Allroad Brake Master Cylinder

[Douglasrkline]

Anybody know if it crosses over with any other master cylinder? Nobody has one in stock and can't wait 4 days to get one in [headbang]. I have a 2001 2.7T. Thanks!

[Scotty@Advanced]

4D0611021B I can get you one in a few days.

I have a used one in stock.

[fR3ZNO]

I just checked RockAuto and the master cylinder from a B5 A4 and an C5 A6 have the same part number.

[fR3ZNO]

However, the allroad has a different part number for some reason. Sorry. [:(]

[lawdogg]

I think they're all the same. I need to replace mine too, so I did some research and found that B5 A4 / C5 A6 including allroad were all the same. I picked one up from a B5 A4 and it looks identical, although I haven't installed it yet.

Scotty, do you know if they are interchangeable from those models, or are there differences? I hope you didn't intentionally not answer the question and just try to sell something.

[Scotty@Advanced]

Scotty, do you know if they are interchangeable from those models, or are there differences? I hope you didn't intentionally not answer the question and just try to sell something.

The part number is 4D0611021B..

I did not answer the interchangeability questions as it's not cut and dry.

That does fit few other models, but there are several different options and VIN splits. If you order that part number from me or someone else you'll get the correct part, but if you go junk yard hunting it's anyone's guess if you'll end up with the proper replacement.

[lawdogg]

Thanks Scotty. What isn't cut and dry about it, i.e., what are the differences? It sounds like there are several different kinds of master cylinders - how many are there, and what modifications would it take to get any one of them to work on a different car?

[Douglasrkline]

Thanks for all the help. Found one and will have it monday.

[lawdogg]

On point, it was very interesting to me when you said there were differences initially, because in all my research, it seemed like they were all interchangeable. (See, e.g., this vendor (http://www.fcpeuro.com/products/audi-brake-master-cylinder-4d0611021b) saying that the 4D0611021B also fits into A6, A4, S4, A8, and S8.) Additionally, 8E0611021, the part number for the B5 A4 / S4 quattro, according to the same vendors, is interchangeable into the C5 A6 etc. I was really hoping you'd elaborate since it appeared that you knew the specific differences.

So I dug a little more myself, and I did find one comparison of the two where there does seem to be a bit of an orientation difference ... I found a post by a guy with a 1998 A4 on Audiworld.


This is my stock 23.81[mm] bore MBC with inlets at 12 o'clock and 3 o'clock, pn 8D0611021

[not his pic but the same one:]
http://c1552172.r72.cf0.rackcdn.com/3309_x600.jpg

Below this you can see the 25.4[mm] bore MBC I got with inlets at the (wrong 9 o'clock) and 3 o'clock, pn 4D0611021

https://lh3.googleusercontent.com/-TbYZYNP--i4/UWC0r9g3x9I/AAAAAAAAD7w/Uv249-plJaI/s542/4D0611021.jpg

Lastly, this is a possibly compatible 25.4 bore MBC with inlets at the right positions, except the pressure inlet in the foreground looks twisted at an angle, pn 8E0611021

[not his pic but same one:]
http://www.gpautobitz.com/image/cache/data/8E0611021%20BRAKE%20MASTER%20CYLINDER%20AUDI%20A4% 20TRW-600x600.jpg

So we can tell that at least a 1998 A4's OEM 8D0611021 is separate from a 4D0611021, in that the orientation of the inlets is off by 90 degrees. ECS confirms (http://www.ecstuning.com/Audi-B5_A4-Quattro-V6_12v/Braking/Master_Cylinder/ES1595/) the difference and notes that there was a model year split in 1999, in that the 23.8mm 8D0611021 fits the A4 up to VIN 8D-X-199 999.

Checking out ECS, judging from that posted picture above, it appears that it has pictured a 4D0611021B here (http://www.ecstuning.com/Audi-C5_S6-Quattro-4.2/By_Brand/K-L/Lucas/Braking/ES3516/) in its application for the C5 Allroad.

After the 1999 split, the reservoir changes too, while consistent with the 8D0611021 the old (http://www.ecstuning.com/Audi-B5_A4-Quattro-V6_30v/Braking/Master_Cylinder/ES437356/) unit had top inlets, the new (http://www.ecstuning.com/Audi-B5_A4-Quattro-V6_30v/Braking/Master_Cylinder/ES1884431/) unit has side inlets, which is consistent with the 4D0611021's side inlets.

So from what I can tell, the only appreciable difference is between the A4 pre-1999 model year split 8D0611021 (having top inlets and requiring a top feed reservoir) and the post-1999 model year split 4D0611021(A or B) (having side inlets and requiring a side feed reservoir) which appears to fit all post-1999 model year B5 A4 / C5 A6 & allroad models.

The one with the angled inlet, 8E0611021, ECS says (http://www.ecstuning.com/ES205354/) it fits C5 S6's and VW Passat B5 1.8T, and another site (http://www.europaparts.com/brake-master-cylinder-8e0611021.html) says it also fits B6/B7 A4s too (depending on ATE / TRW system).

THE POINT BEING ... if you have a C5 A6, it looks like you can source a master cylinder from any A4 post-1999 split, and any A6. Even if you do get one with top inlets, you will just need to grab its reservoir too.

Anyway, Scotty, in reference to our now deleted exchange, it seemed like you knew the differences because you mentioned the dependence on options and VIN splits, and to me it seems like you were hiding the ball in order to make a sale. Hiding the ball to make a sale is something I see from time to time on various message boards, and it is a pet peeve of mine to see board vendors do that, especially when they do it in a thread where someone is simply asking for help with a part # like this. So now it seems like since you know it depends on VIN, year, and brake options, you do know at least some differences between part numbers. So I called you out about it. But I'm glad to hear that you weren't holding out and if you have anything to add that'd be fantastic.