1987 Olds 98 with transmission chatter

I have an 87 Olds 98 with 130,000 miles. When I am driving in OD up a hill, the transmission will start to chatter. I can usually relieve it by shifting back to Drive. However, it even chatters some in
Drive. I changed the transmission fluid about 12,000 miles ago but the fellow simply flushed and did not change the filter. I have tried a couple of the additives but they don't seem to help. Any advice will be appreciated.
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Engine misfire can cause this chatter and feel like a trans problem. Was the fluid burnt, is it discolored now?

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are sure the trans is making the chatter to me it sounds like you got a little of bad gas when you get bad gas and going up hills the values will chatter put the high grade of gas in your car and see if that fix the problem everytime i ised the cheap gas my car chatters
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I am sure it is the transmission. While climbing a hill in Overdrive, it will thump a number of times. Usually it will stop when I put it in Drive. On level roads, it does not do it.
wrote:

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Question - if you push down on the gas pedal and force the transaxle to downshift to third gear (while still in overdirve mode) do you still get that chatter?
If the chatter goes away in 3rd gear but still in overdrive mode, I'd suspect the 4th gear clutch has a problem. If you still have the problem in overdirve range but in third gear, more likely the 3rd roller clutch is not holding. The power flow is different between 3rd gear in overdrive range VS 3rd gear in drive range: in 3rd gear in drive range the 4th clutch is not applied and 3rd roller clutch is effectively locked by the input clutch..
Neither is a cheap repair - either would require removal of transaxle and a teardown (though the 4th clutch is the first clutch in the gearset). . I'd first have the pan pulled and the filter assembly replaced, since low line pressure (which can be caused by a partially plugged filter) can lead to clutches slipping. Look CAREFULLY at the pan for signs of either excess metal debris (which points to the 3rd roller clutch) or excess friction material debris (4th clutch).
130K on a THM440-T4 before rebuild is actually not too bad
Hope this info helps.
Regards, Bill Bowen Sacramento, CA
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I know it is bad form, but let me follow up my own message with an item I forgot. If the problem is still present in 3rd gear in BOTH ranges, then the 3rd clutch (different item than the 3rd roller clutch) may be the cause.
BUT first thing: pull that pan, replace the filter and put some fresh Dexron III in that transaxle. Fresh fluid and a filter that allows full flow will do wonders.
Bill

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