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O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem

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migraine

12-10-2006 17:51:47




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Have 88 1500 H duty half ton 4x4 ext cab long box with 118,000 miles. Last few months the shift pattern is changing with surging to about 2400 rpm before shifting up out of first and then shifting very quickly twice more into 2nd and 3rd. Also has overdrive which is where it has run most of its life. Is this a vacuum control shift or mechanical control? Transmission does not feel like it is slipping at all, justs revs up quite a bit before making that first shift. Have already put new motor and rearend in this truck and now the trans. acts up. Can't win Migraine

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sjh

12-11-2006 16:09:14




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to migraine, 12-10-2006 17:51:47  
You could also try changing your fuel filter. When they are plugged the engine is pulling a vacuum off the fuel line. That does funny things. I had a plugged fuel filter and I thought the trany went bad. I had to let off on the gas to get it to shift.



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buickanddeere

12-11-2006 14:53:29




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to migraine, 12-10-2006 17:51:47  
There is an upgrade to the front drum, seals, pump, 2nd gear servo, 4th servo and some boost valve etc mods required in the valve body. The governor gave me great grief in the GN's TH200R4 trans.A new gov and proper cable adjustment/lube made it into a different vehicle.



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Brokenwrench

12-11-2006 05:46:30




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to migraine, 12-10-2006 17:51:47  
dmj75 is right on.
There is no vaccuum to this trans. If the gov was sticking, it would want to start out in second from a stop.
The TV cable needs to be looked at closely. The cable likes to fray up by the throttle body. IF the cable seems OK try readjusting it. Set it in all the way(towards firewall). Then step the accelerator down hard. You should here a snap as the cable pulls out to where it needs to be. If it won`t adjust, replace the cable.
The throttle valve in the valve body is also known to stick. Sometimes it`ll free up with a fluid and filter change. Otherwise you gotta have the valvebody dropped, cleaned out, and the throttle valve freed. If it comes to that, Transgo makes a 'no-stick' throttle valve that I`d have put in.
The other thing is, if there`s alot of debris in the pan when you drop it, that`s an indication something else is wrong. So, you may be able to get it to work right again for a while, but it`ll probably end up hanging up again. Hope this helps Brokenwrench

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Allan In NE

12-11-2006 06:00:16




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to Brokenwrench, 12-11-2006 05:46:30  
Yeah,

GM should have bought out TransGo in '82 and applied their recipe from the get-go. :>)

Allan



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Brokenwrench

12-11-2006 06:50:13




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to Allan In NE, 12-11-2006 06:00:16  
I`m glad they didn`t:)



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Allan In NE

12-11-2006 05:41:13




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to migraine, 12-10-2006 17:51:47  
Hi Ol' Pard,

I agree; it really does sound like a timing issue.

The way that works is that the governor pressure (ground speed) is always trying to push the transmission into the next higher gear. At the same time tho, pressure on your throttle is always trying to hold it back and tries to keep it from shifting up.

As road speed increases and the throttle pressure eases off, the various ratio thresholds are overcome and the transmission shifts up in an orderly manner.

Now, you must have a good supply of governor oil because you have that triple shift effect going on, but the shifting is occurring at the wrong time and it is stacking. This indicates we ample governor even for the higher 3rd gear. Therefore, the symptom is pointing at the only other player in the game. The throttle pressure or something that "affects" that pressure is keeping the trasmission from sequencing.

I'd pull the dipstick and make sure the oil is nice and pink and up to level. Secondly, make darned sure you have a good fuel filter; this is critical because it directly affects throttle pressure.

If the transmission feels okay otherwise and in particular is not slow to engage reverse when cold (indicating a plugged transmission filter), I would buy a new throttle cable and the boot seal.

Don't even mess with that old one because they stretch, they fray and they just plain "stick" (Especially, if you've changed engines). Just go get another cable and boot. Make absolutely sure it is adjusted correctly and then see where you are at that point.

It will either cure your problem or indicate something deeper is going on and you're only out the minimal cost of that cable.

Allan

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djm75

12-11-2006 03:47:20




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to migraine, 12-10-2006 17:51:47  
Your tv cable needs to be adjusted since you had it off to change the engine did you do that when you put the engine in if not do it soon it will ruin the tranny.



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kyplowboy

12-10-2006 20:32:54




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to migraine, 12-10-2006 17:51:47  
I have a 93 k1500 with an auto. I have had it for 5 years and put about 60,000 miles on it. 2 times in this time the trans has started doing wierd stuff. One time when it was cold I could drive to the end of my road and if I had to stop at the stop sign getting on the two lane it would start rolling backwards. Put it in reverse, back up ten feet and it would be good for the rest of the day. The next time, 20,000 later, when it was hot it would not take off from a stop with out putting it in park for a few seconds. Both times I was able to take it to one of the jiffy lube type places and get the oil changed and get a system flush. Fixed both. May not work but I would try it. Autos with the electronic stuff act funny if they get a little gunk in them.

Hope this helps.
Dave

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Bob

12-10-2006 19:51:43




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to migraine, 12-10-2006 17:51:47  
The TV cable may need to be set. Did you mess with the adjustmentof the TV cable or do something that changed the "geometry" of the lever that pulls on the TV cable when the engine was changed?

Have you changed the filter and oil?

Also, there is a mechanical governor in the 700-R4 that controls shift points. Something could have got in there, making it sticky.

There is a valve or two in the valve body that can stick or get crud in it, too, as well as gall and stick. There are aftermarket fixes for those problems. It has been a number of years since I've dealt with the updates, but any good tranny tech should be VERY familiar with them.

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Aaron Ford

12-10-2006 18:16:08




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to migraine, 12-10-2006 17:51:47  
This ain't the right answer, but this is what I did. The car was a 86 Camaro with a 700r4. I believe this is the same tranny as yours. There should be a four pin connector located just behind the bellhousing (or what passes for one on an auto). Disconnect this harness and test drive. It should fix the problem but will not allow your lockup torque converter to operate. I am not sure what causes this or what the proper fix is. This guy was looking for the least cost option. He was satisfied and never came back to figure out what the problem really was. Hope this helps get you down the road.

Let's go Mountaineers

Aaron

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jdemaris

12-10-2006 18:13:40




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to migraine, 12-10-2006 17:51:47  
To my knowledge (limited at best), all the 700R4 transmissions use a TV cable, not a vacuum modulator. I've got several 88s with 700R4s, but mine are diesel. With mine the TV cable hooks to the injection pump throttle. I assume your's hooks to the TBI throttle.



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migraine

12-11-2006 07:47:39




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 Re: O.T. 88 Chevy 1500 4 x 4 Auto Trans Problem in reply to jdemaris, 12-10-2006 18:13:40  
Thanks for all the replies. We will head to a shop after while where they put in the new motor. The guys there are pretty sharp and should be able to take these ideas and pin it down in a hurry. The fluid and filter were changed at 87000 so maybe we're due again. My gut fear is that we have deeper problems but I could use a cheap fix for once for the pocketbook sake. You know there is this other tractor I've been looking at, well actually two, oh crap I hear the wife stirring. Gotta go....Migraine

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