13 replies to this topic

[tarnofsky]

I have recently bought a Pickup and am in the process of preparing it to get it approved as road legal by German TÜV (our MOT).
The car has been converted to disc brakes on the front and continues to run on 10" wheels.
I noticed that the FAM7821BRAKE LIMITER VALVE seems to be mounted upside down ( inlets connected to front/rear brakes, outlets to master cylinder).
Can you confirm?
It has brakes and all but that would need to be corrected.
Can anybody say if the unions on in- and out-side of the valve are of the same type?
Changing it round and bleeding brakes (again after a fluid swap already completed...) is no big deal unless I will have to bend and flare new pipes. So I'd like to know upfront what to expect.

Your help is much appreciated as always.

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Edited by tarnofsky, 29 September 2023 - 08:07 PM.

[mad4classics]

Yes, that's upside down. Connections are all the same - metric M10.

When you turn it over the whole thing will be lower down - at the bottom you'll hopefully be able to lose the extra length you'll have ( easy in the front circuit ), but your top master cylinder connections are blurred and it's unclear if you'll have the extra 30mm or so of length required; you may need to remake the top pipes and shorten the bottom ones just to get a neat job.

Looks like you've got a yellow tag master - make sure the connections are the right way round to font and rear!!!!!

Edited by mad4classics, 30 September 2023 - 11:50 AM.

[tarnofsky]

Yes, that's upside down. Connections are all the same - metric M10.

When you turn it over the whole thing will be lower down - at the bottom you'll hopefully be able to lose the extra length you'll have ( easy in the front circuit ), but your top master cylinder connections are blurred and it's unclear if you'll have the extra 30mm or so of length required; you may need to remake the top pipes and shorten the bottom ones just to get a neat job.

Looks like you've got a yellow tag master - make sure the connections are the right way round to font and rear!!!!!

Thanks for the confirmation and info on connectors. I checked my other Mins but none have the same yellow tag master cylinder.

When fitted the correct way round, the nut on the connector will still point to the center of the car - does so on my other cars.

I had a look at the Minispares page and checked the yellow tag master cylinder there. It says "Top one is 10mm and the bottom one 12mm for the larger stepped bore size to the rear brakes".

This means that the top connector goes to front and bottom to rear from the master cylinder, correct?

Consequently that means that the master cylinder top feeds into the limiter's top port towards the wing of the car, the lower master cylinder port feeds into the limiter's top port towards the car's centre, right?

From the limiter the bottom port towards the wing feeds the front brakes and the bottom port towards the car's centre the rear.

Am I getting this right?

 

Making brake lines is no issue, I have all the correct benders and flaring tools. I would assume it's all SAE type flares as on the rest of the car.

I'm only a little bit unsure because of the variety of connectors and master cylinders that are available. On my Pickup the master cylinder definitely has been replaced recently.

If I change the whole stuff and bleed the brakes again, I just want to do it all correct as this is highly safety critical and that's where I need some help...

[coopertaz]

while on the subject of this valve am i correct that it shuts off a failed, leaking circuit, so you dont lose all brakes? and does it limit rear pressure or not? we debated this in club when someone had a rear brake issue and replacing this fixed it but never really found out fully how it worked.

[Ethel]

You're correct with your connections if the limiter valve is the right way up.

 

GMC227

Top - front circuit

Bottom - rear circuit

 

 

FAM7821

 

Front in         Rear in

Front out                   Rear out

 

(note the offset rear connections)

[Spider]

FAM7821

 

Front in         Rear in

Front out                   Rear out

 

(note the offset rear connections)

 

Like this ?

 

 

 

 

[tarnofsky]

 

FAM7821

 

Front in         Rear in

Front out                   Rear out

 

(note the offset rear connections)

 

Like this ?

 

 

Thanks for the picture and port descriptions. I intended to fit the limiter just as in Spider's picture and as per Ethel's description.

So, Ethel, could you please have a look again and confirm that that's how it should be fitted to match your description?

[Ethel]

Yes, as Spider's piccy.

