New M/C from SS

[DCTiger]

Have had issues with brake system and troubleshooting comes to M/C.

I rec'd new master cylinder from SS and it has an adjustable length pushrod. Rather than remove/replace with original pushrod (I believe), I want to use the one that is on it.

Anyone know what the length of the pushrod should be? Let's set the reference point from mounting flange firewall side to center of holes on pushrod.

(I previously bought a new VB M/C and replaced the pushrod with my original Tiger unit. This seems to not work.)

TIA,

 

[65beam]

M/C

set the two masters side by side and it should be easy to adjust the new one to the same length as the old one.

 

[DCTiger]

Length Matters

Don't assume that replacement parts are the same as the original.

I bought a VB M/C and replaced the adjustable pushrod with my original. This caused the M/C to not release pressure all the way, which lead to the rear wheels releasing and the fronts still engaged.

Along the way I learned how to rebuild my calipers easier.

After consulting with VACAT33, we concluded that the issue was most likely the M/C and worst case the distro block. Luckily it turned out to be the M/C, only a clog would be the reason for the block to be the culprit.

I received a M/C from SS, which almost looked identical to the VB M/C. Both had an adjustable pushrod. I decided to use the SS M/C unaltered.

It was not as easy to install as a fixed pushrod, but is better because my brakes now work. The original pushrod with the new M/C was too long, therefore the adjustable pushrod allowed a perfect shorter length.

Like 65Beam suggested, I should've compared the lengths from the start.

But this is how we learn and I would like to keep others from making the same assumption. Make sure you measure all critical interfaces.

Now all I have to work on is my low oil pressure and the MK I will be ready for the road. I have some paths fwd on that issue and will tell the tale when that is solved.

Regards,

 

[VaCat33]

The Apprentice

Hi All

I appreciate Rob giving me a "byline" but in reality, I mostly drink coffee and hand him tools.

 

[KettleCarver]

Length Matters

Don't assume that replacement parts are the same as the original.

I bought a VB M/C and replaced the adjustable pushrod with my original. This caused the M/C to not release pressure all the way, which lead to the rear wheels releasing and the fronts still engaged.

Along the way I learned how to rebuild my calipers easier.

After consulting with VACAT33, we concluded that the issue was most likely the M/C and worst case the distro block. Luckily it turned out to be the M/C, only a clog would be the reason for the block to be the culprit.

I received a M/C from SS, which almost looked identical to the VB M/C. Both had an adjustable pushrod. I decided to use the SS M/C unaltered.

It was not as easy to install as a fixed pushrod, but is better because my brakes now work. The original pushrod with the new M/C was too long, therefore the adjustable pushrod allowed a perfect shorter length.

Like 65Beam suggested, I should've compared the lengths from the start.

But this is how we learn and I would like to keep others from making the same assumption. Make sure you measure all critical interfaces.

Now all I have to work on is my low oil pressure and the MK I will be ready for the road. I have some paths fwd on that issue and will tell the tale when that is solved.

Regards,

I have a similar problem with the car I just bought. The front calipers are stuck, but the rear drums will turn. I believe it has the VB M/C. Since it came on the car, I don't have the luxury of comparing it with an old pushrod for length. Can someone tell me what the proper length of the push rod should be adjusted to? The workshop manual does not mention any dimension for that. Also, my car does not have a brake booster, so that is not what is hanging it up.

Thanks,

Marty

 

[0neoffive]

Simple physics of hydraulics: If the pressure is off the rears, it follows that the pressure is also off the fronts in a single line system. Experience has shown me that sticky calipers have other issues like crap in the bores and or corroded pistons. Flexline inner collapse can also leave calipers with temporary pressure. I have used the original rod in new MC's without issue.

 

[Phyrman]

I sourced a piece of firewall off donar Alpine to help set up the MC on my work bench Way easier that upside down and contorted under the dash!

 

[Tiger]

I have a similar problem with the car I just bought. The front calipers are stuck, but the rear drums will turn. I believe it has the VB M/C. Since it came on the car, I don't have the luxury of comparing it with an old pushrod for length. Can someone tell me what the proper length of the push rod should be adjusted to? The workshop manual does not mention any dimension for that. Also, my car does not have a brake booster, so that is not what is hanging it up.

Thanks,

Marty

You've likely found the answer of OEM pushrod length, but for anyone else looking for dimensions: Clevis pin center to firewall-side of spacer is 3 3/8" and spacer is 1/2" thick. (See attached photo - excuse the camera angle but dimensions are accurate).

 

[0neoffive]

I have a similar problem with the car I just bought. The front calipers are stuck, but the rear drums will turn. I believe it has the VB M/C. Since it came on the car, I don't have the luxury of comparing it with an old pushrod for length. Can someone tell me what the proper length of the push rod should be adjusted to? The workshop manual does not mention any dimension for that. Also, my car does not have a brake booster, so that is not what is hanging it up.

