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reverse gear interlock valve seized, PRIMARY REGULATOR IS STUCK


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So I have a ZF auto SWB, 119K, 1993 RRC that has a problem going into reverse. Can someone with experience in ZF auto gearboxes help debug this one:

1. transmission slips and doesn't engage when gear selector is shifted to "R" reverse.

2. all forward gears are working fine, now that I've changed the filter and flushed the fluid about 4 times with fresh. There is about 3 oz of SEA FOAM tranny additive and 24 OZ of lucas just added on the last refill.

3. when the pan was off the pan had more than a sanding of non-metallic parts.

4. the fliud had not been changed for 4 years+. Synthetic mobil1 was used at that time. The problem started 1 week ago. before any service attempts the tranny would drive 1-2-3-4 and at the next light blow the shift into 2nd, free-rev engine/slipping. shut it off, tranny would engage forward or reverse. Then it went 1-2-3-4, downshifts at light, blow the shift into 2nd gear. shutdown. same thing again and again.

From what I read in manuals: Does anyone know what Rover means by "reverse gear interlock valve siezed"? The only other reference to it in the rover manual is the "gear selector interlock" and it's electronic -- no "valve" (that implies fluid, not electronics). I've attached the gear interlock portion. There is an inhibitor switch -- is that related?





Another forum member found: FAULT SYMTOMS that the PRIMARY REGULATOR IS STUCK as the cause of NO DRIVE IN REVERSE GEAR.

what do you think of this tranny pan? gritty junk in there -- I'm guessing clutch parts? Yikes.

I found out you don't have to completely remove the Y-pipe and crossmember to change the filter.... diconnect O2 sensors, 6 nuts on front of Y-pipe, all bolts from crossmember and lower it 3/4 the way. Probably too late for my own good. makes a mess...



Anyhow, ideas on how to fix the the mysterious "sticking regulator/valve"? If I drop the manual valve body can the regulator valve be serviced?

The tranny was slipping in forward and reverse before adding the seafoam (thinner). Sea Foam made forward gears clean up. Reverse instantly failed to engage. I drove about 10 miles, including about 25 stops and through the gears, pulled the pan/filter and refilled with fresh Dex3 + lucas additive. forward gears are fine now. no reverse. no clunk, nothing other than the noise of the selector changing position. I've ran it about 15 miles forward and about 30 attempts into reverse.

Any stories of the "stuck primary" unsticking itself? I keep hoping it will break free.



Edited by geoffbeaumont
Fixed image links (hint: use [img] not [image])
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That is a LOT of junk in your sump. You didn't say what state the first draining of fluid was like. It should be bright red not dirty brown. If you still have it take a sniff. Does it smell burnt / acrid?

Autoboxes generate a lot of heat and hence the need for good cooling. It takes very little time for the clutch plates to destroy themselves (seconds not minutes) once things start going wrong. Plus, once you get bits, the oilways are tiny and block easily.

Although not an expert, with that amount of 'deposit', I would suggest that you are probably looking at a rebuild.

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