904 2-3 Shift Flare

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bobscuda67

bobscuda67

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I have been fighting a 2-3 shift flare in my 904 for over 5 years now. I have tried just about everything to eliminate it with limited sucess. I think I have it narrowed down to a timing issue and not a leaking clutch or servo problem.

I did a pressure test on it and the pressure seems fine.
It has 80 psi in gear at idle. Full TV valve at idle was 115 psi.
87 psi in gear at 1000 rpm. It has 125 psi in gear at 1600 rpm with full TV pressure.
The 2-3 gear change happens at the same 90 psi on the front servo and the accumulator.
Are these pressure readings what you would expect from a TF-2 kitted valvebody?
I had the front band backed off two turns with a 4.2 lever. It flared badly. So I tightend it to 1 3/8 turns and it is much better, but not perfect. Is this to tight, or can I go more? How tight can you go before the band burns up?
Any help would be appreciated.
 
I had the same thing and thought the clutches were probably on the way out. Put in that Transgo T-2 kit you talked about and also a deep oil pan with the drain plug and now it shifts ok. Used the metal trans filter with the deeper pan. Was thinking it was just the transmission fluid or drilling out that one hole for 2-3 shift that helped out.
 
bobscuda67 said:
I have been fighting a 2-3 shift flare in my 904 for over 5 years now. I have tried just about everything to eliminate it with limited sucess. I think I have it narrowed down to a timing issue and not a leaking clutch or servo problem.

I did a pressure test on it and the pressure seems fine.
It has 80 psi in gear at idle. Full TV valve at idle was 115 psi.
87 psi in gear at 1000 rpm. It has 125 psi in gear at 1600 rpm with full TV pressure.
The 2-3 gear change happens at the same 90 psi on the front servo and the accumulator.
Are these pressure readings what you would expect from a TF-2 kitted valvebody?
I had the front band backed off two turns with a 4.2 lever. It flared badly. So I tightend it to 1 3/8 turns and it is much better, but not perfect. Is this to tight, or can I go more? How tight can you go before the band burns up?
Any help would be appreciated.
Click to expand...

Did you install the orifice in the trans case ? If so remove it , the front band is releasing faster than the front clutch can apply.
 
The restrictor was not installed in the case.
The band is releasing to soon, but how can I delay it? I could back the band off one turn but that might burn it up.
I'm using ATF-4 in it. I wonder if switching to a different fluid would cause the direct drum to grab sooner.
 
When you do your test are you driving it?all you are doing is checking the input clutch circuit in drive when sitting still.
Put the gauge on it and watch the gauge when it shifts to 3rd,should have 80 psi or higher depending how much you are on the throttle.
The readings you got sound a little low one the wot test.
Test the reverse port and it should be 120 psi in reverse and jump to 200 psi minimum.If the reverse is good that also checks the high gear drum.
Low line pressure will cause flares band is probably releasing correct,not enough pressure applying 3rd.
Was this a fresh transmission build with a shift kit?or did you install it into a used transmission.
If it worked before the shift kit i would recheck the shift kit install.How does the fluid smell,if you glazed the direct frictions you might as well pull it and find your problem.
 
ALthough I agree with kimmer type F can cure it, a fluid change shouldn't be the end all be all here. There's a problem somewhere and it needs to be addressed.
 
...........Thanks stroker, op where is the line pressure set to as in how many threads from flush........did u or some1 else do the TF-2 kit?.....kim.............
 
The trans is fresh and it flaired from day one. I put the TF-2 kit in it myself to try to stop it frome flaring. The line pressure is set flush right now. I had 3 turns from flush and it still flaired. I think you get 8 psi per turn on a Transgo TF-2 kit. The 2-3 shift happens at 90 psi when shifting at cruise in drive. The line pressure and front servo port are the same at 90 psi.
But all my pressure readings came from the car sitting on jackstands, no actual driving.
Took it for a spin Sunday. Shifting it myself, it chirped the tires on the 1-2 shift, but the 2-3 has a small flair.
Tightening the band from 2 turns to 1 3/8's turns really helped a lot.
Can I go tighter or is that asking for trouble? I will test the pressure on the reverse port and post my findings.
Thanks for the input guys, keep it coming.
 
Do have a delay in reverse?
I think you should try another valvebody with no shift kit,and air check the high gear drum.
If the air check is good try the valvebody.
How much clearance was in the high gear drum?
 
................Is ur kd linkage set properly, no more than 1/8 in from max with the throttle at wot.........do u have the vb mods right, or did u interpert them right........kim.....
 