 

Wonder if the letters threw whoever fitted it? 

 

I suppose it'd be a bit easier to bleed* that way up, but the plumbing would be a bit more spaghetti junction.

 

 

* BL may have injected the fluid from the wheel end on the assembly line.

[tarnofsky]

Thanks all!

I will get to work once the new wiring harness has been fitted, tested and everything works.

No idea who fitted that but on this particular car EVERYTHING that can be incorrectly fitted IS incorrectly fitted. It's all there and by some magic it's been running but whenever you touch anything, it's incorrect.

For example I have not seen any such bodged and pieced together loom as in this car. To give you an example: the front right main beam cable was cut off before the bullet connectors and then 5 (five!) different cables of all different colors were added to gain 40 cm lenght. Wires without insulation at every connection for about 2 cm, cables joined by hand and a tiny bit of (cold) solder connection on it. Then it went into the loom and got taped up with loom tape. When I saw that loom of doom, I decided to throw it out immediately. I'm so glad, you can't imagine how many other issues I found in the process of removing it...

 

I forgot to say that I like challenges

 

Thanks again to all contributors!

[Spider]

I suppose it'd be a bit easier to bleed* that way up, but the plumbing would be a bit more spaghetti junction.

 

 

* BL may have injected the fluid from the wheel end on the assembly line.

 

 

I am reasonably sure on the production line, they were pressure bleed but from the master cylinder.The Tandem Cylinders don't have them, but the Single Circuit Maters have a Residual Pressure Valve in them that don't take too well to reverse fluid flow, though, pressure bleeding back from the wheels makes a lot of sense.

You have raised a good point here though and one I didn't consider (as I don't use those valves). It would be a wise idea after bleeding from the wheels to come back to this valve and bleed further from the tube nuts and then possibly again from the wheels.
 

[stuart bowes]

just tagging on to the most recent thread I can find about this part sorry..

 

I realise this is probably one of those 'if in doubt, replace' items but just asking anyway

 

having dug mine out of the shed and about to clean up and reuse, rather than wasting time and then finding out later when it's fitted and on the rollers at the MOT or when driving it and finding it handling oddly (but at the same time not wanting to just throw away £75 for no reason) is there anything I can do to test this on the bench with an air line or anything like that 

 

when I blow the air line through each side, I get air coming through, hold finger over the relevant output and can feel the pressure build up.. I can't hold it tightly enough to fully seal it off, but nothing escaping through to the other half it seems

 

so fluid flow isn't going to be an issue but what about the 'limiting' part of it

Edited by stuart bowes, 06 November 2023 - 03:42 PM.

[Spider]

Without a test rig, they are very difficult to bench test. The Compressed Air test you did shows in a 'relaxed' position, the valve passes air and should pass fluid, but it doesn't show if it'll leak when fitted or if it's rusted and seized internally, locking out the valve from it's ability to shut off or what the shut off pressure is.

 

Sadly, Brake Fluid is quite hydroscopic, so if the valve has been in service at some time and was removed, unless it was put in to a sealed bag (preferable filled with fresh brake fluid), I'd have a reasonable stab at suggesting that it's started rusting internally.

[stuart bowes]

I hear what you're saying it seems like that's gonna end up being replaced in the near future then as a precaution if nothing else

For now though I've undone the big bolt and tried pressing the internals and it moves reasonably easily by hand so it's not jammed up at least.. and then I immersed it in meths for a while and that didn't make any scary dark crud come out.. flushing through both sides again all clean. So obviously like you say there's not really any way to test the actual pressure required but it does at least move and yes there probably is at least the start of rot inside but it's not terrible yet

For now I've cleaned it up and given it a lick of paint so it looks the same as all the other hydraulic parts I'm building up. Will stick it in for now and see how that goes but at the first signs of any trouble or leakage it'll be the first part to change. And in this case fortunately it's in a really easy to get to location so I'm happy to use it for now

But thanks for the info much appreciated and keeping it in mind

[Spider]

You might have been lucky enough to dodge a bullet there !

 

Generally though, used brake parts don't store well.