Advice and guidance on repair and restoration techniques.
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coppinpr
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Joined: Sun Oct 10, 2010 2:01 pm
Location: Lewes, East Sussex
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Jennings Arm Damper Service

Postby coppinpr » Wed Jan 25, 2017 3:48 pm

Having started on a Jennings Chinese front today I found the Arm damper had been disconnected because it was not working. As I have never done one of these before I thought I'd photo and write up the work for anyone who needs help with it.

In common with the Mills, the damper unit and linkage are not easy to get at and remove. On the Chinese front at least the main base plate needs to come out just to release the bracket holding the linkage arms to the outside case. Once the arms are loose the damper can be removed by removing the four screws holding it to the base.

As you would expect from Jennings the build quality is good and I didn't expect (or find) any actual damage, just our old friend "oxidised grease".
Remove one of the large screws on the top of the unit and one end of the cylinder and the plunger can be pulled out easily.

At first I thought the plunger was just one piece. It was so covered in old grease I couldn't see the six individual parts that make it up!
damp 1.jpg
Once I'd removed the large lumps of grease I was able to unscrew the front nut and remove the star washer, front plate, gasket (this seems to be made of an early soft plastic and had lasted well), the spring flange, and the large washer, in that order.
Although all the parts were reusable it was prudent to clean the gasket and spring flange with care. The gasket has seen many years and the flange is quite delicate.
damp2.jpg
I cleaned out the cylinder making sure the air holes were clear on both ends (there is no adjustment screw on the Jennings, as there is on the Mills), then lightly sprayed the inside with lithium grease.
Once all the parts are cleaned (I used the excellent WD40 specialist de-greaser spay, this really is good and I always use it on this type of job, cheapest at Screwfix just now), insert the plunger through the rear end of the cylinder and re attach the plunger head parts. Slightly push out the spring flange to make sure it causes a snug fit for the gasket. Replace the rear end of the cylinder and attach the large screw, check the plunger moves freely and air escapes from both the air holes when the plunger is moved.
damp4.jpg
damp5.jpg
damp6a.jpg
Pay special attention to the linkage arms when cleaning. These are more complex than the Mills and have several joints and all were clogged with rock hard grease stopping free movement.
damp7.jpg
damp8.jpg
Replace the unit and then the linkage bracket and it's done, Not rocket science, but I thought it worth adding to the tips and tricks section.
damp3.jpg

youngerap
Posts: 314
Joined: Sat Sep 08, 2012 11:10 pm

Re: Jennings Arm Damper Service

Postby youngerap » Thu Jan 26, 2017 8:02 pm

Nicely done, Paul. !THUMBS!

I surprised myself by being surprised at how simple (and effective) this mechanism is. I guess I have gotten too used to looking at a PCB and immediately avoiding any further thought on the matter.


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