MG-Cars.net

Welcome to our resource for MG Car Information.

Recommendations

Parts

MG parts spares and accessories are available for MG T Series (TA, MG TB, MG TC, MG TD, MG TF), Magnette, MGA, Twin cam, MGB, MGBGT, MGC, MGC GT, MG Midget, Sprite and other MG models from British car spares company LBCarCo.

MG MGF Technical - When should the brake fluid be changed.

Hi,

I have just booked my car in for its second year service, (it has only done 13,000).

The MGF garage told me that the brake fluid should be changed every two years and is not part of the service, therefore will cost an extra 23.50.

Does this sound right - should I bother having the brake fluid changed based on its age and short mileage.

Thanks for any advice.
Derren

No!
PAUL.

Derren,

This does sound right. The fluid should normally be changed every two years regardless of mileage and it is marked as a "charge extra" item on the service sheet. The problem with the type of brake fluid used in the f is that it attracts moisture which may eventually lead to rust inside the pipes and as water boils a lot faster than brake fluid may cause problems if you use the brakes hard.

Spyros
Spyros Papageorghiou

Darren,

Maintenance Check Sheet RCL0397ENG(2) states in item 44 "Replace the brake fluid every 24 months regardless of mileage"

Is the extra 23 for the fluid "part" or the labour to change it?

At my 48K service (last Aug) I was charged 14.85 + vat for the labour and 2 for the fluid.

Two years is a good idea for a brake fluid change (time as opposed to mileage) as:-
The fluid is hygroscopic and will "absorb" moisture from the air. This moisture (if heated in the lines/or at a brake caliper) will boil and become steam in the brake line/caliper. Steam in the lines is air, which unlike fluid, is compressable and your brakes could become "spongy" during a heavy/long brake.

What's 23 for peace of mind?

Paul Lane
Paul Lane

Better still, why not upgrade to DOT 5 spec fluid?
DrDave

DOT5 still absorbs water though doesn't Dave?

I have DOT5 in mine, but that's a decision precipitated more by the kind of driving I do rather than anything else.
Rob Bell

Yes DOT5 still absorbs water, but it boils at a higher temp- reducing the possiblilty of brake fade

Will
Will Munns

How can DOT5 change the boiling point of water?

Cheers

Patrick
Patrick

Patrick

You are being difficult again:-)

I think Will means that DOT5 has a higher boiling point.

Ted
Ted Newman

Errm, it can't but it (itself, you know the DOT5 stuff) boils at a higher temp- in fact I seem to remember that it is more hydroscopic than DOT4 (but this you shouldn't quote me on!)
Will Munns

Oh and salt, that changes the boiling point of water so it's not that far fetched!
Will Munns

For normal everyday use then IMO changing the fluid every 2 years is simply lining the dealers' pockets *unlewss* you have signs that it needs doing, ie a spongy pedal or a reduction in pedal 'feel' from new. If it ain't broke, don't fix it. However for 'performance' driving I would change the fluid a lot earlier than 2 years, use DOT 5.1 or Race spec fluid, and change it annualy.
David

Derren

The moisture picked up by the brake fluid not only reduces the boiling point of the fluid and causes rust in the pipes and calipers, it can also cause rust and malfunction in the ABS system. Now that IS expensive to repair/replace. That is the main reason why the 2 year fluid change has come about in recent years..with the introduction of ABS on most cars.

Nick
Nick

David,

I think you are also misrepresenting car builder's intent.

The manufacturers have a vested interest in minimising the cost of ownership as it sells cars. They also surely have no interest in raising maintenance costs as they do not benefit from your spend with the garage. Just look at the reduction in maintenance that cars need with service intervals extending to 15k miles. My first car needed a service every 3k miles!

The manufacturers have improved the safety of cars both out of marketing considerations and to avoid being taken to court. Brakes are, arguably, the most important safety equipement in the car. If in this nevironment the manufacturer says change the brake fluid every 2 years, this seems a very small price to pay for working brakes.

My question on DOT5 was serious. My understanding is that if you have water in your brake fluid, then under heavy braking the heat generated will cause the water to turn to steam and at this point, you have no brakes. How does DOT5 inprove this situation?

Cheers

Patrick

PS Not all my posts are taking the piss. Many, yes. But not all!

