LHM vs. LHM+

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aerodynamica
Donor 2023
Posts: 1299
Joined: 26 Dec 2007, 18:10
Location: Glasgow
Lexia Available: Yes
My Cars: 2008 C5 Exclusive Tourer
1993 Xantia 1.9 TD VSX Mk1 Sinker A.K.A Slugmobile 13'
'Old Katy'
previous convictions: totaling 52litres of LHM in one go:
1968 ID19B 'Old Polly' Stellar white
1993 Xantia 1.9 TD SX Mk1 Sinker Silver
1992 XM 2.0 SEi Turbo Manual Anthracite Grey
1982 CX 20 Pallas 'Old Goldy'
1993 XM 2.1 SD Auto Light blue
1993 Xantia 1.9 TD SX Mk1 Sinker light Blue
1982 BX 16 TRS 'Cyril' Vallelunga Red
1995 Xantia 1.9 D SX Auto Dark green
1977 CX 2400 Pallas C-Matic 'Aphrodite' Regatta Blue
1982 GSA Pallas SE Silver Pearl
1980 CX 2000 Reflex Vallelunga Red
1978 CX 2400 Pallas C-Matic 'Prometheus' Midnight blue
1984 BX 14E 'Cecil the slugmobile' Maroon
1987 Fiat Panda 'the mighty panda'
x 97

LHM vs. LHM+

Post by aerodynamica »

Hi all. as a new member I have been trawling through the back catalogue of the Citroen part of FCF for interesting threads and Xantia specific things to get excited (nervous) about.

This thread about old LHM is interesting

http://www.frenchcarforum.co.uk/forum/v ... hp?t=19597

You see, I'd wanted to know what the difference between LHM and LHM+ was.

I wasn't aware that CX DS etc owners were known to prefer the former LHM but it got me thinking; my CX is full of crystal clear, lumenous LHM+. It's had full rebuild of the suspension and has a new HP pump, cleaned filters and a new Diravi steering column. Despite this mad attantion there are still problems with it!

1. at parking speeds, the steering still goes heavy especially on an incline. On gravel it's dead light as it is on the road and there's not a hint of free play.

2. the suspension at times feels underdamped, especially at the rear and especially with 4 people on board.

Unless this is normal, do you think the 'extra lubrication' properties mentioned in the old thread could be messing with the CX's hydraulic performance? too much leakage in the steering rack and too much slippiness through the spheres' 'leaf valve' dampers?

Is the old LHM completely obsolete now? otherwise I'd like to try it.

Just curious on your opinions. 8)
Graeme M
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Re: LHM vs. LHM+

Post by Mandrake »

aerodynamica wrote: I wasn't aware that CX DS etc owners were known to prefer the former LHM but it got me thinking; my CX is full of crystal clear, lumenous LHM+. It's had full rebuild of the suspension and has a new HP pump, cleaned filters and a new Diravi steering column. Despite this mad attantion there are still problems with it!

1. at parking speeds, the steering still goes heavy especially on an incline. On gravel it's dead light as it is on the road and there's not a hint of free play.
As far as I know, thats fairly normal behaviour for a CX! Especially the earlier models like yours that have a lower capacity pump. The steering does rely a lot on the condition of the accumulator sphere too but I assume you've replaced that.

Our 1978 CX 2400 was the same - while stationary with the engine at idle speed, turning the steering wheel quickly would run out of assistance momentarily until the pump topped up the pressure again.

It seems that the pump wasn't designed with enough delivery capacity for turning the wheels quickly while the engine is idling - so the initial turn is supplied by the accumulator sphere then the pressure drops and the steering gets heavy as the pump lags behind.

I could be wrong though - perhaps someone like DoubleChevron has some ideas ?
2. the suspension at times feels underdamped, especially at the rear and especially with 4 people on board.
Now this I think I know the answer to. Firstly, what spheres did you fit ? GSF ? Other ? What were they listed as in their catalogue, and most importantly, did they list DIFFERENT spheres for Series 1 and Series 2 CX's ? I bet they listed the same spheres regardless of age, right ?

We had a similar problem back in '98 when we got new spheres for the above mentioned CX - too soft and floaty at the front, oscillating up and down uncomfortably. This despite the fact they were genuine Citroen spheres, and also the recommended types.

