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George Constantine
Experienced User
Username: theo

Post Number: 19
Registered: 6-2012
Posted on Saturday, 07 November, 2015 - 08:35 am:   Edit PostDelete PostView Post/Check IP

The power hood on a 1979 Corniche Convertible slams down shut when it's been put up and near the closing stage.I have to put my hand up to stop it slamming down hard on top of the windscreen frame and damaging the chrome fastening clamps.

I would be grateful for any advice.

Many thanks

George
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 672
Registered: 5-2015
Posted on Saturday, 07 November, 2015 - 09:17 am:   Edit PostDelete PostView Post/Check IP

Air in the system.

The rams are double acting. When the hood is going down the oil from the going up side of the ram has to return to the reservoir. This damps the coming down bit. As the weight comes on any air suddenly gets compressed and the top drops.

Symptoms of air in hydraulic systems is jerky rams. The air compresses the ram jerks the air uncompresses then builds again the ram jerks and so on. The pump can't keep up with sudden volume demands.

I would remove the reservoir and clean it out and fit new oil paying attention to suction filters to the pump. Usually mesh so wash and blow out. Cavation causes air in the system. To bleed work hood up and down a few times a bit like bleeding power assisted steering full lock to full lock.

Place cushion on top rail to save slamming while bleeding. Operate 2 times then allow motor to rest for 5 mins then operate again.

Oil any pivots you can find.

To remove reservoir the workshop manual has details in the Shadow 1 manual for the MPW DHC which is a chrome bumper Rag top Corniche. It looks easy and obvious. I think its the only way to change the oil remove and tip upside down.

The original oil appears to be unavailable. If the oil is mineral then suggest LHM. But please check carefully. In case the oil is not mineral but a PAG type oil, unlikely. If RR agent suggests Auto box oil then use LHM. There are hundreds of hydraulic oils so no problem.

This fault us not unknown and the last one I heard about was low oil level and air.

One fault I saw on a Mustang rag top was the linkage pivots wrre so badly worn that the hood used to slam down one side and jam. New over size clevis pins and a reamer sorted it out. But thats a Ford.

These cars give a new dimension to the Shadow and are lovely. Wish I had one. Then again I want a 1950s Wraith and a Dawn as well. I am like a kid in a sweet shop. Jay Leno is like me.

Give it go and lets us lot know how you got on. Nice cheap job just time and a spot of oil. Also a good clean up inside the box that contains the pump and reservoir. Change oil every 50k miles.
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George Constantine
Experienced User
Username: theo

Post Number: 20
Registered: 6-2012
Posted on Saturday, 07 November, 2015 - 11:42 am:   Edit PostDelete PostView Post/Check IP

Hi Robert,

Thanks very much for the advice. If I remember, I still have some oil left over from when I topped it up about 8 years ago, I think it should still be good to use.

Someone also suggested the hood cables may need attention but I'll clean the reservoir etc out and see how that goes.

Regards

George
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David Gore
Moderator
Username: david_gore

Post Number: 1778
Registered: 4-2003
Posted on Saturday, 07 November, 2015 - 02:14 pm:   Edit PostDelete PostView Post/Check IP

I knew the fluid specifications for the Corniche hood hydraulics for vehicles produced during the Shadow era were in my archives but where?

In Section D of TSD2476 of course and here they are:

Lorco 6659, Gargoyle Artic Oil Light. Shell Clavus 27 or Castrol Icematic 66

The Shell Clavus and Castrol Icematic ranges were used as lubricants in refrigeration compressors and as general purpose lubrication in low temperature environments.

Quote:

Specifications and Approvals

Shell Clavus meets the requirements of DIN 51503 KAA, KC and KE

Applications

Shell Clavus Oils are high quality, hydrotreated naphthenic mineral oils without additives. Specific selection of the base oil gives a range of products specially suited for the efficient lubrication of refrigerator compressors.

