Want to get the DOT 5 out
 

I put DOT 5 in my new braking system and have found the brake pedal is terrible, so I want to switch back to DOT 4 brake fluid. The entire brake system is new with about 10 miles on it. I have heard alcohol will clean the silicone out and then I can refill the system, bleed and hope for the best.

Anyone have any other suggestions?

Thanks, Mark

Your not bleeding the system completely in that case!

I have changed over to dot 5 in 4 cars and never had a different pedal feel when all was right!

Is the car Disc & Drum?

If so the adjustment of the rear Drums has a huge effect on pedal feel!

If it's Drum rear and the backing plate is worn then those support pads can hang up the shoes from moving out the distance needed to work well.

Agree, you problem is NOT the DOT 5.

Probably incorrect bleeding.

My 78 TA has had DOT for darned near 30 years and autocrossing and making the first turn around at the strip after 125mph has a good pedal. Something else is the issue.

Keep the 5, that’s all I use In my 78.
The shows on tv say not to use 5, so did the inline boob guys, their all nuts. My pedal is rock hard. TWSS

Agreed, the DOT5 fluid is not the problem. I would say Steve25 is on the right track. if it's a disc/drum setup, check the adjustment of the rear drum. If it's disc/disc, check the adjustment of the parking brake for the rear calipers. Both adjustments effect both the height and the feel of the pedal.

I personally would not under any circumstance even try to clean out a system that has DOT5 in it to run a conventional brake fluid. It's asking for trouble. If you're dead set on this idea, rip the current lines out and replace with new.

We use dot5 in every car we restore.. Some with over 25 years no issues

Wow, you guys like the DOT 5. This is the first time I have used this stuff except for when I used it in the clutch system of my Fiero's. The braking system is totally new, SS lines, new calipers, new rotors, new drums, new springs in the drums, new brake cylinders, new master, new booster.
I'll get the car up on a lift and start bleeding it again and make sure the brakes are adjusted up again. I hope it gets better, I almost wish I had kept the old system on it right now.

Thanks again for all your opinions, you guys have all made this project a heck of a lot easier.
Mark

Hi Mark: What size brake booster are you using, and how much vacuum does the engine make on idle?

Does it pump up?

I'm a little late to the party, but another long time user of DOT 5 in my cars. Absolutely no difference in brake performance or feel.

If you still have problems after insuring there is no air in the lines, then you will need to look at the new parts. I chased my tail for over a week only to finally discover that one of the new wheel calipers had an imperfection and was trapping air that couldn't be bled out - and this fiasco was a DOT 3 filled system.

Also if your system was taken apart, open and dry for a good while then I have had the proportioning valve hang up me, which can take a while to figure out!

The car was in storage for about 4 years when we started to restore it. The braking system was torn out and put back in over the same weekend. We will have to check on the proportioning valve though. As for the size of the booster it is the same size as original, I got it from Ames. Today is the day we refire the engine, so at the moment I am not sure of the vacuum yet. I am using a stock HO cam, so I think the vacuum should be pretty good. This afternoon will tell a lot about what is going on with it once the car is warmed up and idling good.

Thanks again, Mark

Another DOT5 user here. Stuff has been in there 25 years. Works but getting it bled the first time took a little doing. Speed Bleeder zerks did the job for me.

Agree with the others that the DOT 5 fluid is not what's causing the soggy pedal. It's either being caused by trapped air or a parts compatibility issue. There's certainly nothing wrong with DOT 5. It has a higher boiling point, does not attract moisture, and does not damage painted surfaces.

Good luck!

Don't take offense to the question but was engine running when braking checked? I assume it was based on 10-miles on it

We got the car restarted today!!!!!! Still have some minor problems to sort out so the car was not even moved. I will be working on those things over the next few days, so when it moves the first stop will be a telling factor. I learned a lot from you all over the last few days, Thank You!!!!

The motor seems to have real good vacuum, so I am leaning toward a real good bleeding and adjusting coming up.

Mark

Easiest way I know of to test if the rear adjustments are the issue is to turn the car on and have somebody with a pair of pliers clamp the soft line at the bock before the brake line T.

If the pedal is soft/squishy without the line clamped and it becomes high and hard after it's clamped. You know you have an adjustment issue, air in the lines or a leak issue after that T. most of the time it'll either be adjustment, trapped air or a combination of both.

To bleed a 71 and up, you MUST press the button on the end of the combination valve to get a good flow and air out. Also bench bleeding helps, as well as a master with bleeders on the master . I now use a pressure bleeder and a fat zip tie on the combination valve. Been using Dot 5 in my 80 ws6 rear for 12 years. Pedal was a tiny bit softer, but barely noticeable. I love it.

No. Not unless you're using a pressure bleeder with moderate pressure. Low-pressure or vacuum bleeding doesn't close the valve, high pressure pops the valve off it's seat. Moderate pressure from a pressure bleeder is enough to close the valve, but not enough to pop it off it's seat.




I have never used DOT 5. Everything I know about it is hearsay, and from years ago.
1. DOT 5 has a tendency to emulsify air. There's a zillion tiny bubbles that take a long tome to rise and pop. Getting a good pedal requires time and lots of care. For fook's sake, don't pump the pedal briskly until AFTER the system is properly bled.

2. DOT 5 is--or at least, used to be--higher viscosity than DOT 3 or DOT 4 (glycol-based brake fluid.)

3. DOT 5 doesn't lubricate as well as DOT 3 or 4. In combination with #2, this leads to slower pedal return when you pull your foot out.

4. DOT 5 doesn't absorb moisture. Any moisture that is in the system drops to the wheel cylinders and causes corrosion. With glycol-based brake fluid, it's entrained in the fluid until the fluid saturates.

If I were looking for fancy brake fluid, I'd be using 5.1. Still a glycol-based fluid, so probably not paint-safe.