highcking Posted June 20, 2022 Share Posted June 20, 2022 My Roadmaster has the Delco-Moraine one piece power brake unit. About 4 years ago, I sent the unit on the car to a reputable rebuilder whose name I can’t seem to locate at the moment. As all owners of these units know, removing and installing the unit is not pleasant. Fortunately, the rebuild has performed flawlessly ever since. A few weeks ago, before taking the car out for a drive, I looked at the reservoir and found it virtually empty. That surprised me as the car leaks nothing on the concrete and there is no sign of leaking fittings. Today I did locate where the fluid is oozing out, very slowly, while the car sits. It’s a tiny trickle at the bottom of the triangular mounting flange of the master cylinder. Using an angle mirror, I can see that the Dot 3 fluid has eroded the paint on the bottom of the vacuum chamber. When I cleaned the area thoroughly, the fluid reappeared as a droplet or two within 24 hours. It takes about a week at this rate to lower the master cylinder level by an eight of an inch. I’m aware of the known problem with this unit leaking backwards past a seal into the vacuum unit. What puzzles me is that the fluid is actually escaping to the outside of the booster, not the inside. The overall unit continues to function extremely well. To the extent a little Dot 3 escapes into the vacuum chamber itself, several Buick commenters on other sites point out that it would be sucked into the intake manifold and burned up in an instant when the engine starts. For the time being, I plan to watch the issue and live with it unless the leak gets markedly worse. Observations? Link to comment Share on other sites More sharing options...
EmTee Posted June 21, 2022 Share Posted June 21, 2022 If fluid is leaking from the master cylinder it needs to be fixed. What happens when you step hard on the pedal with the engine off? Is the pedal firm and stable, or does it slowly sink to the floorboard? If fluid can get out it stands to reason that air could get in. 3 1 Link to comment Share on other sites More sharing options...
JohnD1956 Posted June 21, 2022 Share Posted June 21, 2022 X2 what EmTee said, and just to mention the continued deterioration of the paint in the engine compartment. Probably sucks to have it down during driving season, but better to make sure it stops and steers, than goes. Link to comment Share on other sites More sharing options...
NailheadBob Posted June 21, 2022 Share Posted June 21, 2022 (edited) I had my brake pedal very slowly going to the floor and eventually to the toe board, I did not have a leak out side the master cylinder as you described but mine leaked internally causing the pedal to slowly go down, I removed the power brake booster and master cylinder as an assembly, not an easy to access job on 1957 and 1958 Buick's, and I don flex/bend like I used to. I used Kent-Moore tool # J-6618 (I also made one not very hard to do see January 2020 Buick Bugle). Once I took it all apart and found the piston slightly pitted, I purchased a master cylinder rebuild kit # 5998 and a piston # 67 from Edwards Bros. in Arizona, and rebuilt the master and cleaned and inspected the booster. When time to bleed the brakes follow the service manual section 9-C paragraph 9-7, as it states sequence to bleed L/F, R/F, L/R, R/R just different on bleeding brakes on other cars that I have done in the past. Once completed my brakes and pedal works as designed. Bob EDIT: There is a gasket between the master cylinder and booster part # 5455882 and you could also make one out of gasket paper, BUT that is not causing your problem with the leak. Edited June 21, 2022 by NailheadBob update (see edit history) 2 Link to comment Share on other sites More sharing options...
lancemb Posted June 21, 2022 Share Posted June 21, 2022 There should be a small hole with a little wire poking out on the bottom of the master cylinder. Check to see if it's weeping out of there and running to the back. That was happening on one of my 57s and I had the slow loss as you describe. I discovered that when this hole weeps it indicates internal seal failure. Link to comment Share on other sites More sharing options...
