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Sun May 08, 2022 4:19 am

I have a new to me '73 super. Just before i bought it, the previous owner had a disk brake kit installed in the front. When I got it, the brakes worked, but seemed inconsistent. Out driving a couple weeks ago, the brakes pretty much quit working. I pulled into a parking lot, did a few stops, and they seemed to work again. Then seemed to work ok on the way home. So my initial thought was that they needed bled.
Tried bleeding them, they would work, then after a few minutes of driving they would get inconsistent again.
Then tried bleeding with the rear drums tight, same thing, I can get a firm peddle, but they don't hold.
When bleeding, I'm not getting much fluid out of any of the bleeders, more like a dribble. When the peddle is pushed, the fronts grab, but then after a few seconds then loose grip and you can turn the rotor by hand.
My thoughts are now, either their is still air somewhere, or the pushrod is not adjusted correctly. I'm still trying to get a feel for where the pushrod starts to push the master cylinder, but it seems to me that there is too much free play.
I've bleed these things probably 6 or more times, sometimes front first, sometimes rear first, but same result every time.
Thanks for any input on what to try next.

Sun May 08, 2022 9:45 am

You have to get that pushrod adjusted correctly. That is paramount.

Next up would be the flexible hoses at the wheels. When were these last changed. They get eaten by the brake fluid and fail internally. It may be your problem. Cheap fix if that is the case! If that does not get it, I would get my pressure gauge out and check the output of the master cylinder.

Sun May 08, 2022 10:28 am

VW_Jimbo wrote: You have to get that pushrod adjusted correctly. That is paramount.

Next up would be the flexible hoses at the wheels. When were these last changed. They get eaten by the brake fluid and fail internally. It may be your problem. Cheap fix if that is the case! If that does not get it, I would get my pressure gauge out and check the output of the master cylinder.

All the lines are new, hard and soft lines.

Mon May 09, 2022 2:19 am

I post on here a lot of times with people changing from drums to discs. My VW came standard with VW discs.

1. Drum and disc MC’s are different. Which one do you have?
2. Disc brake MCs shouldn’t have residual pressure valves fitted. RPV’s are fitted to drum brake MC’s.
3. Change the soft lines. Did the PO say they were new or did you change them?A lot of the time these look great on the outside but are full of atherosclerosis on the inside.
4. Do NOT adjust the pushrod at the pushrod. This should not be touched.It has to be adjusted at the floor plate. You need 1mm free play at the pushrod before it starts pushing in the MC piston. This gives the required ~5-7mm free play at the pedal.
5. Depending on the MC, the bleed process is different. Should you bleed front or rears first? I know that the original VW MC for discs had the reversed sequence of bleeding to that of the drum brake MC.
6. People tend to spend big $ on chrome engine parts but cheap out on cheap Chinese junk MC’s. Brakes are SO important and you need to spend good money buying the best quality you can.

In 50 years of owning this and other VW’s I have NEVER needed to bench bleed a MC or have to use a pressure or vacuum bleeder. The simple clear plastic tube immersed in a clean half filled jar with brake fluid has always worked for me.

Mon May 09, 2022 3:34 pm

I’m trying to get a feel for where my push rod activates the MC piston. Seems like it has way more free play than there is supposed to be. Do the brake lights come on as soon as the MC piston starts to move?

Mon May 09, 2022 4:04 pm

The brake lite switch(es) are activated by about 22psi. I found myself lightly braking in some situations & there were brake lights. I know this cuz I saw the car behind me did a hard nose dive.
There is a vendor in the "new parts" section of the classified on here that has an instant on kit that is EASY to install ... worth every penny in my book. I put one on my '71 a few years ago. Still works like a charm & got to the house quick.

Best wishes ... stay safe

jinx

Edit ... meant to say NO brake lights when pushing pedal lightly. oops

Mon May 09, 2022 4:27 pm

daveg131 wrote: I’m trying to get a feel for where my push rod activates the MC piston. Seems like it has way more free play than there is supposed to be. Do the brake lights come on as soon as the MC piston starts to move?

The problem sometimes is that people, frustrated by their brakes not working, properly, start adjusting lots of things, exacerbating the issue because now there are multiple factors in play.

