Are all pressure gauges the same?

[Leconte]

Thanks everyone for putting me straight. Yes it it just needed under the bonnet to test the torque coverter pressure with engine running, at two different rev rates. From the sound of it the gauges suggested by Col would be better than my initial question and thanks to Jo, Bob and Jaahn for guidance on the fittings to go with it. It seems odd for a decent (or decent enough) gauge to be so cheap? I would go for something reading at or above 250psi given I need to read at least up to 145 psi.

Edit: the testing point on the torque converter takes a standard 6mm threaded bolt (pitch is same as buying a 6mm bolt from bunnings so whatever that is 1mm or 1.25 can check later). So need a 6mm takeoff there To 1/4 inch at gauge.

For those interested in my underlying problem:

At present we cannot engage any gears in the GS with the engine running (a slight deficiency as you would acknowledge) because of some flaw in the "hydraulically automated clutch" or 'Convertisseur' setup (hybrid auto-manual gearbox with friction clutch operated by hydraulics switched by gear lever movements, no clutch pedal).

The electrical side consists of a set of contact switches at the gearbox that provide an earth path which is 'open' (not conducting) when the car is in gear and closed (conducting to earth) when car (gearstick) is in neutral; this circuit runs via a normally open relay (and the ignition switch) to provide current to the famous 'Electroswitch' which is a hydraulic solenoid that switches torque converter fluid (driven by an internal pump) between two flow states: 1. pressurising the hydraulic clutch (unable to change gear) when in gear with the electroswitch NOT energised (a spring returns an internal rod to the position where fluid flows to pressurise the pressure plate) and 2: de-pressurising the clutch when in neutral (allowing the gears to be changed) - in this case the contact switches on the gearbox should be closed and the relay energised which should energise the electroswitch solenoid, pushing the distribution rod to the position where the hydraulic fluid bypasses the pressure plate allowing the clutch springs to decouple the motor from the gearbox, hence gears may be changed.

It is possible there is a flaw in the electrics that means the electroswitch is not getting switched on when in neutral to activate depressurise mode, or it is possible something is wrong with the fluid side.

A pressure gauge can be plugged into the torque converter to check the pressure from the gear driven internal eccentric pump. If the pump has failed or the pressure is not high enough then the factory instruction is to basically replace the whole torque converter unit (as long as a small filter is not blocked which I believe isn't). Hence wanting to check the pressure to hopefully rule out a major issue.

On the electrical side, and being a Citroen, of course, the contact switch box is tiny (about the size of a matchbox) with a delicate mechanism consisting of 4 sets of points - one for each gear 1,2,3 and R - and mounted on a practically inaccessible spot behind the motor/Gearbox in the gear lever tunnel area and only able to be checked (under the bonnet not from inside the car) by removing the gear stick assembly and lying on top of the engine And somehow still changing gear by the stub out of the gearbox (which at this point is lodged in your chest or throat) and with the engine running. Thanks Citroen! So I am hoping that is not the culprit. Although thinking this through, that is looking more and more likely (contact points stuck open hence electroswitch never gets energised when gearstick goes to neutral). Of course, the electroswitch solenoid could simply be not working and thus not redirecting the fluid flow away from the pressure plate.

So many possible points of failure! And all a bit tricky to diagnose at least for an amateur. We did replace the normally open relay (a 30 amp Narva 68024j a couple of years ago so it 'shouldn't' be that. Some fun time ahead of me. Just had one thought, I think I can test if the contact switch is the culprit by bypassing it with a 'hotwire' that earths the circuit, which is what the switch should do ONLY when in neutral, and see if that release the clutch. Theory of that seems sound to me although it is hard to hold all of this design in your head at one time. At least it means I wouldn't have to deep dive into it if it is not the culprit. Hmmm

cheers Leconte

 

[jaahn]

Hi
While it is true that some metric pipe threads might be the same as BSPT but that does not mean that the auto threads are are, nor are all hydraulic threads BSPT or NPT. There are metric standards for those which are often parallel not tapered and face seal with a couple of designs. Hmm
It is wise to be sure of the torque converter 'port' thread as a mistake will cause problems resealing it with the original plug.
Jaahn

 

[COL]

Not sure how handy you are but I would be making an adaptor to go from the 6.0 mm by X pitch thread to a BSP socket for the gauge to screw into. Easily done by getting the right 6 mm bolt removing the head and drilling say a 3 mm hole down the centre. Then I would be silver soldering a 1/4" BSP socket onto the bolt. then you will have your adaptor.

