are my front/rear brake lines crossed?

[drdata]

A silly question but my manuals are not clear. On the 78 I just sold it was clear that the MC had a larger front compartment and corresponding brake line. Makes sense as I understand disks need more fluid than drums, hence bigger reservoir and line diameter.

On my new to me 72, which has dodgy brakes, I note that:

1. The MC seems to have the same size reservoir. Is that correct for a front disk/rear drum 72 blazer? It seems to match that shown in the link below.

2. The larger line from the rear MC port goes to the rear drums. The smaller from the front hits a slitter and goes to the front disks. This seems backward, but given the different thread sizes for the two lines it seems unlikely this could happen by accident.

This link has a decent diagram, but has a nice "air gap" such that I cannot use it to confirm which port on the MC/proportioning valve goes to which set of brakes:

http://www.lmctruck.com/icatalog/cb/full.aspx?Page=151

In my case the rear line is larger, and again goes to the back brakes which are drum. The front thinner line feeds the front disks. Is that correct?

Thanks in advance.

[drdata]

Bumping for some blazer love! C'mon guys.

Perhaps I need to ask in a more direct way.

Can someone with a known to be stock 72 blazer that has disks/drums confirm which brake line feeds their front vs. the rear?

Are your front disks attached to the thicker or thinner of the two lines?

Thanks

[1949gmc]

Here's a picture of my truck. Disc/drum vehicles always have a mc with a large bowl in front for the discs and a small bowl in rear for the drums. If you have a 50/50 mc, then somebody put the wrong one on. In my pic, you can see that the big line that you're talking about is definitely for the rears while the smaller line is for the fronts. I may have a little bit better pic somewhere if this one doesn't help.

[drdata]

Originally Posted by 1949gmc

Here's a picture of my truck. Disc/drum vehicles always have a mc with a large bowl in front for the discs and a small bowl in rear for the drums. If you have a 50/50 mc, then somebody put the wrong one on. In my pic, you can see that the big line that you're talking about is definitely for the rears while the smaller line is for the fronts. I may have a little bit better pic somewhere if this one doesn't help.

Attachment 513358

Thanks for the reply and confirm. At least it seems the brake line routing is correct. On the MC front, I agree that most have larger front than rear, but when I look for 1972 chevy blazer replacements they all seem like mine, which is to say equal sized front and rear. See these links:

http://www.brotherstrucks.com/prodin...number=KORN772

http://www.car-stuff.com/store/?N=98...588+11921+9182

So now my question becomes what is the correct MC for a 72 4wd blazer? Is it symmetric or asymmetric?

Thanks again.

[1949gmc]

I still don't think that the 50/50 mc is correct, unless your truck has drum/drum or disc/disc... holds true for any vehicle. For disc/drum, you'd have to use the 70/30 mc. Now, did Blazers come with drum brakes on the front in '72? If they did, did yours have drums that someone converted to disc w/o changing the mc? Or did someone absent-mindedly just put the wrong mc on?

[lks dcvn]

71 and 72 front disk brakes were standard on chevy and GMC trucks and blazers - my guess is wrong MC installed if you have front disk brakes.

The PO of my 72 4x4 Blazer redid the brakes to drive it up from Columbus - he put in a new booster and the wrong MC (drum/drum) - It will stop, but not that well.

Not sure how he drove it 200 miles on the highway like that, but he did

He said that it is an old truck and the brakes don't work like the cars of today - err - yeah - that is wrong. It is on my 'to do' list.

[jaros44sr]

Same thing happened to me on the '72, disc/drum. PO put the wrong m/c on it, and after much reading and questions asked. I found the problem. Even the counter guy (3 differant parts stores) kept giving me the wrong M/C. Once the board schooled me on the proper setup, I was able to go in there and know what I was looking for. Sooo, with all that being said, get the M/C with the large chamber in the front...

You've come to the right place for information from guys that know what they're talking about! These guys have helped me out alot. Hang around it only gets better with time

Same setup as 1949GMC

But, keep in mind, you may want to do the one ton upgrade at this point in time

[drdata]

Thanks again folks.

