66RFE Downshift Hesitation/Shudder

[ScubaSteve]

It seems like since I tuned my truck recently (Diablo, Hemifever), I have been having a fairly consistent issue with shuddering during acceleration when the truck goes to downshift. Its like it hesitates as if its unsure which gear it wants to shift to, and its hard enough it almost feels like wheel hop, though I'm not accelerating hard enough for that to be a possibility. Happens in the lower gears, usually around 10-20mph or so, I would guess the 3-2 shift.

So, I'm curious if anyone else experienced this before? With or without tune?

[thedriver21]

I have the same exact problem, non tuned on my 66rfe. I suspect that it’s one of three issues.

1. A cross leak caused by the valve body or transfer plate being warped, causing cross-leakage.
2. The solenoid pack is going out, but hasn’t caused any codes yet.
3. Some electronic gremlin we don’t know about.

Mine usually shudders on the 3-2 downshift, sometimes bad enough that I feel like I’m going to pop a u-joint. But if I floor it, then it downshifts fine. It also holds 2nd and 3rd at full throttle without any slippage.

I have a new billet valve body transfer plate and thicker separator plate from rev-max. I also purchased all of the sonnax parts that can be put into the valve body without dropping the entire trans. I was going to have them installed in december but funds dried up unfortunately. When I do get them installed I will give an update.

[ScubaSteve]

I have the same exact problem, non tuned on my 66rfe. I suspect that it’s one of three issues.

1. A cross leak caused by the valve body or transfer plate being warped, causing cross-leakage.
2. The solenoid pack is going out, but hasn’t caused any codes yet.
3. Some electronic gremlin we don’t know about.

Mine usually shudders on the 3-2 downshift, sometimes bad enough that I feel like I’m going to pop a u-joint. But if I floor it, then it downshifts fine. It also holds 2nd and 3rd at full throttle without any slippage.

I have a new billet valve body transfer plate and thicker separator plate from rev-max. I also purchased all of the sonnax parts that can be put into the valve body without dropping the entire trans. I was going to have them installed in december but funds dried up unfortunately. When I do get them installed I will give an update.

Yes, please do. The cross leakage on the valve body is unfortunately my first guess, but other folks seem to believe it's a control issue with the tuning. The only thing that really makes me lean towards the control side of the coin rather than the valve body (or any other internal component), is the anecdotes of users on other forums that have gone through the gambit of torque converters, rebuilds, entirely new transmissions, etc, all maintaining the same problem.

I will say, if HF's tuning results in increased line pressure, then that would lend credence to the idea that cross leakage is the culprit, as I doubt his adjustments to shift points or anything of that nature would result in such erratic performance...and if that were the case, surely more people would be experiencing the exact same issues.

I have been considering going with a billet valve body from World Wide Specialty Parts, as that is the only one that has consistently pulled up when I hop on Google. I would prefer that this is not something that I have to live with, because even if it is "unsolvable", the shuddering/jerking action cannot be good on anything.

EDIT:

Something I would like to mention is that I am rather disappointed in the casting quality of the transmission casing. Granted, castings in general aren't the prettiest, but the amount of jagged and sharp areas, and peaks in various open areas of the trans just reek of low quality. Most of the GM transmissions I've worked with in the past were much cleaner parts, and if the cast channel plate in the valve body is of the same quality, its no question as to why the 66 and 68rfe's are so prone to cross leaks (though primarily for the O/D circuit and SSV).

Really makes me wish the G56 were available still.

[Bigdodge]

I work here where those parts are cast and the outward appearance of the case has nothing to do with the integrity of the case. This is the largest casting facility in the world and the people here know what they are doing and care a about a good quality product.

Now on to the original problem I have always experienced this as well and wonder if this could be the tq not unlocking and slipping, if that's even possible.

Sent from my IN2025 using Tapatalk

[ScubaSteve]

I work here where those parts are cast and the outward appearance of the case has nothing to do with the integrity of the case. This is the largest casting facility in the world and the people here know what they are doing and care a about a good quality product.

Now on to the original problem I have always experienced this as well and wonder if this could be the tq not unlocking and slipping, if that's even possible.

