Brake Master Cylinders
 

I was bleeding the front brakes today on ERA164. I opened the first bleeder on the front and when I went to pump the pedal it depressed as I would expect through about 50% of its travel, then got stiff for a moment, and then collapsed to the floor (the reservoir was full). Now I have a never ending supply of air exiting the system at the bleeder.

I pulled the master cylinder cover and there was some fluid leaking into the boot of the front brake cylinder which I assume began with the odd pedal travel, because the inside of the cylinder cover was dry and they have never dripped onto the floor in the past. So I guess I'm in the market for a new cylinder.

My question is do I need to replace both cylinders at the same time? If not, I'd prefer to just do the bad cylinder as it will eliminate the need to pull the inspection panel to bleed the rears.

If I can just replace the bad cylinder, I assume I shouldn't mix two different makes of cylinders. The manual says that from chassis #220 on, Tilton cylinders are used, but doesn't specify what was used prior. It's definitely not the Tilton on there now. I attached a picture of the cylinders. They're stamped with V-1089 and a Google search seems to indicate they're Volkswagen or aftermarket Volkswagen replacement units. Anybody recognize them?

If I do have to replace both at the same time, is it correct to assume that the Tiltons can replace these without modification on a pre-220 chassis?

Also, based on the manual, it seems to me that the balance bar is angled improperly...that it should slant away from the outer/front cylinder as opposed to towards it. Any idea what's going on here along with the bent rear cylinder push rod? The brakes have always performed nicely and the fronts lock up just prior to the rears, but the setup is a bit different than the manual describes.

On an unrelated note, should the pedal needle bearing be lubricated while I've got the cover off, or not necessary?

I don't know all the answers but that bent push rod definitely does not look right to me. Not sure what is up with that - but I suspect it isn't right. That would also affect the balance bar setting. I suggest calling Bob or Doug if Bob doesn't chime in on your thread.

You only need to replace the master cylinder that is leaking - no need to replace both. However, while down there and bleeding brakes you might want to do it now to possibly avoid doing it in the next year or two.

The needle bearings are not subjected to continuous duty so they are probably fine - but it could not hurt to lube them if you can.

When I google that part number I get a lot of varied hits including a few cross-reference charts. It may be a Nissan or Infinite OEM part.

That's because it's BTBB (big time bent & busted). It has to be replaced and then the balance bar is set up on an angle -- it's right there in the manual. I'm not even sure how someone managed to do that to the rods, but it's definitely BTBB.:cool:

Yes, and I forgot to add that the eccentric loads on the MC piston with the bent rod is probably what wore it out and caused it to leak. (Assuming that is the one leaking). The piston drag on the bore wall is probably what caused it to get stiff when bleeding, before it slipped and bottomed.

That link should definitely be straight...

Here is the page for servicing the VW master cylinders.

http://www.erareplica.com/427man/brakes/index.htm

Didn't think to check the online manual, but the part number there is the perfect info.

I'll just replace both cylinders since I don't know how long the pushrod has been like that and possibly damaging the cylinder bore...surprisingly the one that is leaking has the straight link.

The rod end bearing on the bent link was completely seized in its bore which I guess caused the bend. Anyway, I'll get them fixed up.

Thanks for the help.

It looks like someone used allthread rod to make the pedal shafts. That stuff is soft steel, easily bent and not suitable for brake rods. This car was built by an idiot who does not understand the forces generated by a person standing on a brake pedal under serious deceleration.

I would order new Tilton (or Wilwood) master cylinders and use the shafts that come with them. These have a special shape with a washer and circlip that keep them in place. You can see in the picture below that only the end should be threaded. Make sure the cylinders have the same bore diameters as your originals. You can get these on eBay or Amazon very cheaply.

However, from your picture it appears that the shafts may be longer than the stock rods. I would look for a way to move the master cylinders closer to the balance bar. If that's not possible, I would have a professional welder attach a grade 8 bolt to the end of the rod. If that's necessary, I would also have him weld a sleeve over the welded joint to make it much stronger.

This is important (life or death) stuff and you don't want to screw around.

RS

http://www.clubcobra.com/photopost/d...nder_small.jpg

R.S.,

We use B7 threaded rod, a heat treated alloy threaded rod with 125,000 psi tensile strength.

Dear strictlypersonl,

I assume that by saying "we" that you are affiliated with ERA? If that is the case, then what is your explanation of this obvious material failure and what are you going to do to correct it for your customer?

Do you really believe that threaded rod is the best material for this application?

RS

I would use a bigger heim joint with a larger threaded end (maybe 3/4"). Take a 3/4 bolt and screw it in the joint then drill a hole through the center and tap it. This will allow you to have shorter m/c rods and you can adjust either the bolt or the rod.

Quite the assumptions you've made there, RallySnake.

Given that this car was home built three decades ago and ERA has nothing to do with the components pictured (short of the bracket placement), Bob isn't going to do anything to correct it, nor should he (and their MC setup is different on newer cars anyway). His participation in this forum is already more than I would expect from a manufacturer and is invaluable to ERA owners.

I'm no car mechanic, but I do have a mechanical/structural engineering degree with extensive industry experience in metallurgy/material properties. To suggest that a fully threaded rod is insufficient for this application with absolutely no information about it is off base. As long as the threaded portion of the diameter isn't considered in the rods compression yield characteristics, it's no less appropriate than any solid rod of similar material (that's not strictly true, but the differences are minor and only come into play under 'strain to [material] failure' conditions, which aren't applicable).

The idiot who built this car was my father and I trust his work implicitly, but thanks for the kind words.

In maintaining the car, I have found Grade 9 bolts in all 'critical' applications that experience little to no shearing, and Grade 8 in the 'critical' areas that do. Nobody considers those kinds of things (and it's overkill as Grade 8 would have been more than enough everywhere) and then puts a hardware store grade threaded rod into the brake system (and I can see from inspection that it is a high strength steel variety).

However, using a steel component manufactured to a specific strength standard is no guarantee of anything. There can always be undetected defects which could cause failure.

I have seen welds on nuclear power plant components that were fully engineered and certified through x-ray inspection fail. I've seen fasteners and structural links constructed to the highest standards for applications with exceptionally high safety factors also fail...but maybe it was just that the guys who engineered it were idiots.

I don't think I've ever even seen a Grade 9 bolt, unless it's one of those super duper rocket ship compatible driveshaft bolts that ERA uses.:LOL:

Bob (Strictlypersonl) is from ERA and has been involved with the design and fabrication of their Cobra replica program from their first car. B7 grade threaded rod is pretty much the same as Grade 8 for practical purposes. Car 164 has been around for quite awhile - hard to know if that rod is original or has been changed out for some inappropriate material or what. From the S-bend in it and color I suspect that is not B7 rod but that's just an opinion.

Grade 9 bolts - not something that you normally run across or have a need for in the automotive world (that I'm aware of) - but yes, it's out there.

https://www.fastenal.com/content/fed...0Fasteners.pdf

By the way CriticalMass - love your response. Good luck with the repairs.

Yes CriticalMass, great response, well done.

Bob, please know that we do appreciate your presence here on this forum and this guy is just one guy. There is one in every crowd!

I don't mind people challenging my "relevance". The only thing that drives me a little crazy is when people extrapolate their experience (with completely different designs) to the ERA.

I'll second that. Your help is invaluable and the ERA is a great engineered car. As an engineer (but a civil one - jack of many trades but a master of none) I can appreciate it.

Yes, I noticed he had a Arntz Cobra, but did not want to say anything. It is amazing isn't it!

Bob is about as "relevant" as you can get when it comes to ERA and his participation on the forum and his boundless knowledge about his cars is invaluable. I doubt there is any other offering out there with ERA's depth of involvement with their customers after the car has been purchased.
I love the knee-jerk responses by forum members who know little or nothing about the subject or the reality of these cars. You can't warrant against people's stupidity. All you can do is TRY to provide guidance to try to correct their errors.
Once the car is out the door ERA has no control over what a customer chooses to with it. When a customer elects to use a substandard part through ignorance about materials or applications is totally on the customer.
DonC

Could not agree more! I have owned another brand of Cobra before I got my ERA. This company actually is spoken pretty high of in the Cobra world. I actually like d the car and owned it for 6 years. The only reason I sold it was for the exact reason you speak of. Customer service after the sale including parts that required rework to fit there own car every single time! In some cases it added up to hundreds of dollars. That was the side-pipes made in their jig for their car, or the 4 rear shocks they sold me that needed 70.00 in grade 8 longer hardware because it did not fit their own car correctly. Bottom line is that ERA blows everything I have seen and heard away. In fact Peter and the info on the ERA site helped me do work on my first Cobra. That is what sold me on getting an ERA in the first place!
Let me also say this. My present car has got some issues for sure, and I am slowly addressing all of them. 100% of my issues is from the builder doing wrong things. NONE of the problems with my car is ERA's fault at all
Thanks ERA