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I have an 89 Suburban 4x4 project with a 350 TBI & 700R4 trans. My problem is that once the trans warms up it will have delayed up shifts. The 1-2 won’t happen until 35-40 mph and the 2-3 at 50-55. Forget the 3-4 as I can’t safely go that fast! It will shift if I take my foot off the gas but as soon as I touch the gas it goes back into the lower gear. If I throw it in neutral and put the accelerator to the floor it will fix it, but as soon as my speed drops back down enough to downshift or if I force a downshift by accelerating, it happens all over again. I’ve monitored both trans temp and line pressure. It starts happening right about 140 F. The trans in not getting too hot (160-180F) as I have a cooler and auxiliary fan. Line pressure is about 90 psi in park & neutral, 60-70 in D and 160 at wide open throttle. All normal according to the manual. When the problem occurs the line pressure pegs at 160 and stays there until I rev the engine in neutral. Like the TV valve is getting stuck somehow.

Now that I have described the problem, here is the history. When I got the truck it shifted fine for a while until I put in a ½” tbi spacer. About 500 miles after that the problem began. I didn’t immediately put 2 & 2 together with the spacer. Every shop I talked to (by phone only) said the trans was probably shot. So I tried replacing the TV cable first then eventually got a GM remanufactured trans and replaced it. But it has the same problem. The spacer is long gone and I am on my third (GM not aftermarket) TV cable. I’ve adjusted the cable 1 million times it seems and it makes no difference. I’ve dropped the pan and made sure the TV valve is in the proper position at idle and WOT and it is. I even dropped the valve body after measuring it’s positions and removed the TV valve to verify it is in the correct position internally. I cleaned the valve & bore, put it back together, and it did nothing to help.

I’m at a complete loss and out of ideas.
 

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89 suburban 700r4 problem

with a gauge on mainline tap 90 psi is not normal in park,and indicates that the tv valve is sticking.the stock pressure regulator spring is calibrated for about 70 psi in park.posted last week about problems we had in my shop with tv valves sticking after rebuild.we have been using transgo jr shift kit,it has a redesigned tv valve that will not stick.You pulled the vb and the valve was not stuck,so it may be hard to belive this is the problem,but what you see with the vb on the bench is not whats going on when you drive it.The jr kit is easy to install,and if you don't want to change the shift feel you can just install the valve.By the way what manual did you get your info from?
 

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Discussion Starter #3 (Edited)
Sorry, the 90 psi should have been reverse, not park. Got that mixed up. Got the info from the original GM service manual and unit repair manual. None the less I agree that it's the TV valve sticking. Everything I have checked points to that. I just thought that the odds would be highly against getting the bad luck of two transmissions with the same problem. But from what you say the odds are actually pretty good with this problem. You are the first person who has said this is a common problem for the 700R4. That was just the validation I needed that my diagnosis was correct (I should trust myself more!). Of course, even if I had known that was the problem, until now I didn't know how to fix it.

A very knowledgable friend suggested a while back that I perform the mods outlined in the GM "HO 350 Camaro Conversion Manual". To "increase shift firmness" it includes a new TV boost valve & spring as well as intermediate servo piston & housing (all GM parts). I ordered the parts but never installed them. I was afraid that boosting TV pressure would just makes the problem worse if it was the TV valve. Do you think the extra pressure could unstick the valve or are my original fears correct. If this could help fix it that would be great otherwise I will just put the trans go kit in.
 

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I see a possiblity of 2 things;


A worn TV valve bore will cause eratic shifting when the oil thins out ( warms up)..


Or perhaps you have the TV cable set at the make it or break it setting where your minimum setting allows the fail safe check ball to seat , then late shifts happen.

I make these statements from your comments about checking / cleaning the TV valve & the bore...... OR did you simply remove the sleeve , plunger & spring ? Perhaps you did Not remove the actual TV valve that is behind the spring?
 

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89 suburban 700r4 problem

Just a ton of posts on this concern.Here's a good step by step that will save time and trouble.No upshift,late upshifts,check cable first.Crosley is right about the check ball failsafe some guys end up chasing their behinds on this,although a lot of 700r4s are rebuilt with the ball deleted. If you can get your hands on a pressure gauge you will really cut down on the guessing.In park if you have 90-95 psi the tv valve is sticking.With stock pressure regulator spring pressure should be 65-70psi So if pressure is correct suspect damaged governor gear.Stuck shift valves are rare,stuck governors are rare,and if the governor is stuck,you usually have bigger problems.Up until 11-12 years ago we would drill the tv balance hole to.063 to help tv from sticking,this did help but was not the panacea,we still had problems.Transgo jr kits tv valve will not stick,you could probably dump a pound of fine metal down the filler tube,and it still wouldn't stick,ok maybe not a pound.JoeB the boost valve you speak of is in the pump,it can be installed with trans in vehicle,good choice is .500 boost valve,will not correct or harm tv valve operation,corvette servo is good choice,esp if you dont want a real thumper.Sorry so long a post but this should help.Briscoe
 

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Discussion Starter #6
Crosley, I did remove the whole assembly valve & all and could not find a smoking gun. I had thought the same thing about the return position being on the borderline and was tempted to pull the TV out one more click after adjustment to see if that helped. But I was fearful that I would drop pressures too much at part throttle and fry the clutches.

Thanks for the help guys. I’ve ordered the 700 Jr. kit.. Very informative. I’ve been chasing this problem for at least 3 years now and nobody has been able to give me a satisfactory explanation…until now. I had a feeling it was a sticking TV but had no idea what to do to fix it.

Briscoe, Does the Jr kit come with a new TV boost valve? Since I already have the parts should I install the TV boost valve and servo in addition to the Jr kit or will that be too much?
 

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89 suburban 700r4 problem

Hey JoeB the transgo kit does not come with tv boost.I would put it in,this is a big vehicle,this along with the servo should work well.Manually shifting you will feel a big difference with bigger tv boost valve,because of the way the hydraulic system works,but I doubt you use your suburban this way.Glad to have been of help,please let us know how everthing works out,Briscoe
 

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I wonder if what y'all are calling a 'TV boost' valve is actually the main boost valve in the pump assembly?

:cool:
 

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89 suburban 700r4 problem

Yes crosley,that is correct,made mention of it's location 10-26-06 posted at 8:55.It is main boost,some manuals refer to it as tv boost.
 

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briscoe said:
Yes crosley,that is correct,made mention of it's location 10-26-06 posted at 8:55.It is main boost,some manuals refer to it as tv boost.

oh , you mean books. :D

I have not heard it called a TV boost valve in a decade or so.

glad to see we are on the same page. :cool:
 

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89 suburban 700r4 problem

Crosley,you are one sharp individual,hope your having as much fun with these posts as I am :) And by the way,hows that suburban coming JoeB?
 

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Discussion Starter #12
Still waiting for my 700 jr kit to arrive. I will be sure to let you know how it works when I have it installed.

I got the name TV Boost from the GM Performance Parts "HO 350 Camaro Conversion Manual".

Thanks for all your help guys. I know a lot about engines, etc. but when it come to transmission internals I probably know just enough to be dangerouse, LOL. :)
 

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Discussion Starter #14
No I did not, which is likely what caused the problem initially. But the TBI spacer has been removed and everything set back to stock a while ago. Which is a bummer because I really did notice a difference with the spacer because I cut the divider between the bores out. No different than using the thick q-jet gasket with the open center.
 
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