The Triumph Dolomite Club - Discussion Forum

Thanks for the massive compliment! Don't feel demoralised though, everything I am doing though really shouldn't be beyond the reach of a home mechanic with a workshop manual. I am lucky that I have a nice heated workshop attached to the house though!

I'm going to start today with some good newwwws as Jeremy Clarkson would say. Something arrived in the post today that we all thought was lost, can you guess what it is?



Yep, you guessed it its my NOS master cylinder!



Needs a slight clean but that's a huge weight off my mind. Sorry Alun, I wont be buying a club one now! Do you want the old one for reconditioning?

Back to the LSV, all external components have been bead blasted, the only problem is that if I just left the casting as it was it would have just rusted so I have given it a light dust of my favourite silver enamel, I say favourite because the colour is an exact match for the bead blasted finish.



This now needs reassembling with the club seal kit pictured with it. I cant do this until the spring assembly comes back from the other blasters. Or well I hope that's where it is because I cant find it.

Seriously though I think it's in the blasting box, I remember seeing it last week when I was organising boxes.

So I have moved on to the final part of the braking system that needs looking at, this....



This is your standard PDWA (pressure differential warning actuator) valve. You will have one of these if you have a dual circuit braking system. Note that this is not a brake proportioning valve, this is a device that senses a pressure difference between the front and rear lines and then causes the warning light on the dash to be illuminated by the use of a switch if a difference exists.



Opened up it is simply a brass H valve with each leg providing a link to various parts of the braking system. On my car, the master cylinder enters from the top, the rear brakes exit from the left hand leg and the front brakes exit from the right hand hex plug and bottom leg.



A small piston rides in the cross piece and two rubber o rings prevent fluid flowing between the two sides and maintaining the dual circuit nature of the braking system.

The idea is that if the pressure is the same across all outlets then the piston will not move, if the pressure in one outlet drops then the piston will move towards that lower pressure side triggering the switch which then illumines the brake warning light on the dash. So really, this is a part which most people overlook and could one day save your life.

You can get these new, they are used on series Land Rovers that have dual brakes, only problem is that I think they have metric unions, so if you needed a new one you'd need to change your brake hoses. They also cost around £150 whereas a repair kit only costs £15 from Rimmers, they are so simple it makes sense to just refurbish them.

They are simple to get apart, I cleaned mine up first then removed the plastic switch and large hex nut. Then with a fine pick and WD40 I pulled the piston assembly out, this is where I think it's important to check these out. On mine the piston was quite gummed up and really wedged in there and it was only after a good soak with WD40 could I get it out so I wonder if it would actually work if one of the brake lines failed.

I will end this post here to avoid any confusion and pick it up when I have received the repair kit in the post. By then I should have got the rest of the blasting back so I can get the LSV back together as well.

Have a good week everyone!

James

EDIT: I have edited the union locations because I didn't look at my reference photo and diagram properly!

You sure about that James?
We've had a similar conversation on the forum before...
To be safe you have the fronts on one circuit and the rears on the other. It can't be diagonal as your post
implies...one front and the rears on one and the other side on the other.

That would lead to failure on one circuit leaving you with one front brake or the other front brake and the rears.

Cant be right....

Jonners

You're absolutely right Jonners, I wasn't looking at my reference photo properly, thanks for highlighting that.

I have edited the post to avoid any confusion.

The repair kit has arrived to I can get this put back together.



I have cleaned everything up and lightly polished the piston assembly to remove any burrs, bead blasted the nut to clean it up and polished the housing with some Autosol to protect it.

The kit comes with two different sizes of o rings, the one that came out of mine is on the left and is significantly crushed and deformed. I worked out that the larger of the two o rings was the closest size to the original, the smaller size I think would allow brake fluid past and up through the switch which isn't sealed.



So using the larger of the o rings everything was lightly lubricated with the silicone brake fluid that I'll be using and the valve assembly slid back into the housing, it's a bit of a tight fit with the new o rings but once in there it does move smoothly.





Make sure the piston is central in the shaft, by that I mean the thin central part is in the middle otherwise you'll activate your brake warning light and it could cause some issues when you fill the system! You can see this when you look down the hole for the sensor.

Fit a new copper sealing washer to the end bolt...



This is then screwed in and tightened down. I did this by clamping the assembly in protected vice jaws then tightening it up with a spanner. I did it nice and tight, there's no torque to go by though, but I guess you just want it tight enough so that it doesn't leak.



Because the piston was centralised earlier you can simply screw in the plastic sensor and nip it up. Don't over tighten this, it doesn't seal anything, you just want to make sure it doesn't come out.



