DOT4 or DOT5?

[S1Vixen]

Hello Group,

A perrenial question I'm sure, but I have a once in a lifetime opportunity to select brake fluid type (as I have replaced every hydraulic component in the system). The question is whether to make the switch to silicone based fluid from glycol. The primary driver for me is that DOT5 won't eat the paintwork and the bodywork bill on the Vixen still smarts. I know this sounds a little odd as the brake fluid shouldn't really be coming into contact with the paintwork but I also subscribe to Murphy's Law. On the other hand I read some negative comments regarding a slightly softer pedal with silicone fluid.

So, does the group have a view on the relative merits of DOT4 and DOT5 and any experience on the Vixen series with DOT5?

Thanks

Steve

[TVR_owner]

DOT 5 if your main consideration is paint damage?

[RCK974X]

As explained to me.....

DOT 5 is great because it doesn't absorb water, or attack paint work. It lasts forever (more or less).
Problem is that if you do get water in the system, it doesn't mix at all, so water can boil and cause vapour locks quite quickly. As soon as you put anything else but DOT 5 with it it loses its benefits.

Newer DOT 4 spec only slightly attacks paintwork and desn't absorb nearly as much water as older brake fluids. It still absorbs some though, so does not last forever, but effectively ends up with higher boiling point if some water present.

DOT 5 is therefore good if you don't do a lot of heavy braking (i.e. track work) as it should be considered to have a low boiling point. (not really true, but because of the water).

This of course assumes a damp climate (UK) ...

[bluezeeland]

Not sure about Vixen', but M' used DOT3 ex works
The consensus about these seems to be that DOT4 is 'enhanced' DOT3, while DOT5 is different alltogheter and known to attack rubber parts in the cylinders. DOT4 may not have eternal life, but is quit a bit cheaper to change now and again then your master and slave cylinders (and a lot less work) so..go for DOT4

[RCK974X]

I believe they have fixed the problem with DOT 5 attacking the seals....it was the early formulation that was the problem. I think it still can't be used with some Citroens (or something French).

DOT 5 is silicone based fluid, whereas the DOT 3 and 4 are glycol (? I think)

[Loubaruch]

I ran a 1600M for 24 years with DOT 5. The guy who rebuilt it replaced every brake component including all brake lines and flexibles before filling with DOT 5. Although it was never tracked or driven heavily the fluid was unchanged during the 24 years and the brakes were always 100%. In fact apart from a caliper sticking about 20 years ago and annual cleaning they never needed any work apart from changing the pads. The MOT tester always remarked how impressive the brakes were. I understand that if any old DOT4 remains in the system you could have problems but if everything is new, OK. I sold the car last year but would always opt for DOT5 if given the choice.
As said above for track/race use DOT4 is probably a better option.

[TVR_owner]

S1 vixen, nice and light so even on track I would imagine a dot 5 would do.

[heightswitch]

Loubaruch said:

I ran a 1600M for 24 years with DOT 5. The guy who rebuilt it replaced every brake component including all brake lines and flexibles before filling with DOT 5. Although it was never tracked or driven heavily the fluid was unchanged during the 24 years and the brakes were always 100%. In fact apart from a caliper sticking about 20 years ago and annual cleaning they never needed any work apart from changing the pads. The MOT tester always remarked how impressive the brakes were. I understand that if any old DOT4 remains in the system you could have problems but if everything is new, OK. I sold the car last year but would always opt for DOT5 if given the choice.
As said above for track/race use DOT4 is probably a better option.

24 years on same brake fluid....I am glad I never bought that car knew it had a dodgy service history ..Tell me it didn't go abroad Paul?
N.

[Loubaruch]

How are you Neil? Is that museum exhibit mobile yet?

The fluid was tested each year (I have an electronic device that measures water content etc.) and it always surprised me but it never failed the test and the brakes were always spot on.

Car advertised on the Saturday morning, had a call pm from Hong Kong and another in the evening from Shropshire. Car sold on Monday to Shropshire, buyer remarked that it both outhandled and out performed his MX5, that was a surprise.
I was left with pile of notes thick enough to choke a horse. Miss the old thing but as you know too many other cars and a better investment than money in the bank, sold for 250% more than I paid.

[heightswitch]

Glad it went to Shropshire and not Hong Kong.
That was a lovely car. The Static exhibit is in the final stages of labour at the mo. Just a few more jobs and down to Blackpool for wiring. Just spilt 2.5 litres of Black resin on the garage floor tonight...Fitting the inner wings back on car only to cut them off again and glass them back up to form a flange to allow them to be removable. Fire up should be in about a couple of weeks. I shall pop in when I am passing next..Please do the same.

best.
Neil.

[Astacus]

heightswitch said:

The Static exhibit is in the final stages of labour

Now that is a good money making scheme, breeding TVRs!

Seriously, is she going to be on the track this year?

[Fiscracer]

I've used a DOT 4 for at least 15 years of racing without any problems - never boils, never takes in water and not too expensive.

The only problem I've ever had was when I took my LWT E type for its MOT last year. The mechanic couldn't get the brakes to work (he tried racing pads from stone cold)and then told me I'd put antifreeze in my brake fluid because it was blue. I took the car 400yards up the road, came back and then told him to try the brake test. W****r.

ATL Racing Blue

[S1Vixen]

Thanks for all the feedback. I'm opting for the DOT4 and being careful on filling the master cylinders over the paint!