applies each clutchpack and and servo individually so it make a problem stand out as a big air leak.

Here's the diagram for which ports and what they apply.

Be warned not to pressure test the converter ports or you'll get a nice oil shower. :D
And in your trans the governor ports are useless for testing anything.
Just do all the clutches, bands and servo ports with about 30 lbs if you have a choice because it is possible to blow lip seals inside out and have to take it all apart because of a problem that wasn't there initially.
An obvious "Thunk" sound is heard when you apply air to a clutchpack and you can see servos and bands move when you test them.

I think I covered it.

Right click the name of it below and select "Save target as" and save it to your computer.
 

Attachments

  • Pressure test port pic 1.pdf
    732.5 KB · Views: 112
Hello, I have run this trans before with this Valvebody 2009-2015 with no problems.

I have eliminated the Governor and replaced it and the orig park gear with Aluminum Park gear and Gov. Elim spacer for a few years - no problems there either.

I do have the Plug in the rear of the case as mentioned in the TF-3 Instructions.

I took it all apart last night and scrutinized the valvebody and governor block off plug, and cleaned some of the parts of the valvebody where the Gov 1-2 and 2-3 Valves reside.

The Block off plug etc. was all in good order - still there.
I did clean some junk out of the gov. valves in the Valvebody and I hope that was it.

We'll see when I adjust the shift cable and start it up today.

Thanks for all the help!

Greg
 
I got it all buttoned up last night. after some shift cable adjustment and Throttle valve adjustment, it shifts with 3 gears.. at first I wired the TV all the way back - no 3rd gear - so I backed it off a bit - Then I had 3rd gear again.

No waffling between 2-3 as before. That was on the jackstands - We will see if it holds up at the track.


Thanks!


Greg
 
If backing off the TV pressure via the tied back lever, changes the 2-3 shift, then, it seems to me, the governor circuit is some how still working. The gov should be eliminated in TFIII, as the shift lever is now the supreme commander, and when you select 3rd, you are not asking, you are commanding! The tied back lever should just affect the shift quality, as in big tire-chirp, or little tire-chirp.
When the gov system is eliminated and the rest of the circuit is repurposed with throttle pressure,AND the normal throttle pressure circuits are also eliminated,then you should have full-manual bang-shifts.
Since adjusting the tie-back, is somehow affecting the shift timing, it seems to me that the throttle pressure is still feeding into it's normal circuit, and fighting the supreme commander.
This leads me to believe that the VB is not set up quite right. Ima guessing there is a fight going on inside, that should not be.If you still have the installation instructions, and a bag of left over parts, I would review the install, and make absolutely sure you didn't miss a step.
 
AJ/FormS said:
If backing off the TV pressure via the tied back lever, changes the 2-3 shift, then, it seems to me, the governor circuit is some how still working. The gov should be eliminated in TFIII, as the shift lever is now the supreme commander, and when you select 3rd, you are not asking, you are commanding! The tied back lever should just affect the shift quality, as in big tire-chirp, or little tire-chirp.
When the gov system is eliminated and the rest of the circuit is repurposed with throttle pressure,AND the normal throttle pressure circuits are also eliminated,then you should have full-manual bang-shifts.
Since adjusting the tie-back, is somehow affecting the shift timing, it seems to me that the throttle pressure is still feeding into it's normal circuit, and fighting the supreme commander.
This leads me to believe that the VB is not set up quite right. Ima guessing there is a fight going on inside, that should not be.If you still have the installation instructions, and a bag of left over parts, I would review the install, and make absolutely sure you didn't miss a step.
Click to expand...

Agreed
 
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