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  #1  
Old 06-07-2014, 07:37 PM
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Trying to clear a 3-4 flare

My 85SD had a 2-3 flare and a 3-4 flare (722.303 trans, green vacuum modulator). I removed excess vacuum systems so that they are out of the discussion. My 3-2 valves on the valve cover are gone per another thread as is the EGR.

I have 22' of vacuum out of the pump. I set the VCV per the FSM and the vacuum modulator to 42" per one of the transmission manuals. The modulator seems to hold vacuum. My gauge fitting seems flaky ie holding one minute then leaking if I move the hose. I've got some plastic adaptors being glued to make sure they aren't leaking.

The 3-4 flare is still there. This seems to be the case regardless of how I set the VCV.

So: If my vacuum modulator holds vacuum, is it necessarily good?

What effect is higher or lower VCV settings supposed to have on shifting?

What effect does changing Vacuum modulator pressure have? I increased vacuum Modulator from 35 to 42#. Should I go a little higher?

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  #2  
Old 06-07-2014, 10:54 PM
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I believe the 722.303 has the same k2 accumulator as later boxes. Try replacing the accumulator spring. The accumulators delay the build up of pressure in the clutch packs in order to feather the shifts...like easing off the clutch and onto the accelerator with a manual. If they engage too quickly, you get a harsh shift, if they are too slow, you get a flare. The root cause is usually a broken or weakened spring. The k1 accumulator controls 2-3, K2 controls 3-4.
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  #3  
Old 06-08-2014, 03:43 PM
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How sure can I be of that diagnosis? Pulling the valve body is not a big deal but I changed the fluid last fall and don't want to again just for fun.
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  #4  
Old 06-08-2014, 05:50 PM
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The valve body doesn't need to come out. The K1 spring can be accessed at the front left of the valve body with the transmission in place. The K2 is at the left rear. All you have to do is drop the pan and remove the filter. No need to bother with changing the fluid...just replace the 2.5 qts in the pan.

Cointrolling flares is the function of the accumulators. Especially since the modulator has been adjusted, there's simply no alternative to inspecting the internals. Could it be something else? Sure...you could have low working pressure, leaky K2 seals, or a bad k2 clutch pack. The k2 accumulator is about all you can fix without pulling the entire transmission, it's the most sensible place to start.

Mike Frank
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  #5  
Old 06-11-2014, 12:03 PM
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Is there anything else I should do while I'm there?

Filter is recent. Bowden is recent.
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  #6  
Old 04-24-2015, 12:18 PM
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Just to add a data point, I was able to clear the 3-4 flare in my 1983 300TD(722.315) using one spring(the blue one which replaces one in the K2 accumulator) from the Superior Shift Correction Package. As pointed out above, it can be done with the valve body in the transmission--messy, but doable.

Peter
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  #7  
Old 04-24-2015, 03:46 PM
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A transmission additive can help if the internal seals are leaking. It expands them but also takes some time and milage usually to do this.

I would not count on this but it is one possibility as well. Good automatic transmission guys have sometimes suggested this approach.
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  #8  
Old 04-26-2015, 10:19 AM
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Quote:
Originally Posted by Junkman View Post
My 85SD had a 2-3 flare and a 3-4 flare (722.303 trans, green vacuum modulator). I removed excess vacuum systems so that they are out of the discussion. My 3-2 valves on the valve cover are gone per another thread as is the EGR.

I have 22' of vacuum out of the pump. I set the VCV per the FSM and the vacuum modulator to 42" per one of the transmission manuals. The modulator seems to hold vacuum. My gauge fitting seems flaky ie holding one minute then leaking if I move the hose. I've got some plastic adaptors being glued to make sure they aren't leaking.

The 3-4 flare is still there. This seems to be the case regardless of how I set the VCV.

So: If my vacuum modulator holds vacuum, is it necessarily good?

What effect is higher or lower VCV settings supposed to have on shifting?

What effect does changing Vacuum modulator pressure have? I increased vacuum Modulator from 35 to 42#. Should I go a little higher?
Too much vac holding in the system. I never had the issue until I broke a nipple on main vacuum line and replaced it with a new one. New line caused flaring. Replaced it again, and flaring resolved.