Although we didn't know it at the time, I've since found out Series 1 and Series 2 CX's have DIFFERENT diameter hydraulic rams in the suspension. I'm not sure what the exact cutoff date is, and whether it co-incided with the Series change, but its somewhere around 1982 - 1985.

The later models have larger diameter rams than the earlier ones, and this means for the SAME spheres you will get a different ride - the earlier model with the smaller rams will give a softer less damped ride, and the later ones will give a firmer more damped ride, with the SAME sphere.

The problem is they seem to be supplying "one size fits all" spheres for CX's which are tuned best for the later models, put them on an earlier model and you get a soft rather wallowy underdamped ride as you describe.

What we did to get around it (as there were no other choices of spheres available here in NZ at the time) was to tweak the center damper bypass hole - reducing it from 2.0mm to about 1.5mm on the front spheres - wallowing gone, and a much more stable ride but still very comfortable.

Unless this is normal, do you think the 'extra lubrication' properties mentioned in the old thread could be messing with the CX's hydraulic performance? too much leakage in the steering rack and too much slippiness through the spheres' 'leaf valve' dampers?

Is the old LHM completely obsolete now? otherwise I'd like to try it.

Just curious on your opinions. 8)
The difference in LHM viscocity would have some effect on the suspension damping - but I think it would probably be very small, and the issue of the two different ram diameters is more likely the problem.

Just my 2c worth :)

Regards,
Simon
Simon

1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White

2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
aerodynamica
Donor 2023
Posts: 1299
Joined: 26 Dec 2007, 18:10
Location: Glasgow
Lexia Available: Yes
My Cars: 2008 C5 Exclusive Tourer
1993 Xantia 1.9 TD VSX Mk1 Sinker A.K.A Slugmobile 13'
'Old Katy'
previous convictions: totaling 52litres of LHM in one go:
1968 ID19B 'Old Polly' Stellar white
1993 Xantia 1.9 TD SX Mk1 Sinker Silver
1992 XM 2.0 SEi Turbo Manual Anthracite Grey
1982 CX 20 Pallas 'Old Goldy'
1993 XM 2.1 SD Auto Light blue
1993 Xantia 1.9 TD SX Mk1 Sinker light Blue
1982 BX 16 TRS 'Cyril' Vallelunga Red
1995 Xantia 1.9 D SX Auto Dark green
1977 CX 2400 Pallas C-Matic 'Aphrodite' Regatta Blue
1982 GSA Pallas SE Silver Pearl
1980 CX 2000 Reflex Vallelunga Red
1978 CX 2400 Pallas C-Matic 'Prometheus' Midnight blue
1984 BX 14E 'Cecil the slugmobile' Maroon
1987 Fiat Panda 'the mighty panda'
x 97

Post by aerodynamica »

Thanks matey thats a very comprehensive reply! The spheres on the CX are the original pair that came with it 3 years ago but I have regassed them. I had heard about the diameter difference in the pistons before - I'd forgotten about that. The smaller type will displace a smaller cross sectional volume for a given pushrod stroke.

I wonder if the use of GTi spheres could work - surely they have a tighter damper?

Must say the front spheres seem good. I should say I'm not telling you everything! the spheres were regassed to a higher initial pressure to give a super floating ride. Rears to 45bar instead of 40 and fronts to 80bar instead of 75. It was also intended to make them last longer! I think the percentage change was corrrect for the front but maybe too much for the rear. Anyway it's the damping that's wrong not the spring rate of change.
Especially the earlier models like yours that have a lower capacity pump
!! didn't realise it was lower capacity! - it's the same as the DS pump - 7 piston, thought that was the largest! Having said that, despite the good condition of the CX's hydraulics and the new pump and accumulators, rebuilt correctors etc, it still asends slower than my mate Steve's CX reflex with the later 5-piston 'BX type' pump....

