Rebuilding master cylinder

robotman · robotman's Garage

Can i do this ? does it always work out or will it leak. I have many years ago rebuilt vw master cylinders sometimes it work sometimes not. Its much cheaper to rebuild them.
What do you guys think.

Mike

Rusty Heap · Rusty Heap's Garage

For a performance car, that may or may not sometime see a track or hard cornering on public roads, PLUS for what a pain in the butt it is to pull the mastercylinder assy out of a 911.........I'd buy new. Brakes are NOT an area to skimp on.......plus as I said it's a pain to pull the hard lines off the sides of the master cylinder so you only want to do it once.

I did the whole NEW master cylinder assy in my 82 911SC, and was SHOCKED at the new 400% better braking.

Steve@Rennsport · 07-05-2009, 05:49 PM

Quote:

Originally Posted by robotman

Can i do this ? does it always work out or will it leak. I have many years ago rebuilt vw master cylinders sometimes it work sometimes not. Its much cheaper to rebuild them.
What do you guys think.

Mike

Never rebuild an MC; always replace them, given whats at stake here.

robotman · robotman's Garage

Ok, can i upgrade and use a 19mm on a 1975 911s?

Thanks

Silveresrty911S · Silveresrty911S's Garage

How's about a vac assisted '77 MC on a '76 car?
Sorry for the hihack

robotman · robotman's Garage

I found a new large bore 23mm on ebay, $134, has anyone used these rather than the 17mm bore?

RWebb · RWebb's Garage

upgrade??

mod the size only if caliper sizes were changed

Steve@Rennsport · 07-05-2009, 08:48 PM

Quote:

Originally Posted by robotman

Ok, can i upgrade and use a 19mm on a 1975 911s?

Thanks

Your car CAME with the 19mm MC,.....

A 23mm one is a bad idea unless you have 4-piston calipers at all four corners.

docrodg · 07-06-2009, 04:37 AM

Upping the MC size will increase brake force, but that can lead to over-reactive braking and other problems. Stick with the original size.

Rebuilding an MC is possible, but the risks are high if it is not right. Plus, often it will need a bore honing if not right, and that can cause other issues in the rebuild. Buy a replacement, much easier and much safer.

robotman · robotman's Garage

Got it, thanks for all the good info i will go with a new 19mm.

Mike

911pcars · 07-06-2009, 09:24 AM

I've rebuilt master cylinders and brake calipers; also wheel cylinders with drum brakes - same principle. Hone cylinders, thoroughly clean before assembly, rebuild with the correct parts in the correct orientation. For some, a $20 rebuilding kit vs $200 for a new MC is a no brainer. One large variable might be the person rebuilding it. There's no room for "good enough" in this vehicle system.

I understand and agree as to the liability factor that commercial shops must contend with.

Sherwood

stevemfr · 07-06-2009, 01:12 PM

Quote:

Originally Posted by 911pcars

I've rebuilt master cylinders and brake calipers; also wheel cylinders with drum brakes - same principle. Hone cylinders, thoroughly clean before assembly, rebuild with the correct parts in the correct orientation. For some, a $20 rebuilding kit vs $200 for a new MC is a no brainer. One large variable might be the person rebuilding it. There's no room for "good enough" in this vehicle system.

I understand and agree as to the liability factor that commercial shops must contend with.

Sherwood

Thanks Sherwood. +1

robotman · robotman's Garage

Thanks

Zeke · 07-06-2009, 03:56 PM

Quote:

Originally Posted by 911pcars

I've rebuilt master cylinders and brake calipers; also wheel cylinders with drum brakes - same principle. Hone cylinders, thoroughly clean before assembly, rebuild with the correct parts in the correct orientation. For some, a $20 rebuilding kit vs $200 for a new MC is a no brainer. One large variable might be the person rebuilding it. There's no room for "good enough" in this vehicle system.

I understand and agree as to the liability factor that commercial shops must contend with.

Sherwood

The thing is, rebuild kits have all but disappeared from the market. I guess this is because of the liability issues. If you think about it, if the MC is leaking, it's probably pitted inside. So, you'd need more than a hone job for a perfect seal. Those little honing gizmos don't do that and over size pistons and seals are available AFAIK.

911pcars · 07-06-2009, 04:03 PM

Quote:

Originally Posted by milt

The thing is, rebuild kits have all but disappeared from the market. I guess this is because of the liability issues. If you think about it, if the MC is leaking, it's probably pitted inside. So, you'd need more than a hone job for a perfect seal. Those little honing gizmos don't do that and over size pistons and seals are available AFAIK.

Milt,
Probably so as I haven't seen (or shopped for) a MC rebuild kit for years, and the profit margin is higher for new and/or rebuilt units. Hydraulic cylinders may also have crud buildup at the end of the stroke range, even though the cylinder may have negligible wear. In these cases with + deposits, a minimal honing treatment and scrubbing will bring the cylinder back to service condition. Of course, YMMV.

Sherwood

Jerry1 · Jerry1's Garage

I believe it was common to rebuild MC as a maintenance item. If the MC is working fine a rebuild shouldn't hurt.

john walker's workshop · 07-06-2009, 05:15 PM

so what do you do about the pitting? just put a new one on and everyone will be safe.

docrodg · 07-06-2009, 05:26 PM

Rebuild kits are getting difficult to get. That said, oversize pistons for MC's are even harder to get. Pitting must be completely removed, otherwise you will chew up the seals. Given the time that it takes to replace a MC versus rebuild, the replace is typically the way to go.

RWebb · RWebb's Garage

Exactly. I just tossed out one from a VW Vanagon. New was only $60, BUT for $200, why not prevent a freakin' CRASH and death.

Wait there's more!

Let us suppose that you, owner of a nice 911 and DIYer, refurb the existing one. The brakes fail, the car crashes, and a passenger is injured. During the inevitable lawsuit, their attorneys find your posts here or sales receipts showing that you did not replace the m/c. Guess what happens next?

Now, repeat that scenario, except you sell the car to a new owner...

Just replace the thing and be done with it.

stevemfr · 07-07-2009, 04:38 AM

A lot of the brit cars still have rebuild kits available - some even more readily than new MC's.

If pitting is present, the MC is generally toast - though I have seen a MC that was bored out and received a sleeve due to parts being unavailable (not done by an amateur and there were no issues - before everybody starts hopping all over).

Why do you all make it sound like a rebuilt MC will fail catastrophically? If rebuilt improperly, it will most likely do the same thing as before being rebuilt: leak. Then it's back to the drawing board. It's just simple hydraulics, not rocket science. And back in the 70's when rebuild kits were still readily available, people were not wrecking their cars all over due to failed brakes. I agree with Sherwood - it's a simple matter of economics. And I would not rebuild a MC for a $50 savings - but I might for $200. And I'd be more worried about having purchased a counterfeit Chinese rotor than my rebuilt MC.