 

[jaahn]

"Edit: the testing point on the torque converter takes a standard 6mm threaded bolt (pitch is same as buying a 6mm bolt from bunnings so whatever that is 1mm or 1.25 can check later). So need a 6mm takeoff there To 1/4 inch at gauge."
Hi Leconte
Here is another suggestion, probably what I would do. Get your new cheap gauge and carefully drill the fluid hole out a bit and tap it for the 6mm thread, you only need 6mm of thread. Then get a 6mm bolt, HT would be best, with about 15-20mm of thread and drill a small hole, say 1.5-2mm, up through the threaded section. Then cut off the threaded part and use the 6mm threaded section as the adaptor with a soft washer as a face seal between the end of the gauge and the converter housing. A viton or leather tap washer would be OK. This would also leave the gauge unaffected to use for other things after.

Good luck with your trouble shooting. You seem to be on the right track, checking and thinking of the various possibilities.
Jaahn
PS note if you do use some other solution then note the 1/4" thread on the gauge is a 1/4" nominal pipe size thread. It is not 1/4" diameter outside but is actually about 1/2" outside diameter.

 

[JohnW]

On our CX C-matic you could hear the electrovalve click when it dropped out. You could try a stethoscope on it. I'd be checking whether it is getting 12V at the terminal AND whether the small, conventional relay that switches the 12V to the electrovalve is working. The only trouble we ever had was actually the small relay that was operated by the switch block contacts. The point is that there are two relays in the circuit, not one, at least in the CX system.

One problem I was told about with C-matics was the internal shaft seal that allows the clutch hydraulic pressure to hold it engaged so that it doesn't slip, but that is the opposite problem to yours. The previous owner to us had the seal replaced (that would be fun).

Quite a system, isn't it!

 

[WLB]

PS note if you do use some other solution then note the 1/4" thread on the gauge is a 1/4" nominal pipe size thread. It is not 1/4" diameter outside but is actually about 1/2" outside diameter.

Jaahn,
There's a historically logical reason for that, Jaahn. The size relates to the pipe size, not the thread itself. Technically, a pipe has a thick wall and the its nominal size relates to the inside diameter (ID), whereas a tube has a thin wall and its nominal size relates to its OD.
Incidentally, when you're working with sizes of 1/4" BSP and 1/4" NPT and smaller, and if the application is not a critical one, the difference is so small that you can 'force' them to fit. I put force in inverted commas because it's really to strong a word. It requires very little effort to screw them together and you may not even notice the mismatch.
PS. I've been meaning to ask for a long time; why the choice of Brabham's car for your avatar?

Leconte,
When choosing a pressure gauge, the rule of thumb is to select one where your maximum pressure will only take the gauge to 2/3, or 3/4 scale at most.

 

[jaahn]

Jaahn, There's a historically logical reason for that, Jaahn. The size relates to the pipe size, not the thread itself. Technically, a pipe has a thick wall and the its nominal size relates to the inside diameter (ID), whereas a tube has a thin wall and its nominal size relates to its OD.
Incidentally, when you're working with sizes of 1/4" BSP and 1/4" NPT and smaller, and if the application is not a critical one, the difference is so small that you can 'force' them to fit. I put force in inverted commas because it's really to strong a word. It requires very little effort to screw them together and you may not even notice the mismatch.
PS. I've been meaning to ask for a long time; why the choice of Brabham's car for your avatar?
Leconte,
When choosing a pressure gauge, the rule of thumb is to select one where your maximum pressure will only take the gauge to 2/3, or 3/4 scale at most.