If the pushrod length has been altered from the factory preset length, then sometimes you cannot get the free play correct.

My best advice is to adjust the floor plate to try and bring back the free play into spec. What this spec is may be different between your car and mine. You need to find out from a workshop manual specific for your year model to what it should be. The 5-7mm I quoted was specifically from my Bentley for 66-69 year models. But whatever it is, it isn’t a lot.

If you have excessive free play (caused by the wrong pushrod length or incorrect free play) then the piston in the MC may not push in far enough to build up sufficient hydraulic pressure in the lines or displace sufficient brake fluid to fully displace the disc or drum pistons resulting again in insufficient hydraulic pressure.

Your inconsistent brake operation could just be poor free play. Adjust that first and see what you get.

Mon May 09, 2022 5:27 pm

viiking wrote: daveg131 wrote: I’m trying to get a feel for where my push rod activates the MC piston. Seems like it has way more free play than there is supposed to be. Do the brake lights come on as soon as the MC piston starts to move?

The problem sometimes is that people, frustrated by their brakes not working, properly, start adjusting lots of things, exacerbating the issue because now there are multiple factors in play.

If the pushrod length has been altered from the factory preset length, then sometimes you cannot get the free play correct.

My best advice is to adjust the floor plate to try and bring back the free play into spec. What this spec is may be different between your car and mine. You need to find out from a workshop manual specific for your year model to what it should be. The 5-7mm I quoted was specifically from my Bentley for 66-69 year models. But whatever it is, it isn’t a lot.

If you have excessive free play (caused by the wrong pushrod length or incorrect free play) then the piston in the MC may not push in far enough to build up sufficient hydraulic pressure in the lines or displace sufficient brake fluid to fully displace the disc or drum pistons resulting again in insufficient hydraulic pressure.

Your inconsistent brake operation could just be poor free play. Adjust that first and see what you get.

Things I do know, the push rod length has been changed from factory. There supposedly is this MC installed, as the previous owner gave me the receipts for the parts that were installed.
https://www.jbugs.com/product/17-2808.html
When I bleed the brakes, I’m not getting any pressure at any of the bleeders, just a very small amount of fluid. So either the piston isn’t getting pushed far enough, or the MC is bad.

Mon May 09, 2022 6:22 pm

daveg131 wrote: viiking wrote: daveg131 wrote: I’m trying to get a feel for where my push rod activates the MC piston. Seems like it has way more free play than there is supposed to be. Do the brake lights come on as soon as the MC piston starts to move?

The problem sometimes is that people, frustrated by their brakes not working, properly, start adjusting lots of things, exacerbating the issue because now there are multiple factors in play.

If the pushrod length has been altered from the factory preset length, then sometimes you cannot get the free play correct.

My best advice is to adjust the floor plate to try and bring back the free play into spec. What this spec is may be different between your car and mine. You need to find out from a workshop manual specific for your year model to what it should be. The 5-7mm I quoted was specifically from my Bentley for 66-69 year models. But whatever it is, it isn’t a lot.

If you have excessive free play (caused by the wrong pushrod length or incorrect free play) then the piston in the MC may not push in far enough to build up sufficient hydraulic pressure in the lines or displace sufficient brake fluid to fully displace the disc or drum pistons resulting again in insufficient hydraulic pressure.

Your inconsistent brake operation could just be poor free play. Adjust that first and see what you get.

Things I do know, the push rod length has been changed from factory. There supposedly is this MC installed, as the previous owner gave me the receipts for the parts that were installed.
https://www.jbugs.com/product/17-2808.html
When I bleed the brakes, I’m not getting any pressure at any of the bleeders, just a very small amount of fluid. So either the piston isn’t getting pushed far enough, or the MC is bad.

Exactly! These cars are 50 years old! Of course someone has adjusted the pushrod length. Vw stated to not touch it back in the 70s when these cars were new. Guess what (Viking pay attention) these cars are OLD! There have been many, I mean many hands that have touched everything on these cars.

So, as an old ASE Master Technician that worked as a VW mechanic for many years, I learned to check and adjust the MC rod, AS PER THE BENTLEY MANUAL.

Start with the basics.

