I have a 3.8 E-Type w/Willwood front brake calipers and am using the standard two brake master cylinders and booster unit. Because the Willwood calipers are considerably larger than the original Dunlop units and I presume hold more brake fluid, when applying the brakes, the amount of piston movement for the front brake master is more than twice that of the rear brakes resulting in a low pedal.
While the car stops fine, the pedal travels rather far before the brakes take hold. I was thinking of adding a residual pressure valve in the front brake line to keep a little pressure on the front calipers so as to reduce the amount of fluid needed to move the brake pads. Unfortunately the Willwood site advises using this product only if the master cylinder is below the caliper which it is not on an E-Type. Does anyone have any thoughts on this? Thanks/Mitch
Have you tried driving it with the vacuum disconnected from the booster? I’ve had Wilwoods on my E since about '02, and I have never seen the problem you’re seeing. Do you have 1.75" 4-piston calipers? If so, the piston area is only increased about 35% over stock - hardly a massive change.
Regards,
Ray L.
Have Wilwoods - work reliably with good pedal - same dual master. There for 10 years - need to understand if your’s are similar. Do you have a part number? Paul
In-line back-flow valves are available for this purpose. They allow a certain amount of fluid to return up the line as the caliper relaxes then closes to prevent so much fluid to move that it takes a long pedal stroke to recover.
We use them on hot rods and customs were the capacity of the M/C and calipers (drum cylinders) are not matched (or match-able). There are 2 different pressures available (IIRC, 10 and 20 pounds), Wilwood should be able to help you with this.
With different sized calipers F/R, you might also consider a balancing valve to control braking force F/R.
They are recommended for M/C below the floor (such as a '34 Ford as Wilwood states), but they are used in many other situations. I would ask on a hot rod forum where just about everyone will know what you’re talking about.
Hi Ray,
Nice to hear from you. I don’t know the piston size. I bought the Willwood kit from Classic jaguar in 2006. There’s always been a disparity in the movement of the two masters. However, I had both master cylinders and the rear calipers (larger original fronts that I put in the rear back in ’06) resleeved by White Post last summer. Interestingly, the brake pedal travel seemed to have increased since I put it back together. I was actually a little alarmed but am now sort of used to it…
I’ve never driven the car w/the booster disconnected. Is that to test something or a alternate permanent solution?
I’ve re-bled the front calipers several times thinking there was air in system. There always seems to be a bit of air in the front system but I’ve sucked a lot of fluid though it with my bleeding tool without being able to remove all the tiny bubbles or obtain any change.
Thanks/Mitch
Hi Paul,
I bought the kit from Classic Jaguar 12years ago. I don’t hav a part number other than the CJ # TCJWIL1. Will look at the calipers and see what I can find and contact Willwood. Thanks/Mitch
Mitch,
Worst case, remove one of the pads, and just measure the piston diameter, and count the pistons.
Regards,
Ray L.
Hi Mitch, I will photograph mine and send for your reference. Paul
Some of our answer/suggestions are based subject to what you are comfortable with trying and what spares you might have around… so ……
To eliminate the calipers you might try either disconnecting the flex line to the front calipers and plugging with a blank fitting, OR forcing the pistons back into the calipers and wedging them with a small block of wood or something such that they cannot move.
If you then still have pedal travel you have air in the system or some other such fault.
I am struggling with my memory but where there are twin master cylinders with a balance link I THINK
its possible that the rear brakes will inhibit the front from having full pedal travel ( when bleeding) (the pedal travel will stop once rear brakes are fully on) Far easier to explain when you can see my hands waving about.
Hi Phil,
Re- the comparative movement of the two master cylinder pistons, the rear stops moving at about 3/8" of travel while the front continues to move about 1’’, hence the low pedal. Per the other responses this set up is being used by others without my issue so I’m going to re-bleed the front Wilwoods and see if that helps. Thanks/Mitch
You do know you have to bleed BOTH sides of each caliper, using only the TOP bleed screws on each? Do the INSIDE one first, then the OUTSIDE, then repeat.
Regards,
Ray L.
You could try a vacuum bleed on the front. I had success with that when I had a similar issue.
That’s just what I’m going to do. I suspect that’s the problem. Thanks again.
Hi Phil,
I used a vacuum bleed the first time and always had a few bubbles no matter how much fluid I pulled thorough it. I think I’ll try the old fashion way this time and make sure I bleed BOTH inner and outer calipers chambers. Thanks./Mitch
The actual hydraulic system on the 3.8 seems to be very simple, in particular the front - shouldn’t it bleed itself? The 4.2 system does.
I note that you haven’t mentioned that pumping the brakes gives a higher pedal.
When I first mounted Wilwood Dynalites with 1.750 pistons on a '65 that I tracked I had a very “long” pedal, as you are experiencing. It would go to the floor, but would still stop the car. It also seemed spongy compared to the stock system, but it’s possible I was using silicone brake fluid. I attributed the long pedal to the need to move more fluid, and the sponginess at least partially to the fact that using the larger pistons increases the mechanical advantage on the front brakes which leads to greater deflection in the calipers. (I suspect that Wilwood’s are not anywhere near as stiff as stock calipers). Part of the solution was to go to s.s. braided brake lines (makes a big difference), but ultimately it was replacing the calipers with smaller pistons. I ultimately modified a set to use differential pistons - 1.375 and 1.750 which gives you a total piston area nearer the stock system. That worked the best, but it’s a bit radical.
That’s a common problem. The issue is normally that you are pulling air in via the threads of the bleed nipple. If you put a little brake fluid around the bleed nipple it will seal it. It’s an instant fix if it’s the problem. I’m a great advocate of the traditional bleed method but the vacuum will get every last drop of air plus it negates the need for two people and stops putting the master cylinder seals into areas of the cylinder that might be a bit rough. I just prefer it to a pressure bleed set up.
Always gravity-bled mine --stock, and Wilwoods. Never an issue.
Hi,
No, pumping the brakes does not raise the pedal. I also have braided brake lines at the wheels. I’m going to rebleed the fronts and see what happens. Thanks/MC
How much head space is there?
Not sure what you mean by “headspace”. The pedal travels about 1/2 way to the floor before any braking action takes place. A little alarming…