GS Hydraulic

[Andrew B]

Just like to ask if anyone knows how different the early hydraulic system is to the later system with the extra brake sphere. Was this extra sphere to meet local ADR requirements? If so was it installed in Australia by the importer or fitted in France at the factory.
Our GS has some doggy plumbing round the extra sphere supply and return lines. Thinking it may be easier to return to the earlier setup.

 

[DoubleChevron]

The CX had an extra brake accumulator too. It'll be to do with the diagonal braking setup used (each circuit will have its own sphere). If you have another GS to scavenge the bits from, I'm sure you could re-plum it. They are a bastard thing to bleed from memory as they removed the bleeders.

 

[Citroenfan]

The CX had an extra brake accumulator too. It'll be to do with the diagonal braking setup used (each circuit will have its own sphere). If you have another GS to scavenge the bits from, I'm sure you could re-plum it. They are a bastard thing to bleed from memory as they removed the bleeders.

A bit confused - The CX - at least the ones sold in the rest of the world - used the same basic set up as the DS/SM's/XM and I would have to think the GS, etc. The main change between the DS/SM and later cars is that DS/SM used an intergrated brake accumulator - IOW the actual accumulator and pressure protection function were as one unit. Starting with the CX it was modified to accept a standard accumulator spher. The basic layout is that the front brake pressure is supplied via a brake accumulator (1 only). The brake accumulator's function is to isolate front brake pressure from overall system pressure in the case of overall system pressure failure. The rear brakes are feed via pressure from the rear suspension. The respective brake pressure in each circuit is apportioned via the double acting brake control valve with the majority of applied pressure going to the front brakes where as the rear units available pressure is dependent on the weight in the rear of the car. The actual brake controller design has changed over the years but functionality remained the same. Have attached a file showing the braking circuit of a CX.

The CX has 6 spheres - 4 suspension accumulators, 1 accumulator for the system pressure regulator and one for the front brake pressure isolation valve. The XM's layout is identical. OTOH, AFAIK, only LHD V6 XM's with DRAVI steering had a brake accumulator.

 

[sparkey]

.... how different the early hydraulic system is to the later system with the extra brake sphere...Our GS has some doggy plumbing round the extra sphere supply and return lines. Thinking it may be easier to return to the earlier setup.

Andrew B – apart from dodgy plumbing, curious if the current system is giving you any issues - if it ain’t broke don’t fix it (optics are important though)
Having worked on ’73 and ’74 GS’s, when I worked on a ’77 Pallas, I asked my club mate WTF is that? (extra brake sphere)

Apart from the extra sphere giving up the ghost, blew with a very loud bang, the only issue I had bleeding NS/R nipple (contrary to Double Chevron’s bleeder absence issue) was rear swing arm had to be jacked up

My '73 & '74 GS's have been on the road 7 years now and all going well without the extra sphere

Have blocked the Oct ’20 GS anniversary tour in my diary, just waiting to see how Covid pans out. Thanks for organising

 

[Ken W]

Andrew,

There was a period where ADRs required a dual diagonal braking circuit fitted so that if one circuit failed, the other one would still work on one front and the opposite rear wheel. While I have never seen it documented anywhere (if someone does have details please post them up here) I think the main accumulator and the front valve in the brake control feeds one diagonal and the extra accumulator and the other valve feeds the other. Then the outlets of the front calipers run in dual pipes down to an extra valve at the back of the car which uses the rear suspension pressure to provide an upper limit to the front caliper pressure going to the opposite rear wheel caliper. As mentioned above, you have to bleed the brakes using the bleed nipple on the rear caliper and that bleeds the opposite front caliper as well.

This is all guess work here so I would be keen to find out what others have found in their investigations although I did own one of these from 1978 to about 1990 and I am working on another one at present. I know Woody was having some problems with his rear valve???

Cheers, Ken

 

[Citroenfan]

Andrew B – apart from dodgy plumbing, curious if the current system is giving you any issues - if it ain’t broke don’t fix it (optics are important though)
Having worked on ’73 and ’74 GS’s, when I worked on a ’77 Pallas, I asked my club mate WTF is that? (extra brake sphere)

Apart from the extra sphere giving up the ghost, blew with a very loud bang, the only issue I had bleeding NS/R nipple (contrary to Double Chevron’s bleeder absence issue) was rear swing arm had to be jacked up

My '73 & '74 GS's have been on the road 7 years now and all going well without the extra sphere

Have blocked the Oct ’20 GS anniversary tour in my diary, just waiting to see how Covid pans out. Thanks for organising

From the first DS in 1956 all have had the brake accumulator. And the system will work just fine if all circuits are bleed correctly. The ONLY problem with blown brake accumulator is that there is no back up for the front brakes if there is total hydraulic system failure. The vary early basic spec ID's - no power assisted brakes and with manual steering (from introduction in 58 or so to around 63 - IIRC) used a bog normal master cylinder. And remember that back in those days master cylinders had a nasty habit of failing - due to the fact that EDPM, the first rubber compound that could actuall stand up to gylcol base flluids was not invented until 1960 or so. Cit, however, put in a 'safety' system. If the master cylinder ever failed, there was a valve incorporated that if pressed due to master cylinder failure let all of the pressure in the front suspension into the front brake system all at once. My parents referred to it as the "Jesus Brakes" as that was the expression one used when it happened - "Jesus Christ!!!!" what just happened. Hopefully no one was following too close.

 

[Citroenfan]

Andrew,

There was a period where ADRs required a dual diagonal braking circuit fitted so that if one circuit failed, the other one would still work on one front and the opposite rear wheel. While I have never seen it documented anywhere (if someone does have details please post them up here) I think the main accumulator and the front valve in the brake control feeds one diagonal and the extra accumulator and the other valve feeds the other. Then the outlets of the front calipers run in dual pipes down to an extra valve at the back of the car which uses the rear suspension pressure to provide an upper limit to the front caliper pressure going to the opposite rear wheel caliper. As mentioned above, you have to bleed the brakes using the bleed nipple on the rear caliper and that bleeds the opposite front caliper as well.

