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MG MGB Technical - Shock fluid recommendation

All:

Wondering what type of oil should be used when topping off the rear lever shocks on an MGB?

Thanks,

Shawn
Shawn Herndon

Motorcycle fork oil works well and comes in different weights. I think I am using a 10W. Cheers - Dave
David DuBois

Shawn-
Be aware that petroleum-based fluids are not compatible with the natural rubber seals. Armstrong, the manufacturer of your lever-arm dampers, still makes its specially formulated fluid available. It can be obtained through Brit Tek at http://www.brittek.com/ . If necessary, 20W mineral oil may be substituted for this fluid during warm weather.
Steve S.

We just had an excellent class on this at our club house by Peter Caldwell owner of World Wide Auto Parts in Madison WI. One of the best rebuild shops for lever shocks in the US.

Peter recommended 20 wt. Also he was very explicit that one of the largest causes of problems with lever shocks is overfilling them. The top dome on the MGB shock is an expansion chamber. If you fill the shock all the way to the top, you leave no space for expansion when the fluid gets hot. This will cause excessive pressure and cause leaks.

Given the only oil needed for the B lever shocks to function properly is oil up to the bottom of the pistons, you can have the fluid down about 1/3 of the shock and still have a totally functioning shock.

Peters advice. If you rock the car and the shock is working do not fill it. If it is leaking, have it rebuilt.


BTW. World Wide;s prices are good, and service and quality are second to none. They can replace your B shock with one's off the shelf or rebuild yours if you want (that takes a little longer).

I have no financial interest, but have used Peter;s shop for my MGB and my MGTD and the shocks are great.
BEC Cunha

20W motorcycle fork oil is fine. I prefer to use fluid designed for these shocks, as sold by the big suppliers including Moss Motors.

I have to disagree about using mineral oil. It lacks anti-foaming agents necessary to prevent agitation and air pockets within the shock. The same goes for hydraulic jack oil.
Steve Simmons

Steve-
The factory said that 20W mineral oil could be subtituted in warm weather. However, not all mineral oils are the same. During WWII the germans made a lot of advances in this area, so Mineral oils are much more common in europe than on our side of the pond. Mineral oil with an anti-foaming agent was (and may still be) used in the power steering system of Audis. I suspect that the factory intended for mineral oil with an anti-foaming agent to be what they suggested, and just presumed that the customer would be knowledgable enough to use the right stuff in a pinch (b-i-g presumption!)
Steve S.

It might be of interest to do an archive search on this subject. Peter C., whom I respect a great deal, has had some very interesting comments in this area over the years. One of which is related to "what is 'mineral oil'" which may be of interest.

As to the quality of his rebuilds, I have some limited experience. I installed a set of his rebuilt shocks on my 68 GT some years ago. I was, then, using the GT as a daily driver/casual racing car. I have friends who are professional MG mechanics. The use Peter's rebuilt shocks whenever they need new ones. Their experience is greater than mine. I do know that, when I need to replace shocks, I will replace them, in pairs, with Peter's. We have, as a group, not been able to find any that held up as well, nor that worked any better.

Les
Les Bengtson

I also can give a vote of confidence to Peter's skill and the quality of his rebuilt lever arm dampers. Better than new, in my opinion.
Steve S.

I use Peter's shocks whenever possible.

As for mineral oil, I've never seen one with anti-foaming agents sold in a place you would typically buy mineral oil. There may be some specialty mineral oil out there which would do the job, but unless (as a consumer / home mechanic) I was told so then I would use the stuff sold pretty much everywhere, which isn't the right fluid for a shock. I feel it's easiest to just order the Armstrong shock fluid or drive over to your local motorcycle store.
Steve Simmons

Out here Mobil make a 20W fork oil, the only oil company that appears to still make this product available in Oz, from my search experience late last year. Only available from the local distribution depot however, servos not carrying it. They told me at the time it might not be available forever! Might be worth trying any local Mobil distributor?

Bike shops were not able to help me, explaining that 20W was 'old technology' for bikes these days, modern bikes typically taking 5-10W. I was told that Harley shops might be able to help but warned about likely price shock if I went that way.

In the end I bought several Mobil 1 litre containers - figured others in our local club might benefit as well.

Regards
Roger
Roger T

I also support Peter C's rebuilds. Best I've seen / used and I can certainly believe that they're better than new ones.

Peter C himself has stated 20W fork oil to be a readily available and acceptable replacement for the original stuff. I got my bottle from the local Harley Davidson shop for a few bucks, and to be honest I haven't had to use any since I put Peter's rebuilds on the car!!
Curtis Walker

For those that do MG racing. Peter's shop now makes a kit that they can transform your shock into a variable adjustable shock. It is a very slick modification.

In the couple of hours Peter put on his show and tell for our club, I learned more about lever shocks than I ever knew. Good Shop, Good tech class and great person.
BEC Cunha

This thread was discussed between 07/10/2007 and 10/10/2007

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