Changing the brake fluid from DOT 4 to DOT 5

[MikeNash]

Dear all,
Once again I've got dodgy brakes and will have to remove the cylinders to restore or replace them, and I intend to take the opportunity to make the above change. While removing the cylinders will enable me to clean them, for the pipework I can only blow through with an airline and perhaps (as recommended in places on the interweb) wash through with meths. For the master cylinder I'll drain as best as I can and perhaps wash and drain with meths as well.

Has anyone else made this move with an installed system? I'll be grateful of your experience and recommendations, MikeN.

[Bill_qaz]

Why not use brake cleaner rather than meths, being in aerosol you can blow it through the pipes etc.

[MikeNash]

Well Bill, Wikipedia suggests that some brake cleaners aren't good for rubbers and plastics, and while they're designed to evaporate away and leave no residue and so should be OK for cleaning pipes, at the moment I favour the less worrisome meths. I suppose getting the DOT 4 out of the master cylinder completely will be the real difficulty, but that said, I can't see that a little drop of remaining DOT 4 will cause any major difficulty. And that's why I'd like the advice of anyone who's already done it.
MikeN.

[svenedin]

I can't offer any advice on the switch over on an installed system but I can say I have never regretted the switch over to Silicone brake fluid some years ago. At that time I replaced the entire braking system; all of the pipework, master cylinder and all of the cylinders. I have not had a seized cylinder since and I no longer worry when bleeding the brakes because Silicone brake fluid is not going to ruin paintwork.

I would suggest a warning sticker next to the Master Cylinder saying "DoT 5 Silicone Brake Fluid Only!". I made one with my label machine but found a better one at https://www.isaydingdong.co.uk/ourshop/ ... ite-3.html or https://www.isaydingdong.co.uk/ourshop/ ... ite-3.html
This is in case a mechanic tops up with the wrong fluid. Automec Dot 5 is a rather nice colour of purple but it could still happen.

Stephen

[Bill_qaz]

Well Bill, Wikipedia suggests that some brake cleaners aren't good for rubbers and plastics, and while they're designed to evaporate away and leave no residue and so should be OK for cleaning pipes, at the moment I favour the less worrisome meths. I suppose getting the DOT 4 out of the master cylinder completely will be the real difficulty, but that said, I can't see that a little drop of remaining DOT 4 will cause any major difficulty. And that's why I'd like the advice of anyone who's already done it.
MikeN.

Don't believe everything on Wikipedia it can be freely edited.
Better to check manufacturers information for suitability.
As an example Holts product states paintwork safe, so I doubt its going to harm seals or covers. As it sprayed on brake components.
But you have to do what you feel comfortable with.
https://share.google/iGbgK3zj5sNhlYAfA
Product Details ( source in above link)
As one of our most popular professional products, Holts Brake & Parts Cleaner is also one of our most versatile. It can be used anywhere around the workshop, on a multitude of different metallic parts.

Fast acting, powerful cleaner
Quick drying
Cleans and degreases any surface
Paintwork safe – Acetone and silicone free
360° spray
It’s a powerful and fast acting cleaner and degreaser, ideal for cleaning metallic parts such as callipers, drums, springs, brakes and clutches. Holts Brake & Parts cleaner is best used to remove brake dust, brake pad residue, grease, dirt and oily deposits.

It’s not always easy to access components in modern vehicles, so our specially designed product will work at all angles. The 360° spray can be used upside down, this means you will be able to get to all of those hard-to-reach spots with ease.

Finally, Holts Brake & Parts Cleaner cleans faster and uses less product than competitors, giving you great value for your money

[Mervin]

I changed to Automec silicone (DOT5) brake fluid over 20 years ago. I was renewing all the wheel cylinders, flexible hoses and master cylinder so decided on DOT5 on completion.
I didn't use anything in the lines and only relied on flushing/cleaning them with the new fluid as part of the bleeding process. I have not experienced any problems since then and those same components are still in place.
All I have done is change the fluid about 5 years ago in spite of Automec suggesting it's not necessary. https://www.automec.co.uk/products/sili ... luid-dot-5
Possibly any residue of DOT4 in the master cylinder would be flushed out during bleeding? However, I did read, some years ago, don't ask where, that when changing to DOT5 from DOT4 the recommendation is to renew all the rubber seals etc..

[King Kenny]

I too replaced the whole system fitting Automec pipes and used silicone fluid. That was over thirty years ago and I have never has a problem. No more rear cylinders seizing. I can only remember changing the fluid once in that time. I fitted front disks and new flexables. Well worth it.

[MikeNash]

Thank you for all your replies and advice. It's been encouraging, and so in a few weeks time I'll start the repair or replacement of the cylinders, replace the hoses and thoroughly blow through all the pipes. The master cylinder will need especial care to inspect and empty. I'll keep you all informed how it goes.
Regards from MikeN.

[svenedin]

Depending on how old the master cylinder is and how long it is since it had an overhaul, it might just be better to take it out and overhaul or fit a new one. It's such a tedious job to remove it that my thinking is it is better to go ahead and do it than to have issues when switching fluids. Silicone brake fluid is rather expensive so you don't want to have nightmares trying to bleed the system due to master cylinder problems.

Stephen

[MikeNash]

Stephen,
I changed the original 1963 master cylinder a few years ago and it should remain good enough. (It's not a job to be repeated without good cause.) I'll be replacing the brake hoses though.
Thank you for your comment, MikeN.

[Allen70]

As, I also run a classic Harley-Davidson which has Dot5 for its brake fluid. One day just for curiosity after changing the B/F in the Harley I had a jam with Dot4 in it and I decided to mix Dot 4 with Dot 5 in the jam jar to see how the mixture reacted, and the result was the combined mixture turned into millions of black shards, very strange. As I say, it was only for curiosity.

[King Kenny]

If you remove the master cylinder by bending the torsion bar make it easier to refit and remove next time by grinding the top off the hex on the bolt head. All the force is front and back so there is no stress on the bolt head and it is safe to do. Don't fit the bolt back to front as this may result in more problems with clearance. The torsion bar will not need to be forced down as much when the adapted bolt is removed.

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