This is all guess work here so I would be keen to find out what others have found in their investigations although I did own one of these from 1978 to about 1990 and I am working on another one at present. I know Woody was having some problems with his rear valve???

Cheers, Ken

If Australia used such a system it would have been installed at the factory during build. Doing it as an 'add on' would have been very expensive . The factory did do special specs for different markets - RH drive for those who drive on the 'wrong' side of the road..... Post 68 D's and the SM were sold in the US sans headlight covers. This was because the both California and New York, Citroen' biggest sales market prohibited covered lights. Also the reason the US did not get LHM cars until 01/69 was due to our DOT not blessing a mineral based fluid as an 'approved' brake fluid - though it had been used in aircraft beginning in the early 50's. Go figure.

 

[Andrew B]

Hi Guys
Why I ask this is that I have a leak/s of Green Gold from around the brake accumulator. Seems some of the nitrile hose has been replaced with PVC
like tubing. All my past GS had no problems with leaks and using as every day drive back in the past. This is 1st GS with the later brake system I have as a hobby car. Just thinking it might be easier to to go back to the earlier set up or may be not.
Yes Ken a diagram of the later system would be great.

Sparky not looking to good for the 50th GS tour at this time, but few months to go so lets hope.
For those interested check the CCOCA web site for details.

 

[Ken W]

Hi Folks,
I have been and had a closer look at the GS subframe I have in my garage and also the GS Pallas that young Ken (AXGT) is restoring in my shed and found that there are also two early looking priority valves mounted on each side of the front subframe. The output of the hydraulic regulator goes straight to the priority valve under the brake accumulator and there is a feed from this PV to the brake accumulator above and across to the priority valve on the other side. The two outputs from the brake valve do feed each front caliper, and the outputs of each front caliper do head off to the rear of the car. So it seems there is some truth in the words I wrote above.


Cheers, Ken

 

[DoubleChevron]

From memory, you must bleed the front brakes through the rear (which is stupidity). They have used the bleeder valve connection to run diaginal braking lines. I think I just cracked a line nut and let LHM flood the brake pads ( ) to bleed the air from the front calipers (don't worry, the pads were pre-oiled for me either way).

The CX has two brake accumulators (all the locals refer to the 2nd accumulator as the "steering accumulator"), but its not, its a secondary brake accumulator (for the second brake circuit). At least you can bleed the CX system!

seeya,
Shane L.

 

[SMSM]

Hi Andrew. If you have a 6 sphere GS there should be 2 warning lights retro fitted in the dash above the pull out handbrake. "STOP BRAKE FAILURE' and 'PARK BRAKE'. This set up was an ADR requirement of the time. If you look under the car at the rear left there will be the bleeding points I think for the brakes. Just behind the fuel tank. I was looking at reinstating this setup on my GS platform I was rebuilding. Read somewhere that they decided to do away with the 6th sphere as it effected the rear suspension as the 2 where interconnected. I decided to do away with mine and return it back to a 5 sphere setup.

 

[Bruce Llewellyn]

I have a '75 D special with 5 spheres, rear brakes from the rear suspension i.e. not diagonal split and a 65 safari with 6 spheres (or I will when I put it back together...) The diagonal split brake system is a phurphy - while there was discussion in the late '60's the difference in front to rear balance makes the car pull hard towards whichever front brake is working. The Pug 504 always had front brakes on one circuit and rears on the other, so does the D and everything else I've worked on. Some Volvos might be different.

The easy way to tell if you need to bleed the rear brakes in D, CX or GS is to put the car in normal ride and push the brake button - if it stays level it's fine, if it needs bleeding the fluid between the rear height corrector and the rear suspension will rush into the empty rear brakes. The height corrector keeps the suspension circuit shut off - so back will drop.

Because the hydraulics keep pushing fluid into the front brakes when the button is down, if they need bleeding there is a delay between applying the brakes and getting any braking.

With the front calipers completely empty of fluid (full of air) it takes 4 to 5 seconds to get a response out of the brakes (tried it on the airstrip one time just to find out).

 

[Dave Rogers]

Showing my ignorance here but I had no idea about 6 sphere GSs. I have an early GSA (1979) and it only has 5 spheres, so I guess I never considered that there had been 6 spheres at some stage of production.

 

[Ken W]

So in summary, GSes from 1970 to 1977 only had one accumulator and 4 suspension spheres and no priority valve. So if there was a pipe breakage in the high pressure system, there would be no front brakes and the front suspension would collapse next time it asks for a top-up of pressure LHM. The only braking available would be from the rear suspension pressure on the rear discs and the handbrake. I don't think pipe breakage in the HP part of the system was a very common occurrence. I don't think you would get much braking from a lightly loaded rear suspension system operating on the very small rear discs.

Then for the GS Pallas series as mentioned above, the system was reformatted with 2 accumulators, 4 suspension spheres and 2 priority valves with the brakes configured to work in a diagonal format front to back without being able to directly source rear suspension pressure.

With the GSA, the system returned to 1 accumulator and 4 suspension spheres as per the earlier design but did include a priority valve to prioritise brakes over suspension to cover the case of a failure of any of the suspension hydraulic pipes. This would retain some front brake ability in the case of a rear suspension hydraulic failure.

I would think that those deleting the diagonal braking system from a GS Pallas should retain at least one priority valve so that there is at least some backup for the front brakes in the case of a pipe breakage in the suspension hydraulic systems.

Cheers, Ken