Brake Problem

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gracie
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Brake Problem

Post by gracie » 12th September 2018 - 7:44am

Following some brake problems, I opted to go for what is pretty much a full rebuild but the problem persists and it's odd!

When stationary the car has a good firm pedal, but start moving and the pedal fades badly to the point where it's almost to the floor, the faster you go the worse it gets.

The system has been bled 6 times, gravity and pressure and the front calipers have been bled via the top nipples

Parts changed: all rear drum parts, master cylinder, flexi pipes, metal brake pipes to accommodate the LHD derived master cylinder, front discs and pads. Only the calipers were not changed as they are only a couple of years old and look fine. There are no obvious signs of any leaks in the system.

All insights/suggestions would be appreciated :)

Graham

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broady_6
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Re: Brake Problem

Post by broady_6 » 12th September 2018 - 7:53am

Rear drum parts including the drums?

Only via the top nipples or via the bottom ones and then the top ones?
The sultan of swing

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purplepeter
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Re: Brake Problem

Post by purplepeter » 12th September 2018 - 9:00am

Type 3's do tend to be a pain to bleed, Graham, so You're not the first to encounter problems!
You'll forgive me for raising these points?
Shoes adjusted?
pushrod adjustment checked? (freeplay)
New components compared to old?
New brake fluid?
What kind of quantity of fluid have You pulled through?
As Broady said, use both nipples if You have them.
Starting at furthest point from M/cyl?

I've always found that they don't like the eezibleeder, so a combination of using the eezibleed to keep the fluid reservoir full & a teeny bit of pressure in the system and then asking Your glamorous assistant to help with the traditional bleeding method works well. I recall, but can't explain why it worked, using a block of wood to partially depress the pedal whilst eeezibleeding.

Oh, and when you get to the point of thinking You'll try a much higher pressure in the spare tyre... resist, all it does is blow the low pressure pipes off the m/cyl thus spraying brake fluid everywhere!

gracie
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Re: Brake Problem

Post by gracie » 12th September 2018 - 9:44am

Hi Guys, thank you as always for the quick responses:

New CSP drums were fitted
Shoes adjusted
I'll need to check the pushrod adjustment
Yes to new fluid and lots of it pulled through

The point you both make on the calipers has me wondering, to date bleeding has only been via the the top nipple, but researching online a Samba article notes:

"While I totally agree with johnny and tim's replies here, I recently read an interesting comment in my brown colored type 3 Bentley manual. In the brake section #2, page 13, "The main function of the additional bleeder valve at the bottom of this new-type caliper is to permit old brake fluid to drain completely when the brake fluid is changed. The older-type calipers must be disassembled to drain the fluid from the lower brake fluid passage."
I will admit, I have not performed this method to flush out brake fluid. My norm has been to slowly pump the brake pedal approx. 30x for the rear cylinders and 20x for the fronts. Some may say this many times could possibly damage the master cyl internals, but I try and not bottom out the master cyl"

New to me but worth a try.

I'll let you know how it goes

Best Wishes
Graham

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purplepeter
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Re: Brake Problem

Post by purplepeter » 12th September 2018 - 9:57am

Don't dismantle the calipers Graham.. All the advice I've ever seen was that You shouldn't, & I've certainly never seen a Torque figure published

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937carrera
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Re: Brake Problem

Post by 937carrera » 12th September 2018 - 11:12am

A couple of thoughts:

Make sure the hubs are clean and pads are not being knocked back by discs that are out of line.

You can remove the old brake fluid without splitting - turn the caliper upside down and use an airline to blow any remaining fluid out of the top nipple. I doubt that's your problem though. You'll need a wooden block or something to stop the pistons coming out

One question: Is the pedal spongy or is it simply long travel ( from your description it sounds like the latter)
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

gracie
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Re: Brake Problem

Post by gracie » 12th September 2018 - 2:18pm

The issue is long travel, not a spongy pedal David. It is very odd, when the car is static it seems fine but when moving the pedal travels almost to the floor

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937carrera
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Re: Brake Problem

Post by 937carrera » 12th September 2018 - 2:59pm

That's why I suggested discs knocking the pads back.

Seen it with warped discs and rusty hubs behind the brake disc. Thinking about it, with a type 3 it's also probably also possible with a slack / damaged wheel bearing ?

Put the car in the air, press the brake pedal to confirm it's good and then spin the hub (wheel off) to see and listen to what contact the disc / drum is making with the pad. One corner at a time and then recheck travel each time.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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sparkywig
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Re: Brake Problem

Post by sparkywig » 12th September 2018 - 5:31pm

I had really long pedal travel after changing the master cylinder. I modified/extended the pushrod to get the minimum free play and it's been fine since.

gracie
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Re: Brake Problem

Post by gracie » 12th September 2018 - 6:36pm

OK progress update; blanking the rears off created a perfect hard pedal; so the front calipers seem fine and all is bled properly up front. Tomorrow the plan is to blank off one rear side at a time to see what we learn but could it be that:

The new master cylinder isn't pumping sufficient volume to get everything working (Sparkywig's comment is interesting on that point) - this one came from Machine7 and I've no idea if others may have a higher throughput capacity - does anyone know? (Certainly, I found this to be true in a similar position with my Triumph Vitesse recently and a higher volume MC made a big difference)

Alternatively, could it be that the new rear wheel cylinders require more pressure than the old ones (new ones came from Heritage) - again are there any differences in wheel cylinder specifications?

all thoughts appreciated
Regards
Graham

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937carrera
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Re: Brake Problem

Post by 937carrera » 12th September 2018 - 7:19pm

I seem to remember of people having issues with new MC (from Machine 7), but not sure if it was on here or on the T25 site.