There we go, one refurbished PDWA valve assembly ready to go back on the car.



I'll give it another final polish and remove that pitting before it gets fitted.

Apologies in advance James for taking your thread off-topic but as a moderator I feel I should comment on Jon's post......

Jon Tilson wrote:You sure about that James?
We've had a similar conversation on the forum before...
To be safe you have the fronts on one circuit and the rears on the other. It can't be diagonal as your post
implies...one front and the rears on one and the other side on the other.

That would lead to failure on one circuit leaving you with one front brake or the other front brake and the rears.

Cant be right....

Jonners

For clarification and to repeat what has already been discussed in other forum threads.....
there hasn't been a car sold new in Europe for about three decades with a front/back split, the last were maybe Solaras or Itals.
Dolomites did have the front/back split.

The front/back split is no longer used on safety grounds, instead, for dual circuit brakes, a diagonal split is used (i.e. front right and back left/front left & back right).
Whilst it is no fun trying to stop a car with one front brake, this is somewhat better than trying to stop a car with no front brakes at all.

During the production run of the Dolomite, BL, on other models were already looking at moving away from the front/back split. In fact the Princess range
came with tandem brakes (each circuit consisting of half of each front caliper and one back).


Personally, if I was ever to own a late car , I would fit a Saab 900 brake master cylinder, since these a very durable and also convert to a diagonal split.




Ian.

No problem Ian!

I saw a Talbot Solara the other day!

I agreed with Jon because he highlighted that I incorrectly described the links to the various parts of the braking system as fitted to my car, possibly confusing people. This was mainly because I couldn't read my own drawing!!

How would you convert a Sprint with a LSV to a tandem split? The front I imagine with the Saab 900 ms would be easy but what about the rears? I'd imagine you'd need two lines running down to the rear? Then how do you deal with the LSV? Install a modified one of just get rid of it?

James467 wrote:How would you convert a Sprint with a LSV to a tandem split?

The dual circuit split would be one front/the other front and back.
(This is the way Sherpa vans have it arranged. Their PDWA is actually in the brake master cylinder and brake pipes' T-piece
attached to the brake servo, so a pretty neat installation plumbing wise. I converted a T2500 to this arrangement.

With a Saab BMC you have have to retain the Dolomite PDWA.
Most cars now, I suspect, use a BMC low reservoir level sensor instead of a PDWA, which is easier and cheaper whilst working as well.)



Ian.

Ahh I see, that makes sense.

I don't want to start a huge conversation about this because as you said it's been discussed in other threads however, I have one question...

Could this not be achieved by simply swapping the bottom outlets on the PDWA? see my pic below...



So you'd end up with...

Front Left and Rear on one line and the Front Right on the other.

James467 wrote:Ahh I see, that makes sense.

I don't want to start a huge conversation about this because as you said it's been discussed in other threads however, I have one question...

Could this not be achieved by simply swapping the bottom outlets on the PDWA? see my pic below...



So you'd end up with...

Front Left and Rear on one line and the Front Right on the other.

Not as easy as that, the outlets have different size unions to avoid this sort of confusion!

Steve

Not as easy as that, the outlets have different size unions to avoid this sort of confusion!

That's a good point!

Carledo wrote:Not as easy as that, the outlets have different size unions to avoid this sort of confusion!

But if you knew what you were doing and were replacing the original pipework, you could fit the appropriate unions to the appropriate pipes?

Pippin wrote:

Carledo wrote:Not as easy as that, the outlets have different size unions to avoid this sort of confusion!

But if you knew what you were doing and were replacing the original pipework, you could fit the appropriate unions to the appropriate pipes?

Well yes you could! certainly I could, the pipework on the Carledo is almost entirely bespoke, incorporates an eclectic mix of metric, unf and bsp unions, has no lsv or pdwa but does have a rear brake pressure limiter valve and an electrically operated front brake line lock.
But why would you want to mess with the circuitry to produce 1 circuit for 1 front wheel and one circuit for the other 3? It doesn't make sense, especially as a rear wheel cylinder leaking is THE most likely fault. Left unattended this will leave you with only the o/s/f wheel braked, whereas the original design will leave you with both front brakes still working after a similar failure (a failure I would regard as "operator as responsible as component"

Steve

I'll only say this....
Assymetric braking is the last thing you want in an emergency situation...especially in a car with no anti
lock brakes.

Jonners

I'll only say this....
It's going back on the car as it came off....only because I don't want someone at a show to hold me up on it!!

James