Hi WLB
No particular reason I just like it and remember that era with pleasure. Racing cars looked like real cars that normal mortals might drive. The car is viewable in the National Museum.
Jaahn

 

[WLB]

Thanks Jaahn,
I was curious because it was stored for years at a private collectible car storage facility near Moorabbin airport, that was managed by an old friend. I have a few photos of it over the years, including some of my son sitting in it when he was small. Frank Matich's car was next to it.
Are you also the Jaahn on the old Energy Matters forum?
Warwick

 

[jaahn]

Thanks Jaahn,
I was curious because it was stored for years at a private collectible car storage facility near Moorabbin airport, that was managed by an old friend. I have a few photos of it over the years, including some of my son sitting in it when he was small. Frank Matich's car was next to it.
Are you also the Jaahn on the old Energy Matters forum?
Warwick

Oui c'moi
That Forum is still just alive, or should I say not totally dead, but collapsed when the moderator Gordon was 'let go'. A shame really as I found it good and there were some well informed people on there. C'est la vie !
Jaahn
PS I just went on there, maybe it is really deceased now !

 

[Leconte]

"Edit: the testing point on the torque converter takes a standard 6mm threaded bolt (pitch is same as buying a 6mm bolt from bunnings so whatever that is 1mm or 1.25 can check later). So need a 6mm takeoff there To 1/4 inch at gauge."
Hi Leconte
Here is another suggestion, probably what I would do. Get your new cheap gauge and carefully drill the fluid hole out a bit and tap it for the 6mm thread, you only need 6mm of thread. Then get a 6mm bolt, HT would be best, with about 15-20mm of thread and drill a small hole, say 1.5-2mm, up through the threaded section. Then cut off the threaded part and use the 6mm threaded section as the adaptor with a soft washer as a face seal between the end of the gauge and the converter housing. A viton or leather tap washer would be OK. This would also leave the gauge unaffected to use for other things after.

Good luck with your trouble shooting. You seem to be on the right track, checking and thinking of the various possibilities.
Jaahn
PS note if you do use some other solution then note the 1/4" thread on the gauge is a 1/4" nominal pipe size thread. It is not 1/4" diameter outside but is actually about 1/2" outside diameter.

Hi Jaanh, what a great suggestion (although I had to read it a couple of times to understand your crafty plot). And possibly not beyond my limited capabilities. I don't have a lathe or similar equipment or skills but I do have a (cheapish) tap and die set and a drill press.

The discussion around the tapering pipe thread types BSP, BSPT, NPT and tapered metric isn't relevant in this case as the GS pressure testing 'port' is definitely just a standard 6mm thread opening into the upper end of the torque converter fluid passages. Also checking the factory manual (00801 section 320-0) the two expected PSI readings are 55 psi at idle and up to 95 at 5000rpm (not 145 psi at 5000 rpm as I previously thought). So a dial gauge up to 145/150/200 psi will be fine.

I did find some brass metric thread to hose barb fittings on AliExpress from China but of course deliveries from there take months. I will probably buy a selection of these but am looking for a faster solution in the next week or so locally.

Thanks WLB for the tip on the pressure gauge capacity.

regards leconte

 

[bob]

G'day,
there are some weirdo brass adapter fittings on rotating stands at auto accessory places, forget the brand, there are lots of little blister packs with US small [number series] nuts 'n bolts there as well.
Easiest is probably the home made adapter fitting, just soft solder the threaded bits together to ensure a seal and use a fibre washer under the bolt head to get a seal there - soft copper is best, but this is only a test rig.
Bob

 

[WLB]

Oui c'moi
That Forum is still just alive, or should I say not totally dead, but collapsed when the moderator Gordon was 'let go'. A shame really as I found it good and there were some well informed people on there. C'est la vie !
Jaahn
PS I just went on there, maybe it is really deceased now !

PM sent. (Sorry, I mean I've "started a conversation" with you).

 

[Kenfuego]

G'day,
there are some weirdo brass adapter fittings on rotating stands at auto accessory places, forget the brand, there are lots of little blister packs with US small [number series] nuts 'n bolts there as well.
Easiest is probably the home made adapter fitting, just soft solder the threaded bits together to ensure a seal and use a fibre washer under the bolt head to get a seal there - soft copper is best, but this is only a test rig.
Bob

Bob I don't know where Leconte is located, but if he was near Skipton Vic, I'd reckon "somewhere" in your sheds would be plenty of connectors of all varieties or if located near Melbourne, I think I would have quite a few new and used "unusual" threaded connectors and the means to weld braze or make up a Frankenstein like made-up adapter on the lathe.

And the bits at this time in life are giftable, as I don't think I will get to use them in this lifetime......

Ken
(now I wonder if Mistarenno finished the super boosted Fuego, haven't heard from him for a few years.. ? anyone know ?)