I have certainly heard tell of new rear drums for the T25 not being round, quite recently.

From your description the issue is not one of pressure, it is one of flow. With the car stationary the pedal is short and good. When moving the pedal goes long, therefore you are having to move more fluid to get the friction material in contact with the metal. If it was a pressure issue you would still have a short pedal to initial resisteance, then more movement than expected to get the retardation.

I do recall one of Editors favourite warnings is not to mess with the pushrod length :roll:
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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broady_6
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Re: Brake Problem

Post by broady_6 » 12th September 2018 - 9:37pm

937carrera wrote:
12th September 2018 - 7:19pm
I seem to remember of people having issues with new MC (from Machine 7), but not sure if it was on here or on the T25 site.
Memory almost serves, it was a csp master cylinder from machine 7 viewtopic.php?f=26&t=13783&hilit=muddy

Gracie could you post links to the master cylinder and rear wheel cylinders you purchased?
The sultan of swing

gracie
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Re: Brake Problem

Post by gracie » 12th September 2018 - 11:39pm

good point on the flow David and Broady having checked, both parts came from Heritage

https://www.vwheritage.com/361611067a-b ... r-vw-spare
https://www.vwheritage.com/311611015k-d ... e-vw-spare

mine is a 67 typ34

best wishes and thank you
Graham

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broady_6
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Re: Brake Problem

Post by broady_6 » 13th September 2018 - 7:45am

id love to see some photos of your car, the razor is by far the best looking thing VW produced!

Not wishing to patronise, they both seem to be the right bits, give 937s ideas ago, I cant remember if it was on here or not, but someone I know has had new discs and found one to be warped. So its not completely out of the question, you might have a dodgy one!
The sultan of swing

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937carrera
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Re: Brake Problem

Post by 937carrera » 13th September 2018 - 8:04am

Having read the first post again I'm getting less convinced by my solution, but it's still a decent diagnostic step.

Were you having the same problem before you changed all the brake components ?

Once the pedal goes long, does it stay long, or revert to a normal position after applying the brakes, then start to go long again ?
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

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Kai
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Re: Brake Problem

Post by Kai » 13th September 2018 - 10:04pm

Interesting thread chaps. It’s like a “who done it?” But more of a what is it???

My money is on the master cylinder.

Might I suggest transferring the rear line onto the front port of the master cylinder. Could be a iffy rear port of the master cylinder. In my experience soft pedal is due to not enough fluid. I ran 2x 1/2” master cylinders on my brembos and the brake pedal did nothing. Back to the mixed .6 and .7’s and the pedal was firm again.

gracie
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Re: Brake Problem

Post by gracie » 14th September 2018 - 12:40am

excuse my ignorance Kai, what does the mixed .6 and .7s mean?

Regards
Graham

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sparkywig
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Re: Brake Problem

Post by sparkywig » 14th September 2018 - 3:13pm

937carrera wrote:
12th September 2018 - 7:19pm
I do recall one of Editors favourite warnings is not to mess with the pushrod length :roll:
That's fine if you're dealing with Genuine VW parts straight from the factory.
We couldn't get enough pressure to the rear brakes to stop the wheels rotating with the pedal pushed down, and the pushrod wouldn't adjust any more because it fell out of the pedal.
Extended the pushrod so that it will adjust, and it will lock the rear wheels now.

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Kai
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Re: Brake Problem

Post by Kai » 15th September 2018 - 8:42pm

gracie wrote:
14th September 2018 - 12:40am
excuse my ignorance Kai, what does the mixed .6 and .7s mean?

Regards
Graham
Not ignorance, I’m spouting irrelevant information. My vehicle uses stand alone master cylinder unlike the dual set up of production vehicles. Without starting on hydraulic setups theory, when I fitted a smaller master cylinder my pedal lost all feelings and was pants until I went back to the larger master cylinders. My reference was to the act you said by disconnecting the rear line you achieved a firm pedal. So if the rear is not moving enough fluid the issue could be the master cylinder.

gracie
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Re: Brake Problem

Post by gracie » 16th September 2018 - 12:00pm

Many thanks Kai, your comments echo my instincts - off to research my master cylinder options

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937carrera
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Re: Brake Problem

Post by 937carrera » 16th September 2018 - 1:16pm

gracie wrote:
16th September 2018 - 12:00pm
Many thanks Kai, your comments echo my instincts - off to research my master cylinder options
Why ?

If you are on standard parts, then no reason why the MC wouldn't work properly on your car, assuming it is not faulty.
David
1974 412LS Variant
1973 412LE 4 door Fastback / Saloon

gracie
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Location: Lanark, Scotland

Re: Brake Problem

Post by gracie » 6th October 2018 - 12:44am

We finally have brakes!

There was no easy solution and I imagine usage will help. One big help was changing the rear wheel cylinders from the squareback 361611067AATE to fastback 311611067C 22.2mm units; after this, it was simply a matter of mass bleeding! I suspect changing everything in one go contributed to the issue but my good friend and longtime VW guru Ed still rates them as the hardest VW brakes to set up ever!

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