Anyway if it's known to be working OK like this then I'm happy.
Graeme M
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Post by Mandrake »

aerodynamica wrote:Thanks matey thats a very comprehensive reply! The spheres on the CX are the original pair that came with it 3 years ago but I have regassed them. I had heard about the diameter difference in the pistons before - I'd forgotten about that. The smaller type will displace a smaller cross sectional volume for a given pushrod stroke.
Yep exactly.
I wonder if the use of GTi spheres could work - surely they have a tighter damper?
Well they will certainly "work" but you might not like the result! They'd probably be too firm. If you had some around you could just try I'd give it a try and see, but I certainly wouldn't be buying any to try just on the off chance.
Must say the front spheres seem good. I should say I'm not telling you everything! the spheres were regassed to a higher initial pressure to give a super floating ride. Rears to 45bar instead of 40 and fronts to 80bar instead of 75. It was also intended to make them last longer! I think the percentage change was corrrect for the front but maybe too much for the rear. Anyway it's the damping that's wrong not the spring rate of change.
Yes, but the springing and damping are inter-related - the optimum damping is different when you change the springing rate (gas pressure) so if you run at a non standard pressure you may have to tweak the damper as well for a satisfactory result.

So your choices are to either change the gas pressure to normal, tweak the damper valve hole slightly, (reduce the diameter by approx 25%) or replace the spheres. (Or put up with it)
Especially the earlier models like yours that have a lower capacity pump
!! didn't realise it was lower capacity! - it's the same as the DS pump - 7 piston, thought that was the largest! Having said that, despite the good condition of the CX's hydraulics and the new pump and accumulators, rebuilt correctors etc, it still asends slower than my mate Steve's CX reflex with the later 5-piston 'BX type' pump....
Yep, the later 5 piston pump has a significantly higher cc/rev delivery rate than the earlier 7 piston types, I'm told. It's not just the number of pistons that counts. :wink:

Regards,
Simon
Simon

1997 Xantia S1 3.0 V6 Auto Exclusive in Silex Grey
2016 Nissan Leaf Tekna 30kWh in White

2011 Peugeot Ion Full Electric in Silver
1977 G Special 1129cc LHD
1978 CX 2400
1997 Xantia S1 2.0i Auto VSX
1998 Xantia S2 3.0 V6 Auto Exclusive
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Post by alan s »

Common mod in Oz used to be to fit a BX pump as you mentioned one of your friends have done.

I have driven one with that fitted and the steering was light as a feather even at parking speed.


Alan S
RIP Sept 19th 2008.

She said "Put the cat out" She didn't mention it was on fire!!
aerodynamica
Donor 2023
Posts: 1299
Joined: 26 Dec 2007, 18:10
Location: Glasgow
Lexia Available: Yes
My Cars: 2008 C5 Exclusive Tourer
1993 Xantia 1.9 TD VSX Mk1 Sinker A.K.A Slugmobile 13'
'Old Katy'
previous convictions: totaling 52litres of LHM in one go:
1968 ID19B 'Old Polly' Stellar white
1993 Xantia 1.9 TD SX Mk1 Sinker Silver
1992 XM 2.0 SEi Turbo Manual Anthracite Grey
1982 CX 20 Pallas 'Old Goldy'
1993 XM 2.1 SD Auto Light blue
1993 Xantia 1.9 TD SX Mk1 Sinker light Blue
1982 BX 16 TRS 'Cyril' Vallelunga Red
1995 Xantia 1.9 D SX Auto Dark green
1977 CX 2400 Pallas C-Matic 'Aphrodite' Regatta Blue
1982 GSA Pallas SE Silver Pearl
1980 CX 2000 Reflex Vallelunga Red
1978 CX 2400 Pallas C-Matic 'Prometheus' Midnight blue
1984 BX 14E 'Cecil the slugmobile' Maroon
1987 Fiat Panda 'the mighty panda'
x 97

Post by aerodynamica »

That's interesting Alan, I should clarify; my mate's was not modified, it's a later 'Douvrin' engined model and these had the 5 piston pump as standard - the old 7 piston one went obsolete at that time.

I can't change it now, I have had a shiny new recon pump on for only a few months... :roll:
Well they will certainly "work" but you might not like the result! They'd probably be too firm. If you had some around you could just try I'd give it a try and see, but I certainly wouldn't be buying any to try just on the off chance
-yea but surely if any later CX sphere is gonna feel too soft surely that includes the GTi ones. They'd be firmer sure, but not as firm as they'd be if they were on a thicker pistoned CX.

Your'e right, it doesen't really matter because I have no spare ones and am not splashing out for experiment's sake!
Graeme M
2008 C5 Exclusive Tourer 2.0 HDi
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