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Old 03-25-2003, 07:34 PM
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Post 700r4 shifts in and out at shift points?

This one is hard to explain. Seems like the other day, when it was warm (been riding all over town) when I would leave the light, somewhere between 2 and 3 or 3 and 4 it would act like it was shifting back and fourth until a was going faster. Can anyone explain this? Oh, this is an 87 Iroc.

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Old 03-26-2003, 05:21 AM
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I had a problem similar to what you are describing in my 86 Firebird with a 700R4 auto trans. It turned out to be the torque converter lockup switch. This device "locks" the converter into 1:1 when in overdrive and you have a load (it was designed to improve fuel efficiency). When teh switch goes bad, the trans shifts (READ: Not the same as SLIPPING) between 2nd, 3rd, and 4th erratically. If you drive it in 2nd, you should notice that the back and forth shifting stops. In mine, if I drove in 3rd, it would shift back and forth between 2nd and 3rd. If I was in 4th, it would shift between 2nd, 3rd, and 4th, all of this going on between 25-30mph. I think it is an internal switch that would require you to remove the trans to replace. My garage buddy just disconnected mine when he installed a new mount for me, and the problem disappeared. This was the cheapest fiz for me.
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Old 03-26-2003, 02:00 PM
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disconnecting your lock up plug is not something I would advise this will increase your transmission temp and decease fuel mileage along with basically defeating what you have an overdive transmission for. take your car in to a transmission shop and get lock up checked out.
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Old 03-27-2003, 07:23 AM
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From what I've read about the lock-up, it was an add-on to improve fuel efficiency when the vehicle is put under load, that later evolved into standard equipment design. Not all overdrive (or should I say 4-gear autos) transmissions had them from what I understand.

I do understand that if you are hauling, or doing the highway drive and wanting to cruise, you could run hotter if you are shifting up and down, but for travel in the city, locking into 1:1 would be intermittant at best. Also, with the way the TH700R is geared at overdrive, it doesn't seem the TC lockup would noticeably impact fuel economy.

If the car is taken into a "transmission shop" (if an "honest" shop can be found), you have the choice of economics. Do you want to pay to have the trans removed and the switch replaced? If so, the trans might as well get rebuilt and modded while its out. For me, I decided to have the switch bypassed because I wasn't financially ready to have the trans removed and rebuilt, and I didn't know much about the car.

Regarding trans oil heat, an external trans cooler can compensate, and should be used if you're going to hot rod, in which case the TC lockup switch is not a factor. You can buy an after-market cooler kit for as low as $40. Its an easy DIY for the backyard mechanic. I'm in the process of installing the trans cooler, a remote trans filter, and a deep dish pan, which should take care of any heat problem (I'm doing this as preventative medicine). With the tranny in there now, I'm hoping these mods will extend the life. When I stuff in the beefed rebuilt trans, all the cooling components will still be in place.

You are right though, obviously, that replacing the switch is going to provide the best benefit and serve its intended purpose. However, I would not feel comfortable at all taking the car into a transmission shop and expect a fair shake or a cost efficient alternative such as a bypass. The mechanic that services the heavy stuff on my car (he did the switch bypass) has owned a profitable auto repair business for 30 years, and he has built more strip machines than I can remember, so I am able to trust his judgement. And the matter of economics perhaps effects me more than it would others.

I can only speak from my experience. I know the car has miles, so I don't bear down on her too hard, and I don't haul. Bypassing the switch has not given me any negative effect. In the city, I get 16.5mpg (I measured this yesterday) which is not too bad considering there are a handful of gas-savers that still need to be done. On the highway, I get much better mpg, but I haven't gauged that yet.
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Old 03-27-2003, 02:24 PM
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Okay, this is a freshly rebuilt tranny. I have a warrenty. I just wasn't sure if I needed to take it in. It does have a trans cooler. I guess I could unplug the harness connection on the tranny and see if it quits. Trouble is, I can't get it to duplicate. This happened the other day after driving all over the place. ??? Would temp be a factor here?
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Old 03-27-2003, 02:40 PM
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check your throttle valve cable,it might be broken
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Old 03-27-2003, 06:29 PM
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ok you dont fix transmissions but I do and thats ALL I do day in day out 700 r4 needs lock up clutch to keep inside trans temp down. you can trust your friend no sweat off my back and have been doing transmission work for 25 years own my own shop and family owns 3 others here in Houston. Honest shops can be found just like any thing else there are bad people in every profession dont lump all of us together!!! fyi lock up drops rpm 150- 300 rpm dont beleive that have your buddy check out data stream on late model gm car or truck trans rpm slip engine data with snap on scanner!!!!You dont need to remove transmission to replace lock up solenoid remove trans pan and look toward front pump can be replace with in 15-30 minutes!!!

[ March 27, 2003: Message edited by: airworld2 ]

[ March 27, 2003: Message edited by: airworld2 ]</p>
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Old 03-29-2003, 06:15 AM
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Lightbulb

Thanks to everyone for the input. Here are a couple of details that I have to add now that I have paid more attention to the symptoms. When I leave the stop light, nice and easy, go through all my gears, it seems that between 3rd and 4th and after 4th, if the rmps are just right (around 1250-1500) it will shift back and forth. The "shift" does not feel as strong as a regular shift, so I feel like it does have to do with the lock-up. It does not do it with a load on the engine (like accelerating) it only seems to do it when I am maintaining speed. Any help is greatly appreciated.
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Old 03-29-2003, 06:31 AM
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I would disconnect the lock up plug at the transmission case just for one day (as to not cause any confusion). This will allow you to isolate the problem. If this doesn't change anything then it's not the lock up. If it makes the problem go away then you can look into the lock up wiring, etc for problems.
If this is a stock vehicle you can ride the brake enough to activate the switch and this will unlock the converter and you can see if the problem goes away.
It could also be an engine problem like a fouled plug or weak plug wire, bad injector, etc.

[ March 29, 2003: Message edited by: Jason ]</p>
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Old 03-29-2003, 09:39 AM
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As for the last post good point and often over looked. Alot of good people have pointed to the transmission When if fact the trouble was engine related. If dpjmw would contact my trans shop in Houston I'll test drive it and scan it at no cost! That way you can take it back if you need to for warranty work.Email me if you need this done west houston area.
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Old 03-29-2003, 10:58 AM
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Hey Airworld2...please check your private messages...K
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Old 03-30-2003, 12:32 PM
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Lightbulb

I was doing some other work on this car today and I found a little relay looking plug that is mounted near the drivers side front on the inside fender. Does this 'plug' have any thing to do with the lock-up power supply? The hot going into this plug was frayed badly and could not have been making a very good connection. Right now the harness is disconnected from the tranny, I guess that I need to plug it back up and see if it is doing it now.?? Does anyone know for sure what that plug might be or if there is one is the lock-up circuit? <img src="graemlins/crash.gif" border="0" alt="[crash]" />
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