Brake Fluid swap?

[79avantiII]

Thought I might ask one more question about brake fluid. After fixing up the avanti, the rear driver wheel would lock up so I replaced the wheel cylinders as they were leaking. After doing this I bleed all the lines out but instead of using dot 5, I used dot 4. I don't like dot 5 becuase one its expensive and two bubbles seem to get in it so easy. I have read different opinions on this swap. One being its dangerous as the seals will deteriorate very quickly and cause brake failure to its fine as long as you flush out the line completly. Most of the postings though are of motorcycle conversions from dot 5 to dot 4. I still have the original bendix master on the car. I did the swap and it seems to work much better than before (easier pedal, less spongyness) but I don;t want to put myself in a dangerous situation.

[Gunslinger]

Anytime you change from or to DOT 5 fluid you have to completely flush out and dry the entire brake hydraulic system. Any mixing at all will create problems. In fact, most, if not all, manufacturers of performance cars specifically state not to put DOT 5 fluid in their products.

The seals won't suddenly fail...they have to already be wearing out. It would be a good idea to change all the seals if you've changed fluid types. Seals have to be kept lubricated. If the car isn't driven regularly, once a month or so simply pump the brakes and that will make the pistons move and keep the seals lubricated.

If you're having a rear brake locking up, it could be from a misadjusted brake shoe or from being soaked with brake fluid from the leaking wheel cylinder. Pull the rear drum and if any shoes are fluid soaked, all you can do is replace them. There's no getting the fluid out of them.

[SBCA96]

I have been using Dot 3 Synthetic .....

http://www.valvoline.com/pages/products/pr....asp?product=51

SynPower High Performance Synthetic Brake Fluid is recommended for ABS, hydraulic drum and disc braking systems and hydraulic clutches requiring DOT 3 and DOT 4 fluids. Its premium, synthetic, low-moisture formulation provides superior anti-vapor lock protection. It has a high dry-boiling point up to 500°F that reduces the risk of fluid vaporization and possible brake failure.

*Exceeds DOT 3 and DOT 4 specifications

*For most ABS, disc or drum brake systems

*High boiling point reduces risk of brake failure

*Compatible with conventional brake fluids

Tom

[79avantiII]

I have been using Dot 3 Synthetic .....

http://www.valvoline.com/pages/products/pr....asp?product=51

SynPower High Performance Synthetic Brake Fluid is recommended for ABS, hydraulic drum and disc braking systems and hydraulic clutches requiring DOT 3 and DOT 4 fluids. Its premium, synthetic, low-moisture formulation provides superior anti-vapor lock protection. It has a high dry-boiling point up to 500°F that reduces the risk of fluid vaporization and possible brake failure.

*Exceeds DOT 3 and DOT 4 specifications

*For most ABS, disc or drum brake systems

*High boiling point reduces risk of brake failure

*Compatible with conventional brake fluids

Tom

I was reading a post on the stude site about brake fluid posted the other day about the guy with the steeltech conversion and low brake pedal. Mine is a 79 and the owners manual still called for silicone fluid. How do you know when the line is clear. Simply looking in the reservoir for cloudyness???? I saw the line had to be dried. Is this still applicable with a silicone based fluid??

[SBCA96]

A brake shop should be able to pressure flush the system.

Tom

Mine is a 79 and the owners manual still called for silicone fluid. How do you know when the line is clear.

[WayneC]

I've used dot 5 in several Avantis. I didn't take any special precautions drying out the lines, but in each case the changeover was done in the process of overhauling the brake system with new/rebuilt wheel and master cylinders and new flex hoses. I did it in an attempt to avoid any condensation/corrosion issues when I lived in northern climes, but I moved to milder climate a few years after the change.

I've had no problems I could attribute to dot 5 over about 25 years of using it, so Imy opinion is that the fears of mixing very small quantities of older fluids with dot 5 are overblown.

I certainly find no reason not to use dot 4, either, and I wouldn't be overly concerned about getting every last spec of dot 5 out of the system, but I would want to change the fluid throughout the whole system, not merely the rear or front brakes.