Patrick

Patrick,
No DOT5 will make no diffrence here. However, under heavy breaking the breaks get hot, and localy some of this heat is transfered into the breaking system, this causes local bubbleing of the fluid (like the bubbles you get on the bottom of a pan before it actually get to boiling) The bubbles expand, pushing break fluid back up the pipes, then they cool and turn back to fluid, leaving a vacume - this effect causes break fade and is more lightly to happen if you use the breaks alot (racing etc). DOT5 has a higher boiling point and so the breaks need to get much hotter before it is a problem. This is for the case when the fluid is not contaminated. water will have the same effect in both systems.

Will
Will Munns

Having ridden superbikes for many years the difference felt from a 2 yearly fluid change is quite amazing - Obviously you are more sensitive to brakes on a bike and also as the pressure is felt through the fingers it is easier to gauge the difference

In my opinion change the fluid - for a mere 20 odd!
tony

I am not sure about which is which but some DOT calssifications use different bases for the fluid. These should not be mixed as it can cause damage to the seals in the system. If you want to upgrade to a silicon base fluid that does not absorb water then you should also change all the rubber seals in the master and slave cylinders.

Spyros
Spyros Papageorghiou

Thanks for the info Will and also Tony and Spyros. I think I will stick to the regular "cooking" brake fluid!

Cheers

Patrick

PS This thread is a fine illustration of why the BBS is useful as well as fun!
Patrick

>>it can also cause rust and malfunction in the ABS system.<<

Nick - do you have any more information ?
My ABS recently malfunctioned - despite the brake fluid being changed every two years. It's apparently been fixed by another complete brake fluid replacement.
*but* testing ABS is very difficult (for the end user).

Is there any testing I can do on the ABS unit to show that it works correctly: a road test may show that it detects one locking wheel - but how can I test for any locking wheel ?

>>Now that IS expensive to repair/replace.<<
and how do you find an expert in this area ?

Steve
Steve

A good rolling test is to find a nice lane or track this is surfaced with loose gravel - get the car going at a reasonable speed and slam on the anchors and see what happens.

It is best to have an assistant to stand by (but not too close) to the braking zone and watch the wheels he/she can also be your look out to make sure that there are no other vehicles in the area - after you don't want to be a danger to other road users do you!

BMW use this method to demonstrate the usefulness of the ABS on motorbikes (they have outriggers on the non ABS bikes) and I saw it done at Knebworth during a BMW Bike Rally back in in 1993.

Ted
Ted Newman

Test in the wet. Will be better for the tyres. Hard kick to the pedal at 10mph should give the ABS modulator a go.

Test can me done as well if the car is jacket up. One wheel after the other or all released is anyway.

Switch on the ignition and turn only one wheel. After a half or what turning one wheel the ABS modulator should do a rattling noise. Indication on the function only.
Dieter Koennecke

Patrick - agreed the manufacturers have adopted a 'cover the ar5e' approach which translates as 'if in doubt then renew it'. It may not benefit them directly but a financially healthy dealer will sell more cars, and I hear frequently that they make sod all on new sales but loads if they can retain the servicing for 5 years.
Spyros, I recommended DOT 5.1 because this spec is the only one AFAIK that is compatible with all other types DOT 3 and 4 and 5.
David

Steve

I'm afraid I can't give you any more specific information other than from what I have read about this, the moisture causes corrosion in the workings of the unit which apparently contains moving parts (pistons etc) machined to very close tolerances which will obviously seize if any bits of rust etc get in the way. Likewise, I'm sorry I haven't any experience of having to find someone who can repair these units. I just know that a friend of mine had to have his (not MGR) replaced (under warranty) at a cost to the manufacturer of over 1000.
Nick Pinches

maybe a dumb question - I thought both water and air were required for the rusting process (oxidisation). So if there's a drop of water mixed with the brake fluid, how does air get to it to create rust ?
David

The anchor chain on my mooring ball seems to have no trouble rusting, even though it is completely submerged. Could it be that water is H2O perhaps?
George B.

Dieter - Water > H20 so oxygen - hence rust is always a threat even in a vacumn enviroment

Shame really as water is an excellent lubricant !


A tip for increasing brake performance is to wedge the brake pedal down with a weight overnight

This compresses the fluid and forces air into the resevoir so effectively bleeding the brakes

tony

Interesting fact:
The 'air' which forms in the radiators in your house is actually from the corrosion process- water gets robbed of the Oxygen, so the 'air' in your system is actually pure Hydrogen!

Don't beleive me? then light it! - Note this does work but the flame is almost invisable so switch off the lights and watch your fingers!

Will
Will Munns

This thread was discussed between 08/03/2002 and 14/03/2002

MG MGF Technical index

This thread is from the archive. The Live MG MGF Technical BBS is active now.