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No front brakes
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legotech7
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PostPosted: Fri Oct 22, 2021 8:38 am    Post subject: No front brakes Reply with quote

I've been working on my brakes for a few weeks now, and have no braking power in the front. Theses are drum brakes on a 67 pan. Every thing as far as the brakes is brand new. Everything!... I bleed the brakes with a power bleeder on all 4 sides and couldn't find any air in the lines. All seemed good. I did notice the the brake peddle was hard to depress.. Moved about 2 inches from the top, and just barely stopped the car. I had to really press down hard to get it to slow down. Had a friend hit the brakes while the car was on jack stands and check each wheel by rotating each one for movement. The rear wheels would not move they were tight. But the front ones, I could rotate about one revolution, with my friend still pressing hard on the peddle. I did fail to replace the right front soft line. I thought I did when doing the brakes, but I didn't. Could this be the problem? I will be replacing that today. Readjust the brakes and bleed them again.... Any other thoughts on why the brakes won't hold on the front?
Thanks folks in advance. This brake thing is driving me crazy!
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PostPosted: Fri Oct 22, 2021 9:32 am    Post subject: Re: No front brakes Reply with quote

Master cylinder push rod adjustment. So often overlooked and forgotten about.

I am not a fan of the power bleeders. They do not communicate with you, the mechanic. Have you tried just bleeding the brakes with the pumping the pedal procedure? That can tell you a lot!
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legotech7
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PostPosted: Fri Oct 22, 2021 11:33 am    Post subject: Re: No front brakes Reply with quote

Yes VW_Jimbo, I have tried adjusting the push rod. I turned the rod in till I felt it snug up then backed it off about a quarter of a turn. Measured the peddle to about the same distance. About a 1/4 inch. I just replaced the right side rubber hose. and am waiting for my friend to help me peddle bleed the system, and hope that works Never had so much problems with vw brakes before and the power bleeder always worked well for me. We shall see.. Thanks for the response...
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ashman40
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PostPosted: Fri Oct 22, 2021 11:53 am    Post subject: Re: No front brakes Reply with quote

legotech7 wrote:
Yes VW_Jimbo, I have tried adjusting the push rod. I turned the rod in till I felt it snug up then backed it off about a quarter of a turn. Measured the peddle to about the same distance. About a 1/4 inch.

Glutamodo's pic below show that there needs to be a 1mm gap between the tip of the push rod and the inside of the MC piston. The piston must be allowed to fully return to its at rest position. The push rod cannot be applying any pressure on the piston when the pedal is released.
Image may have been reduced in size. Click image to view fullscreen.


Did you only replace one front brake hose? If it was a bad right side hose it would only affect the right front brakes.

When you replaced the brake shoes and drums did you measure if the drum ID was smaller than the max runout spec stamped into the drum? Have you adjusted the stars so the shoes lightly drag on the drum ID when the brakes are at rest?
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legotech7
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PostPosted: Fri Oct 22, 2021 12:27 pm    Post subject: Re: No front brakes Reply with quote

ashman40, I don't know how you could possibly measure that 1mm except to measure the brake peddle for e small measurement. But I think I got it pretty close. I did replace both side hoses. Still have to bleed them. I adjusted the brakes to where the wheels are tight as per some recommendations here on Samba, then I will bleed them one wheel at a time, then readjust and hope they will stop the car safely.
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PostPosted: Fri Oct 22, 2021 2:13 pm    Post subject: Re: No front brakes Reply with quote

legotech7 wrote:
ashman40, I don't know how you could possibly measure that 1mm except to measure the brake peddle for e small measurement. But I think I got it pretty close. I did replace both side hoses. Still have to bleed them. I adjusted the brakes to where the wheels are tight as per some recommendations here on Samba, then I will bleed them one wheel at a time, then readjust and hope they will stop the car safely.


The pedal ratio is about 6:1, so the way you measure that 1mm gap is by measuring 5-7mm of play at the pedal before the push rod contacts the piston.

Note that this is NOT 5-7mm of play before brakes are activated.

It's 5-7mm of play before the push rod contacts the piston. This can be very hard to feel by foot, but if you use your hand to move the pedal slowly, you can feel when the push rod contacts the piston.

