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MG MGB Technical - 'Topping up' leaver arm shocks

I have a rubber bumper B GT that sat in a garage for 12 years before being sorted by a garage, MOTed and then bought by me to finish the restoration. Its all done except dealing with sloppy shocks. I have been told that before I go down the road of exchanging the shocks I should try topping them up. I have ordered the SAE 20 but wondered if anyone has ever done this and just what difference it made to the ride. Its obviously a fix as the manual does talk about it and they sell the oil to allow it to happen. The shocks that are on are not leaking, just give a spongy ride.
Any information is greatly received.
Doug E


I have done this in the past but have used motorcycle fork oil. It comes in various grades and is perfect for this application. I was told once that if it was formulated for motorcycle forks then it would certainly work in lever arm shocks and so far I have no complaints.



the manuals recommanded a top up, or even a check, every 3000 Mls.
If the car was not on the road for so many years, i would check the oil level in the dampers and top it up to 1/2" below the top of the threads of the refill screws. Do not overfill!

There are different grades of oil available. You can use the 20 grade oil but you might risk a leakage at the seals. Good resulds have been achived with motorcycle forg oil or special damper oil. Both types do not penetrate through the seals of the dampers but some comparable wight motoroils do!

If the car was not used for such a long time, sometimes it is usefull to take the dampers off the car and put them in a vice. Take car to the body! Just use solid areas as the botteom flange of the front shocks or the mountig holes for the bolts of the rear shocks. The refill opening must allways face upwards during this procedure. Then refill, pump and refill again until they are toped up as stated. Take care when refitting the front dampers, if done so. They aught to be torqued to 5.5 KpM as far as my memory serves me well.



Peter Caldwell of World Wide Auto Parts runs one of the premere shock rebuilding shops in the U.S. I had the opportunity to listed to a lecture Peter did on the MGB shocks. His advice. If the shock oil is decreased, the shock is leaking. If it is leaking, it will continue to leak until rebuilt. Of course, you can periodically check them and refill when needed, but that also requires a bit of work each time you want to check them.

The other thing Peter showed us is that the MGB shock has to have some space at the top to allow for expansion. If you top it off right up to the top, you actually reduce the life by creating increased pressure in the shock that will lead to leaking.

The Workshop Manual specifically warns against using 20W in low temperatures, but should be OK for UK summer use, or winter above freezing. It's not so much a problem with the seals as damaging the valves as they will be under too high a pressure with too high a viscosity. You say 'spongy', do you mean bouncy? That could be because there is no fluid in them, which will almost certainly be because they are leaking. If you haven't topped them up yet you won't know whether they are leaking or not. OTOH the valves could be faulty, and topping-up won't make any difference. Top-up by all means, then you will know one way or the other. When you push down hard on a corner of the body you should only get 1 1/2 rebounds. If you have side-fill dampers you fill to the bottom of the threads regardless, as unless the car is on its side that leaves a huge air space above the fluid level. Even top-fill the manual says to fill to the bottom of the threads, which hasn't caused me a problem, I believe there is an air-space inside anyway. It's the expansion of the fluid as it gets hot and overfilled that is supposed to force fluid past the seals. I've also never had a problem with light hydraulic jack oil, even though people say it will foam and lose damping in use.
Paul Hunt

Thank you all for the advice so far. I received my 500ml Pentrite shocker oil number 1 today and will hopefully have some time early next week, or even tomorrow afternoon, to top the shockers up. I did consider motor bike fork oil but could not get a 20 grade and was kind off put off by the auto factors I use as it is synthetic oil and not mineral. They did not advise mixing them. I might of used it if I was going to empty the shocks and start again but feel top up to begin with hopefully will be enough. If they then appear to be leaking it will be exchange units. I have fitted these to the front of my chrome bumper B recently as the ones that were on were leaking after just 36 years of use, I wonder if I should ask for my money back under the guarantee?
Paul, you mention the problem of 20W operating under low temperatures, not too worry there, I live in Devon and we know the sun always shines there, I wish.
Well gentlemen I will top up and let you know the results soon. Thank you all.
Doug E

I just top mine up with ATF, miles cheaper than anything else. I use it in motorbike forks as well.
Martin Layton

Hi everyone who has an interst in this subject
I topped my shockers up with the Pentoil Shocker oil number 1 last Friday afternoon with the desired effect, no bouncing around like a, no I can't say that. It was nicely firmed up on all four corners. I let it settle over the weekend and checked the levels yesterday with just a ml or so added and taken away here and there. Result is I don't need to take them off and replace them with recon units, not yet anyway. The old manual I have (I have several) actually does recommend a six monthly top up as Ralph also points out. Where does it go I wonder!
Anyway thanks to everyone for your advice.
Doug E

This thread was discussed between 24/09/2008 and 02/10/2008

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