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Old 11-19-2012, 09:39 AM
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700R4 line bias valve and pressure regulator.

Hi Guys, I've been doing a lot of research as I prepare to put my 700R4 back together. I read Tony's 700R4 pages and found some interesting points. One thing that Tony talks about is blocking the line bias valve. Apparently, the line bias valve bleeds off line pressure above 1/2 throttle. Blocking it prevents the bleed off and maintains higher line pressure which I would imagine produces faster firmer shifts. I am very interested in this since making sure that the 3-4 clutches don't slip and burn is of great importance to me. My question is, why did GM design this valve into the system to begin with? Is there any down side to disabling it?

One more question I have concerns the pressure regulator valve. My trans had the .500 boost valve already installed. It also had the regulator valve modified by grinding down the valve between line pressure and converter feed. This would create constant flow to the converter(clutch maybe) when it would have normally been closed off. What is the purpose of this? Does it increase flow through the cooler? Thanks in advance for any input.
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Old 11-20-2012, 11:19 AM
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While Im asking questions, I am also wondering about the 2nd accumulator valve. I understand that this valve has alot to do with 1-2 shift firmness. My trans has always had a bang 1-2 shift at light throttle, ever since it was built 13 years ago. I have worked around this by manually shifting from 1-2 and running the speed up a little. I am wondering what the overall effect might be of changing to a smaller valve. Mine is the largest or letter "B" valve, which is supposed to produce the firmest shift. Would going with a smaller valve cause a slow 1-2 shift at higher speed and throttle opening? If so, this may not be the way I should go since this trans is meant for performance use behind a higher HP motor. Again, any input is appreciated. BTW, I am installing the Superior 2nd servo and the extra wide 2-4 band.
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Old 11-21-2012, 10:38 AM
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Quote:
Originally Posted by ASE Doc View Post
Hi Guys, I've been doing a lot of research as I prepare to put my 700R4 back together. I read Tony's 700R4 pages and found some interesting points. One thing that Tony talks about is blocking the line bias valve. Apparently, the line bias valve bleeds off line pressure above 1/2 throttle. Blocking it prevents the bleed off and maintains higher line pressure which I would imagine produces faster firmer shifts. I am very interested in this since making sure that the 3-4 clutches don't slip and burn is of great importance to me. My question is, why did GM design this valve into the system to begin with? Is there any down side to disabling it?

One more question I have concerns the pressure regulator valve. My trans had the .500 boost valve already installed. It also had the regulator valve modified by grinding down the valve between line pressure and converter feed. This would create constant flow to the converter(clutch maybe) when it would have normally been closed off. What is the purpose of this? Does it increase flow through the cooler? Thanks in advance for any input.
Line bias valve operates as you mention. Why GM designed it that way? Ask GM engineers. You can block the line bias valve fully or install a stronger spring so main line pressure ramps up quicker & higher. A .471 main boost valve with .282 or .296 secondary boost valve with a blocked line bias valve works well on the street for main line pressure and proper TV linkage operation.

The mod to the main PR valve does increase flow. GM cut notches on the PR valve in later design changes

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Old 11-21-2012, 10:41 AM
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Quote:
Originally Posted by ASE Doc View Post
While Im asking questions, I am also wondering about the 2nd accumulator valve. I understand that this valve has alot to do with 1-2 shift firmness. My trans has always had a bang 1-2 shift at light throttle, ever since it was built 13 years ago. I have worked around this by manually shifting from 1-2 and running the speed up a little. I am wondering what the overall effect might be of changing to a smaller valve. Mine is the largest or letter "B" valve, which is supposed to produce the firmest shift. Would going with a smaller valve cause a slow 1-2 shift at higher speed and throttle opening? If so, this may not be the way I should go since this trans is meant for performance use behind a higher HP motor. Again, any input is appreciated. BTW, I am installing the Superior 2nd servo and the extra wide 2-4 band.
You miss part of the equation in shift firmness.

The 1 - 2 accumulator is the bolt on housing with springs and piston inside. 3 bolts hold it on the case next to the v-body. .. That accumulator may be blocked or broken or very stiff springs inside.

The shift hole in the separator plate may be large diameter from a previous ''repair or rebuild''
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Old 11-21-2012, 12:38 PM
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Hello Crosley, Thank yopu for your response. My trans has the .500 TV boost valve in it and I was planning on reusing it. I understand about the 1-2 accumulator spring. My accumulator piston was not stuck, it seems fine. It did have a fairly stiff spring. The spring was actually like none I've seen before. It has 8 turns and it obviously doesn't compress much, which would really limit accum. piston travel. I am planning on trying the stiff brown spring instead. The orifices in the separator plate were drilled larger also. I just read about the accumulator valve size being a possible cause of bang shifting and was curious. I will definitely go with blocking the line bias valve. It makes since that my 1-2 and 2-3 shifts have always been softer above 1/2 throttle.

