Gearbox Teardown & Refurbish - 6HP28A61

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After the loose items are cleaned move onto the spools valves

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And then individually clean all of those too

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We will come back to the vacuum test of the valve spools later

Time for some reassembly (I need some bench space!)

Now for the overhaul ZF in their infinite wisdom have decided NOT to provide an overhaul kit for the 6HP28A61. Hmmmmm. But all is not lost. You can get the overhaul kit for a 6HP26A61, and as long as you appreciate there are subtle differences and deal with them, I list them in the relevant posts, it is a much more economical route than buying all of the seals separately, even at the extortionate rate that overhaul kit costs (Over 300 spondoolies). Be very conscious though the A61 kits are the ones you need, that suffix is for the 4WD versions.

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Give the gearbox body a good clean, and install the 5 new plugs with integral seals from the overhaul kit (or was it 6?)


Install the new double seal from the overhaul kit


And ensure that vent hole to the middle of that double seal is clear and clean

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Give the side shaft protective cover a good clean


Fit 2 new O-Ring seals from the overhaul kit and smear the outer face with vaseline to aid install


Did I not mention the invaluable aid a White Board can provide; record any data as you go; oddities you visually note; components you need to order; Screws you haven't yet torqued up; and Then you can photograph it for posterity (or just before you clean it cos you've run out of space !!


I know I mentioned cleanliness, but here it is again, keep the bench clean

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Remove the old seals from clutch C/D and clean the clutch body



Note those 4 counterbored holes in the side of the clutch body; they interface with those 4 pressure port outputs in the valve body


Now inspect and measure all of the frictions and steels for the clutches and tabulate the results
When you are measuring the thickness of them take 4 point measurements 90 degrees apart and take an average
Clutch C here there are clear burn marks on the steels; if these are 20mm apart or more the book says they can be reused; these do not pass that test so new 3.0mm steels ordered; ZF Part 1068.377.020
As far as frictions expected thickness go; Clutches A and D and E are 1.59mm thick; Clutches B and C are 2.13mm thick (new)
These clutch C frictions are very worn, one measuring 2.02mm, almost smooth!! (suggestive its been sticking, or was installed too tight, we will come back to measuring stack clearances later)



Clutch C ready for reasssembly, awaiting new steels

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Mark that clutch stack so you dont forget which it was!


Now lets take a look at Clutch D; These frictions are hardly worn at all, so much so they could easily be re-used. However since I've already bought new frictions and come this far it would be remiss of me not to fit the new ones. These frictions will go on the used but good shelf.


These steels also reflect this clutch has not had any issues; no evidence of burn marks at all. Re use these.


Clutch D stack with new frictions ready for install, and mark that stack!

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Now clean the output shaft and the annular gear of the planetary gear set




And refit them together


Hang on, dont fit that circlip yet weve yet to replace the bushes!!


To get the bushes out i use a cape chisel, sometimes they come easily, sometimes like this one they do not



The bushing kit I used is the Sonnax part No. 95030-26K,which comes with a full set for the 6HP26/6HP28 boxes
This one goes flush with the bottom of the chamfer of the bore

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I wont win any awards for the sequencing here, seems to swap and change a little
Remove the old seals from the Clutch D piston and give it a good clean, ** Note which way round that profiled outer seal was fitted **


Fit the 2 new profiled seals to the Clutch C piston, note on the 6HP28 these seals are square lipped (an improvement over the 6HP26) so you will need to order these over and above the 6HP26A61 overhaul kit; ZF Part numbers; 501.322.212 and 501.322.213. Discard (or sell on) the round sealing O-Rings from the 6HP26A61 overhaul kit.
Lightly smear vaseline onto the outer working face of the seals and fit the piston to the clutch C/D body





Fit the new inner and outer O-Ring seal to the Clutch D piston from the overhaul kit.

[bam_bam]

Epic!

Thanks for taking the time to share it.

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Now clean up all of the parts for reassembling the planetary gear set I


One item we missed at tear down was the bearing washer sat at the bottom of the output planetary gear set, I had to blow this off its seat with the compressed air to get to clean it



Clean up planetary gear set I

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Now clean clutch A body


Now lets change those bushes; these are not scored, but the wear does not look particularly even across the faces



Cape chisel out with the old and these came easier



And in with the new

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Now lets change that seal on the oil pump, on checking the needle bearing looked good


Again there is some scoring on this bush, so out with the old


And in with the new


Give the housing and the pump body a thorough clean



And fit the new seal from the overhaul kit

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Give the gears a good clean


And lightly lubricate and refit, ONLY use recommended fluid (Shell M-1375.4) which ZF re-badge as Lifeguard 6
If you trawl the net for ZF document TE-ML11 this lists the various equivalent oils from other manufacturers they supply these gearboxes to


Fit the new O-ring seal to the pump body from the overhaul kit, and always lightly lubricate the needle bearings at reassembly, again ONLY with recommended oil


Dont bother with the ZF tooling for this, just cut yourself a couple of short lengths of M6 threaded bar to use as guides for refitting the pump body to the housing and stub shaft, insert the remaining screws, then remove the threaded bar and fit the remaining 2 screws. T27 Torx torqued to 15Nm, diagonally in stages. (Audi declare 10Nm, ZF declare 15Nm, go figure)

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Fit the 2 new O-Ring seals to the piston for Clutch A from the overhaul kit, (the rib on the outer O-ring is into the groove) lightly vaseline the outer working faces and fit the piston to the Clutch A body


Fit the spring


Fit the seal into the retaining plate from the overhaul kit (rib inserted into groove), lightly vaseline the outer seal face and fit the retaining plate



And with the new circlip a trip to the press is required