Brake bleeding - which order?

[Carboy0]

My brakes are spongy and need a bit of a shove to slow and stop. I have done a visual inspection and the pads are fine, a PO has fitted braided hoses, there are no leaks front or rear.

The next step is to bleed the system, the fluid in the reservoir looks a bit murky, so I am going to replace it with the purple synthetic stuff.

My question is what is the best place to start on a Stag? I normally start at the rear nearside as it will have the longest pipe run, then the rear offside, front nearside and finally the front offside.

Are there any special tips at all and does the PDWA make any difference?

If this fails then I will need to look at the master cylinder and servo, fingers crossed that it is just air in the system.

[DJT]

You are right to do the longest run first. Remember that the front chamber of the m/cyl feeds the rear brakes and vice versa. If you are too enthusiastic with pumping the pedal you may dislodge the PDWA shuttle valve (red light on dash) and have to centralise it again. Instructions are in the ROM.
Changing DOT4 to DOT5 isn't always that simple. Stories abound of seals swelling, etc.

[scotty57]

Check your braided hoses too, the metal braid can hide cracking & bulging in the rubber if they are old. I had the same problem with my MGB and on checking the braided hoses found the rubber underneath was shot.

[Carboy0]

Thanks Guys

Scotty57 - the flexis are the thin braid over nylon/PTFE type.

[roverv8stag]

The best quality braided hoses will be Teflon lined not rubber. The Silicon brake fluid will have no effect on the PTFE liner but the wire overbraids can still fracture and damage the liner from the outside if they are allowed to rub on moving parts etc. Mine are fitted with a clear outer cover and they just wipe clean when they get inspected whenever I have the wheels off. I also paid the extra and had stainless steel fittings.
Bleed brakes from rear first then front. Reset the PDWA switch as per the manual... it takes a bit of practice but with a careful press of the pedal you can feel the valve move and with the ignition on the bright red light will go out or go dim if its wired to the oil pressure light like some were.

[Staggard]

I would suggest you have a good read up before changing to silicone. Just to be clear what could be involved.

[marshman]

Hi Chris,

Not going to get involved in the Silcone vs DOT4 debate but would add the following:

1. I would strongly advise if you do change to silicone to change ALL the rubber seals and thoroughly flush the system through. I changed to silicone fluid many years ago on my old vanguard and had problems with the seals in the master cylinder swelling and holding the brakes on - I hadn't changed them - it was all OK after I changed all the seals.

2. When changing the fluid and bleeding the system try to avoid pumping the fluid through using the brake pedal. Use a vacuum bleeder or pressure bleeder such as the Gunsons Ezibleed. The reason is that pumping the fluid through using the brake pedal pushes the piston in the master cylinder beyond its normal travel and into a possibly dirty/rusty part of the cylinder bore. This can damage the seals and also push more rubbish through the system compromising other seals. This will then obviously cause more problems.

Personally I would just bleed the system through with DOT4 first to get a good firm pedal then change the fluid afterwards when it is all working correctly. That will only cost a couple of pounds. Otherwise you could flush it all through change the fluid and still find the brakes are no good. Basically Silicone fluid is not magic and will not fix a faulty system.

Roger

[StagJonno]

Everything I've seen in the past week says mixing Dot5 (silicone) with Dot3 or Dot4 (both glycol based) is an absolute no-no. Here's one of many sites:

http://www.epicbleedsolutions.com/resources/faq/difference-between-dot4-and-dot51-brake-fluid/

To confuse matters, there's also a Dot5.1, which is glycol-based and it seems can be mixed with Dot3 & Dot4, but absolutely not Dot5.

I'm just off to confirm that my brake fluid is Dot5 (as advised by the PO) and not Dot5.1 or other. Similarly want to find out what's in the clutch as a new slave cylinder will be fitted soon. Seems that one test is to put a drop of fluid into water - the glycol-based ones will easily mix; the silicon (Dot5) won't.

Watch this space.

Jonno

[roverv8stag]

Agreed silicon fluid as a "fix" is just wrong. You cant change the hydraulic principle that air in a closed system is compressible therefore spongy pedal will remain.

In a new system with clean new parts then the debate can take on real meaning... but its still up to the user to decide.
The amount of fluid I've used is massive and expensive. But I did eventually find the leak without damaging the paint now I wouldn't change back. (The damaged paint would have found the leak sooner ????)

[Robmsharp]

When I rebuilt my Stag all parts in the braking system were new, so I took the opportunity to use Silicon brake fluid and all has been fine ever since then.
As many people have said, ONLY consider Silicon if you are confident all parts in the braking system have been either renewed or thoroughly cleaned.

[Carboy0]

Lots of useful advice thanks guys.

I saw that using the Dot 5 fluid as an upgrade rather than a problem fix. I don't know the age of any of the rubber components (except that they are not new), so I will head the warnings and use some Dot 5.1. It's in the garage on the shelf next to the Easibleed kit.

I will read up on the PDWA for future reference.

Assuming a full flush and bleed does the trick, then I'll think about changing to DOT 5 at some other time.

[rac]

Check your braided hoses too, the metal braid can hide cracking & bulging in the rubber if they are old. I had the same problem with my MGB and on checking the braided hoses found the rubber underneath was shot.

Will second that about the flexi hoses-tried for ages to get fluid out of my NSR and eventually found the hose at fault-looked fine externally but must have collapsed inside totally blocked-new flexi sorted straight away

[mole42]

M

My question is what is the best place to start on a Stag? I normally start at the rear nearside as it will have the longest pipe run, then the rear offside, front nearside and finally the front offside.

Don't forget that on the Stag, the longest run is the rear offside. It seems odd, but the PDWA valve is on the nearside and so the front-to-rear pipe runs along the nearside which is where the rear tee is positioned.