Now that you have clarified why the regulator valve was modified, I will reuse the modified regulator valve in my new pump.

Now that I'm thinking of it, do you have a suggestion as to what size drill is good for the 2nd clutch orifice in the separator plate? I was thinking of just dropping back to the next smaller bit from where the hole is in the old plate.

Thanks again for you expertise.
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Old 11-22-2012, 09:12 AM
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Quote:
Originally Posted by ASE Doc View Post
Hi Guys, I've been doing a lot of research as I prepare to put my 700R4 back together. I read Tony's 700R4 pages and found some interesting points.
700R4 Info Page 1
A link to the Tony Pages for those wondering.
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Old 11-23-2012, 01:46 PM
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Thank you Texas T for posting the link to Tony's 700R4 pages.
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Old 11-25-2012, 10:42 AM
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700R4 Info Page 1

A link to the Tony Pages for those wondering.

the fellow that created those tech pages and maintains them is named Sumner, located in Utah.
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Old 02-12-2013, 08:30 PM
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Line bias valve

I've been researching the purpose and function of the line bias valve. My parts for the buildup of my 700R4 are on the way and as I prepare to put this unit together I wanted to be sure that I have everything as close to right as possible. In my research I found an article from Bowtie Overdrives that explains in a general way how the line pressure management system works. The line bias valve's role in this system is to "tune" line pressure rise to match the engines torque increase with throttle opening. The GM engineers intended that most line rise would occur in the first 50-65% of throttle opening, as this is where engine torque increases most in stock applications.

You can understand how our modified engines might want different tuning in the line bias valve. By blocking the valve in place, we delete this bias tuning so that line pressure will rise in a more linear curve from closed throttle up to WOT. In my case, my trans had a bang 1-2 shift at light throttle, and seemed to have a soft 2-3 shift at 1/2 throttle. I am going to use a smaller accumulator valve to help the 1-2 shift and I think that blocking the line bias valve might be the right thing for me. If my full throttle shifts end up being too harsh, I can always go to a stiffer spring instead.
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Old 02-12-2013, 09:09 PM
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is the tv cable geometry correct if your running a holley or edelbrock carb u need a tv cable geomerty correcter kit that will case a hard light throttle shifts soft wot shifts
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Old 02-13-2013, 08:45 AM
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While not specific to the 700r4 here is an article about the 2004r and the principles are similar..

gmay98p7

I wouldn't block it open as it introduces a part throttle harshness. Stiffer spring would be the direction I would go. The hydramatic engineers spent untold time designing the system, and it can deliver smooth part throttle and crisp full throttle shifts if adjusted properly for your situation.
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Old 03-08-2013, 10:49 AM
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Thanks Texas T, I ended up removing the block and going with a stiffer spring setup that still allows full travel. I also installed a lighter spring on the accumulator valve as recommended by Dana from Pro Built Automatics. I am running the stiffest brown 1-2 accumulator spring and the Superior 2nd servo and I'm hoping that it all comes together for a firm and solid 1-2 shift, 3-2 shift without the low throttle bang shift I was getting before.
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Old 03-08-2013, 11:16 AM
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I don't see where you indicate the size of the accumulator holes in the vb plate. While I'm not as familiar with the 700r4, I believe the principles in that link are the same and getting the pressure up with the tricks, using a stiff spring which you indicate you are, and using stock ish holes in the plate can produce tamer part throttle while delivering a much firmer shift at wot.

What size are your holes? Did you drill them bigger? Might need to get a new plate to start with a stockish size and sneak up on the size that works best.

Also, from my studies and advice from the knowledgeable, a spring in the servo is needed to not have a clunky 3-2 downshift. Is this what you are doing?
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Old 03-08-2013, 11:39 AM
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I don't see where you indicate the size of the accumulator holes in the vb plate. While I'm not as familiar with the 700r4, I believe the principles in that link are the same and getting the pressure up with the tricks, using a stiff spring which you indicate you are, and using stock ish holes in the plate can produce tamer part throttle while delivering a much firmer shift at wot.

What size are your holes? Did you drill them bigger? Might need to get a new plate to start with a stockish size and sneak up on the size that works best.

Also, from my studies and advice from the knowledgeable, a spring in the servo is needed to not have a clunky 3-2 downshift. Is this what you are doing?
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Old 03-08-2013, 11:55 AM
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I'm sorry. No I didn't say what size holes I used in the separator plate. I laid the modified plate that was in the trans over the new transgo plate and matched the sizes of the new plate to the old one. The accumulator hole is stock size, the 2nd clutch holes are .125, the 3rd clutch hole is .156, the RND4-3 hole is .092, the TV hole is .092, the 3-4 clutch hole is .092. I haven't read the article you linked to yet but I am going there right now.
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