Thanks,

Marty

Older calipers can often have a sticking piston(s). Examine the pads and see if one is wearing more than the other. The rears can also have enough air in the line that they will "release" even though there is still some pressure in the lines. Bleeding the rears is another gremlin. The booster can also not be returning to full release. I often find scarring in the lower forward part of the vacuum can which catches the piston trying to relax. Rebuilding the calipers requires deep cleaning and making darned sure that the dust boot is properly seated. Etc.

 

[KettleCarver]

You've likely found the answer of OEM pushrod length, but for anyone else looking for dimensions: Clevis pin center to firewall-side of spacer is 3 3/8" and spacer is 1/2" thick. (See attached photo - excuse the camera angle but dimensions are accurate).

View attachment 14220

No, I never did get an answer. Thanks for the reply.

How does that pushrod adjust? I don't see any obvious adjustment point.

 

[Tiger]

No, I never did get an answer. Thanks for the reply.

How does that pushrod adjust? I don't see any obvious adjustment point.

In disassembling the external parts, I find that the master internals are retained by a black, crimped collar (see attached photo). I didn't un-crimp it but found online, a disassembled 1965 Alpine master showing the same crimp and a non-adjustable rod. With that, I agree that the OEM master appears to have no adjustment, with the correct rod length pre-determined in design.

So, adjusting your rod to the length I've given should be a good starting point.

 

[KettleCarver]

Thanks for all the replies. I am working on getting the windshield re-installed right now. I will take some measurements once I get back around to working on the brakes.

 

[KettleCarver]

Well, after much delay on the windshield, which is now in, I am back to working on the brakes. I am finishing up rebuilding the calipers with stainless steel pistons from SS. I also bought their M/C with an adjustable push rod, so I will be able to use the measurements above.

Did you guys do any sort of bench bleeding on the M/C? I am not sure how you would do that with its design.

 

[Austin Healer]

Well, after much delay on the windshield, which is now in, I am back to working on the brakes. I am finishing up rebuilding the calipers with stainless steel pistons from SS. I also bought their M/C with an adjustable push rod, so I will be able to use the measurements above.

Did you guys do any sort of bench bleeding on the M/C? I am not sure how you would do that with its design.

You will find that the original return spring for the operating rod will be near impossible to fit. I have taken to re-use of the original rod if it isn't ovaled out where the clevis pin fits. As for bench bleeding, I've never had to (in the last 40 years, anyway!) By the way, the caliper internals (type 16P) are identical to the later Mk3 3000 (Healey 64-67) and the Triumph TR4-TR6, 61-73. Rear brakes are 9" Triumph TR4 with 3/4" wheel cylinders. Girling system, everything but the brake drums.

 

[Theorangetiger]

Did you guys do any sort of bench bleeding on the M/C? I am not sure how you would do that with its design.

I agree on not having to bench bleed. You can install it dry. Dual circuit American master cylinders are a different story though.

 

[KettleCarver]

Great, that is good to know. That sure makes it a little easier.

 

[Austin Healer]

Another thing to remember is that there has to be some free play at the push rod when the pedal is in the "off" position. This is why there is a return spring. No free play will allow the piston to block the pressure bleed off hole in the bore causing the brakes to lock/partially lock.

Randy is quite correct about the calipers. Original pistons were hard chromed and can seize in the seals or bores of the caliper. This is because brake fluid absorbs water, the cars don't generally get driven enough to evaporate it out, and people aren't in the habit of changing brake fluid on a regular basis. Stainless pistons are cheap ($16.50 my price/$22 retail). The same issue will strike rear wheel cylinders and masters if you hone them. The bores in alloy brake parts are anodized and the pistons are steel. Damage the anodized coating and the steel and aluminum will react seizing the cylinder. Masters and wheel cylinders are cheap, just buy new ones. More important to be able to stop than go!

 

[Warren]

I was disappointed to get a cast iron brake master from SS. If going stock be sure to ask ...

 

[KettleCarver]

I have installed the freshly rebuilt calipers with stainless pistons and blead them thoroughly. The calipers still don't release. So, we can eliminate them as the source of the problem. The new M/C is next.

 

[KettleCarver]

Older calipers can often have a sticking piston(s). Examine the pads and see if one is wearing more than the other. The rears can also have enough air in the line that they will "release" even though there is still some pressure in the lines. Bleeding the rears is another gremlin. The booster can also not be returning to full release. I often find scarring in the lower forward part of the vacuum can which catches the piston trying to relax. Rebuilding the calipers requires deep cleaning and making darned sure that the dust boot is properly seated. Etc.

So, what is the gremlin with bleeding the rears? Is there some special technique to be used?

My car does not have a booster installed, so that is not the problem.