If someone could point me to the correct mc part # I would be very happy.

Most of the hits for 72 blazer MC, all the hits come back with the same 50/50 design. I see different options relating to drum/drum vs. disk/drum on the proportioning valve, however.

I did locate a few options at rock auto:

http://www.rockauto.com/catalog/x,ca...,parttype,1836

Oddly, of the three listed the raybestos is 50/50 while the others are 70/30 and none specify disk vs drum.

Leaning toward:

DORMAN Part # M71285 {First Stop #18008630, 3956521, 3979629, 406389, 5458528, 5463558, 5469489, 5472157, 5472650, 5472725}
w/Power Brakes; Bore = 1-1/8"; Moraine


As another data point, here's a power brake booster kit for 69-72 trucks. Again does not specify drum vs disk and is 50/50, but same site has proportioning valves that are specified to disk/disk or disk/drum:

http://estore.websitepros.com/126980...EVY/Detail.bok

[drdata]

Originally Posted by jaros44sr

. . .


You've come to the right place for information from guys that know what they're talking about! These guys have helped me out alot. Hang around it only gets better with time

[/IMG]

Dude, I wish I had your engine compartment. Very clean.

Thanks for the pics, and tips. I agree this site is awesome. I just ditched a 78 for a new to me 72 and finding its somewhat a whole new game.

The PO indicated he had put a new booster and MC on, and they do look new, but the tip off should have been the xtra vacuum can/reservoir. He claimed it was needed because the aggressive cam had low idle vacuum. I find the extra boost to be worse, as you go from really good brakes to somewhat wooden when you exhaust the supply. I'd rather have wood all the time so I know what to expect. (no pun intended).

I added a road demon carb and fixed his goofy dual pcv setup and now get about 17 inches at idle, which I believe should be enough for the booster. Still, when compared to my 1978 this 72 stops for crap. Then again I note the booster is smaller than the 78, and now seem he put the wrong MC on.

Regards

PS> I would consider a booster/mc upgrade (1 tom) but so far all the options are very confusing. Not clear what will just bolt up to the existing firewall and pedal linkage.

[lks dcvn]

Here is the replacement stuff my PO put on - duh!

It is new - but it isn't correct...

[1949gmc]

Fixing the PO's nonsense can be a real PITA. Can cost a lot of money, too. There are a lot pf people out there that are . Sometimes it's better to tear it all the way down and build it back up the right way.

Post some pics up if you get a chance. We like to look at pictures.

[1949gmc]

Originally Posted by lks dcvn

Here is the replacement stuff my PO put on - duh!

It is new - but it isn't correct...

It looks nice and shiny, though! Who cares if it stops?!

[jaros44sr]

Originally Posted by drdata

Dude, I wish I had your engine compartment. Very clean.

Thanks for the pics, and tips. I agree this site is awesome. I just ditched a 78 for a new to me 72 and finding its somewhat a whole new game.

PS> I would consider a booster/mc upgrade (1 tom) but so far all the options are very confusing. Not clear what will just bolt up to the existing firewall and pedal linkage.

Trust me when I tell you, it didn't start out looking like this,but it is what I enjoy doing to relax

Check out AJ's one ton thread, may be in the faq section. Good reading, and not hard to do

I had that same M/C in my hand 2 or 3 times, kept telling them it was wrong. Finally they believed me, dam counter kids

[drdata]

Pics of my none-too-kosher setup. Note the black canister, now disconnected, which was the extra vacuum storage tank.






[IMG][/IMG]

[old man jimmy]

I know this is going to start a bunch of controversy, but they did come with the 50 50 master cyl. I just went out to the garage to take a picture of mine. And I know for 100% sure mine has never been changed. So don't blame to PO's for everything. After all aren't we all PO's?

