1997 express 3500

[chaddy721]

hey guys..nebie here..picked up a 97 g3500 van to haul my motocross bikes in....runs great..but about 55mph when the van shifts into overdrive i think it sort of rumbles a bit..like on rumble strips but not nears as bad..just a mild shake when it shifts..just when it shifts around 55...other than that its strong..any ideas>?..bout rying an additive?..thanks

[MagicRat]

Are you sure its not the TC lock up that's making the vibration?

Drop the transmission pan, clean it out, change the trans filter, reassemble and refill with clean fluid.
If the old fluid is really dirty, remove the trans cooler return line at the transmission, and start the engine, after filling the transmission. Let the fluid pump out until the new, clean fluid is visible, the reattach the line.

I have found this basic service often fixes about one thrid to one-half of all shifting problems.

BTW, do not do for a professional transmission 'flush' unless the pan is dropped and the filter is changed.

[chaddy721]

thnaks for the reply..not sure on the tc lock up your talking about..but i did do a lucus oil tranny adative..it did help...so you think do the normal flush with a filter?..it just chteers a litttle when it goes into drive...it does hesitate a bit when its in drive..maybe a tun up would help..thanks