Bus master cylinder conversion

Bill K. · Post by **Bill K.** » Sun Apr 29, 2007 11:19 am

Ray has posted on his 412 conversion to a late bus master cylinder: click here for link

I'd like to do the same and report here. I'll have 38mm rear and 48mm front disk brake pistons.

First, picking the correct master cylinder. Ray - is this the one?

from busdepot.com (click here for link) it's p/n 211.611.021 AA from Brazil. It has bore of 23.81mm designed for disk brakes of 71+ bus.

raygreenwood · Post by **raygreenwood** » Mon Apr 30, 2007 9:01 am

That one in the picture is actually from a power brake model. You want the manual (non-power) model. I will see if I have the part # close by. Ray

Wally · Post by **Wally** » Mon Apr 30, 2007 1:09 pm

raygreenwood wrote:That one in the picture is actually from a power brake model. You want the manual (non-power) model. I will see if I have the part # close by. Ray

Didn't power brake models have smaller diameters? 23,8mm seems large with power assist?
Just wondering..

Cool to document your conversion Bill!
Nice caliper balance

Its identical to a BMW/944 front/rear caliper size

raygreenwood · Post by **raygreenwood** » Mon Apr 30, 2007 1:13 pm

Yes...it does seem large. Is this a bus or vanagon cylinder we are speaking of. I believe tehcylinder we need is the 21mm bus cylinder from one without power brakes....like 72 on without power brakes.

But...the cylinder pictured....IS a power brake cylinder. You can tell from that metal "ferrule" that sticks out teh back. That is power brake only. Of course the cylinder pictured may not be the one for the part #. Ray

Bill K. · Post by **Bill K.** » Mon Apr 30, 2007 6:10 pm

The above is a bus master cylinder for 71-79. Yes, it is for power brakes (per BusDepot.com). I haven't found a manual version for similar years.

How about this 70 bus manual brakes master cylinder? 22.2mm, 1 brake light switch port. p/n 211.611.021 T BusDepot.com link here

Or, this 68-69 bus manual brake m/c? Also 22.2mm, but with 2 brake light switch ports p/n 211.611.021 Q BusDepot.com link here

Wally - I've been watching you

albert · Post by **albert** » Mon Apr 30, 2007 7:00 pm

hi,guy ,,for the 412 master,, look in the ,,,rock auto prts ,,they sale all we have need for to restore ,,master cylinder for brake or caliper or cluth or slave cylinder,,

SureFit Travis · Post by **SureFit Travis** » Mon Apr 30, 2007 10:11 pm

Hmm......Albert, tell me about this 'Rock Auto Parts'.....where are they located, and do you have a phone number???

I just pulled my 3 VW's out of storage, and the 412 weeped a bit of brake fluid on the rubber floor mat over winter.....and my clutch master is the unlucky culprit. I haven't had a chance to examine it yet, but I suspect it needs a rebuild.

If anyone else has info on a guaranteed place (parts store) to find rebuild kits, I'd appreciate the tip.

Thanks guys,

Travis

albert · Post by **albert** » Tue May 01, 2007 3:55 am

hi, travis go to see your ,,pm,, for the url,,it, www.rockauto.com

raygreenwood · Post by **raygreenwood** » Tue May 01, 2007 6:59 am

Bill K has the correct cylinder in his pictures. My brain is slipping. Could have sworn it was 21mm. That is the correct cylinder though (the one in the top picture). You could use either, but if you use the one with twin seconadry circuit ports...you would plug one to remain with a single brake line to the rear. Ray

hoodsy · Post by **hoodsy** » Tue May 01, 2007 5:25 pm

hey travis, if you are thinking of getting one of those master cylinder rebuild kits for your clutch master, you may be disappointed with what you get. I got one and most of the seals don't fit properly, only two of them where even close and even then they were too tight and tended to bind. I ended up pulling them out and resealing mine without using a single part from that kit. but the brake caliper kits are great.

ubercrap · Post by **ubercrap** » Tue May 01, 2007 7:29 pm

I got a centerlink from them that wasn't the right one, so watch out. At first they said they were sold out, but then they said they had found one. It arrived and had the correct part number on the tag, but it definitely was not the right one. It looks like something for a full size truck or something (still in storage somewhere- I never got around to returning it).

Anyway, looking under the brake master cylinders, they also have the ones remanufactured by A-1 Cardone (like I got from autopartsgiant.com), which everyone has warned will most likely be crap. I have a few, but haven't disassembled them to check them out yet or tried to use them. More interestingly, they have some now shown as Raybestos brand and aren't labeled as remanufactured. The picture shows the correct picture too and price is listed at $120.79. Sounds fairly good.

I'm about to do some rebuilding of the hydraulic system on one of my cars, and I must say I'm nervous, as I haven't ever rebuilt a hydraulic part before, just pulled and replaced stuff in the past.

