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Hot Rod Forum : Hotrodders Bulletin Board > Tech Help> Transmission - Rearend> 700R4 line bias valve and pressure regulator.
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Topic Review (Newest First)
10-01-2013 06:27 PM
ASE Doc Im sorry Texas T for not keeping up on this thread. Just now saw your last post. The shifts were great all around until I started to smoke my 3-4 clutches again. Everything was working great until I cruised the car on the freeway in the summer heat at low rpms in OD. I never did get the TCC working and I knew I was taking a risk running it that way. I guess I just thought it would take it alright. I also installed the Transgo 3-4 bleed orifice that goes with the high rev kit. It bleeds off fluid behind the 3-4 apply piston and may have dropped pressure a little too much. I guess that was a mistake for me. I have been working with Dana at Probuilt Automatics to help me make sure that I get things right this time around. I have also harassed Crosley with PMs to verify some information I've picked up in my research.

I'll be doing the repair soon and I'll post my results. I will also verify pressures and line rise before I drive it. I feel bad that I have to go in and fix this thing so soon but I also feel good that I've got things figured out this time so I won't have to do it again.
09-28-2013 01:28 PM
TexasT How did your part throttle shifts turn out?
09-20-2013 03:17 PM
ASE Doc What max line pressure should I expect to see with the line bias valve blocked? I run the Sonnax line boost kit with their stiffer spring and .500 boost valve, .297 low/rev boost valve.
03-19-2013 09:03 AM
ASE Doc An update on this thread for anyone who happens on it looking for information: The noise it turns out is there in 3rd gear as well which means it must be a bearing or some such thing. I won't worry about it for now since it is barely noticable and the trans is working beautifully.
03-12-2013 05:21 PM
ASE Doc Thank you again Kawabuggy. The noise is a barely audible oscillating growl, like a bearing or gear set. It could be the front planet I guess, but the front planet is in excellent condition. The thrust bearings are all brand new as well, except of course for the captured bearings in both planets. I was wondering if the rear planet could cause a noise in second gear. I knew at one time what the combination of planets was for first, second, and overdrive, but I forget.
03-12-2013 07:57 AM
Kawabuggy ASE doc, typically when the low planet set is bad it will make a high pitched whine in 1st gear only, and the noise will immediately stop as soon as it shifts into 2nd gear. If you have a noise that spans both gears you may have something else going on.
03-12-2013 07:45 AM
ASE Doc Thanks Kawabuggy for posting on blocking the line bias valve. I don't know for sure what gen my 700R4 is. The car is an 87, the trans code is MXM, which isn't even an option for my car's year model. The valve body was obviously replaced in the overhaul 25K miles ago because it's brand new.

As it happens, everything worked out just about perfect. I finished the build and installed the unit this past Saturday and on two road tests I have been very pleased with it's behavior. The light throttle bang shift I used to have from 1-2 is gone. Now the light throttle shift is firm and solid but not harsh. The shift is progressively firmer with throttle pressure as it should be and above half throttle it is quick and confident. The 2-3 shift is the same, firm but pleasant at light throttle and firmer as the throttle is depressed further.

One thing I want to mention is the 3-2 and 2-1 shift with the Superior servo. I have not noticed any clunkiness in the shift. I just barely hear the servo clicking against the sealing piston(no cushion spring) but there is no unpleasant shift feel. Both shifts are quick and clean and I don't mind the click sound. It just adds character.

One thing though and a point of concern for anyone planning on overhauling their 700R4, I really wish now that I had replaced my rear planet. The gear teeth all looked good and the pinion gears and shafts were all solid. Still, as I assembled everything, I noticed what seemed like excessive gear lash between the rear sun and pinions. Now that the unit is back in, I hear the same noise Ive always heard since this unit was built 14 years ago as I wind up the motor in 1st and 2nd. I know now that it's the rear planet growling.