Refrigerator compressors

Shell Clavus is designed for the lubrication of compressors with ammonia (R717) as refrigerant. It can also be used when hydrocarbon (e.g. R600a) are the refrigerant. It may be used with halogenated hydrocarbon (R12,R22) if Shell Clavus G is not available.

For all refrigeration and air-conditioning applications: domestic, commercial and industrial systems with high, moderate or low evaporation temperatures.

General lubrication

Apart from the application in refrigerators Shell Clavus can also be used for general lubrication at low temperatures.


I would expect Dexron Automatic Transmission Fluid or Power Steering Fluid from a reputable manufacturer would be a suitable alternative
however owners of Corniche dropheads in extremely cold climates may find the refrigerant lubricant oils are a better alternative due to their inherent resistance to gelling [of course someone will comment why would you drive with the top down in sub-zero temperatures; I plead guilty having done this in Canberra on a cold winter's morning to see what it was like - not very comfortable was the conclusion .
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 1726
Registered: 6-2009
Posted on Saturday, 07 November, 2015 - 03:41 pm:   Edit PostDelete PostView Post/Check IP

I have a section entitled Corniche Top Hydraulic Oil Options in the RR & Bentley Parts, Repair, Restoration & Other Resources Compilation.

Brian
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gordon le feuvre
Frequent User
Username: triumph

Post Number: 92
Registered: 7-2012
Posted on Saturday, 07 November, 2015 - 08:40 pm:   Edit PostDelete PostView Post/Check IP

Have a 1986 Corniche with only 9000 miles on and it does exactly same, slamming onto header rail. Have changed oil, checked level and operation of all electrical parts. This car did not do this when new (I was After sales manager of local dealer) in fact it was the opposite, it was really hard to close. Have researched as much as possible. Manual is useless. There seem to be lots of cars around world with this problem. I am leaning towards the fact that the hood material was tight when car newish and this acted as damper, assisted by the rams being of the differential type that should have internal damping? The motor was made by a company called Smith's Industries (not sure about rams). They have gone out of business and their business taken over by company called Fluidlink in the southwest of UK. Have spoken/emailed them, but they cannot find any info. Have also found another company in Cheshire UK called Hydraulics on line. Will e-mail them with problem and model no. off car pump. Maybe they can shed some light on whether rams have in built damping?
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 673
Registered: 5-2015
Posted on Sunday, 08 November, 2015 - 03:22 am:   Edit PostDelete PostView Post/Check IP

Smith Industries was owned by Lucas CAV at the time these cars were made. They made heaters and car instruments and wiper equipment such as the racks and wheel boxes. Brown Brothers (Dana) was their main distributor.

So ask Lucas.

The theory about the roof material damping the closing sounds good. Trouble is these hoods are very expensive to replace. Can the wires be tensioned a bit.

I wonder if a restrictor could be fitted to going down side of the ram. So when the fluid is moving from the ram it damps the going down bit. This will slow the going down bit which may be unacceptably slow.
By down I mean hood open.

Maybe something adjustable. A needle in an orifice sort of thing.

Or a sprung loaded whatever inside the catches to catch the hood.

Note. The motor is a bit like a starter motor in that the duty cycle is short. So do not operate hood excessively in a short period else the motor could overheat.
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David Gore
Moderator
Username: david_gore

Post Number: 1779
Registered: 4-2003
Posted on Sunday, 08 November, 2015 - 07:38 am:   Edit PostDelete PostView Post/Check IP

The following links may be of general interest covering most of the Corniche variants from RRMC and the Bentley convertibles after the VW acquisition.

It may be relevant to keep in mind the RRMC practice of trying new modifications on the Corniche before introducing them to the entire vehicle range so it is possible some or all Corniches from around 1978 on may have been "test mules" for the hood system used on later models. it is highly probable a 1979 Corniche would have the mechanism for the Silver Spirit derivatives.

One area I would closely examine is the hood tensioning cables; if these are not properly adjusted and have too much slack - it is possible this could be a contributing factor to the slamming shut problem. Conversely, too much tension can cause problems especially with the later models as detailed in one of the links.

