Vacuum diff switch - believe its broken- NOW FIXED

harry potter · Post by **harry potter** » Sun Apr 08, 2012 5:07 pm

yesterday l found that the diff lock does not work.
l have checked that l am getting a vacuum at the switch - the black pipe that runs to the back of the induction manifold and there is good vacuum.

with the engine running and the pipes attached, the plunger in (in off pos) l can hear a noise from the vacuum switch unit - there is no sucking/blowing from the red or clear pipe ends.

with the engine running and the black pipe attached, the plunger out (in on pos) there is a vacuum from the red pipe but not the clear pipe.

does anybody have any experience of these vacuum switches? does mine appear broken? just missed a new one on ebay - it went for £32
if there are other tests l can do, please advise,

disco2hse · Post by **disco2hse** » Sun Apr 08, 2012 8:58 pm

They do wear out and I found the rubber that creates the vacuum perishes. I replaced mine as the cheaper option of replacing with a new part (which was stupid money).

I know you could grab a second hand one from a Rangie, but I didn't want to have to replace a worn part with another.

This is what I did http://www.stage1v8.org.uk/phpBB2/viewt ... hlight=cdl

harry potter · Post by **harry potter** » Sun Apr 08, 2012 9:45 pm

l remember reading that thread years ago, couldnt find it on here.
going to try and free it off first.
as you state in your thread, it's a 30 year old part thats been stuck under the truck, and mine certainaly hadnt been used for the last 7 years.

thanks for the response.

map1275 · Post by **map1275** » Sun Apr 08, 2012 10:38 pm

Is there a reason you can't do a simple suck/blow test on the switch and lines yourself?

You will need a small handheld pump to test the actual valve and fork, plus the vehicle being in motion. Such pumps are readily available.

firemanshort · Post by **firemanshort** » Mon Apr 09, 2012 2:40 am

I had this problem with mine once. I pulled the knob and no vaccum. I fussed with it testing it 6 different ways. Finally, on one of my tests, it pulled and extra 1/2 inch or so. It seems it was just dirty from lack of use and not pulling all the way out.

They do break and wear out, though.

Spray some cleaner / WD 40 or other potion around it and push it in and out a dozen or so times to really make sure that it is all the way out. Then start looking into a replacement.

harry potter · Post by **harry potter** » Tue Apr 17, 2012 9:04 pm

evening all,
l have discovered why the diff lock is not working - a rust hole in the actuator unit itself.
l now have 3 vacume switches to try. one even has a light in the end of it!

reading through the manual (Rover V8 supplement) it instructs to remove unit without draining the transfer box oil -
if l remove the actuator will this not require the box to be drained of oil?
the misses will kill me if l removed the unit and flood the driveway with gear oil.

l had to remove the drivers floor pannel to get to the top of the diff unit.

thanks

map1275 · Post by **map1275** » Tue Apr 17, 2012 10:08 pm

Oil is cheap so I would drain it. If only to see what's like.

I would also refit the old part and degrease and pressure clean the entire accessible area before you go ANY further.

Mrs Bingham · Post by **Mrs Bingham** » Wed Apr 18, 2012 9:39 am

Hmm, been there

You can remove the whole actuator housing in situ from above. Arguably one bolt is awkward due to the gearbox mount. Only a very small amount of oil will escape when you break the gasket seal so no need to drain off unless you need to. Don’t forget the felt seal between the actuator and housing otherwise the diff lock will engage ok but it won’t disengage – guess how I found that out

Note* When reassembling I had to engage the diff lock to be able to achieve sufficient space to get the housing back in.

