Allison 5sp: 2004 LLY Shift Issues

[joshd472]

Hey guys, my first post here.

About a month ago I bought a high millage (250K) LLY for cheap that has some issues that i was hoping someone could help me out with.

The truck has the following mods. Bully Dog gt (which i have uninstalled so the truck is on the stock tune now) S&B intake, LBZ turbo mouth piece, pvc reroute, and it appears to be the stock exhaust with the muffler and cat deleted.

The trans was rebuilt by A1 transmission in Pensacola about 30k miles ago.

The problem I am having is what I have heard described as "flare" 1-2 up shift. If i really baby the throttle it's barley noticeable. The more throttle the more it "hangs" until you let off the throttle then it shifts really hard into 2nd. All other up shifts are fine.

It also has a 3-2 and 2-1 harsh downshift 90% of the time.

I took the truck to a local shop and the only code he could get from a snap on scanner was p0700. A1 told me everything had been replaced but the valve body so I replaced it with a bd diesel valve body the new valve body came with all new solenoids, except for the shift ones. I also replaced both trans filters and put in a new fuel filter. The first mile the truck drove great then right back to how it was acting before.

I have also got on the throttle hard trying to throw the truck in limp but could not do it.

The guy who scanned it also told me I have 4 bad injectors on the passenger side (per his return test). I was hoping to get the trans issue sorted before I replace the injectors. The truck is not a delay driver. I have put maybe 20 miles on it since I got it. The motor actually runs very well expect for a slight surge at idle that goes away if you prime the truck before you crank it.

Thanks for any help in advance.

 

[Mike L.]

I would do the injectors first. As far as the trans problem; you may have a ripped C4 piston.

 

[joshd472]

Thanks Mike! All this is knew to me, I will have to research and see what the function that does and how hard it is to replace. I was holding off the injectors because if i had to rebuild the tranny i was probably just going to cut my losses on this one.

One thing i forgot to mention is the tranny fluid looked/smelt fine and i didn't have any debris in the pan. Also my trans averages around 140 degrees what little bit I have drove the truck.

 

[joshd472]

Another thing i forgot to add. Ever since i put in the new valve body it hasn't thrown the p0700 again. I know it probably means nothing, just trying give as much info as possible.

 

[PureHybrid]

Thanks Mike! All this is knew to me, I will have to research and see what the function that does and how hard it is to replace. I was holding off the injectors because if i had to rebuild the tranny i was probably just going to cut my losses on this one.

One thing i forgot to mention is the tranny fluid looked/smelt fine and i didn't have any debris in the pan. Also my trans averages around 140 degrees what little bit I have drove the truck.

The c4 piston and clutches are for 2nd gear. It's a cheap fix parts wise, but you have to open the rear of the trans up.

 

[joshd472]

Could this also be what's causing my harsh down shifts?

 

[Mike L.]

Could this also be what's causing my harsh down shifts?

Yes.

 

[joshd472]

Any suggestions on the best place to order the parts and a manual? Also does anyone know of some good tutorials of this that might be out on the web?

 

[PureHybrid]

As for parts, most larger truck shops should be able to get them. Our local Freightliner dealer is where I go for individual small parts. If you order a seal / gasket set for the whole trans I'm sure a vendor here could set you up, I've gotten them from Allseason diesel before, under $300

For no further into the trans that you'll be digging, get an ATSG book.

 

[joshd472]

As for parts, most larger truck shops should be able to get them. Our local Freightliner dealer is where I go for individual small parts. If you order a seal / gasket set for the whole trans I'm sure a vendor here could set you up, I've gotten them from Allseason diesel before, under $300

For no further into the trans that you'll be digging, get an ATSG book.

Thanks for all the help! If i have to pull the trans i will probably check everything else while it's out. I would hate to go through all the trouble of getting it out and back in only to have to pull it back out 10k miles later.

 

[joshd472]

Mike, when you say a ripped C4 piston what exactly are you describing? I took the trans out today. And the only defect I see on the old piston compared to the new one is the rubber lips on the inside and outside of the piston are worn flat.

 

[Mike L.]

Mike, when you say a ripped C4 piston what exactly are you describing? I took the trans out today. And the only defect I see on the old piston compared to the new one is the rubber lips on the inside and outside of the piston are worn flat.

If there was no tension when you pulled that piston out, you found your problem. There are more things wrong in your trans. You just need to look.

 

[joshd472]

Any advice on what I should be looking for? All of the clutches we pulled out to get to the c4 look good.

 

[joshd472]

When I went to install the new C4 piston I quickly found out what Mike was talking about. Tight fit.
Anyways, we couldn't see any obvious signs that anything else was wrong with the trans so we put it back together and went for some test runs. It started out acting exactly how to did before. After a few pulls it started acting better. I still have a slight shutter on the upshifts at low throttle (sometimes) but at full throttle it shifts great.
It still has the harsh down shifts but they are not has harsh as before. I hope it's just relearning and I just need to have the TAPs reset.

 

[joshd472]

I haven't drove the truck much but all the shifts are fine now. Still have a slight hiccup at half throttle on the 1-2 up shift but the harsh down shifts are gone. Hope resetting the TAPS clears the up shift hiccup.

 

[joshd472]

Got the TAPS reset yesterday drove it around for about 20 mins and it now shifts perfect. Thanks for the help everybody.