'02 Allison 1000 limped.P0735, P0840, P0700

[Von Wilsonator]

I know, I know, low post count Newb in desperate need of an already covered topic. Well here's my novel, thnx in advance for your patience.
Ok. 2002 LB7 5-speed Allison 1000. Banks 6-gun, full exh, and K+N... So no REAL upgrades. 150k,no load, and I drive like a grandma.

On the hiway yesterday getting up to speed, and tranny dropped out of gear and RPMs reved up. Pulled over and found nothing wrong. Another 20 mi, and once again out of gear, engine revs. This time I get a SES light. Tranny seems to degrade slowly. Little power to the wheels, no reverse, you know, limp mode.
Got home, truck off, cleared codes which were:
P0735 (gear 5 ratio incorrect)
P0840 (transmission fluid pressure sensor/switch A circuit malfunction)
P0700 (transmission control system malfunction)
And all back as if nothing happened.
In paranoia, I drained the pan straining the fluid, pulled the spin-on filter cut it in half, and dropped the pan. No clutch shavings, metal chunks, or signs of catastrophe; also fluid was deep red, and not burnt.
Normal silt on magnet:
I re-serviced with Valvoline full Synth Dextron lll, new filter, and assembled.
Drove to work today, slipped out on the way there, and once on the way back. I put it in tow/haul, and it didn't slip again.
I've searched this and other forums but am unable to find someone with this particular code combo. I need to tow my rock crawler 2hrs each way this weekend, so I need a direction to go in.
Leaning on it being an electrical issue rather than mechanical judging by what I'm seeing.
Any advise is muchly appreciated.

 

[trevrosborough]

check the main harness running into the trans on the pass side pull it apart and see if there is trans fluid in it if there is clean it out reconnect and test drive the truck

 

[Von Wilsonator]

check the main harness running into the trans on the pass side pull it apart and see if there is trans fluid in it if there is clean it out reconnect and test drive the truck

That's what I spent the evening doing.
Seen better days.

All the pins seem fine transmission fluid is seeping through from the male end of some of the pins though

I'm just going to clean it all out and reassemble.

 

[Von Wilsonator]

I also heard I should look at the t-case fluid, speed sensor, and a possible issue with shift forks. Think I'm barking up the right tree?

 

[Von Wilsonator]

I'm going to Look into the t-case tomorrow. I'm pretty sure I have Dex lll in it from about 10k ago (pump rub fix). I'll change over to the 3 qts of synth 5w-30 through the speed sensor that everyone's talking about. Will follow up. More suggestions still welcome.

 

[trevrosborough]

I would brake clean the plug out and try it

 

[trevrosborough]

Usually the Speedo will act up if the case fluid is bad or full of metal

 

[Mike L.]

If you have a stock Allison and running a banks 6 gun with a P0735 code; your C2/C3 clutches are toast. Leaking connector will throw valve body codes but never incorrect gear ration. That code is a big slip.

 

[Von Wilsonator]

I would brake clean the plug out and try it

Usually the Speedo will act up if the case fluid is bad or full of metal

I see. I'm expecting to find something along those lines.

If you have a stock Allison and running a banks 6 gun with a P0735 code; your C2/C3 clutches are toast. Leaking connector will throw valve body codes but never incorrect gear ration. That code is a big slip.

Thanks for piping in Mike L!
So it sounds like a rebuild is in my near future.
I'm very surprised this happened. I always leave the tune in 1, and am very light on the throttle. With only 150k on the truck, it's pretty frustrating.

 

[ThebigGids]

Lift big wheels and tires don't help either

 

[Von Wilsonator]

Lift big wheels and tires don't help either

I agree with the lift being too high. Got it as low as I can with the front leaf mounts where they are.
But I have 4.63 gears on 37s... So the truck thinks the Tires are too small. At 70 mph, my speedo reads 85.

 

[Uncle Jesse]

Kick out the O/D to get you through the weekend towing, you'll be stuck going slow but you shouldn't limp the tranny.


Keep 'er 'tween the ditches

 

[Von Wilsonator]

Kick out the O/D to get you through the weekend towing, you'll be stuck going slow but you shouldn't limp the tranny.


Keep 'er 'tween the ditches

Thanx Jesse. I was able to borrow a friends LBZ for this weekend.
Drained the t-case today. Looked like liquid neverseez. Very metallic in color. After it drained, I could see chunks in the drain hole. I fished what I could, and cleaned it up for y'all to see.

Yellowish pieces are plastic, a couple metal shavings. Obviously not good. Anything anyone recognize?
Seeing this further solidifies my t-case suspicions.
I know Mike L. Says the P0735 codes guarantees it to be bad clutches... But what are the chances it's the t-case causing all the trouble. Broken chunks interfering with the speedo offsetting the the 5th gear speed tolerance putting it in limp mode?

 

[mackthehack]

Time for a rebuild... Nice trucks by the way

 

[ThebigGids]

Its very possible its the transfer case. Like I said I've seen these exact codes and its due to a broken fork in the tcase and tcase being all messed up!! But there is always a chance there is a problem in the trans.

But the way the tcase looks...man. I'd just fix that first since its obvouisly got issues and see how it turns out

 

[Mike L.]

Yes the transfer case can cause all kinds of trans codes. Rebuild it first and see what codes come back, if any.

 

[Chevy1925]

Looks like the shift fork came apart amung other parts. Pull that thing apart and fix her up. They are simple to tear down and fix but damn are the parts costly compared to other tcases I've rebuilt.

 

[Von Wilsonator]

Time for a rebuild... Nice trucks by the way

Hey thnx!

Its very possible its the transfer case. Like I said I've seen these exact codes and its due to a broken fork in the tcase and tcase being all messed up!! But there is always a chance there is a problem in the trans.

But the way the tcase looks...man. I'd just fix that first since its obvouisly got issues and see how it turns out

Time to research rebuild and shift fork replacement.
Anyone have a preferred kit for the job?
Thnx fellas.

 

[Uncle Jesse]

I just replaced mine last Christmas (they like to go around the 250,000 kms mark) with a factory GM t-case with a 3 year 100,000 km warranty. $2,100 installed while I waited ( took them about 2 hours and it was done). Didn't even go to a dealership, I went to drive train shop that specializes in high performance stuff and that's what he recommended. With that kind of warranty you can't go wrong IMO


Keep 'er 'tween the ditches

 

[Chevy1925]

Hey thnx!


Time to research rebuild and shift fork replacement.
Anyone have a preferred kit for the job?
Thnx fellas.

i cant remember right off the top of my head but i dont believe there is a kit that would entail everything needed, specially with yours knowing parts got destroyed that may or may not be included in the kit. your best to tear the case down, find what went bad and order the parts. i did that with mine a few months back. i would get bad clunking when going from forward to reverse or doing a hard 2wd WOT run, then slowing to a stop. wound up finding a bad rear output bearing, both shift forks were worn out, speed tone wheel had a groove and was bad, 2wd/4wd shift collar was quite worn as well and a couple other little things. merchant auto has all the parts you would need and i cross referenced some of the parts over onto amazon for a better price on somethings. its common for the 2wd/4wd shift fork to wear out and cause alot of slop come to find out, they have new updated styles that last longer. i also put a new nickle plated slip yoke on as well as mine was worn out and causing part of the clunking i was getting.