Good luck…

harry potter · Post by **harry potter** » Wed Apr 18, 2012 9:52 am

Cheers guys.
I plan to give the whole area a good clean and de-grease before removing.
The oil was changed in the gear and transfer box only 120miles ago (1month) so if l can get away without doing it l will.
Thanks for the tip on re-fitting and gaskets.

harry potter · Post by **harry potter** » Wed Apr 18, 2012 12:08 pm

l found this interesting thread on the DiffLock forum.
gives some interesting reading on this very topic.
l hope l havnt broken the spider gears.
http://forum.difflock.com/viewtopic.php?t=57492

harry potter · Post by **harry potter** » Mon May 07, 2012 11:33 am

why my diff lock didnt work - big rust hole didnt help.

a lot of sand and dried mud fell out. l have pulled the switch apart and that is full of sand too which has been drawn up.

pic to show the inside of the housing. home made gaskets.
replacement is very simple. l removed the drivers floor plate for access above.
drain transerbox oil oil to have a look at quality -
remove all bolts
lightly tap casing to remove the housing catch the spring and ball
clean up.
to remove the actuator - remove the switch - l didnt and have damaged it so require a replacement now

drive the roll pin out - send it down the switch hole - long slender punch does the job.
to get the selector fork in position, move the slider on the shaft forward and wiggle the unit back into place-
should take no more than 1 hour to replace - (includes cleaning and making new gaskets ect)
all my replacement switches do not work - the rubber slider in the switch does not form a good seal due to corrorsion inside.
the picture in the previous posts of the switch - the previous owner had put the pipes on incorrectly. l believe the black pipe which draws the vacuum from the engine should be in the middle pipe.
the red pipe which runs to the front of the actuator which engages the diff lock should be on the top pipe and the yellow pipe should be on the bottom pipe (correct) this runs to the other pipe on the actuator pulling the diff lock off.
l am able to engage the diff lock but have to swap the pipes round on the switch to pull it off agian. to clean the switch l need to remove the small roll pin that holds the black plunger onto the metal shaft which then allows the simple rubber plate to be cleaned. l will upload some internal pic of the switch for anybodys interest incase they havent opended theirs.
if anybody has any comments on the correct instalation of pipes please say, l havent found a diagram that shows the orientation of the pipes.

Mrs Bingham · Post by **Mrs Bingham** » Tue May 08, 2012 10:35 am

Looks good, but I will comment on the green gasket you’ve made. Originally it would have had a felt washer over the actuator shaft sandwiched between the housing and actuator. A gasket isn’t suitable and I am worried because the actuator flange is prone to bending thus not allowing a vacuum seal between the two units. A leak here will prevent the diff lock from disengaging!!! I think I can see the rubber o-ring in the housing but that just stops the oil from being drawn out. Also be mindful on whether you have the correct bolts for the actuator unit. Mine were countersunk so if you use regular bolts you risk splitting the housing flange if over tightened

There isn’t an exact science on the pipe fitment but obviously easy to work out. Common sense would suggest the red one is for diff lock on (front of actuator) and yellow for diff lock off (rear of actuator) but this counts for nothing if the plunger orientation is wrong. From memory I can’t remember which way is which, but a simple suck test should sort that out but you would think the middle one is the feed from the engine. I can confirm this tomorrow if necessary.

FYI
Felt Washer 591345 but easily home made.

harry potter · Post by **harry potter** » Fri May 11, 2012 9:54 pm

thank you for the felt washer part number. there was not a washer fitted when l removed the unit, there was just the gasket which is why made another one.
lesson learned - do not go on what the previous owner has done! also there was only one counter sunk bolt, not the two!

l am assuming (hate thay word - never assume - always prove) that there is a good seal between the actuator and the housing as the diff lock does disengage when the pipe work is swapped on the switch unit.
then diff lock engages and ungages when the pipe work swaps on the switch.

my next stage is to strip out some switches - clean up and re-build.
await some progress photos!
ps- theres some local RTV trials comp very close to home that l want to get the truck ready for next sunday. pressures on.
thanks

harry potter · Post by **harry potter** » Sun May 13, 2012 4:25 pm

I HAVE A WORKING DIFF LOCK SWITCH and selectable 4x4 now!!!

stripped out the old switch - cleaned up the plate and rubber, and re-assemebled.
l now have 4 working diff lock control valves!
just need to install the new electric switch.

disco2hse · Post by **disco2hse** » Sun May 13, 2012 7:59 pm

Great. I gave up on my switch, the rubber worn down to half its original thickness.

I think the next time I have to go through a similar exercise, I will dispense with the vacuum switch altogether and go manual.