Even if it seems okay, replace this gear set when you're in there. Now I'm going to have to go back in. I'll wait til next winter and since I know everything else is solid, I can just go in quickly on a one day R&R at the shop and swap out the rear gear set. I'll save up and go with a 5 pinion AC Delco unit. I have heard that the aftermarket 5 pinions aren't worth bothering with.
03-08-2013 04:46 PM
Kawabuggy One thing I would like to make note of here about the line bias valve spring.. It has been my experience that blocking the line bias valve & raising line pressure on the EARLY 700's (82 through early '86 Non-aux) can have some seriously detrimental effects.

I can recall having blocked the line bias valve in an '85 trans and it made it hyper-sensitive to accelerator pedal movement. By that I mean if you bumped the gas pedal a bit, it would instantly down-shift to the next lower gear. The vehicle was almost undriveable as it had some really weird issues with shifting & holding gear. As soon as I un-blocked the line bias valve, the problems magically went away. I have never had that happen with 2nd gen. 700's, but have experienced it on numerous other occasions with the 1st gens. This is one of the reasons I stopped building the 1st gen 700's for performance applications. I found that my attempts at raising line pressure by way of boost valve, blocking line bias valve, & stiffer pump pressure regulator spring over-powered (over-pressured?) the valve body and basically rendered them non-operational or gave them super-funky shift characteristics. I never tried one of the re-programming kits that are available though and probably should have. Due to the other short-comings in the 1st. gens. I just stuck to 2nd. gens for performance apps.

Those of you with 1st gen. 700's be careful what you do with those VB's as they are a bit picky in my experience. The 2nd gens will work with blocked line-bias valves no problem. If you are modifying a 1st. gen. KEEP the original springs in case you have to go back in with them.
03-08-2013 02:57 PM
TexasT The .125 size in the 2nd hole might be too large. Might want to scale that back to the .092 since you have that size bit.

I'm not sure on the 700r4 accumulator valve and it may be different than the 2004r. I do know the trick for the 2004r is to replace the linebias valve with a stiffer spring and put the line bias spring in the accumulator valve. At least that is what I am doing.
03-08-2013 12:22 PM
ASE Doc That is a very good article. It causes me a little confusion as it seems to counter what I understand about the accumulator valve. I was under the impression that the accumulator valve, in the 700R4 anyway, controls exhaust from the separator plate side of the accumulator. I was given the impression, by someone who's knowledge I place great faith in, that installing a lighter spring allows more accumulator action and therefore produces a milder light throttle shift while producing a firmer full throttle shift. This seems to fit my interpretation of the hydraulic schematic.

The trans had been built with a corvette servo, a stiff accumulator valve spring, and a weird high coil count spring in the 1-2 accumulator that only allowed partial movement. The result was a 1-2 bang shift at light throttle. Above 1/4 throttle, the 1-2 shift was perfect. The 2-3 shift was great at light throttle and full throttle, but was a little soft at mid throttle, thus the stiffer line bias spring to hold line pressure a little better through 3/4 throttle. The trans already had many great upgrades, such as the Sonnax line boost kit with .500 TV boost valve, corvette governor that produced 6,000 rpm full throttle upshifts and allowed me to manual shift at 6,500. The changes I made to the 2nd gear package will, I hope produce a firm but reasonable light throttle 1-2 shift and a rock solid 1-2 shift at any more than 1/3 throttle. For the 2-3 and 3-2 shift I hope for the same thing. I also installed the Transgo high rev springs for the 3-4 clutch to help with high revs in 2nd gear. There are several other upgrades to this new trans that I will list once it's all done and tested. If it doesn't work the way I planned it, I will just have to drop the pan and make changes.
03-08-2013 11:55 AM
ASE Doc 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.
03-08-2013 11:39 AM
TexasT 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?
03-08-2013 11:16 AM
TexasT 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?
03-08-2013 10:49 AM
ASE Doc 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.
02-13-2013 08:45 AM
TexasT 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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