Tue May 10, 2022 1:01 pm

VW_Jimbo & viiking are correct

Get that pushrod & freeplay set correctly first. Use both the pedal stop plate & pushrod adjustments ( they are different ). It's a fiddly operation but important. This will allow the proper amount of "push length" the rod goes into the MC.
Not enough push & you get poor performance - too much & you block the ports in the MC, also poor performance. There's a sweet spot that you must find.
You said rear shoes are adjusted tight to the drum ... I'm hoping you got both shoes tight, not just one.
Bleed front disks first, then rears.

Which method are you using to bleed ?
A) pump & hold
B) vacuum pumper
C) pressured ... fluid pushed into reservoir
D) siphon

3 years ago I had an MC failure so I replaced the MC & all 4 soft lines. I got everything from local auto parts house. I had similar results but I have 4 drums. After moving my stop plate about an 1/8th of an inch I pulled the rubber boot back from the front firewall & used a brite lite to get super close to MC piston without touching it ( scientific, rite ? ). Before tightening the pushrod nut I ended up with about 5/8 inch of "free play" or brake pedal movement before the pushrod touched the MC piston.
That worked for my situation in my '71 & have no clue what brand the MC is. It took me almost an hour between youtube, my Haynes manual, theSamba, & a lot of cuss words. Maybe I finally got lucky, too.

After 4 rounds of SLOW PUMP & hold I broke down & bought a bleeder kit that acts like a cup gun paint sprayer ... for paint. That worked a treat & just used it last month to change brake fluid.

Sorry for long post ... just what I went thru.

Stay safe ... jinx

** hope you get this sorted **

Tue May 10, 2022 1:14 pm

I had to adjust a push rod without a Bentley a few times. It’s a lite touch to be sure.
Some solid advice posted previously.

Wed May 11, 2022 5:15 pm

Ok, so I think I'm getting somewhere. First thing I did was buy the Bentley manual. Now things are a little more clear in my head. Next, I took a closer look at the free play. Found my reason why I couldn't feel any, because there was none. Was set so the push rod was just in contact with the piston. So I adjusted the pedal stop and now have the 1mm between push rod and piston. Also, I have more than the 200mm between the pedal and floor.
Next I tried the front right bleeder, and while pressing the brake, still very little fluid pressure coming out of the bleeder. That's as far as I got this evening.
I'm beginning to think that the MC may be bad.

Fri May 13, 2022 6:50 pm

I just finished this with my car. 4 wheel disc brakes. I did regular bleeding , power bleeding and finally took the calipers off the hangers and put a 2x4 where the puck is and put the caliper on the top of the rotor. The last one fixed everything. If you're bleeding the brakes and they're in their bolted position you won't get the air out. The bleeder screw needs to be the highest point.

Fri May 13, 2022 7:42 pm

RLFD213 wrote: I just finished this with my car. 4 wheel disc brakes. I did regular bleeding , power bleeding and finally took the calipers off the hangers and put a 2x4 where the puck is and put the caliper on the top of the rotor. The last one fixed everything. If you're bleeding the brakes and they're in their bolted position you won't get the air out. The bleeder screw needs to be the highest point.

if the bleeding screw is on the bottom the caliper is upside down.

Fri May 13, 2022 8:56 pm

New disc conversions have a bleeder at the top and another at the bottom, so you can put the caliper on either side.

I adjust the MC rod like this: turn the rod easy until it just contacts the MC rear piston. Then turn the rod back out one half turn. With your hand, press on the brake pedal. You want to have the desired 1/4 inch freeplay before you feel the rod contact the MC piston. If not, turn the rod in or out a tad, then test again. Use a ruler, one end of which should be against the firewall, to find the 1/4 inch freeplay. This 1/4 inch of pedal freeplay will give you 1 mm inside the MC.

This procesure seems to be daunting to some, but it's really very simple. No one would worry about resetting the rod, if not for the weird warning in the Bentley.

Tim

Wed May 18, 2022 5:39 pm

I solved my problem. It was a bad MC. Got my new one installed this evening. Brakes bleed like they should, nice consistent, firm pedal. Ran out of time tonight, but tomorrow I’ll get the wheels back on and take it for a test ride.

Wed May 18, 2022 10:36 pm

Thanks for chiming back in with a final update! Always good to read a good ending!

Be sure to adjust your brakes after installing the wheels.