If you get that gap too large, you will have way too much pedal movement before good braking action.

If you get it too small, the piston will not return to its full rest position and eventually the brakes will lock themselves on while driving as the fluid heats up.
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viiking
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PostPosted: Fri Oct 22, 2021 2:26 pm    Post subject: Re: No front brakes Reply with quote

It's pretty easy to work out how much to turn to get the requisite pushrod to MC gap.

It's called thread pitch. That is why it's written M8x1, or M10x1.25 etc. So for M8x1, one turn of the bolt/nut will give you 1mm of change.

So measure the pushrod bolt pitch. It may be documented somewhere or use a thread gauge and you have your answer.

If you need to get 1mm, then a quarter of a turn is probably not enough for a 1, 1.25, or 1.5mm pitch.
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legotech7
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PostPosted: Fri Oct 22, 2021 3:51 pm    Post subject: Re: No front brakes Reply with quote

Thank you gentleman.. Duly noted. Guess I'll be busy this week end...
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frenchroast
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PostPosted: Fri Oct 22, 2021 4:06 pm    Post subject: Re: No front brakes Reply with quote

Did you have the new linings arced to match the drums? If not, you can do it yourself: https://youtu.be/PWgulHvItxg
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legotech7
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PostPosted: Sat Oct 23, 2021 6:18 am    Post subject: Re: No front brakes Reply with quote

Great video, frenchroast That's what mine feel like. With the wheel adjusted fairly snug, I can still turn the wheels about one revolution. The peddle feels hard, and I have to really press hard to get the car to just slow down. More work than I wanted to do, but better safe than sorry. With all the other things I have to do as I mentioned in my previous post's. I'll add this to the list.

Thank you so much.....
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MTT3107
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PostPosted: Sat Oct 23, 2021 7:55 am    Post subject: Re: No front brakes Reply with quote

I recently had the same issue with my '73 beetle, although in the front, it had already be converted to disc brakes.
When I got the car, it didn't brake well very long pedal travel, it would only start braking when the pedal was almost to the front bulkhead.

Looked things over and found that with the exception of the front brakes, everything was old & crappy. Rear brakes were worn and rusty, bleeder nipples sheared off on both sides, adjusters frozen solid. So we replaced pretty much everything, master cylinder, hoses, backplates and cylinders on rear brakes, brake shoes..

We bled the rear brakes no problem, but could not get any pressure to the front brakes, and they were not working...

In the end, it turned out to be the adjustment of the master cylinder rod.
Followed procedure for adjustment outlined in the manual, and that was it..
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viiking
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PostPosted: Sat Oct 23, 2021 7:38 pm    Post subject: Re: No front brakes Reply with quote

I don't think you have mentioned whether you have single circuit or dual circuit master cylinder fitted. I'm assuming the latter.

Are you aware that for a dual circuit ORIGINAL master cylinder with drum brakes that you have to bleed the front brake circuit first NOT the rear?

My understanding was always that you had to do the furthest wheel cylinder and move forward to the closest, but this was not the case with the original parts.

Now in saying that, you may have an aftermarket MC, but given that the principle of how the dual circuit works by the movement of the pistons, you probably still have to bleed fronts before rears. Perhaps you have installation instructions for your MC.

It might be this simple.
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legotech7
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PostPosted: Sun Oct 24, 2021 6:49 am    Post subject: Re: No front brakes Reply with quote

viiking Yes I am aware of the bleeding procedure with the dual MC witch I have.. I had to replace the one I got from AutoZone with a new German MC hopes It would work better. Still have to bench bleed it, witch I never had to do with other projects before. Need to double check the peddle rod adjustment. Wish me luck......

Thanks.....
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vernonc
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PostPosted: Sun Oct 24, 2021 9:37 am    Post subject: Re: No front brakes Reply with quote

legotech7 wrote:
viiking Yes I am aware of the bleeding procedure with the dual MC witch I have.. I had to replace the one I got from AutoZone with a new German MC hopes It would work better. Still have to bench bleed it, witch I never had to do with other projects before. Need to double check the peddle rod adjustment. Wish me luck......

