1996 Suburban Transmission

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I have a 1996 GMC Suburban 2500, 6.5 TD, 4x4 and I'm concerned it may be developing a transmission problem. About a month ago I noticed didn't want to shift up (to 3rd I think?). Only noticed it once though. A couple days ago, after being on the interstate for about an hour, it started shifting to 2nd with a significant "jolt" and to 3rd with reduced "jolt." Have not noticed this again, but have not replicated that hour on the interstate again either. No other problems noted with it.

I bought this used about 1.5 years/20,000 miles ago. Have not really done anything with the transmission to this point and I don't really know the service history. At this point I'm assuming the transmission is going out, saving money and shopping for a transmission shop.

I am generally a mechanical novice; I change the oil, replace belts, etc., but this is beyond anything I have any knowledge about.

Thoughts? Anything I might do to delay the demise of this transmission?

Thanks,
Josh
 
Did you check the fluid level?
That would be the first thing i would look at.
I would consider doing a line off fluid exchange and filter,a job that can be done fairly easily with basic tools at home on this truck.
 
The diesel ones of these trannies are tricky. I'd get someone with a decent scan tool like a tech 2 to look at all the speed sensors (there are several). My FIL's 94 1-ton van had the 6.2 or 6.5 (I forget) and tranny OD problems got it traded when noone could figure it out.
frown.gif


But they were looking at the speed sensors and a special "ignition module" that has nothing to do with ignition but is a dummy device to make the tranny computer behave. There is also a special something that tells the computer/trans your level of load in place of engine vacuum.

You probably have the 4L80E, the "E" would make it electronic, but maybe those came later with diesels. If you crawl under your trans ID may be stamped in the pan; if not, take note of its shape and number of bolts. An RPO code will also tell us.

I would first crawl around under and find every electrical plug and ground that's there and make sure they're clean & tight. Get the one on the pumpkin too, it might be for ABS but they all have to jive.
 
This is what my '93 6.2 4L80E did when I bought it-TPS was out of adjustment, causing a CEL, shifting hard & late, no OD/torque converter lockup, burnt fluid-but it has mechanical injection & basically a stand alone transmission computer. There's a big jump electronically to the 6.5 TD OBD II 4L80E, though-you may need a REPUTABLE transmission shop to look at it.
 
Thanks for the quick replies; I'll go through all that this weekend or sooner. Would dropping the pan, changing the fluid, and replacing the filter be a waste? I'm sure it needs done.
 
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OK, after doing more research here and elsewhere, I'm thinking I'll drop the pan, replace the filter, refill with a store brand ATF, run it for a while, and then put a good quality ATF in after a 5K or so. I also think I'll put a higher capacity aftermarket pan on (B&M?).

Recommendations on filter? I'm thinking a standard AC Delco.
Recommendations on ATF for the long term?
Any reason not to put the aftermarket pan on?

I obviously don't expect this will reverse a transmission that is going out (though I'm not convinced that is the case yet), but I know it needs to be done and I was going to do the pan at some point anyway.

Also, is the different number of pan bolts a difference between 4L80E and 4L60E? I think I have a 4L80E, but will have to look to make sure.
 
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I would definitely drop the pan, change the filter, and see how it responds. Any full synthetic or highmileage ATF is a good choice.

If the transmission is back to normal, then you should start maintaining it. If not, troubleshoot it.

For everyone else, when buying a used vehicle, make an effort to get ALL fluids bled, flushed, changed, replaced, exchanged.... so that you have a baseline for your maintenance.
 
Originally Posted By: eljefino
.. I'd get someone with a decent scan tool like a tech 2 to look at all the speed sensors (there are several). .



I second this, and you should also have them check for trouble codes. If you are afraid of being taken advantage of at a trans shop, at least go to AutoZone and have them put their code reader on it. There is a torque converter apply valve which can wear out its bore and give trouble code P-1870. That is a prelude to an almost certain rebuild, although catching it quickly might save your skin. The difference between catching it now and not catching is that if that transmission has not failed, all you need is a rebuild of the valve body, rather than the whole transmission.

I will add that your symptoms sound like this might be the problem. Google "transmission trouble code P1870" and see, or reference this article.
 
Aftermarket oversized transmission pans seem to be a lot of money for little benefit. If you tow or otherwise work this rig very hot & heavy, an additional transmission fluid cooler will give you more benefit for the buck.
 
One of the draws of the aftermarket pan is the drain plug, but if the benefit of an aluminum pan and extra fluid capacity is minimal, I'll delay or not do it at all.

Research here indicates most any filter is OK -- I'm thinking Purolator?
 
I have one of those, 1 year older. No problem.

I have put Amsoil ATF in it around 40K miles ago. With oil pan drop and filter and fluid change. At that time I used Wix filters. Purolator is also good filter. Adding Magnefine will probably help although I have not done it in mine. I have put one in a Camry since it is only rubber hose as suppose to metal tube in the GM trucks.

I know people here don't like it but Auto-rx seems to work very good for transmission. It will solve any mechanical issue but it is good in cleaning it and deposit the cruds in the pan.

My dad said that the good trans shop can put their reader and drive it around to see what is going on. This trans have a history of slow to change gear in extremely cold temps.
 
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I do a pan drain once a year with dino ATF. I have an inline spin on filter, that I just remove to pump out 1/2 the sump. Super easy, takes maybe 15 mins total. I have over 200,000 miles on mine and I tow with it during the summer months, never had a hiccup, still shifts like new.
 
The fluid level is fine, but I can tell it needs changed. I'm doing that this weekend; does anyone have the torque spec on the pan? I found on here 97 in/lb for a 4L60E, but is it different for a 4L80E?

As an aside, I had sort of "emergency" trip where I had to tow my (mostly) empty utility trailer about 75 miles each way with some city driving in the middle. Not a bit of trouble from the transmission. I really did not want to put the stress on the tranny, but really didn't have a choice on the trip. I paid very close attention for any problems, but didn't detect any problems. I'm concerned they are still lurking out there though.
 
Originally Posted By: unDummy
For everyone else, when buying a used vehicle, make an effort to get ALL fluids bled, flushed, changed, replaced, exchanged.... so that you have a baseline for your maintenance.
As usual, unDummy has it exactly right. That's the first thing I did to my DD Marauder when I bought it in '07 with 87,000 miles. Now has 145,000 and still runs strong. Transmission gets a drain & fill every 15,000 miles and the fluid comes out as clear and red as the new stuff going in.
 
Update on this -- no further symptoms of transmission problems. Have replaced the fluid with Maxlife high mileage, old fluid was dirty, but could have been much worse.

Shifting from 1st to 2nd is better but noticeable; every other shift is almost unnoticeable unless you are really paying attention.

Hopefully this problem wasn't a problem. Almost 195,000 miles now; will continue to "improve" by adding a cooler and better filtration at some point, but I don't feel any emergency at this point. Keeping my fingers crossed and knocking on wood that this keeps together until I can afford a newer, lower mileage version.
 
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