TheSamba.com :: View topic - 59 dual master cylinder upgrade, should i change push rod?

Mon Apr 27, 2015 10:24 am

Im in the process of doing the upgrade, should i change the pushrod to a 67 as well? How different are they?

I have forgotten the exact model and threw away the box, but this master cylinder is a direct replacement for a 67. Figured i should match push rods as well. Moot point?

Mon Apr 27, 2015 3:21 pm

Think they are the same. Bolt the MC up to body for testing how the original push rod fits. You need .040" (1/32" is .031"), which is ever so slightly more than 1mm space between the rod and MC piston.

If rod is too long or needs shortening, you can use a piece of all thread or a spare bolt to cut and grind one push rod out of. Have done this with our buses.

Thu Apr 30, 2015 7:34 pm

Even though in theory it's a "bolt on" conversion, please keep in mind you are in effect becoming a novice engineer by modifying the braking system of a vehicle.

Yes, you should change the push rod. VW designed a new dual circuit M/C push rod for a good reason. Simple engineering is why...

-Due to it's most basic design, in normal operation the angle of the push rod changes as it pushes the piston down. This is the primary reason the tip is rounded because the angle is constantly changing as you apply the brakes.

-With this known change of angle, the design has to allow for the maximum stroke that a push rod/master cylinder will travel without the OD of the push rod binding within the piston bore's ID.

-A single circuit M/C has a short body and only one piston, so a fairly short overall stroke with only a slight change in push rod angle. The stock push rod is pretty short, straight tapered and beefy.

-A dual circuit M/C however is a little longer, has two pistons to operate, and has a longer overall stroke in the event of ultimate failure. The push rods designed by VW's engineers for dual circuit M/C's are turned down narrower in the middle to allow for a longer stroke without binding, and the ends feature a more prominent tip for a greater change of angles.
(Tried to find some good comparo pics in the Gallery and couldn't find any :x )

Sure, it's all based on theory and it may never happen, but isn't that the very point of changing to a dual circuit M/C in the first place...just case it does?
Following VW's designers lead in this instance just makes good sense.

Be Safe and Drive Carefully :wink:

Thu Apr 30, 2015 10:19 pm

And then adjust the whole assembly correctly; that is, first set the pedal stop for 8-3/4" distance form the pedal tip to the bulkhead, then adjust the pushrod length to get the 1mm play (about 10mm at the pedal tip. Lock down the rod and never adjust it again... use the pedal stop for any future adjustments, just like VW advised.

Fri May 01, 2015 5:43 pm

I sanded down the original piston rod so i could get 6 mm of pedal free play :oops: :shock:

i did this because the original rod is completely rusted in plqce. My pedal stop plate doesnt seem to do anything. Im bench bleeding with the master cylinder in place and have 6mm of pedal free play. Because im bench bleeding, theres no pressure to prevent the pedal from hitting the bulkhead. Its dark now and i dont have a flashlight, but i measured the distance from the pedal to the bulkhead as a little under 9 inches.

I definitely want to do this right!!!

Fri May 01, 2015 6:18 pm

With either push rod I've spoke of, early or late, you only need about 1 mm of play between the tip of the push rod and the primary M/C piston, and not 6 mm as you say.

This is best felt by hand by pushing the brake pedal down lightly. You should feel no resistance for ~1-2mm then feel and hear it stop against the piston.

Depending on how much wear and tear there is in your pedal, push rod and stop assembly, this little amount of play at the push rod can equate to as much as ~2-3 inches of travel at the tip of the pedal pad.
It's a matter of give and take to find the sweet spot, and all parts must be functional and adjustable, even if that means all new replacement parts. You simply do what it takes to get them in serviceable condition.

The critical factor in all cases is that there is at least 1 mm play in the push rod as described so the piston returns fully in it's bore to uncover the refill port from the reservoir.

Please recall I've already outlined the "right" way to do it.
If you want to play Brake system engineer on your own, you might just have to learn by trail and error :shock:

Fri May 01, 2015 6:38 pm

I definitely appreciate the information! The 6mm of free play is at the top of the pedal. Searched the classifieds for a 67 piston rod, no luck just yet.

I think i need to post photos or a video of whats going on. The more i think about it the more i think my pedal assembly isnt stock. This is my first bug, previous owner replaced the pans and the pedal assembly seems out of place vs all the patina

Ill take photos tomorrow morning! Definitely appreciare the help. I want my bug safe.

Fri May 01, 2015 7:01 pm

Mayor Marion Berry wrote:
I definitely want to do this right!!!

To do it right you need to take out that push rod and soak it in phosphoric acid at least over night to get rid of that rust. Push rod needs to be adjustable.

If your brake pedal stop was not doing anything the brake pedal would flop over to the rear and be laying pedal down on the floor.

Fri May 01, 2015 7:11 pm

Eric&Barb wrote: Mayor Marion Berry wrote:
I definitely want to do this right!!!

To do it right you need to take out that push rod and soak it in phosphoric acid at least over night to get rid of that rust. Push rod needs to be adjustable.

If your brake pedal stop was not doing anything the brake pedal would flop over to the rear and be laying pedal down on the floor.

the pushrod itself prevents it from flopping over. Once i take out that cylinder/pin dealy that locks the piston rod to the pedal, it flops out like you mention

Fri May 01, 2015 7:20 pm

With all the possibility's, pictures of the pedal assembly in position would surely help.

Basically, you want the brake pedal foot pad to be about vertical and perpendicular to the floor boards when at rest, while maintaining that 1mm of push rod clearence.
You juggle the stop plate and push rod adjustments until they are in harmony.

