fishin fever

Hi; paranoia time While backing truck up today[slight grade almost level] i got a shutter this was at idle into a tight spot.......hmm lets check this again dead level ..slight shutter@idle...some fuel no prob drive home try again hmm no problem. have just got this truck dont like autos but this truck was twice as nice as all the sticks i saw and half the ks only 100,000 miles first owner 80k with camper, 2nd owner 20k sometimes with 2 horse gn. has factory hd cooler under box ,and shifts perfect forward ,fliud is up and clean/red I,m changing and flushing all systems but the tranny has not been done yet [reverse band?] .I warm her up in neutral and lock out od below 45mph,neutral at long lights. oh the only thing different today i was gently shifting her thru the gears 1st to 15mph second to 30/35 mph od at 50 Hmmmm maybe this has never been done befor and the pressure changes made it a little touchy?????????

wannadiesel

I'd adjust the low/reverse band before you panic.

Winr

It's called an Automatc for a reason. I'd use it like one. The parameters are set for upshifts and idle issues. If its stock, just drive it.

Haulin_in_Dixie

Wannadiesel gave you the only simple thing you can do. Reverse uses the rear band and the front clutches that are shared with third. I would look for slippage in third also, if you have this the trans is most likely on the way out. If the rear band is slipping you would get shudder or slippage.

So what casues it.... As you discribe the symptom it goes away with a little throttle, read when the pressure goes up. That could mean low pressure from any number of reasons. The most likely is a pressure loss in any number of places, valve body, slip rings, front clutch lip seals hardened, sealing of the rear servo that engages the rear band.

You might make sure the throttle valve is adjusted right, or even raise it a little, which will give a harder higher shift, but more pressure at idle. If you have the means to pressure test the trans, that would be the way to go. And do make sure the fluid level is in the safe zone. Also make sure the filter is clean.

Another thing that is "special" with mopar trans systems. Is this doing it when you first move the truck? If so try something before getting worried too much. Start it up, put it in neutral, not park and let it run a minute, then try it. The check valve likes to leak on these and some of the converter fluid drains. When you first put it in gear, the trans is trying to fill the converter and has low pressure to the rest of the system because of it. Once full it will be ok. If this is the case just do the neutral thing in the morning and drive it. No harm to it. I have driven many thousands of miles on a trans with the leak back problem. Park does not pump fluid to the system, only neutral.

The servo can be done with the trans in the truck, the only thing that means a rebuild is if the third gear clutches are bad or the lip seal on them.

fishin fever

Hey guys thanks for the the informative replys; tranny worked fine today; to answer some of H.I.D questions today's tests.. no shutters forward.. very mild reverse shutter at idle.. no hesitation when put in gear... shifts smooth ..with mildly aggessive take offs it shifts at higher speeds as expected but crisp and firm ..at 50 mph in overdrive I kicked her down hard. it promply shifted to 3rd and pulled hard and strong [ I think this truck is stock but won't know till I take it to the Western Star dealership to get valves adjusted..2 of the Cummins mechs are 1st gen owners so everybody who knows better gets the little guys serviced there ] till I backed off at 70 then it shifted up no slip ..note nice clould of brownish black smoke out the pipe from the heavy dose of injector cleaner I'm taking it to a tran shop to be flushed,new filter and band adjustment and mention your good ideas and have them check all accessable items. Any other ideas or imput guys?? Thanks Eric

wannadiesel

Don't get it flushed. Lots of transmissions that were fine fail right after a flush. Just get the fluid change, the band adjustment, and have them check the throttle pressure adjustment that Bill mentioned.

ChrisLib

This is JMO but, like wanna said don`t flush it, unless your prepared to roll the dice, sometimes the gunk is the only thing keeping them sealed up. But I would service the unit, new filter etc, use Dexron fluid, and a bottle of Lubegard http://www.lubegard.com/automotive/trans_atf.html . The reason i say don`t use the mopar fluid is that it is alot "slippery`er" than dexron. On a late model computer controlled/electronically shifted unit (97 and up) the friction coefficient is VERY important for many reasons, but on older hydraulic units like ours the "tighter" fluid will lessen slip between shifts, and the Lubegard is there to pump up the high temp stability of the fluid.

Redleg

DO NOT POWER FLUSH!! Cost me $1500 and no truck for 3 weeks back when I had my Z-71. Had to work on it in a cold pole barn in the middle of February. Uncle wasn't happy about the mess and imposition either. The components are designed for flowing in 1 direction. Seals take a shape when fluid flows in one direction. When they back flush it, it can damage those seals and break any debris free that may have been stabilized, causing it to temporarily hang up in one direction, and only break free after they send you on your way and fluid is flowing in the correct direction. Also, on later trannys with the elctronic servos, flushing can caause debris to plug them up which is what happened to me. Flushed it in the fall getting it winterized (babied that truck), and it took a dump within 2 months. No hauling involved. Lost O.D. on the freeway, then third, and limped home in 2nd.

Chris, I understand what your saying, but it was explained to me that synthetic, even though slippery, would help the tranny more by reducing the temp, than any slippage it would cause. Not saying your right or wrong, just looking for more views.

ChrisLib

Synthetics are`nt nesessarily slipperier than dino oil, but they do have better protection in extremes of temperature. You can get a slippy type of synth and also an aggressive type of synth, here`s a pretty good article I found on trans fluid friction characteristics, I`ll even agree on the flush part IF and ONLY if the trans has been serviced REGULARLY since new.
http://www.garage-pak.com/pat-goss-w...ty-flushes.cfm
If ...or I should say WHEN the trans in my truck get rebuilt I`m going to be using a fairly aggressive sythetci, such as redline
http://www.redlineoil.com/products_g...59&subcatID=19
or amsoil
https://www.amsoil.com/storefront/art.aspx

fishin fever

OK OK no power flush ya'll sound like like my good friend and mechanic back east that maintain my company vans[gms with lousy 700-4 trannys] he had a saying about flushing old trannies was like waking a sleeping dog unless you knew the dog it's whole life ...the end result could be nasty!!!o thanks for the good replys and advice we shall defer to the collective knowledge Eric

andyr354

I have flushed the fluid by myslelf with no problems yet on other rigs. I don't do the powerflush like you are talking about though I don't think.

I first pull the pan and put a new filter in and refill the pan like a normal service. Don't start it up yet.
I then just pull the pressure line to the trans cooler and put it in a bucket, then line up a row of open ATF bottles for the trans overall cacpacity. Have a budy start it up and pour them in as quick as you can. When you get them all in kill the engine, reatach the line, start it up and check the level. If you have to much drain it out.

Has worked for me. On some rigs it came out faster than I could get it in so I would stop the engine a few times durrign the process to catch up.

wannadiesel

That's a good flush, I don't have any problem with that procedure.

jughead

bad news is that shudder is almost always clutch pack problems. just like the clutch in a standard trans. in my 40 years of auto trans repairs i do not recall a band that shuddered. not saying it cant. first thing i would do is check pressures and raise them a little above specs.