brake pushrod retention with dual master cylinder

[woody6]

What is everyone doing to retain the brake pushrod when switching to a dual master cylinder. Using a 280zx master cylinder, I reduced the diameter of the washer on the stock pushrod, and added it below the c-clip in the master cylinder. When it came time to bleed it, it appeared that the added thickness moved the piston enough that the rear reservoir port was blocked, as I never had any fluid enter that half of the system.

Thanks,
Woody

 

[0neoffive]

What is everyone doing to retain the brake pushrod when switching to a dual master cylinder. Using a 280zx master cylinder, I reduced the diameter of the washer on the stock pushrod, and added it below the c-clip in the master cylinder. When it came time to bleed it, it appeared that the added thickness moved the piston enough that the rear reservoir port was blocked, as I never had any fluid enter that half of the system.

Thanks,
Woody

Bench bleed it and all will be fine.

 

[woody6]

Bench bleed it and all will be fine.

So you are saying that with the 280ZX master, the washer that holds the pushrod on (when added under the c-clip) is not thick enough to cause piston to block the rear port? I saw another forum thread where someone else seemed to have the same problem as I did, and had to dispense with attaching the pushrod to the master with the c-clip. The Nissan master was used on the Z car with a booster, so retaining a pedal pushrod was not a concern on the OEM application.

Full disclosure, I did not bench bleed it, but I did try pressurizing the reservoir, as well as vacuum bleeding from the caliper, and couldn't get fluid to enter the front brake system.

Thanks,
Woody

 

[spmdr]

A quick fix is to run a 1/4" bolt across the two pedal brackets to hold the Brake peddle from coming too far back.

Depending on where you want the height of the brake pedal, put a bend in the bolt to move the pedal back or higher.

And of course, you want some free play in the rod from the pedal to the master piston, at full pedal retraction, with a spring.


Note, When CHANGING from OEM brake parts, YOU are taking on the status of Brake engineer, proceed at YOUR risk!

DW

 

[woody6]

Thanks, spmdr, that's the option I was looking for!

I'm also glad to report that oneoffive's suggestion to bench bleed the master cylinder seems to have worked. I pulled the master yesterday and bench bled it today, and it looks promising. I'm not thrilled about trying to mount and connect a filled master cylinder without making a mess, but I will be elated when I have brakes on all four. The nissan master cylinder with its bottom connections makes for awkward service, but hopefully that need will be very infrequent!

 

[0neoffive]

Thanks, spmdr, that's the option I was looking for!

I'm also glad to report that oneoffive's suggestion to bench bleed the master cylinder seems to have worked. I pulled the master yesterday and bench bled it today, and it looks promising. I'm not thrilled about trying to mount and connect a filled master cylinder without making a mess, but I will be elated when I have brakes on all four. The nissan master cylinder with its bottom connections makes for awkward service, but hopefully that need will be very infrequent!

Yup; can't say that I'm fond of those bottom feeders either. . . . .messes up the compartment paint!

 

[woody6]

Yup; can't say that I'm fond of those bottom feeders either. . . . .messes up the compartment paint!

I'm using the DOT 5 fluid for that very reason, but the job is still a pain and makes a mess. I capped the line fittings and managed to get the now-full master back into place with surprisingly little fluid on anything. I needed to pull the steering column out to access the lines underneath, but that was easy since the column shroud and turn signal switch are not yet back in place.

As for bench bleeding, I was encouraged when it yielded a filled tube with no bubble for both reservoirs, and thought that was the fix (it was no doubt a good idea). Unfortunately, once back on the car, neither the mity-vac vacuum bleeding method nor the the old fashioned method with my wife pressing the pedal resulted in any fluid to the front brakes. This is with a 7/8 280ZX master that has the bleed ports on the drivers side, but I have a 15/16 280ZX master with the bleed screws on the right arriving Wednesday. I hope that one somehow makes a difference.

 

[0neoffive]

I'm using the DOT 5 fluid for that very reason, but the job is still a pain and makes a mess. I capped the line fittings and managed to get the now-full master back into place with surprisingly little fluid on anything. I needed to pull the steering column out to access the lines underneath, but that was easy since the column shroud and turn signal switch are not yet back in place.

As for bench bleeding, I was encouraged when it yielded a filled tube with no bubble for both reservoirs, and thought that was the fix (it was no doubt a good idea). Unfortunately, once back on the car, neither the mity-vac vacuum bleeding method nor the the old fashioned method with my wife pressing the pedal resulted in any fluid to the front brakes. This is with a 7/8 280ZX master that has the bleed ports on the drivers side, but I have a 15/16 280ZX master with the bleed screws on the right arriving Wednesday. I hope that one somehow makes a difference.

Break the line before the flexible caliper hose and check for fluids under pressure at that point.

 

[woody6]

Break the line before the flexible caliper hose and check for fluids under pressure at that point.

Will do. Leaving the master cylinder, there are only 6 pieces downstream including the calipers, and it seems like something is blocked. Strange since it is all new, but I'll check to see that fluid or air passes in each one individually if I have to.

 

[woody6]

I've been able to pass air through every line, fitting, and caliper on the front, so the next move is to try the second 280zx master cylinder which should arrive late today. Bench bleeding the rear reservoir (front brakes) took several times as long as the other reservoir, so hopefully another master cylinder will resolve the issue.

Thanks everyone for the suggestions. I'm trying to get the car mobile to attend SUNI in September, and I'm feeling down to the wire already.

 

[woody6]

Finally, some resolution. The master cylinder I was originally working with was a 7/8" 280ZX master cylinder with the bleed screws on the left side. This put them up against the clutch master, but the cylinder could still be bolted in place. I used the original Tiger brake pushrod after making the retaining washer smaller, and added the retaining washer behind the C-clip. I could not bleed the front brakes, and while I am not 100% sure, I think the additional thickness of the washer moved the piston forward enough to not work. Its a scenario wilwood describes here:
https://shop.wilwood.com/blogs/news/troubleshooting-no-fluid-pressure-at-the-rear-brakes

The second 280ZX master I purchased was a 15/16" size, and had the bleed screws on the right side. More importantly, it arrived with a washer already between the piston and the c-clip. I substituted my own washer with the pushrod through it, and reinstalled the c-clip. Bench bled and installed on the car, I am now getting fluid and pressure to the front brakes.

Fitting this master cylinder is not fun. This is in part due to the way I made my connections, but the fittings are underneath, and that corner of the engine compartment is crowded. I was lucky in that I had just installed the steering column and had not fitted steering wheel, column shroud, or turn signal switch. It was only about 3 bolts to remove it (this time), but I hope this master cylinder is very reliable. Its not a job I would want to do often!

Here's the second master cylinder on the bench and in the car: