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Drain Nipple - Front Brakes
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pgtips
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PostPosted: Fri Dec 03, 2021 1:42 am    Post subject: Drain Nipple - Front Brakes Reply with quote

Hi,

This is about the brakes, Front. I feel like I should know but I don't.

A search for drain nipple nothing came up, searching drain plug gives too many oil, atf etc results.

So my Q, on the front bus disc brakes there are 2 nipples. I know what they are but I don't understand why.

Bleed nipple, yes obvious, but why a second drain nipple, to drain what? i.e I can drain fluid using the bleed nipple and as I have recently found out (I was experimenting) I can also bleed fluid using the 'drain nipple'

Is drain for the whole system somehow or is drain nipple needed just for the front caliper i.e it has it own store of fluid maybe ? but then the mc has a reservoir and I have a filler tub under the seat so I'm not sure.

Why 2 when maybe 1 nipple would do. They (nipples) are different sizes as well.

I'm changing my MC to an ATE one later today and would love to crack it (the drain nipple) open and leave it to drain the brake fluid while I go off and do another job ... I live and dream Smile

thanks as always,
PG
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Abscate Premium Member
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PostPosted: Fri Dec 03, 2021 2:45 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

Commonly called a ‘ brake bleeder valve’ or just ‘bleeder’

Bay window Busses came with either ATE or Girling brakes, I think it was Girling that had two brake bleeder nipples on the caliper. The Bentley manual says only one should be used. I don’t remember which one (upper?) but someone will fill that in here.
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Slip356
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PostPosted: Fri Dec 03, 2021 5:26 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

Last year, my adult son & I were replacing rear brake calipers on his F250 diesel truck. We tried to bleed the brakes at least ten times over several days on all four wheels and could not get a hard pedal. Went thru multiple quarts of brake fluid. Assumed his new master was bad. We were both very frustrated.
The bleeder was on the bottom of the calipers.
It finally dawned on us he had the calipers switched side to side as the bleeder needs to be on the top. Made the switch and had hard pedal the first time.
Lesson learned!
At least he now has clean brake fluid throughout the system.
Is it possible this is the reason there are two bleeders on some VW calipers?
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Bonesberg55
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PostPosted: Fri Dec 03, 2021 5:38 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

The upper bleeder screw is for bleeding the brakes. The lower one is for flushing the caliper. Because it's on the lower portion it does a better job of emptying the line of impurities including rust and moisture. At least that's the way I understand it.
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germansupplyscott
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PostPosted: Fri Dec 03, 2021 8:48 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

Abscate wrote:
Commonly called a ‘ brake bleeder valve’ or just ‘bleeder’

Bay window Busses came with either ATE or Girling brakes, I think it was Girling that had two brake bleeder nipples on the caliper. The Bentley manual says only one should be used. I don’t remember which one (upper?) but someone will fill that in here.


If you think of why you are bleeding the brakes it will make sense. You are removing air, air will be at the top of the system (it floats up!) so the top nipple is for bleeding the air from the hydraulic system.

Some calipers have two screws, some have one. There doesn't seem to be much rhyme or reason to it*. Both should be the same m7 thread but calipers get rebuilt and repaired over the years so PG says he has two nipples that are different and that isn't super surprising, but from the factory they were probably the same.

Girling calipers are only used (as far as I know) on '78 and '79 Buses. This is not a scientific statement, just observational. Also (observationally speaking) '71-'72 calipers seems to have the two nipples, and the wider '73-'79 calipers usually (but not always) have only one nipple.

*As I have commented before, because of the nature of brake calipers as a 'rebuilt-from-old-cores' product, you get all sorts of anomolies with the products. The rebuilding companies mix up lefts from rights and they are clueless about how the pistons are meant to be oriented inside the caliper. If you buy a rebuilt caliper they will be 'sided' but you 100% cannot ever trust that f you buy a RIGHT side caliper that it is in fact a right side. The VW manuals have very clear info on how to verify this and identify and locate the calipers correctly, and normally (not always) a wrong-sided caliper can be corrected by rotating the pistons. Later Buses with the stepped mounting screws can make this a problem but it can be solved.
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KTPhil Premium Member
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PostPosted: Fri Dec 03, 2021 8:59 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

Having two bleeders also means the left and right calipers can be the same part number.
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sjbartnik
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PostPosted: Fri Dec 03, 2021 9:02 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

The dual bleeder caliper exists so that you can make one caliper that can be used on either side rather than having to make separate right and left caliper bodies. Instead you just flip it over to use it on the other side.

