brake fluid dot 5 to dot 4
 

I've have had my backdraft sense 2004 car #84
my question is should i change out my dot 5 to dot 4 ??
wilwood brakes when called them does not recommend dot 5 in any car
so can i flush dot 5 out, and put in dot 4 with the seals i have in my car
any ideas

Ed, Flush out a couple of times with alcohol. Then flush Dot 4 through once.

what type and strength of alcohol?

I use high percentage 91 to 99% Isopropyl alcohol. Some of the stuff in your medicine cabinet is only 70%. 30% water.

I know a lot of cobra from backdraft use dot 5 brake fluid , just like to know how many have change to dot 4 . also have they run into any problems after a flush ,and do they think it's worth it ??
ed

Why? You've been driving it like that 17 years. What makes you want to change now?

The big problem with 5 is that it can attract water, which then ends up in the calipers. And that's bad for a number of reasons. As long as you flush the system with new DoT 5 fluid regularly, it won't be an issue.

Most brake fluid is hygroscopic so I don't really think your fixing anything by changing

This is actually backwards, Dot 5 does not absorb water. Dot 5 is silicon based and was developed to be used in cars where excessive moisture would cause problems. Dot 5 also has a higher boiling point and offers better corrosion, rust resistance and generally lasts longer than Dot 4. I don't see any advantage to changing. Incidentally, I'm running the Wilwood brakes on mine with no issues.

Dot 5 does not absorb water, so any moisture (condensation, possible if not a fully sealed system) can end up sinking to the lowest point (calipers). The water corrodes the calipers. Water also has very low boiling point at the worst possible place in the system (again, calipers), which can lead to sudden no brake condition because of water vapor, but the fluid in the reservoir looks pristine. Regular bleeding helps avoid this unlikely but possible scenario.

Conventional Dot 4 and below: any moisture mixes readily, leading to a gradually lowering boiling point and degradation of the fluid. The fluid in the reservoir looks bad too. More predictable and gradual compared to the silicon fluid situation. Regular flushing to remove the degraded, moisture containing fluid.

Be sure you are not confusing DOT 5 with DOT 5.1 which are two totally different base fluids.

DOT 5 is silicone based, and DOT 5.1 is Poly Glycol Ether based, much like DOT 3 and DOT 4 are. DOT 3/4/5.1 are all compatible with each other and can be recognized by their clear color, even though the color will turn a dark rust color over time. The disadvantage to this fluid is that it is hydroscopic and over time, will absorb water which in turn lowers it's boiling point.

DOT 5 being a Silicone based fluid is not compatible with Poly Glycol Ether. DOT 5 can be recognized usually as a purple color. If added to a system that previously used Poly Glycol Ether, the reaction between the two fluids will cause any rubber parts to break down and leak.

If you taste them on the tip of your tongue, DOT 3/4/5.1 will be 'bitter', almost like anti-freeze is. DOT 5 silicone will taste 'bland', and almost like nothing... much like mineral oil.

The primary advantage to Silicone is that it is non-hydroscopic. It will not absorb water as poly glycol ether will, therefore making is a much longer lasting fluid. The most significant disadvantage to silicone fluid, is that it is much more compressible than Poly Glycol Ether. Used in either brakes or the clutch system, it would give the clutch a spongy feel, and not present a desirable condition for a performance car of any type.

As an aside, The dry boiling point of DOT 5 Silicone fluid is 500º F and Wet is 356º F. However, Wilwood's economical DOT 4 based fluid has a 571º F boiling point, and the more expensive Motul is at 600º F.

The following is in addition to the previous posted comments. My understanding, given I’m not a brake system expert: DOT5 doesn’t absorb moisture, where DOT3/4 will absorb moisture. All hydraulic brake systems ingest moisture from the atmosphere. The moisture ingested into the hydraulic brake system is detrimental to the system. Moisture in small quantities and at less than extreme braking conditions is not a significant degradation to the performance of the system. However, over time as the moisture increases in the system it has an increasing negative impact. For this reason, brake fluid either DOT5 or DOT3/4 need to be flushed periodically with clean fresh fluid of the same kind as previously in the system. DOT5 is not compatible with DOT3/4, which are usually compatible with each other. DOT5 doesn’t absorb the moisture and it will settle to low points in the system, usually the calipers. The pool of moisture in the low point of the system, if not flushed can corrode the system where it pools. DOT3/4 absorbs the moisture, which keeps it from pooling, although still detrimental. If it were me, assuming no existing damage to the system or performance issues, I would sufficiently flush the DOT5 with new clean DOT5 and continue to do so every 3 years. When I have transitioned a brake system in the past from DOT5 to DOT3/4, I always completely rebuilt all the components in the system, eliminated all the previous fluid and then introduced the new non-compatible fluid.

Thunder1, Sorry for the hijack, but I'm glad you posted this.

I think I screwed up, I looked on the cap (actually for the clutch ) and it's says "Dot 3" so that's what I topped off my fluid with. I just discovered that my MC is leaking through and filling up my brake booster. That in turn, leaked all over the carpet of my footwell. (was that because I mixed 5 & 3?)
I have ordered a new MC and Booster about 5 min ago. Upon flushing the system, Im assuming with Alcohol like above, I should refill with Dot 5? Because I would have gone right back to 3. Build is #496

This thread started to get me concerned as to what brake fluid was in our BDR Roadster. I prefer to stay away from DOT 5.0 Silicone fluid.

Our vehicle order number is 2228 delivered in August, 2021 & the owner's manual states Dot 3 or Dot 4 Synthetic.

Have a good rest of the weekend.