The Stovebolt Site Forums The Shop Area Driveline Dual MC Upgrade install questions

Hello,

I am upgrading to a Dual MC. I have the brackets and all. My question pertains to the brake lines used for the modification.

The tech-tip calls for 1/4" tubing going to the front end. I describes routing a 1/4" tube from the MC to a three way (recovered from the old system), and two other 1/4" lines going to each front wheel. Ok, but, the three way accepts only ONE 1/4" flaring nut, and TWO 3/8". So, how do I get by this? Are there flaring nuts that fit into the 3/8" port on the three way, but accept a 1/4" tube?

Similar are the tubes to the rear. The 1/4" should go to a 1/4" union, with a 3/8" tube coming off of that to the rear brakes.

As I am in Italy, and sourcing these is proving VERY difficult, I may have to order then from the UK.

Any insight to this? Are 1/4" necessary to the front? Or can I take a 1/4" to the three way, and 3/8" off that to the front brakes?

What year of truck are you working on? It had some 3/8" brake lines? That doesn't seem right.

If I remember correctly, on my 53 Chev. 3100 the new master cylinder was set up to be plumbed out of either side. Left front brake came out of the left[drivers] side of MC, right front brake out of the right side of MC, and rear out of right side. Section of MC with largest reservoir went to front brakes. Plug in other port.

LMC has "fittings" and "adaptors"

http://www.lmctruck.com/icatalog/ca/full.aspx?Page=94

Sorry, it is a 1953 3100.

The old single MC had a 1/4" to the three way. From that went 3/8" lines. Ok, maybe my conversions are slightly off, as I am measuring in metric, and converting to inches.

The lines going into each rubber brake hose are smaller than the line going off of the MC. The three way accepts one larger size, and two smaller.

I believe your metric-to-fraction conversions are incorrect. Most stovebolt brake systems use 1/4 inch steel tubing from the master cylinder, going to the front and rear, and 3/16 inch steel tubing to each wheel (not 3/8"). That would be approximately 6.3 MM tubing to the front and rear and 4.8 MM tubing side to side. The T fittings at the front and rear will have one 1/4" inverted flare opening, and two holes for 3/16" inverted flare fittings. Those would be easily available in the USA, but possibly very difficult to find in Italy. There are conversion fittings to adapt metric-size brake tubing to American Standard thread brake parts. The smaller-diameter brake lines will still carry plenty of fluid to allow your brake system to work properly. Good luck!
Jerry

Jerry,

Thanks, I was trying to adapt a tech-tip on a dual mc upgrade that requires 1/4" to the front end, 1/4" to a rear T fitting that has 3/16 off of that. (I probably mis-typed when I wrote 3/8").

Unfortunately, I am dealing with metric here. I think that I have found a source in the UK that has some parts in inches.
He sells the copper, bendable tubing in 1/4" and 5/16", and associated fittings. I will see if he can source the 3/16", otherwise I will have to bite the bullet again and order from the US.

Don't think you should use copper. Steel is what was used from the factory.

I am upgrading to a dual MC from CPP. It was purchased by the previous owner of the truck so I have no instructions, just a few parts in a box. I have the old MC out and 3 of the 4 bolts that hold the old MC support bracket in place. A quick measurement looks to me like the new MC will be too close to the frame rail if bolting the mounting bracket directly to the rail and too far away if bolting it to the support for the old MC. Was there supposed to be a spacer of some type with the new bracket/MC to get the correct spacing from the frame rail?

Yes Jim. The secret is just mounting the bracket to the original MC bracket. This will make it appear as if the shaft is too far out, but the way they compensate for that is a 3/8 ID by 3/4" spacer and a long bolt to make it all line up. SO, the shaft is too far out, then a bolt goes across with the spacer to make the connection. Am I making sense? Look at my bolt bucket pics and you should see what you are looking for. Should be on the last page. If not, let me know. I will try to explain further.

Thanks for the pics. Looks like you have your spacers at the front where the new MC bolts into the new bracket. What I meant is that the original MC bracket looks nothing like yours and if I bolt the new bracket to it, the new MC looks like it will either be too far to the passenger side or too close to the drivers side if I try to bolt it to the frame rail. Front to rear doesn't seem to be the issue.

