Dot 5 & Spongy Brakes

39 STD

39 STD

Senior Member
I've got my brake system ready, with cleaned lines & new MC and wheel cylinders, for fluid.
All the past posts state that Dot 5 gives a spongy feel to the pedal. And that this is normal. My question is, Now Spongy? Is it enough that you feel that you have to pump the brakes? Or maybe 1/2" more pedal travel?
How does the "Spongy" feel on a system set up correctly?
 
It is firm once correctly bled.The stuff intraps air really bad. You have to be carefull in poring and when pumping the brakes to blead them. Bubbles stay in the fluid and dont rise like with Dot 3.
 
My experience on a 53 ford is they are not spongy but I have to press harder coming up on a red light to stop,say 50-100 ft out. Only change that I have noticed since I switched about 7 years ago. On a 39 ford, no noticeable change. Charles
 
My first change to DOT 5 was in a '57 Ranchero. I felt no change in brake pedal, the only change was the end of replacing brake cylinders. When I built my '40 as a street rod and activated the brakes in about '90 I used DOT 5 because of the positive experience with the '57. It has ALWAYS had a spongy pedal. It isn't really noticeable until a really hard stop, then the pedal goes down about another inch under the pressure. No power brakes, just manual. I've driven the car about 70,000 miles, so I guess I've leaned to live with it.

To be fair, it could be a faulty master cylinder but it was a new dual chamber (or rebuilt, I don't remember). I just have never changed it to be sure.

My thoughts are that the firewall mounted master cylinder is better for DOT 5 maybe because it is above the wheel cylinders and can throw off the air better.
 
The difference in the "feel" between the dot 4 and the dot 5 is a fine point of difference. If you can notice a problem, then something else is wrong.

Charles, I cannot see that the type of fluid in the system could make any noticeable difference to your stopping ability. If you changed linings then yes because there are many possible lining types.

If you change more than 1 thing at a time, it is hard to know where the fault lies.
 
Ditto on the something else is wrong, faulty components, bleeding etc. etc. Been using DOT 5 for over 15 years, never had spongy pedal.
 
I have a number of old Fords with DOT 5. When bleeding you don't want to pump the peddle. I put a 8 or 10" clear plastic hose tight over the bleeder valve with the box wrench on the valve. Take a clean dry plastic water bottle and put a little DOT 5 in the bottle. Put the hose down into the fluid and have someone press the peddle slowly down holding it firm at the bottom, crack the valve, let a little fluid into the bottle and close the valve, Do this 3 or 4 times to each wheel not pumping the pedal and I think you will find a normal brake pedal feel. You can reuse the clean fluid. G.M.
 
Fluids don't compress any noticeable amount unless it has gas mixed in in the form of bubbles (trapped air). Brake systems with low mounting of the master cylinder (like most old Fords are) don't allow for self bleeding of the system well since there is little gravity flow to help. Modern systems with high mounted master cylinders are much easier to purge than the older types are. Modern bleeder nipples usually need some teflon tape to seal the threads due to leakage past threads during pressure bleeding attemps. The threads are just a little too loose for easy bleeding with a hand pump or pressure pot.

The Lockheed type brakes used by FoMoCo in the early hydraulic brake era have to have good shoe fit to the drum. Most auto shops back in the day either had their own shoe grinders or had a local shop that could grind the shoes for them for best shoe to drum fit. This is also something that can cause spongy pedal feel if the fit is marginal.
 
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