Eaton 8LL

[jimbo40]

Hello everyone,

I'm new here and came to where the Mack folks hang out because I have an issue with my 8LL.

I have been running Macks for 43 years in the dirt. This problem is in a quad axle, 97  Mack cl700

I'm an owner operator and know evey clunk and odd sound and pay attention to it, and fix it myself usually.

The other day I took a load into a soft dump site, this is the first time out in the spring for this truck.

The backin was showing some stress so I stopped put it in low low, and drove right out, maybe half throttle max. Back in for a flat dump and the pulled out no problems about 70000 was the haul. I've been in much worst with this truck.

Read to roll back for another load and pu it in direct, but nothing, neutral. 

Back in LL and it drives fine all gears and reverse, no strange sounds but main stage and high are neutral.

Drove it 3 blocks back to my shop at about 10mph and began to work on anything obvious.

No air leaks, checked reg /filter, pulled the splitter valve and clean it and checked  orings.

I can hear all the clunking when shifting the stages, and if I sit at 1000 rpm in direct low, (not low low) with it in 1st gear it is just neutral but every once in a while it will grumble and slightly move like it's trying to connect.

But still LL seems to work fine. Obvious I won't work this way.

1000 a day down time. They've been so good i had never had to do much to them, I'm a good mechanic but don't have any time with these 8LL

All tech advice welcome.

And thank you.

Also, I away follow up with final result to help others with the same problems 

Edited 7 hours ago by jimbo40

[Joey Mack]

Pull the figure 8 looking cover off the range shifters on the rear of the trans and look for a loose shaft nut and/or a cracked piston. No special tools needed.  The gasket/ oring kits and the filter regulator on the back is still available.. 

[Geoff Weeks]

Here is the service manual:

https://www.eaton.com/content/dam/eaton/products/transmissions/vehicle-transmissions/8ll/eaton-fuller-heavy-duty-transmissions-service-manual-trsm1500-en-us.pdf

If what JM doesn't show anything, then you are going to have to go into the back box.

If the range syncro cracks in 1/2 (something they can do) or the LL splittter dog can't slide for some reason.

1st test is can you get anything in high range?  Try it from a stand still with the range in high and the front box in the lowest gear, and see if will move. If nothing in high or low range but only LL I'd be guessing the high/low range syncro has come apart and jammed.

[Geoff Weeks]

In short: if it will go into deep reduction and come out (even to "neutral") then the peanut valve and deep reduction piston is moving.

If it will pull in high range but not low range, (goes to Neutral in low) and you've check the air at the range ports, then it has to be the syncro, if you aren't getting air to the respective hi and lo range ports, then it is likely the slave on the side of the trans isn't shifting position when the main box goes through neutral.

I had one go like that, pulled fine until I went to shift to low range, and got nothing, I could pull in high.  Since on a 15 or 8LL the splitter either locks the LL to the output or the low range gear to the aux shaft output.

Hard to explain in word, but the manual I linked to has good diagrams.

[jimbo40]

53 minutes ago, Joey Mack said:

Pull the figure 8 looking cover off the range shifters on the rear of the trans and look for a loose shaft nut and/or a cracked piston. No special tools needed.  The gasket/ oring kits and the filter regulator on the back is still available.. 

I pulled it and the nuts are tight, pistons looked good. Reg is putting out 61psi

[jimbo40]

41 minutes ago, Geoff Weeks said:

Here is the service manual:

https://www.eaton.com/content/dam/eaton/products/transmissions/vehicle-transmissions/8ll/eaton-fuller-heavy-duty-transmissions-service-manual-trsm1500-en-us.pdf

If what JM doesn't show anything, then you are going to have to go into the back box.

If the range syncro cracks in 1/2 (something they can do) or the LL splittter dog can't slide for some reason.

1st test is can you get anything in high range?  Try it from a stand still with the range in high and the front box in the lowest gear, and see if will move. If nothing in high or low range but only LL I'd be guessing the high/low range syncro has come apart and jammed.

Nothing in high range, I can feel the gears spinning through the shift handle but nothing make it through to output.

10 years ago that box blew up on me, we pulled it but I can't remember how difficult it was, I'm rememberKing not to hard, but now it seems hard.

[Geoff Weeks]

Put it back together and see if it will pull in high range.

[jimbo40]

21 minutes ago, Geoff Weeks said:

In short: if it will go into deep reduction and come out (even to "neutral") then the peanut valve and deep reduction piston is moving.

If it will pull in high range but not low range, (goes to Neutral in low) and you've check the air at the range ports, then it has to be the syncro, if you aren't getting air to the respective hi and lo range ports, then it is likely the slave on the side of the trans isn't shifting position when the main box goes through neutral.

I had one go like that, pulled fine until I went to shift to low range, and got nothing, I could pull in high.  Since on a 15 or 8LL the splitter either locks the LL to the output or the low range gear to the aux shaft output.

Hard to explain in word, but the manual I linked to has good diagrams.

Thanks for the manual, its just such a trip that there was no noise, or snap, or bang indicating a failure.

[Geoff Weeks]

Ok, you have confirmed that the range syncro is the problem, either the piston/fork is not moving, but more likely the syncro itself has come apart not allowing it to move forward or back

Take the lines off the range section at the back and make sure air is comeing through when you shift the range flipper on the stick

[Geoff Weeks]

3 minutes ago, jimbo40 said:

Thanks for the manual, its just such a trip that there was no noise, or snap, or bang indicating a failure.

That's the way mine went. I had been driving for 200 miles, came to a stop at the top of a ramp, and no low range!

A cabover it is easier to get the back box off with the trans in the truck.  A conventional it is going to working under the cab.