The M/C mounting on your frame is the one sure thing though, the same part fits all Beetles...
http://www.wolfsburgwest.com/cart/DetailsList.cfm?ID=113701131
...so that means as long as you have the M/C firmly mounted with the spacer tubes in place you can proceed from there.

It's the pedal assembly's that changed the most, but I'd say offhand w/o research that if you have most any later Beetle pedal assembly, you can probably use any late model push rod say '67-up to '77 and make it work. You don't have to look for any one year onlys as long as it's Beetle and not Type III or something.

One basic question, does it have cast iron looking brake and clutch pedal arms used up to-mid '66, or are they of the mid '66-up stamped/formed metal variety?

Fri May 01, 2015 7:37 pm

Mayor Marion Berry wrote:
the pushrod itself prevents it from flopping over. Once i take out that cylinder/pin dealy that locks the piston rod to the pedal, it flops out like you mention

Be aware that some people here have reported having to modify, shim up or even fabricate a new pedal stop to work with their "new" floor pans as they are not all created equal or installed the same way for that matter.
No experience, but here is one product for use on repro pans as such in the classifieds...
http://www.thesamba.com/vw/classifieds/detail.php?id=1459021

Sat May 02, 2015 10:52 am

Ok, makes sense. Here some photos!

Pedal cluster!

Back of the pedal cluster

A little under 9 inches of distance between pedal and bulkhead

push rod disconnected

stock (I think) 59 push rod. I shaved off maybe 1/4-1/3 mm to get 6mm of free play at the top of the brake pedal

Sat May 02, 2015 3:37 pm

Mayor Marion Berry wrote: Ok, makes sense. Here some photos!
Back of the pedal cluster

Right there is one problem.
Hint: That shiny silver bracket on the floor is called a brake pedal stop for a reason.

There is clearly a gap between yours and the pedals. Both pedals have little stop nubs cast into their bottom sides for that stop to rest against. In fact, don't know why your clutch pedal hasn't fallen back and is laying on the floor :?
Do you have a service manual? That plate should be adjusted backwards until it hits those stops to hold to brake and clutch pedals vertically at the same plain. Use that to get the 1mm push rod clearance and you won't need to adjust it's length (even though it is still the wrong style :roll: ).

Good luck and best wishes.

Sat May 02, 2015 3:58 pm

Ill fix the stop plate and hold out for a proper piston rod. Might be a dumb question, but is this the correct/proper pedal assembly for 67? Figured if im changing the piston rod, my pedal assembly should be 67 to?

I have a bentley service for 58-60. Nothing on 67

Sat May 02, 2015 5:29 pm

Can someone throw up up a picture of the late duel circuit pushrod? The old one seems to work with duel circuit brakes in my '63, but I keep the brakes well adjusted. I might want to swap it next time I'm reworking the brakes. I can see how the long body of the old pusbrod could be a problem.

Sat May 02, 2015 6:02 pm

@Mayor Marion Berry, no that's not '67 pedal ass'y, but it should work just fine.

As far as manuals go, the '58-'60 Bentley will show you all you need to know about adjusting the pedal stop and pedals.

@EVfun
Best I can find was in the classifieds, year is not specified but it is good for reference only...

...among others currently for sale there...
http://www.thesamba.com/vw/classifieds/search.php?...ton=Search

Sun May 03, 2015 5:32 pm

Thanks all for the help! Though can someone help me understand why changing the rod is beneficial if i theoretically had 1 mm of free travel between the cylinder and rod witg the original 59?

Wouldnt it be true that no matter which rod you went with, stock 59 or 67 piston rod, the lengths would have to be the same? Why change the rod if im not changing the whole assembly to make sure all geometries are correct? Not disagreeing with anyone, its just i dont understand how a simple rod has such a benefit.

Sun May 03, 2015 5:49 pm

Is that a legit 67 piston rod? Tempted to buy it no matter my confusion

Mon May 04, 2015 7:27 am

Mayor Marion Berry wrote: Thanks all for the help! Though can someone help me understand why changing the rod is beneficial if i theoretically had 1 mm of free travel between the cylinder and rod witg the original 59?

Wouldnt it be true that no matter which rod you went with, stock 59 or 67 piston rod, the lengths would have to be the same? Why change the rod if im not changing the whole assembly to make sure all geometries are correct? Not disagreeing with anyone, its just i dont understand how a simple rod has such a benefit.

sorry to blow this up, but i think i solved my confusion

1) dual master rod is longer to allow for a longer stroke. So i DEFINITELY want to replace my single for a dual.

2) once i install the dual master rod, adjust brake stop plate to allow for 1mm of dead travel between rod and piston.

3) once i have the correct free play, i should still have just under 9 inches of distance between bulkhead and brake pedal? However since this rod is longer, wont the pedal/bulkhead distance also increase?

Thanks all for the help! Goal is to make this my daily driver so i definitely want this safe

Mon May 04, 2015 7:58 pm

Mayor Marion Berry wrote:
1) dual master rod is longer to allow for a longer stroke. So i DEFINITELY want to replace my single for a dual.

2) once i install the dual master rod, adjust brake stop plate to allow for 1mm of dead travel between rod and piston.

3) once i have the correct free play, i should still have just under 9 inches of distance between bulkhead and brake pedal? However since this rod is longer, wont the pedal/bulkhead distance also increase?

KTPhil wrote: And then adjust the whole assembly correctly; that is, first set the pedal stop for 8-3/4" distance from the pedal tip to the bulkhead, then adjust the pushrod length to get the 1mm play (about 10mm at the pedal tip. Lock down the rod and never adjust it again... use the pedal stop for any future adjustments, just like VW advised.