Downshift at stoplight.

Downshift at stoplight.

Postby jflynn [OP] » December 30th 2011, 3:18pm

Hello everyone. First post to this forum. Thanks to all who make it possible!
My van seems to downshift when i come to a full stop at a traffic light. I drove an 87 c1500 that use to do it and was told the trans, spline yoke was binding in the trans. A little grease fixed the problem. Is this a commom problem with GM vehciles/trans, or could i have other problems? Again Thanks for the help.
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Re: Downshift at stoplight.

Postby Phantom » December 30th 2011, 3:34pm

Welcome...Can you be more specific.. trans is designed to downshift into first gear when rpm gets low enough ,,,the grease may have been for the U joints , and U joints and trans splines are common on many types of vehicles
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Re: Downshift at stoplight.

Postby 93xtmoney » December 30th 2011, 3:39pm

Welcome aboard
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Re: Downshift at stoplight.

Postby jflynn [OP] » December 30th 2011, 4:51pm

I was told that the splines in trans, output shaft get dry and cause the yoke to bind and not slide on the shaft. Giving the impression that the trans is shifting when the load is off the driveshaft (at a stop light) and the yoke pops back in the transmission. Apparetly the drive shaft slides in and out of the transmission as engine load is sent to the rear axlle while driving. I could be wrong. I do have a high idle which i think is from a vacum leak from the line that feeds the ac system. Got to pull the doghouse this weekend.
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Re: Downshift at stoplight.

Postby Mr_Bowtie » December 30th 2011, 4:55pm

If its idling higher then it might be that down shifting may just be more apparent to you now. Check your tranny fluid and fix the possible vacuum leak.
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Re: Downshift at stoplight.

Postby jflynn [OP] » December 30th 2011, 4:58pm

Will do. Thanks
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Re: Downshift at stoplight.

Postby Phantom » December 30th 2011, 5:35pm

Here are some pics to help you see how they look the spline slides in the trans trans and is lubed by trans fluid not grease ,, but the U joints , the things that look like a cross or plus sign are the
u- joints and have grease fittings to accept grease ,when it is all bolted together the splines should not move in or out , maybe what you are feeling is dry u-joints that move up and down slightly , and agree with previous post , you can either lube them your self or just go to any oil change shop and ask for a grease lube job , should only be a few bucks and they will lube everything that needs grease
Attachments
trans spline.JPG
trans spline.JPG (19.96 KiB) Viewed 721 times
trans spline 2.JPG
trans spline 2.JPG (22.63 KiB) Viewed 721 times
u joints and driveshaft.png
u joints and driveshaft.png (6.31 KiB) Viewed 721 times
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Re: Downshift at stoplight.

Postby jflynn [OP] » December 30th 2011, 8:38pm

Ok. Didnt think about trans oil being back there on the output shaft. After all thats why theres a seal there. Just took somebodys :screaming: word for it. Will check this weekend a see if the u jnts have fittings on them. See what happens. Thanks
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