Harder Brake Pedal?

[stangs400]

Ok, so right now I have completed the 1le brake upgrade with Wilwood d52 calipers on my 71 Trans am and have the remaining stock drums. I want to convert to disk in the rear and will probably get the Right Stuff kit from summit. As of right now my brake pedal moves probably half way before any braking is done and you have to push it nearly to the floor to get the car to stop. I cannot lock up any of the tires with the pedal to the floor. Now with that said, I will be purchasing all new master cylinder, brake booster, and proportioning valve for a 80' trans am with disc/disc. Am I going to run into the same soft pedal/ travel issues I have now? Is there anyway to make sure I have immediate firm pedal pressure aka High and hard? Do I need a different size Master cylinder?

[79-TA]

First, you should double check to make sure nothing is wrong:
- make sure there are no leaks in any of the lines or connections
- make sure the brakes are properly bled
- make sure all of the linkages from the brake pedal to the master cylinder are attached properly

Did the brakes work fine before the upgrade?

Did you change the pads and rotors also? If so, did you bed them in?

The Wilwoods you installed are two piston calipers. Despite this, it seems they actually offer less hydraulic force multiplication than the stock calipers with one big piston. This is simply a function of the piston area. To check, measure the diameter of the piston on your old caliper and calculate the area, then do the same to the Wilwoods (calculate the area of both pistons in this case.)



The front calipers with 2.00” piston provide 6.28 square inches of piston area per caliper, in order to maintain the original front to rear brake bias and use of the OE master cylinder. Kits contain Wilwood’s hardened slide pins and BP-10 high friction pads. Matching rear calipers are also available for custom installations. Vehicles 1978 & Up (with M10-1.5 banjo bolts) will require new brake lines available below.


The D52's consist of two 2" diameter pistons. The area is then 2*pi*r^2 = 2*3.14*1 = 6.28, just like it says in the description. Wilwood tries to make up for the reduced front braking force with higher friction pads. Without the pads, this upgrade actually reduces front braking force. The kit should work as advertised, so I'd make sure the pads were bedded in properly and everything else was in proper working order.


Other things you can do to improve brake feel include:
- installing steel braided brake lines so that none of the hydraulic force multiplication is wasted on flexing rubber lines
- running an even more aggressive pad compound: more friction means less force is required
- installing new pads so that they engage earlier in the pedal's range of travel (seems you've already done this)

[stangs400]

Ya ive got new hawk pads all around. the braking before was nothing special either. Everything is bled out. I even swapped new fluid to DOT 5, mostly because some of my lines were getting warm and didnt want to push the boiling point with regular fluid. Ive also got all new lines on the car, so im hoping with the new parts that everything should be good.

[NOT A TA]

Silicone based DOT 5? Some info about swapping it into older systems here. http://importnut.net/brakefluid.htm

The low spongy pedal that can go to the floor sounds like one of the causes listed below. My bet would be A or B if the pedal wasn't like that before you worked on the car.

A. Rear drum brakes are not adjusted properly.

B. There's still air still in system even though it's been bleed.

C. Rubber hoses to the front calipers or the body to rear axle rubber hose is puffing out instead of the fluid pushing the pistons in the calipers or rear wheel cylinders.

[79-TA]

Were the new pads put on new rotors or freshly turned rotors? That can affect bedding.

If you're running the same pads as before, these Wilwoods will give you less braking force. If you had a 3" diameter piston on the old rotor, you now have about 8/9 of the braking force in the front.


Also, the rule of thumb is that you're not supposed to add DOT 5 brake fluid to a system that previously ran a glycol based fluid such as DOT 3 or DOT 4. I'm really not sure how much of a difference that makes though.

NOTATA pointed out that the drum brakes are a factor. Most of your pedal feel comes from the rear shoes, so definitely check that out.

[stangs400]

This was happening before I changed anything to the brakes. I properly bedded the new pads and rotors together from different mph stopping points and so on...the rear drums i have adjusted a couple times...the rear drums initially locked up prior to the fronts, which was due to my overall tire size change in the rear.

I just purchased an all new mastercylinder from an 81 trans am, and power booster, and adjustable proportioning valve, along with a disc brake conversion for the rear...hopefully this should get rid of all the brake problems, as long as there is no air in the system.

[NOT A TA]

If the low spongy pedal /unable to lock the wheels symptoms were happening BEFORE you did anything to the system then the master was probably NG-worn out.

[79-TA]

Good luck, keep us posted on how it goes.

[MonzaRacer]

If you used DOT 5 silicone fluid and didnt flush it all out good its contaminated AND silicone fluid is spongy anyway. Besides if you use a DOT 4 high boiling point fluid from local store your good to go.
There is a standard DOT 5 non silicone fluid but I havent seen any benefit or need for it in any car so far, but then my needs may change. Any of the good brand name DOT 4 fluid is plenty good unless running at Road America or something like that.Also it takes a proper ratio of master to caliper(s) to keep a good firm pedal and this means if it takes more stroke to get firm you may need a smaller bore master.

[stangs400]

Yeah, actually I just looked and I used DOT 4 fluid because I didnt wanna deal with two different fluids in the lines. So I now have all new rear disc conversion, new MC, new Booster, both from a 81' trans am with rear disc, and a new wilwood proportioning valve. I used a vacuum to suck all the fluid out of and bubbles, and then also did the good old pump the brake pedal method. Im almost 100% sure I have no air in the lines, as I went through two 32oz bottles of brake fluid. But I still have a soft pedal? Even when the car is off, It gets hard quick but then slowly fades out. Does this mean there is still air in the lines? Ive check all connections and they are all tight, I bench bled the MC and it got extremely hard to where I couldnt push the piston in anymore...Do I need to just keep bleeding these brakes? Everything is literally brand new now.

[Skip Fix]

I've had silicone fluid in my 78 TA with an 81 4WD booster, MC and rear disc setup for over 20 years and no spongy feel and stops well at 125mph in the 1/4 mile and autocrossing. Tired of hearing folks say it always gives a bad pedal.

The 4WD booster is a dual diaphragm and needs LESS pedal ratio than a single stage booster. If you don't change it, it will stop but provide no pedal feel. The 4WD pedals moved the hole DOWN on the pedal. Some pictures on www.nastyz28.com I believe. The old Hot Rod article discussing this swap in about 1980 incorrectly said disc need more pedal ratio and did not account for booster difference so I didn't initially swap the pedal-so I know how that felt.


Most of the late 70s disc/drum setups as well as the 4WD used a 1 1/8 MC if yours is smaller it may not have the volume for the disc pistons until it is halfway down. And new MC can be bad out of the box also.

[stangs400]

I also wanna note that when driving, after you press the brake pedal to the floor or any distance, it seems to return very slowly?