Thanks.....


Lego, if you have a 'true power bleeder' like the one shown below,

Image may have been reduced in size. Click image to view fullscreen.


you do not need to 'bench bleed' the MC nor do you have to 'bleed in any specific order'. Also, you do not have to have the shoes 'adjusted tight to the drums'. Just be sure the 'peddle rod' is adjusted properly and don't be stingy in running fluid through the system for each wheel.

Hope this helps.

ol' mort
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legotech7
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PostPosted: Sun Oct 24, 2021 9:56 am    Post subject: Re: No front brakes Reply with quote

vernonc, I do have one and have used it with good success in the past. This the first time I have had any issues with the brakes. As I mentioned before, my problem was that the peddle upon depressing was very hard and I had to press the with a lot of force to bring the car to a stop. Just barely stopping. Right now I'm in the process of readjusting the peddle stop, and once I get the new MC in I will adjust the peddle rod, hopefully in its proper position,. Then I will commence bleeding. Thanks for the advice, will take heath.....
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PostPosted: Sun Oct 24, 2021 11:52 am    Post subject: Re: No front brakes Reply with quote

VW_Jimbo wrote:
Master cylinder push rod adjustment. So often overlooked and forgotten about.

I am not a fan of the power bleeders. They do not communicate with you, the mechanic. Have you tried just bleeding the brakes with the pumping the pedal procedure? That can tell you a lot!


Image may have been reduced in size. Click image to view fullscreen.


Image may have been reduced in size. Click image to view fullscreen.

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There is never enough time to do it right the first time, but all the time necessary the second time!

TDCTDI wrote:
Basically, a whole bunch of fuckery to achieve a look.


67rustavenger wrote:
GFY's Xevin and VW_Jimbo! Smile
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legotech7
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PostPosted: Sun Oct 24, 2021 12:23 pm    Post subject: Re: No front brakes Reply with quote

VW_Jimbo , I will be bleeding them the old fashion way this time. I might have better luck..... Thanks...
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PostPosted: Sun Oct 24, 2021 1:01 pm    Post subject: Re: No front brakes Reply with quote

legotech7 wrote:
VW_Jimbo , I will be bleeding them the old fashion way this time. I might have better luck..... Thanks...


Bugs are funny like that! Sometimes you just have to get out of the box and try something different. Try bleeding rears first. It goes against the standard procedures, but some Bugs respond better to it.

Sometimes they will only gravity bleed. So, you may need to try that one out too!
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Basically, a whole bunch of fuckery to achieve a look.


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legotech7
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PostPosted: Sun Oct 24, 2021 3:19 pm    Post subject: Re: No front brakes Reply with quote

A friend of mine did the gravity fed rout. Took him about a week. But he got brakes. If all else fails....lol....
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PostPosted: Mon Oct 25, 2021 2:17 pm    Post subject: Re: No front brakes Reply with quote

legotech7 wrote:
I will be bleeding them the old fashion way this time.

The MC is just a fluid piston. Actually two pistons stacked on top of each other. When you step on the pedal you are increasing the pressure in the cylinder. The harder you press the more pressure you create in the front and rear brake systems. Because there are no opening the pressure increases in the entire system.

When you have your buddy pressing on the pedal while you open the brake bleeder at one WC at a time... they should instantly feel the pedal stiffness fall away and the pedal drops to the floor. If you open the bleeder valve just a little it will fall to the floor slowly. If you open the bleeder valve a lot, the pedal will instantly loose pressure and fall to the floor quickly. What this shows you is that the MC piston is free to move when fluid is free to flow out of the system (leak). If the pedal does not fall all the way to the floor or does not feel like the pressure has been let out of the system you have some issue with the MC or possible the WC.
Another place you can check is at the MC steel line fittings. Just as you would bleed the system at the WC end, you can bleed the fluid from the MC by cracking the seal at the steel line fittings where the attach to the MC. This opens a leak and the MC pistons should push the fluid out just like when you opened the bleeder valve at the WC. If they feel different it could mean a blockage in the brake system downstream closer to the WC.
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