Sent from my IN2025 using Tapatalk

I have read of people having had their issues resolved with a new torque converter, and others have not. I've also read forum posts where the issue seemed to be resolved with the converter, and then came back a short time later...it's also hard to identify who is actually talking about this specific issue, and who isn't just dealing with the shudder/surge caused by EGR valves or bad solenoids. This does not feel like torque converter judder in my experience with other vehicles that have had such issues, but at this point and with how little hard info there is out there, anything is possible.

With the casting of the case, obviously I understand that the appearance does not dictate quality, but it is a difference I have noted from other brands. And you can't deny, casting is only one part of the equation; there are machining operations that are performed to the casting afterwards. Somewhere along the line, be it casting, machining, or just basic design flaw, something causes these valve bodies to warp and experience cross leaks, and burned clutches and such are fairly well documented issues.

[JackSprat]

Great info guy's thanks.
I have some very similar issues as described in here.
I just ordered the valve body from "World Wide Specialty", I bought the TOW valve body from them ($379/Free Shipping).
Now I need to order up a Shift Solenoid pack and get to work getting this thing healthy again.

16PW/66rfe/75,000mi

[ghaugo]

Let us know how the new valve body works out. I have been thinking of preemptively changing mine before it has any issues. I was looking into the same part from World Wide Specialty.

[ScubaSteve]

Figured I would post a little bit of an update here.

I have had a few trials and tribulations with Sonnax replacement valve bodies (CHR145 and 146, without and with solenoid pack respectively), but after the first defective unit, I was able to find another one earlier this year and get it installed a few months ago.

Overall, at first, there was seemingly a large improvement in overall driveability and shift firmness. Those improvements have since diminished to an extent, but not quite as bad as they were before the new valve body. I noticed that the shudder before downshifting from 3 to 2 has come back to a lesser extent, and then earlier this evening did it again before downshifting at WOT, from what gear to what, I'm not sure, but I believe it was a higher gear than 3-2. Either way, its the first time it has ever done that under WOT conditions and makes me wonder with the new VB if it is not a TC lockup clutch issue at this point, be it trans tuning or otherwise.

Not sure if anyone else has had any further developments since.

[iammattjones]

::Sigh:: I know this is an older post, but I have some pertinent info you all will appreciate.

Well I have the exact same issue. I even had some slippage in higher gears and it wanting to constantly upshift under load going up the mountain to my house. Well it eventually got bad enough that I had a rebuild. All new internals and TC and the issue is even worse with the higher line pressures. I think this is a TCM issue rather than a hardware issue. Literally everything in my transmission has been replaced and the issue still exists.

[jeep_boy02]

Geez, that sucks to hear. Are you planning on getting it flashed or changing it out?

[iammattjones]

Geez, that sucks to hear. Are you planning on getting it flashed or changing it out?

Well I asked Hemi Fever about their tunes and I got a "we dont do that" reply, which was incredibly frustrating. I paid 6500 for this build, I'm not swapping anything. The shop will make sure it operates properly, but finding the issue is the problem. With all the parts basically being new, I think that points to software. So I need to talk to someone that can do shift programs. Anyone have suggestions? The transmission shop I used aren't much help in that aspect. They build a hell of a transmission, but software tuning I dont think is a strength of theirs.

[jeep_boy02]

Tried to contact someone like monster transmissions?

[unitedwagon]

Late to this discussion, but I've had this same issue with my '14 since day one. Two different reflashes and a rebuild at 156,000 miles and it STILL does exactly the same thing. IIRC it's on a downshift from 3rd to 2nd under moderate throttle. Feels like its quick shifting back and fourth between two gears and only stops if throttle is increased or decreased. Years ago this happened at times on our old school busses with the old Allison 4 speed Whine O Matics. Felt like it was going to snap the bus in half! On my wagon the trans shop says he's 90 percent sure it's programming after looking at this several times... especially since so much has been changed in the trans. I now have a failing valve body (198,000 miles) that's being replaced with a rebuilt from NextGen Diesel. I'll let you know if anything changes. Just have to wait to get the truck back from some front suspension work.