I would say tweak the the vcv again to increase the amount of vac released.

Remember; High vac = flaring
Low vac = firm shift
No vac = harsh shift and even tire chirp
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  #9  
Old 04-26-2015, 05:38 PM
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Should have posted. I cleared it up. I set governor pressure to spec I found in one of the trans manuals I downloaded then adjusted vcv to the best shift. I don't remember the vac measurement but it was also close to published spec.

Now onto the engine shake.
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  #10  
Old 04-26-2015, 10:24 PM
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Good luck with the engine shake. In my 81 300SD sometimes it will shake like a mixer at one light and then at the next light be as smooth as cream. Have no idea what makes the difference. I had my indy idle it up about ten years ago but do not think that made much difference.
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  #11  
Old 04-27-2015, 11:59 AM
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Junkman, thanks for the info about the 3-4 flare. I've been battling this on mine and it looks like I will need to establish a baseline of verifying pressures and checking the vcv. I've tried adjusting the bowden cable but it isn't helping. Before, it was only an occasional slight flare, but now that I've replaced the rear diff. with a 2.47 it is really pronounced and nearly constant.

tyl64, another possibilty I read about, here on the forum, was the linkage for the manual shut off lever. Another forum member mentioned that the linkage was causing the IP to go slightly into shut down. A very slight adjustment of the linkage cleared the problem. This may be due to wear, over time, to the linkage pivots.
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  #12  
Old 04-27-2015, 07:35 PM
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My understanding of the process is to:
Set the governor pressure. Mine is green and the trans manual had similar pressures for each transmission based on governor color.
Adjust the VCV. the vac is to be set at x and drop to 0 by 10 mm of opening. There is a factory gauge which is really just a disk with a hole in it. I made one by drilling a 1/8" hole in a nickle. The diameter/2 - 1/8'/2 ~10mm. Close enough for government work.

Now, adjust the VCV.

Test drive. Harsh(er) or firm(er) shifts than you want mean you have too little vacuum. Soft or flare means too much vacuum. I think the bowden affects the curve a little but others claim that it only affects shift timing.

You can try varying the governor pressure but I didn't get enough data to know the effect. Low vac can be caused by any leaks in the system which can include the door locks or climate control. I took those out of consideration by plugging all vac the lines going into the passenger compartment. It is easy to do with golf tees. Plastic work better than wooden as they seal but also come out easily.
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Last edited by Junkman; 04-27-2015 at 07:48 PM.
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  #13  
Old 04-27-2015, 09:15 PM
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Quote:
Originally Posted by Junkman View Post
... I think the bowden affects the curve a little but others claim that it only affects shift timing.
...
I definitely see an affect of the bowden cable on my shift firmness in my w124. If I adjust it to have shifts at low RPM, I am more likely to have a soft shift or mini-flare. If I adjust it to have high RPM shifts, the shift quality improves. It may be an indirect effect that at higher RPM... perhaps there is more vacuum or something like that. But regardless of the reason, I can say with 100% certainty that tightening my bowden cable improved my shift quality.
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  #14  
Old 04-28-2015, 06:38 AM
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Quote:
Originally Posted by tyl604 View Post
Good luck with the engine shake. In my 81 300SD sometimes it will shake like a mixer at one light and then at the next light be as smooth as cream. Have no idea what makes the difference. I had my indy idle it up about ten years ago but do not think that made much difference.
if usual suspects are eliminated.... weird shakes at traffic light after longer drive or on hw checks/ramps are in 95% cases produced by worm DV's in IP.
the rest 5% is to IP internals...

new ones with new washers has to be acquired..no test bench is needed
you can do it in 30min or so...

cheers

.
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  #15  
Old 04-28-2015, 01:02 PM
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Junkman - do not understand you comments about vacuum. Unless I am mistaken, the SD uses vac only to smooth out the downshift. AT WOT when you are headed for an upshift, it is supposed to bleed down for zero vac at upshift. IE

Upshift - no vac needed.

Downshift - vac needed for smooth shift. Otherwise downshift will clunk.

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