For bleeding you use the upper bleeder, as air will naturally rise to the top of the caliper.
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pgtips
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PostPosted: Fri Dec 03, 2021 9:07 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

Thanks everyone.

I forgot I am having my booster jab so is parked for a day or so.

But if I understand when I empty the system of fluid in order to change my master cylinder, I'd best using the lower bleed nipple/valve at the front will flush all (I am hoping to reuse fluid as I only put fresh in 2 weeks ago)

Fill up but now only use the upper nipple/valve to bleed. I'm going to do it manual, 5 pumps, open close etc.

It makes sense, air rises so bleed at the top but they must have experienced an awful lot of crud in the system that they felt the need to have a "drain the caliper" valve.

ah, just seen message from @sjbartnik and @KTPhil .. now that makes sense apart from why not just call it upper or lower. Calling it a drain valve is a bit confusing. No real problem just thinking it that's all. So my lower nipple is just a blanking nipple really.

Thanks again, its good to know Smile
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Trim ring info here -> http://www.thesamba.com/vw/forum/viewtopic.php?t=559668
http://www.thesamba.com/vw/forum/viewtopic.php?t=451210
http://www.thesamba.com/vw/forum/viewtopic.php?t=479721
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adventurebob
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PostPosted: Fri Dec 03, 2021 9:36 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

Bleed from top, air wants to go up. Drain and flush from bottom, dirt and liquid want to go down.
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germansupplyscott
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PostPosted: Fri Dec 03, 2021 9:52 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

KTPhil wrote:
Having two bleeders also means the left and right calipers can be the same part number.


Kind of. Not exactly though. They are different part numbers because the pistons need to be oriented correctly, and that is why the mounting screws are fitted and the manual tells you where to put the fitted screws — this orients the caliper on the vehicle which should (see *) orient the pistons properly.

The mounting ears of the caliper have counterbores to accommodate a shoulder on the fitted mounting screws. This is to ensure that the caliper is installed on the correct side. If you try to install a correctly assembled* left caliper on the right side the pistons will be clocked incorrectly and the fitted screws will have to be reversed.

As I stated in my post above, a 'left' caliper can be installed on the right side but normally you have to do some stuff to accomplish this. First of all, rotate the pistons to suit the new location (on a correctly (again*) assembled caliper they will be 180° off), and second, install the fitted screws in the 'upside-down' locations. As long as you understand these details there is nothing wrong with swapping the calipers side to side, at least not as far as the brakes functioning. The piston orientation is important. Location of the fitted screws less so.

•most rebuilt calipers are not correctly assembled! If using mass market rebuilt units, check them closely before installation!
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ToolBox
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PostPosted: Fri Dec 03, 2021 11:44 am    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

pgtips wrote:
Thanks everyone.

I forgot I am having my booster jab so is parked for a day or so.

But if I understand when I empty the system of fluid in order to change my master cylinder, I'd best using the lower bleed nipple/valve at the front will flush all (I am hoping to reuse fluid as I only put fresh in 2 weeks ago)

Fill up but now only use the upper nipple/valve to bleed. I'm going to do it manual, 5 pumps, open close etc.

It makes sense, air rises so bleed at the top but they must have experienced an awful lot of crud in the system that they felt the need to have a "drain the caliper" valve.

ah, just seen message from @sjbartnik and @KTPhil .. now that makes sense apart from why not just call it upper or lower. Calling it a drain valve is a bit confusing. No real problem just thinking it that's all. So my lower nipple is just a blanking nipple really.
Thanks again, its good to know Smile


Don't try to reuse brake fluid. Just replace with new, it's inexpensive enough.
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sjbartnik
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PostPosted: Fri Dec 03, 2021 1:56 pm    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

I defer to germansupplyscott’s expertise on this issue and retract my bad info Very Happy
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PostPosted: Fri Dec 03, 2021 2:00 pm    Post subject: Re: Drain Nipple - Front Brakes Reply with quote

sjbartnik wrote:
I defer to germansupplyscott’s expertise on this issue and retract my bad info Very Happy


It wasn't bad info! I just added to it in my typical (verbose) fashion.
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