1954 B31 Plunger - suspension bottoming out

[Fraz]

Hi.
Need some advice please.
My B31 plunger keeps bottoming the rear suspension on relatively small bumps when I'm two-up.

Is this "normal" behaviour?
Is there a way to stiffen up the suspension?
Are the plunger units relatively easy to strip and re-build (and if so, how?)

Incidentally, the front forks are really soft too - can they be serviced to make them stiffer?

Thanks

[idie]

Springs in the plunger units may be worn. Try thicker oil in the forks this will make them stiffer.

[Kernowpete2]

I was interested in stripping the plungers on mine just for checking and cleaning. Decided against it as reassembly looks very tricky unless you have special tools. Springs need compressing to get them back in the frame. I opted for pumping grease in on each ride until I see some new stuff ooze out. I read somewhere that filling them with grease gives a damping effect but I've no idea who said that or how credible it is. Seems to make sense though. I like the soft forks on my B31. There are a few off-road routes around here that it rides beautifully on (very mild green lane riding really)

[DAVE BRADY]

Hi,

The only cure for the rear springs being too soft is to replace them.  I think I got some from C&D Autos. They had the covers as well.
It is essential to always ensure plenty of grease as the bushes can get quite worn resulting sloppy handling (even more so).  Perhaps consider doing the bushes at the same time as the springs.

Dave.

[Kernowpete2]

Dave, that's good info. How did you get on with reassembly? Did you need special tools etc?

[V500]

I didn't use any special tools other than a sturdy block under the rear frame stays, and a good strong downward push to get the assemblies back into place before the central pillar was tapped through.
Norton plungers are the ones to avoid; those springs really are under compression.

[DAVE BRADY]

Hi,

It was a while ago that I did fit it but I think I used a length of threaded bar to compress the assembly enough to fit it in - the covers will be the limiting factor.  The threaded bar must be no longer than is absolutely necessary and should be tightened so that most of it is out of one end.  The longer end is put in to the bottom part of the frame and the assembly eased in to the top.  Once in place the threaded bar can be removed with everything else staying in place.  The centre tube can now be carefully inserted and the clamping bolts tightened up.  Use plenty of grease on the bush and pump grease in to the finished assembly until it oozes out.  The main reason plunger suspension fails is a lack of grease.  It may look a bit messy but it will keep the bush in good order for a lot longer.
Don't forget to put the wheel spindle bit the right way up in the middle.
I hope this is clear enough for you to give it a go.

Dave.

[Kernowpete2]

That's great - thanks Dave 👍