However, this is one area where the advice of convertible specialists should be sought before attempting any repairs to avoid a DIY expensive learning curve.

https://www.convertibletopguys.com/convertible/1873/1966-86-Rolls-Royce-Silver-Shadow-Corniche

http://www.tophydraulicsinc.com/en/33-rolls-royce

http://robisonservice.blogspot.com.au/2014/11/convertible-top-repair-in-bentley-azure.html
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George Constantine
Experienced User
Username: theo

Post Number: 22
Registered: 6-2012
Posted on Tuesday, 10 November, 2015 - 07:55 am:   Edit PostDelete PostView Post/Check IP

Thank you all for your suggestions.
I removed the reservoir, cleaned it all out and refitted it with fresh fluid. Unfortunately no change. The next job will be to examine the hood tensioning cables, I presume the roof lining would have to be moved to gain access?
If this doesn't work It will have to be the rams which I cannot seem to obtain a service kit for them in the UK.

Thank you all again

George
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Brian Vogel
Grand Master
Username: guyslp

Post Number: 1729
Registered: 6-2009
Posted on Tuesday, 10 November, 2015 - 09:04 am:   Edit PostDelete PostView Post/Check IP

George,

If it comes down to the rams and you can't find either a service kit or any rebuilders in the UK, definitely check out the previously mentioned resources file. I have a section on those who rebuild convertible top hydraulic rams, too. All of those included came directly based upon recommendations from those who had used their services.

Brian
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 679
Registered: 5-2015
Posted on Wednesday, 11 November, 2015 - 06:46 am:   Edit PostDelete PostView Post/Check IP

I would think that the cables are adjustable without stripping down to much because otherwise the hood would be a servicing nightmare for the main agents.

So have a good look a the mechanism.

Rams are simple things that if the don't leak and move then they are fine and rebuilding does nothing.

By changing the oil etc the hydraulics are now serviced.
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George Constantine
Experienced User
Username: theo

Post Number: 23
Registered: 6-2012
Posted on Friday, 13 November, 2015 - 07:57 am:   Edit PostDelete PostView Post/Check IP

Thank you all for your help.

The hood works a lot smoother now I've serviced the hydraulics but not perfect. I've located the hood tensioning cables but they are very tight and I'm not going to disturb them just in case.

George
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gordon le feuvre
Frequent User
Username: triumph

Post Number: 93
Registered: 7-2012
Posted on Saturday, 14 November, 2015 - 05:30 am:   Edit PostDelete PostView Post/Check IP

George can you enlighten me where the cables are please
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George Constantine
Experienced User
Username: theo

Post Number: 24
Registered: 6-2012
Posted on Saturday, 14 November, 2015 - 09:31 am:   Edit PostDelete PostView Post/Check IP

Hi Gordon

The hood tension cables are woven into the edge of the everflex all along the side of the hood. The cables are visible at the front of the hood if you carefully lift the everflex upwards slightly. They are about 1/16 of an inch thick, similar to a bicycle inner brake cable.
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Robert Noel Reddington
Grand Master
Username: bob_uk

Post Number: 692
Registered: 5-2015
Posted on Saturday, 14 November, 2015 - 10:52 am:   Edit PostDelete PostView Post/Check IP

Maybe we are looking at the cables back to front in that maybe the cables are actually too tight and they are going over centre causing the roof to try to snap shut.

It's surprising how a hydraulic fluid change makes hydraulics work better. I have worked on lots of hydraulic things and 2 things I always do check the pump intake filters and change the oil. Often that fixes the problem with just the leaks left.

The intake filters often catch engineers out. Seen loads of pumps stripped down looking for a fault when it was the intake filter part blocked.

The only thing that sends the oil to the pump is Atmospheric pressure which is 14.7 psi. Hydraulic pumps aren't good vacuum pumps so even less than 15 psi probably about 10 psi.

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