68 RFE transmission Problem

I am hoping to get a response from Transengineer for this problem. I have a 1,000hp truck with a built 68 rfe transmission that we are testing and tuning on the dyno for a race this weekend. On a recent dyno run we believe the transmission torque converter unlocked while doing a pull on 6th gear at around 3500 rpm. The engine rpm increased to 4600 rpm before we got out of the throttle and made a loud pop or bang. we checked everything on the engine and the transmission was still working perfectly so I drove it home for the weekend. It threw codes on Saturday P0868 and P0944. Truck was still shifting perfectly. We changed fluid, both filters, checked the valve body. Next run truck shifted back down to 5th at the same 3500rpm which again sent engine rpm to 4600 or so rpm. Installed pressure sensor. next run same thing again, unlocked and shifted down. Do you have any idea how to proceed? we're all out of ideas. Truck still shifts and drives perfectly but something is telling the transmission to unlock the torque converter at around 350rpm.

 

He doesn't get on here much anymore since retirement. Send him a PM.

 

Are you sure it’s not a tuning issue?

 

68rfe TC is electronically controlled , if its disengaging at the same RPM its maxs out, remove the RPM limiter, But you had better have 1 hellva trans build to run that RPM, not to mention the Factory rotating mass had better be spec out or your wallet is going to get suck dry $$$$$

 

Thanks for all the replies. We do have a tuner working on it and we sent them the data logs and video of the gauges during the run. We are thinking the torque limit may not be set high enough on 6th gear. The transmission is an 850 built by RevMax and we have been in contact with them as well. They're confident this transmission will hold in this HP range. They have been testing a 68rfe in their race truck. I think we are going to make a run this morning in tow haul to limit the transmission to 5th gear and see if the torque converter unlocks or not.
Thanks,

 

Awesome , lets us know what happens...Ahhh the smell of HP in the morning....

 

I am wondering do you even see 6th in the 1/4 mile?

 

Yes, it does go into 6th at the end of the 1/4 mile. This truck has 35" tires and 4.56 gears. I am pretty sure we can make it to the end in 5th gear though. We just completed a dyno run limiting the transmission to 5th gear with no problems. I Still have the problem with the torque converter unlocking when testing in 6th gear though. I am going to race it on Saturday limiting it to 5th and keep working on the problem next week.

 

Update: We calculated rpm at the end of the 1/4 mile and decided we could not make it to the end in 5th gear without potentially over revving the engine. We decided it needed to go to the track on Friday evening to see if it would make it to the end of the track in 6th gear without the torque converter unlocking. 1st run I tripped both staging lights by mistake and the car in the other lane was already staged leaving me very little time to build boost. I left on only 2 or 3 pounds of boost but made it to the end of the track without the torque converter unlocking. That was good news but I had to try it again to make sure. That run was 12.18 at 119.85 mph. With more boost that run should have been in the 11's with a higher mph. 2nd run, after letting the transmission cool down, I staged without anybody in the other lane so I had time to build boost. Launched the truck and something in the front end broke and locked up causing the front driveline to break. The front driveline took out a fuel line, wiring and I am not sure what else. I should find out at the first of the week what caused the front end to break. After it is repaired, I need to confirm the torque converter is not going to unlock in 6th gear again. I should add that our tuner sent us a new maximum effort, low duration tune for the Saturday race and he was aware of our problem. That may be the reason the torque converter did not unlock in 6th gear. Bottom line, I still am not sure why the transmission is not unlocking the torque on the track like it did on the dyno and why the transmission codes did not come back since the last time they were cleared.

 

It looks like 120 should be right at 3400 rpms, which is lower than where you have been experiencing the issue.

What rpm is it shifting at in the other gears?

 

Thanks for the info AH64ID, that is good information. It is set to shift at 3500 rpm. As soon as the repairs are made I will pick up where I left off and make some more runs. If I can get a good launch I should be able to get past the 3400 mark by time I get to the end of the track. I'm not going to lie, at the end of the track my heart is pounding in anticipation of the potential torque converter unlock, LOL.

 

VM, IMO the front failure will occur again if you don't make some upgrades...

 

Forgive my ignorance. I just always thought you might throw a rod or do other damage at 4600 RPM's. I guess you have alot of upgrades?

 

Yes, This engine was built for the 1,000 to 1,200hp range. It has billet rods, balanced rotating assembly, and a "Gorilla Girdle" to stabilize the rotating assembly.

 

So, we got it up on the rack at the end of the day today and it looks like the drivers side U-joint in the front differential broke and locked up the differential which broke the front drive shaft. The drive shaft took out 2 sensors on the side of the transmission, the transmission shift linkage, some wiring and fuel lines, and put a hole in the floor. We will be inspecting the front and rear differentials and the transfer case in addition to making the necessary repairs. We will also be upgrading the u-joints in the front differential.

 

May I ask what diesel engine oil you use?

 

Schaeffer brand but not sure what weight or anything else about it. The shop that works on the truck takes care of that for me.

 

Probably the 7000 racing oil. I use that in the Canned Ham

https://www.schaefferoil.com/documents/258-708-td.pdf

They offer it in I believe 3 different viscosities.