Something else neat is they have Monroe air shocks listed for the rear!

albert · Post by **albert** » Tue May 01, 2007 8:01 pm

hi,uber ,, look in ,,mercedez 73 parts ,,in ,,,, www.importparts.com they show , cluth master cylinder , ,, 2 bolts on the top ,, he have the 412 look

albert · Post by **albert** » Tue May 01, 2007 8:07 pm

ops,,error on the ,,url,, it is,, www.importpartsspec.com

albert · Post by **albert** » Wed May 02, 2007 5:43 am

for the 412 cluth master cyl. we can look in mercedez parts ,73 ,, they sale appx, the same master cluth cylinder , with the 2 bolts on the top , it is a bit more long but i thing he can do a very good job on the 412,,,,,,for information ,,the master brake cylinder is sale by napa,pn,39060,, new ,, and the master cylinder kit is the same on the type3-4 for 72-74 ,pn,,411-698-471 ate,, kit for fag is pn,kg 190371.1

raygreenwood · Post by **raygreenwood** » Wed May 02, 2007 3:09 pm

I always applaud someone trying any new source of any 411/412 parts...especially brakes. But here is about what you end up getting from a lot of these establishments.
If the part is rebuilt...beware...unless it is factory rebuilt by ATE or FAG.
There is no really good way to properly rebuild most of these cylinders. Here are the problems. (a) Most all of the core cylinders by this late date have the classic rust pits around the outer end of the primary plunger. This is a 411/412 problem. Being under the dash, these cylinders do not evaporate condensation like the master cylinders under the car of types 1,2,3. And....if you have the chronic windshield corner leaks like most old 411/412's have....all of your cylinders will rust in this manner. (b) If a core cylinder has these rust pits...it must be bored oversized and then lapped smooth....meaning new oversize pistons and seals......only ATE and FAG factory would have such items. They were never offered oversized. Its common to find that rebuilders do not have oversized pistons..so they don't bore oversize...and your cylinder still has the pits...which generally means about a 15K mile lifespan..as it grinds the seals up....and leaks air into the system.
(c) I have found a common problem with rebuild cylinders is that they re-use pistons (not really a problem per-se)....but some have poorly resurfaced compensation port sealing areas on the old pistons. The worst problem is that some of the crappier rebuilders do not pay attention to the fact that there were two main makes of cylinder ATE and FAG.....that were OEM. There were a couple more that were aftermarket...like wagner etc. None of the pistons are interchangeable...and only a few of the seals are. I have found rebuilt FAG cylinders with ATE pistons...and vica versa. I have never personally seen a Wagner cylinder myself...just pictures. If you swap pistons between any of these brands...usually the cylinder works very poorly if at all.....due to compensation port location differences.
(d) The few rebuilders (short of factory) that I have seen who do get the parts and seals correct....get the honing wrong.

If you hazard to open up a new German master cylinder of any type...you generally see no cross hatch marks. If you do...they are exceedingly finer than anything you are likely to see in say...an engine cylinder bore. Usually they are bored an lapped...or honed with something much finer than the average 320 grit hone. Honing brake master cylidners with a brush hone....yes....works.....but.....those cylinders never see any real high milage usage. This is because we are not trying to seat piston rings...we need a smooth as glass surface (well...not that smooth)......with just enough tooth to hold oil film.....but very smooth so as not to wear the cup seal edge.
If you hazard to measure the piston versus the bore diameter you will notice that the piston is smaller than the bore. This is because the seal cup is the ONLY part that rids on the bore.

When everything is operating properly...the inflated (by pressure) seal cups....center the piston in the bore.

Its common to see.....on a cylinder that has pits....that the seal leaks fluid as it crosses the pits. As it gets worse, the seal cup collapses on that edge as it crosses the pits and leaks fluid. The piston does not stay centered well. You wil see heavy scuffing of the piston on that area closest to the pit area....because the collapses of the seal skirt allows the piston to contact the bore.

In short...I think you are better off rebuilding your own cylinders....if they are pit free still. You can use a fine oil stone or a glass plate with 2000 grit paper to clean the compensation port flap seal areas. The typ3 3 master cylinder kit seals and flap valves work perfectly in the type 4...but again...make sure you use an ATE kit with an ATE cylinder and pistons...or FAG with FAG. DO NOT use the type 3 pistons. They are not the same and cannot be made to work.

If you are pit free...make a lapping tool. A wood or aluminm dowel with a slot cut in the center longer than the depth of the bore. Take several sheets of 600-800 grit wet dry sandpaper cut into clean strips...layered on top of each other..each offset about 1/4" over. Insert these into the slot and roll them around the dowel. These will fan out and make a "flap wheel". It must be just smaller than the diameter of the cylinder when rolled tight.
Pour in a little brake fluid for lubricant and with either hand or a drill set on low speed...speed the tool to lap the bore. Do this again with 1000 grit or better paper.

This level or rebuild with good sealing surfaces under the flap valves ...on old pistons with correct new seals...will give factory results.

The only reason I ever started looking for another cylinder is the terrible core situation of 411/412 cores, coupled with the high cost of new cylinders when you can find them......and the inevitable rusting issue...and leakage potential. It was just easier to relocate the cylinder to the trunk and use a more readily available cylinder. ray