As a follow up, did you mean that I may only need to use one spacer either on the drivers side or passenger side of the new MC to "tilt" it so that the MC piston push rod is more or less in a straight line with the new MC.

OK, I think I see what you are saying. In your photo of the MC front view, the spacer you are talking about is on the rod swivel where it mounts to the brake pedal lever. Since the new MC is more to the passenger side, this moves the MC piston rod out so that it is in line with the new MC . Is that correct?

Huh? NO. There are no spacers concerned with the mounting of the bracket. Just mount the new bracket straight to the old one. As far as I know, all 47-54 MC brackets are the very same. If you bolt it right up, it will be 3/4 of an inch to far to the passenger side. There are NO spacers. The only single spacer is to re-align the plunger. No spacers in the mounting at all.

So, even if they look different, those years everything was spaced the same. So, bolt directly to the old MC bracket. Notice how its too far to the passenger side. By about 3/4 of an inch. Right? Once you are there, its easy to fix that 3/4 with a spacer ON the plunger system. Its how CPP does it.

Has anybody thought about using hanging pedals on the firewall??? I want to upgrade my 1951 Chevy truck but I want to do it with more standard firewall master cylinder and booster too. Still trying to figure out a year and make to use to make the conversion. To me it might be easier to maintain and fill with fluids too. Bleeding them I know is a lot easier.
Just a thought that's all.

MikeC

that's been discussed Mike, one thing to keep in mind is that the firewalls on these trucks weren't designed for the stresses that'd result, so will need careful re-enforcing

Bill

And.. some of us think its really cool and innovative way beyond its time to have the MC system where its not in the way of anything. You can add a booster under the floor too if you want. Same with the battery. How cool is that?

Jim, too many rapid posts for this old man.. sorry but the answer is yes... you understand completely. (in answer to the 2nd post on this page.)

Sorry for the confusion. I need to refresh posts more.

Everything is in place, bolted up & should be attaching the last two brake lines and filling the system over the next few days. Hopefully everything will work smoothly and as designed and I can get in a test drive by the end of the weekend. Thanks for all your help! The pics really made the difference.

Well the new brake lines are in and I used the neighbors reverse bleeder pump. Got everything back up thru the system & into the MC. Figured the hard part was almost over. Stepped on the brake pedal & it went straight to the floor! Spun the front wheels & barely hears the shoes rubbing. Same with the back wheels. Adjusted on the rod going into the MC, but all that seems to do is to move the brake pedal stopping point farther away from the floor. Now I'm trying to figure out why I have no pedal at all. My thought now is that the old MC had better (longer) travel so the shoes had to be farther away from the drums. Did you have this issue with yours? Or is it that I'm just not getting enough travel in the MC? I am using the short rod that came with the kit as I haven't been able to get the longer rod in where it will bolt up.

I would say the plunger rod I used was about 5 or 6 inches long. There should be no difference in adjustments at the wheels at all. Did you bench bleed the MC before bleeding the rest of the system? Don't preload the plunger by adjusting it so it starts the braking process before pushing the pedal. Just take the slack out. It's something simple. We are here to help!

I used my neighbors reverse pressure bleeder to push fluid from the wheels back to the MC, so nothing was done to the MC. Figured it would fill up as needed and that was one of the purposes of the reverse bleed.

I didn't get two different sized plunger rods, so not sure what size you have installed. I don't know anything about reverse bleeding. This is actually the first time I have heard of it, so I am not sure how that works. I guess I would bench bleed the MC, then bleed the system normal just to see if it makes a difference.

Well, I am an old man, but I still learn something everyday it seems. Frustration got the best of me, so I took the MC back off the vehicle to see if it was working as designed. It was, so while I had it off I found that there was no pressure when pushing the rod in by hand! So, I went ahead & did the usual bench bleed of the MC. Reinstalled it, re-bled the system & it seems to be working fine now. I was under the impression that reverse bleeding (from the wheels up to the MC would fill the entire system from the bottom up & forcing any trapped air up & out. Well, it does a good job on the lines, but apparently doesn't fill up the MC very well. Guess there is something to be said for the old ways of doing things. Hope this helps the next person trying to reverse bleed a system. ALWAYS, bench bleed your MC before installing it on the vehicle & bleeding the lines!

Great! Always good to hear about success!