480le NO reverse

:mad:Howdy
OK....couple of issues, I will start with the minor one-
1986 blazer with 6.2 T400 trans. Speedo was off by about 10-15 MPH, lubed the cable got a little better but not much. kinda bouncing around. When I replaced my tires I went with larger ones. Now when the truck is cold the speedo reads almost right on, things warm up and I get the bounce and it might be right on or off by about 5MPH. I thought these speedos were a direct gear/cable drive. So...it should work or NOT work, right:confused:

Next question-
!996 3500 dually 4l80e trans. NO REVERSE:mad: Happened very suddenly with no other trans problem symptoms. No noises or slippage, went to put it in reverse and no go.
It works perfect with nice hard shifts in all gears. Fluid is red with no stink or metal. No noise from trans mission. No indications of shift issues or drivability except for the no reverse. Any help????

Thanks!

Bouncing mechanical speedo. Could be a gear missing a tooth/teeth (at either end), or cable "memory". Working right cold then not when hot is curious. It's usually the other way around. Could also just be a worn out speedo, but lubing the cable shouldn't change that. Lubing the cable could minimize an issue with a worn gear by reducing the resistance. It could also be a combination of the issues.

No reverse. The "E" is for Electronic, so I'd start there. Check for codes first, even if the SES isn't on. Most common is poor electrical connections, usually at the transmission, but these will almost always set a code and the SES. The NSBU could be worn out (no SES), solenoid died or an internal connection could be lost (should set codes). Or, a valve passage could be obstructed, but there's usually some prior symptom or slow/intermittent engagement. If the R circuit of the NSBU has failed, the back-up lamps won't work, either. It's a relatively simple rotary switch, and R is the most visited position.

For the speedometer problem, I would reach up under the dash and confirm that the speedo cable is snapped tightly onto the back of the speedometer. I would also recommend putting a finger tip of wheel bearing grease in the top flange of the cable housing (where the cable comes out). I have fixed many jumping speedometer needles this way.

New symptom for the 4l80e issue....It will not hold first gear. in other words: If I keep it in 1st up to about 3k rpm and then let up on the fuel, it will drop to idle and coast. I am thinking it is a reverse band that is out.

Back-up lights work and no codes in the system.

Input...?
Thanks!

Quote:

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Originally Posted by Dvldog8793

New symptom for the 4l80e issue....It will not hold first gear. in other words: If I keep it in 1st up to about 3k rpm and then let up on the fuel, it will drop to idle and coast. I am thinking it is a reverse band that is out.

Back-up lights work and no codes in the system.

Input...?
Thanks!

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Hey Dvldog, I had the very same No reverse problem last year. It turned out to be the Reverse band. My transmission guy said 4L80e is famous for losing Reverse without warning. He couldn't gaurantee the tranny would last, if he just fixed Reverse.. So I bit the bullet, and paid $2700 for a complete Rebuild. Sorry to be the bearer of bad news, Good luck.

Ya...I did some more research and it seems that the reverse band is not really fixable without puling out all the other guts anyway.
looks like I will be rebuilding.
Wish this would have happened before winter and not after it....time is a short commodity!!!:mad:
Thanks.....

your test of manual low pretty much confirms the diagnoses of a failed low/reverse band.

Be sure to get one of the super duty bands when you replace it.

There is a slight possibility that the servo failed (seal failure) but more likely the band snapped.

Bummer for sure


Missy

Please guys I am having problem with my reverse gear that I believe came from no overdrive that I have been experience for a while now.

When my engine is cold, I have strong reverse, though I have to accelerate a little harder than normal to get it going. However, once the engine is hot, it is harder to get it in reverse. when it gets in reverse, it is slower than normal and requires much more acceleration to get it going. and the going is rougher than normal too. Thus transmission is less than 5,000 miles. Please likely the problem, bad band? Bad clutches or what?

Howdy
Hopefully the trans will have some warrenty with it...? Take it back and have them fix it.
If not it sounds like it might also be a torque converter failing. Is it throwing any computer codes?