[drdata]

Originally Posted by old man jimmy

I know this is going to start a bunch of controversy, but they did come with the 50 50 master cyl. I just went out to the garage to take a picture of mine. And I know for 100% sure mine has never been changed. So don't blame to PO's for everything. After all aren't we all PO's?

Interesting. that explains why most searches come back pointing at what I already have. For the money I think i will try a 70/30 swap (should do the valve also). At least then I will know what it's not if the issue remains.

I try to console myself knowing the dude that bought my 78, which I owned for the last 21 years, will have his own PO issues. Still, not all POs are created equal. When I investigated why the front seat would not latch, I found the floor mounter catch to be rotated 180 degrees (the catch hole was on the wrong side). And the latch bolts were pretty much stripped anyway. I tell myself he must have known, and did this on purpose so folks in the rear could tilt the seat up easily...

But that make no sense given the latch release works and is accessible to those in the rear; what a safety hazard. This on a truck where "everything works". Right...

I did this in part to have something to do. Just did not plan on having that much. Have to keep repeating its the journey, not the destination...

Cheers

[old man jimmy]

if you're going to go that far with the brakes. I'd recomend converting to 3/4 ton, their's a lot of post on here on how to. Especially if you plan to run big tires. When mine was new it would lock em up pretty easy. Then I went to Armstong tru trak, which was about the only big tire out their at the time. But they weigh about 75 lbs. each. And all that rotating mass really put a hurt on my breakes. They still lock up, but you almost need both feet to do it.

[Burt4x4]

Here is what the 1Ton dual diapram Booster/Master looks like. The masters resavors are the same size but the lines are swaped...

When I bought the parts I used 72K304x4 Pickup to bolt right into my 72K5 and it doubled my braking power.

[drdata]

Originally Posted by Burt4x4

Here is what the 1Ton dual diapram Booster/Master looks like. The masters resavors are the same size but the lines are swaped...
. . .

When I bought the parts I used 72K304x4 Pickup to bolt right into my 72K5 and it doubled my braking power.

I am interested. Thanks for your post.

To confirm, are you saying that a 1 ton booster and MC will bolt right onto the 72 1/2 ton booster mount with no modifications needed to the brackets or rod length? Sounds like the only issue was reversing the line attachments, which even I can handle.

Did you also swap the proportioning valve?

Regards

[jaros44sr]

I thought I said that up in post # 7

[drdata]

Originally Posted by jaros44sr

I thought I said that up in post # 7

In fact you did. At the time it did not seem this was strictly a MC/booster swap. I was of the mind that I would then need to swap brake calipers, backing plates, etc, to complete the 1 ton upgrade.

I did read a faq on upgrading brakes, but it seems there were so many options and none were as straight forward as "bolt on a new MC/booster".

Hence my followup questions if the 1 tone MC/booster is really just a bolt on upgrade while the rest stays the same.

regards

[jaros44sr]

I was thinking the cost that you will have to get it right would be the same if you set it up as a one ton, but do the calipers later. Calipers have a problem fitting on 15" wheels, some grinding required or go with larger wheels

Just kidding about the "I told ya"

[Burt4x4]

Originally Posted by drdata

I am interested. Thanks for your post.

To confirm, are you saying that a 1 ton booster and MC will bolt right onto the 72 1/2 ton booster mount with no modifications needed to the brackets or rod length? Sounds like the only issue was reversing the line attachments, which even I can handle.

Did you also swap the proportioning valve?

Regards

Yes & No ~ look for a post from AJ, can't recal the exact title but 1Ton Brake Upgrade should work in the search here. Depending on the style of Booster mount you have will make or brake the "bolt right in" answer. THe post that AJ provided out lines the different booster mounts. My 72K5 the 1Ton master/booster did bolt right in but I had to modify the support brackets as the 1Ton booster is FATer than the 1/2 ton.
good Luck
Burt

[Burt4x4]

Here I found it:
http://67-72chevytrucks.com/vboard/s...highlight=1Ton

[drdata]

Burt, thanks for posting the link.

I should have the correct bracket. If so does sound an easy swap.

Will keep the thread posted.

Regards