I have a 4 clutch direct drum with 5 Red Eagle disc and Kolene steels set at
.070 clearance. it was air checked in and out of the case at least 50 times by 3 different people.
Tried another valvebody without the kit, and with the kit.
Reverse is good with no delay. I did a pressure test on it the other day and
it had 150 to 175 psi in reverse at idle. The needle was bouncing because of the lopey idle. At 1100 rpm the pressure was 275 and at 1300 rpm it was about 350 psi.
The linkage is set correctly with the 1/8 inch play at wot, but also off idle it starts to depress the TV valve.
As far as installing the kit, I had a trans tech look at how I did installing it and he said it was fine. Human error is the first thing I check in my case.
 
I wish I knew about the type F fluid trick to solve this issue with my 999. I was pulling my hair out trying to figure out it flared on the 2-3 shift. In my case it started after I installed the TF-2 kit, there was no orifice plug, and I was also running atf+4.
 
I'm thinking the problem is the front servo is releasing to soon.
I wonder if a weaker inner spring or a shim between the pushrod and the piston would slow down the servo release. Maybe a orifice plug installed in the servo release port?
Has anyone done these mods? What was the result?
 
But,,,,,
The flare is most likley because of the clutchpack clearances in the drum being way too large causing the drum's piston to require more fill time.
You may be better off just drilling the separator plate's 3rd gear oil passage.
This would get more fluid to the drum and accumulator both faster.



bobscuda67 said:
I'm thinking the problem is the front servo is releasing to soon.
I wonder if a weaker inner spring or a shim between the pushrod and the piston would slow down the servo release. Maybe a orifice plug installed in the servo release port?
Has anyone done these mods? What was the result?
Click to expand...
 
That would be the way to go but the clutch pack clearance is .070 with 5 clutches, not really to large. The 3rd gear apply hole is already drilled out to the TF-2 kit max size. What else can I do to speed up the drum fill rate?
 
oldkimmer said:
..............how many springs r in the front servo................kim.......
Click to expand...

I was just going to ask this question , also what spring setup do you have in the front drum.

A 727 I worked on had a 2-3 flare. It has the mr.randyj billet front servo and a 3.8 apply lever in it with the billet band strut . Combination of too many springs in the front drum and both springs in the front servo , fix was to lower the spring count in the front drum and pull the outer spring from the front servo.
 
I have the stock front servo with two springs. I took out the single spring in the direct drum and replaced it with a multi spring setup from A&A transmission. I have all the springs installed. Bob
 
............u could try taking out the outer spring in the front servo, but i think as John RR SAYS, NEED LESS SPRING IN THE FRONT DRUM ALSO.......KIM.......
 
What did the ring land grooves look like on the high gear drum?The pressure readings you have are really high and you still have a flare?I would pull the unit to find the problem.May have a cross leak,did you flat file the case and valve body half's?:glasses7:
 
I had one that started the 2-3 flare(just a real quick little flare) right after we did the shift kit on my brothers 904 & what we found was the drum seal was worn just enough to bleed a little pressure for a split second before it would seal itself when it was applied, probably caused by the increased line pressure of the shift kit. One of those weird things.
 
That's what my trans has, is a quick little flare. I got most of it out by tighting the band to 1 3/8 turns.
My drum seals are new and the ring lands looked fine. It was air checked with fluid in the drum and there very few bubbles.
I did not file the case or the valvebody when it was apart.
The thing shifted perfect when it just had a TransGo TF-SC kit in it. It was behind my 273. The problems started when I switched to a 340. I had a local shop install a low gear set, 68 up input shaft and a different output shaft. I was thinking a parts mismatch also. Thats when the flair started and I've been throwing parts at it for five years.
I'll try and take out the outer spring in the front servo to see if that helps.
Thanks for the ideas guys.
 
bobscuda67 said:
That's what my trans has, is a quick little flare. I got most of it out by tighting the band to 1 3/8 turns.
My drum seals are new and the ring lands looked fine. It was air checked with fluid in the drum and there very few bubbles.
I did not file the case or the valvebody when it was apart.
The thing shifted perfect when it just had a TransGo TF-SC kit in it. It was behind my 273. The problems started when I switched to a 340. I had a local shop install a low gear set, 68 up input shaft and a different output shaft. I was thinking a parts mismatch also. Thats when the flair started and I've been throwing parts at it for five years.
I'll try and take out the outer spring in the front servo to see if that helps.
Thanks for the ideas guys.
Click to expand...
AHH HA! The plot thickens! Lol! Make sure the feed holes line up where they are supposed to & the seal rings on the shaft & pump aren't damaged. Also very few bubbles may be enough to cause it to flare. Remember it's not slipping(total failure) just aint grabbing quite fast enough. Think about it like a spongy brake pedal, it will stop the car, but not as good or as fast as it should.
It's time for some real close keen eyed inspection of the internals here my friend. :study:
 
If the flare has been going on this long you have probably glazed the frictions at this point,this will also causes a flare.I think you need to start over and check the internals,you may take out the outer spring but i think its a band aid fix at this point.
 
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