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5hp24A preventative / planned maintenance advice

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5hp24A preventative / planned maintenance advice

Old 11-29-2018, 07:37 AM
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Location: Iowa
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I'm almost done with my transmission rebuild, so i can tell you what I've found. The previous owner just kept driving after the "A" drum lip cracked, most of his driving was highway miles between New Jersey and Kentucky so he just drove in limp mode for an indeterminate period of time. The cracked lip (similar to the picture above) was completely missing on my A drum, with only some largish (5mm sized) pieces found between the outside of the A drum and the B drum that it fits into. There were scratches and gouges in this area, showing where the pieces of broken-away A drum lip were ground up into smaller pieces. The middle parts of the transmission (C,D,E drum and planetary gears) were surprisingly clean and undamaged, the B and F drums on the ends had quite a bit of gray steel paste centrifuged on the inside. The transmission cooler had some glittery bits come out when it has flushed, but not much. The transmission pan itself had no magnets (!), so not much to see there, just a barely visible coating of gray paste.

It was only when I opened up the valve body that most of the debris was found. LOADS of glittery steel bits in every single passageway. Vacuum testing showed that the pressure regulator valve bore and lubrication valve bore right next to it were trashed (pressure regulator supposed to hold 16 inches but held zero, lubrication supposed to hold 18 inches but held 5, and only for a few seconds). I chose a rebuilt valve body that used three new housings from Sonnax.

I also found some interesting info on the Sonnax site regarding the "hunting" problem at highway speeds. They claim it is due to a combination of lock up clutch wear and pressure regulator valve wear.

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Old 11-29-2018, 01:36 PM
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Thanks samilcar
Very informative.

I think really as I already have the front lower valve block assembly it would be stupid of me not to fit it. I understand it's not a fix all solution as these box's seem to have multiple failure modes but as the one part that is easy to get to from a diy point of view it seems to make sense to just do it.

I just need now to decide wether to stick with the updated Zf presure valve or swap to a transgo valve. Any thoughts?

i really would love to swap out all the week links, A clutch basket, f drum piston, thrust roler bearings etc but this would need a full strip down which is not practical for me.

the valve body is a minimum but maybe will prolong the life of the box.

Thanks for your reply.

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Old 11-30-2018, 06:07 AM
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From what I've been told (or concluded from several conversations), the A drum is less likely to break if the pressure valve is changed out to keep it from sticking in its bore. Over time, the original bore gets a ridge worn into it, at some point the driver mashes the throttle, the oil pressure goes high, the valve gets hung up on the ridge and can't relieve the high pressure, and the end of the A drum gets broken out. I can't speak to the advantages of the valves available. I put in a substitute valve body with upgraded valve from Eriksson Industries when I rebuilt my trans about a year ago. I do have a thump on 2-1 downshift when coming to a stop, but I don't know why.
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Old 11-30-2018, 11:13 PM
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You raise a good point-- Even after rebuilt my S8 has never been shifting "like new"-- and as I've tracked down threads reporting similar issues it tends to point to clogging in the cooler, or else sensors that have fouled/failed internal to the box.

Given the propensity of the baskets to "throw shrapnel", I've wondered how hard it is to get "all" of it out. Gabor does a very, very thorough teardown on them-- completely cleaning the valve body, and everything else through the parts washer.
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Old 12-03-2018, 04:47 AM
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Originally Posted by hillpc View Post
I do have a thump on 2-1 downshift when coming to a stop, but I don't know why.
This went away on my cars when I installed the TransGo valve. I thought it was one of the indications My A8 trans was not long for this world, and a big disappointment when I felt it on the S8 I bought to replace the A8. I think it's the pressure sticking high a bit (?) as I think high pressure makes for harder shifts. I had some experience with this on a GM transaxle which would rail the pressure and shift hard after the TCU felt clutch slip. You'd get a CEL and hard shifts.

Post Transgo (in new VB housing) I sometimes feel that the S8 off-throttle downshift is harder than it needs to be but it's very subtle and not something most drivers would notice and probably no passenger would notice. When I had VB issues I think the passenger could have heard/felt the rough downshift bump.

When the pressure sticks low you can get a freewheel condition and then a BANG shift into gear, which will crack/break stuff. I think the low pressure prevents the clutch from grabbing, then you get the RPM flare, then the pressure jumps, clutch grabs, BANG.

Did you address VB wear when you rebuilt your trans?

Last edited by jfrahm; 12-03-2018 at 06:17 AM.
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Old Yesterday, 06:49 PM
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Originally Posted by jfrahm View Post
Did you address VB wear when you rebuilt your trans?
I'm editing this post a couple of hours after I first posted it to clarify valve body stuff.

I installed a rebuilt lower valve body with oversized pressure regulator valve from Eriksson Industries ($125) when I rebuilt the trans. I did not take the valve body apart to look at it after I received it, and I don't know the difference between oversized and Transgo. I also sent in my upper valve body to Eriksson for welding ($135) because of a crack, potentially (?) due to the same overpressure that broke the A drum. They also sell the complete upper valve body ready to go, but I was unclear about part numbers, so I took the upper valve body apart and sent in the casting for welding. I wouldn't know what to look for in terms of wear, except none of the valves were loose or rocking in their bores. I also replaced the plastic manual valve with a metal one from Eriksson ($15) because it was jamming, but only after being warmed up (in limp mode before rebuild). (I had broken the plastic ring at the shifter end of my shifter cable trying to get it into Park after a 5 mile drive.) Nat at Eriksson told me the plastic ones can swell and jam. Everything else but the 2-1 downshift thunk seems to work flawlessly. But I do have a slow drip from somewhere up front, so I top up the trans with fluid every few months. I've used about 2-3 quarts in almost a year. I'm not pulling the trans out again to fix the drip, at least not for now.

Last edited by hillpc; Yesterday at 08:47 PM. Reason: fixed erroneous statements
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