Hi Guys,
Probably a really basic question/answer but I wanted to double check with the experts first. Havent owned the car long and need to top up the brake fluid for the first time.
Says dot3 on the reservoir cap but heard some people saying that you can put either dot3 or dot4 in it makes no difference. As I have no clue what the owner before me did, can I just top up with Dot4 and it doesn’t matter if dot3 and dot4 mix, or is that a no no?
Thank you in advance
DOT 3 or DOT 4 will be fine. They are compatible.
If you are buying fluid, Dot 4 is the choice to make - more readily available, more regularly used and very little doubt that your braking system would have been upgraded to Dot 4 some years ago.
Dot 4 has a higher boiling point than Dot 3 and is less hygroscopic. Both of these properties make it superior and the obvious choice.
Dot 3 and Dot 4 mix without issue but Dot 5.1 cannot be mixed with these.
The only time to use Dot 3 would be in an emergency when Dot 4 not available. Difficult to understand why the supply of Dot 3 can be justified.
Thank you!
I’ll top it up with DOT4 fluid.
OOPs! DOT 5.1 IS compatible with 3 and 4. DOT3, 4 and 5.1 are all glycol based. The one to avoid is DOT 5 which is silicone based!
It’s a totally bizarre situation that the silicone based fluid isn’t clearly differentiated in the DOT numbering system.
JS
Yes, Wilson you spotted my mistake - I wondered how long it would take you:-)
This explains better…
Nothing about hygroscopic qualities though that are required to encapsulate any water in the braking system but adversely effect braking efficiency as water molecules compress.
Wow. Dot 3, Dot 4 and Dot 5.1 compatible but Dot 5 not compatible. Crazy! I wonder how many of your average Joes know that? The specifications designations are completely illogical. I hope the blurb on the bottles lists the incompatibilities for the different Dot specifications!
Can I suggest rather than topping up the fluid if there is no proof of the fluid being changed in the past two years, you buy 1.5 litres of Dot 4 fluid and give the system a good flush to clean out the system and then flush a bit more and get new dry fluid in place.
I agree with Eddie on this.If you have no idea when the brake fluid was last changed then it should be replaced and not just topped up. If you have a pair of ramps then a relatively easy job. Alternatively not too expensive if you get a local garage to do.
The one thing not to take any risks on is your brakes, having experienced brake fade it is not something I would ever want anyone else to suffer, absolutely frightening.
Is this brake fluid issue a common problem with MX5. Is it something that needs doing every 2 years or after so many miles?
I don’t have access to ramps but can’t it be done from the “further away” brake calliper bleed nipple?
Thanks!
Brake fluid maintenance is an issue with all motor vehicles, so no, nothing special about the MX5 in this respect.
Two years is the recommended replacement interval for fluid but it can be effective for longer than that. The best way to assess brake fluid is efficacy of the brakes, sponginess of pedal, etc. Basically if the brakes stop you in an efficient manner without any unwanted side effects(excuse pun), your fluid along with the other brake components is probably good.
Having said that brakes are probably the most neglected service item on a car - criminal really.
Many threads and how tos on brake fluid replacement - just do a search.
Brake fluid replacement is something that needs to be done as part of the maintenance of every car, not just the MX-5. The recommended service interval is commonly set at two years, by most manufacturers.
its not possible to bleed all of the old fluid from only one caliper, all of them need to be bled individually. Each brake line to the calipers is in effect a separate “dead end street” and the only way to get the old fluid out is through the bleed nipple of each one.
I agree, and on 1960s cars with drum brakes it came as standard - “engage low gear now” signs before the top of steep descents were not to be taken lightly.
Changing fluid won’t stop fade however. But it might stop old, moisture-laden fluid from boiling which is even more frightening. Happened to my brother on a 2 litre Vauxhall Viva, in the days when changing brake fluid was never thought of. Pedal went straight to the floor, no retarding effect whatsoever. The car was probably 10 years old, and had certainly never had a fluid change.
Fluid changes on the ND are scheduled every 24 months or 25,000 miles.
Having driven, in my early 20’s lots of '60’s stuff…, bikes with drums, single leading shoe things like BSA C15’s, twin leading shoes… Suzuki Hustler,
and cars with drums…, Hillman Minx, Morris Minor, Mini’s, Ford 100E…, I can honestly say that I never experienced brake fade in any of them.
Probably because, though I drove briskly, I wasn’t actually caning them. Basically, the brakes were reasonably well up with the dynamic capabilities of the
rest of the car.
At the time, I was more concerned about making sure I didn’t impale myself on the steering wheel. Hence seat belt.
I’ve owned around 40 cars. I’ve never sat down and done a complete brake fluid change on any of them. I’ve obviously worked
on a brake(s), bled it well through, and given the master cylinder a substantial top up. But never a complete change.
I generally view 24 month changes of brake fluid to be a ‘luxury’ service item. As in not particularly necessary.
Similarly I drove a Morris Oxford, Minor, Minis etc. My brother had a Minx that he took me to my wedding in, before parking it out of sight.
There were several notorious hills within a short distance of where I lived then in West Yorkshire - the kind that lorries would run away on from time to time and I can remember at least two of those ending with fatalities. I actually attended the aftermath of one of those in 1973 while I was working for a motorway contractor, and we were called to shore up a half demolished shop. I also drove far too fast in those days, being immortal of course.
Brake fade was certainly something I was aware of, especially on the Minor. My younger brother worked in a garage that many years before had been a Morris dealer. He cleared out a storeroom and found a load of old brake shoes which we thought would keep the Minor going for years. I don’t know whether they go off, but they were truly awful and cooked very easily with the most terrible smell.
'I’ve owned around 40 cars. I’ve never sat down and done a complete brake fluid change on any of them. I’ve obviously worked
on a brake(s), bled it well through, and given the master cylinder a substantial top up. But never a complete change.’
Now that is interesting!
You can use 100% water in the brake system and it will work---------to a point. The water will soon boil and the pedal will go. How much water you are prepared to let into the system over time is a personal choice but even if you never do an emergency stop from 70 your car should always be capable of it.
I would say 4 years in the UK is the maximum I would leave the same fluid in the system. Fluid is cheap and it is a DIY job.
Just goes to show how important it is when getting a new second hand car that all the fluids are changed so you know where you are before you contemplate any spirited motoring.
If your fluid is low enough to need topping up I would suggest you check disc and pad wear as having the pistons further out in the calipers probably increases chances of sticking/seizing on a lightly used car.
Seems looking through all the Service information I got when I bought the car the Brake Fluid was changed during a service in Sept '15 but that was only 5000 miles ago.
Will check over the brakes at the weekend, no spongey feel though and just pasted an MOT so can’t be drastically worn.
Cheers for your help guys
Concerned at the number of people who don’t regularly, or even ever, renew brake fluid.
The issue is brake fluid does absorb water. Under normal braking not an issue but when you need the brakes in an emergency with a laden car and brake heavily from high speed or downhill then the heat input can boil the water in the fluid and you lose all braking.
Follow the recommendations and change the fluid, just not worth risking your’s and other road users lives for a few pounds.