Bill Shields Posted June 21, 2022 Share Posted June 21, 2022 Thanks for the replies! EmTee - I have a solid pedal in the situation you describe, remains solid with pumping. in general I agree, just pull off the master cylinder and rebuild or replace, then bleed. The issue is that on a '58 Buick, the master cannot be removed separately, the whole combined unit has to come out. Due to an inaccessible locknut under the dash, this is a very unpleasant task even if you've done it before, as I have. Then there is the $1,000 for the rebuilt unit plus shipping unless you take on the rebuild yourself with a kit. There is now available a custom booster/master setup for '58 Buick that provides a dual master, for about the same cost. John D - agree also. Not enough leakage to get on anything besides the bottom of the booster unit -- and in any event, my engine compartment is not cosmetically detailed. Bob - as said to EmTee, the pedal is solid and does not sink to the floor under pressure. I've never touched the innards of these complex units. I'd give it a shot if it was an easy removal and install, but it's not. On the leak itself, it is not sensitive to multiple brake applications. I thing it is leaking very slowly past a "secondary seal" that is not in contact with the pressurized part of the piston assembly (primary seal). If that's right, the unit will perform fine as long as the fluid level is up. Disappointing that a seal leaks after just a few years. Lance - no weep hole. It does have an unusual plugged brake line port at the bottom of the reservoir. I don't know what this is for. In any event, it's in plain sight and is not leaking. Overall, I'm leaning towards the brand new dual unit, available on eBay and other places. Custom-made for the Buick. However, I have a question in to the eBay vendor. The description seems to imply that this unit blocks off the driver's air vent. That would be an unacceptable loss, as my car is not air-conditioned. I have a friend with a '58 Cad who went through 3 rebuilds in 12 years, same power brake unit. The last rebuild is holding so far ... UPDATE: eBay vendor answered instantly: "This kit blocks off the driver side air vent that is by the driver's knees. Passenger side is unaffected." Very bad unless you have AC. 1 Link to comment Share on other sites More sharing options...
usnavystgc Posted June 21, 2022 Share Posted June 21, 2022 Well, IDK the specific problem you're facing but, I do know that these units are not hard to rebuild and with the exploded view diagram @NailheadBob posted, that makes it even easier. I know its hard to take out but, unfortunately, that's what I would suggest. 1 Link to comment Share on other sites More sharing options...
highcking Posted June 21, 2022 Author Share Posted June 21, 2022 Understand. But I would be doing everything for the first time. If I get it back in and it still leaks, or doesn’t function properly, I’m looking at buying yet another costly rebuild. It’s odd … my first ‘58 which was an original condition, one owner Century with 50,000 miles on it, never leaked brake fluid in 15 years of owning and driving. This multiple-owner Roadmaster is somewhat cursed. After a year of fiddling, I just finished getting the Carter AFB tuned right using an exhaust gas analyzer. Idles and drives just fine. Now this. FYI to all 57-58 Buick folks - it looks like Fusick is the last visible vendor offering an exchange on these units. 1 Link to comment Share on other sites More sharing options...
old-tank Posted June 21, 2022 Share Posted June 21, 2022 THIS is who supplies Fuscik... 1 Link to comment Share on other sites More sharing options...
usnavystgc Posted June 21, 2022 Share Posted June 21, 2022 The rebuild is not expensive. I just rebuilt mine for about $35 total. Yes, I made my own gaskets and yes I sourced the seals separately but, the process was not hard. The manual is very detailed. When you DIY it, you save about $500. 3 Link to comment Share on other sites More sharing options...
highcking Posted June 21, 2022 Author Share Posted June 21, 2022 (edited) Old-tank, thanks for that link! I wondered about that. Phil - you almost have me convinced to DIY the unit. Bill Edited June 21, 2022 by highcking (see edit history) 1 1 Link to comment Share on other sites More sharing options...
NailheadBob Posted June 21, 2022 Share Posted June 21, 2022 Bill, if you want to use/borrow either tool, Kent-Moore J-6618 or homemade one, just pay the shipping with insurance to you and back to me is all I would ask you to pay. Bob @old-tank thank you for posting the link "THIS" for us to use! Bob 2 Link to comment Share on other sites More sharing options...
Bill Shields Posted June 22, 2022 Share Posted June 22, 2022 Bob - thanks for the special tool offer, I will take you up on it when I actually start on a rebuild. Old Tank - where does that very detailed schematic you posted come from? The one with a two-letter designation for each part. A parts book? To all - it's been awhile since I've been on the forum. Not clear to me how to reply to a single post as opposed to replying to the topic. Link to comment Share on other sites More sharing options...
old-tank Posted June 22, 2022 Share Posted June 22, 2022 35 minutes ago, Bill Shields said: Old Tank - where does that very detailed schematic you posted come from? The one with a two-letter designation for each part. A parts book Not me... Link to comment Share on other sites More sharing options...
Bill Shields Posted June 22, 2022 Share Posted June 22, 2022 Sorry - it was Bob. My mistake. Link to comment Share on other sites More sharing options...
NailheadBob Posted June 22, 2022 Share Posted June 22, 2022 Bill, That photo was from the Master Parts book "Bendix Power Brake Cylinder-1957" they did not have photo of the "Moraine" unit. Bob Link to comment Share on other sites More sharing options...
highcking Posted June 22, 2022 Author Share Posted June 22, 2022 Bob - thanks. The diagram is much clearer than some others. I just snagged off of eBay the 1958 Moraine power brake manual! I’ll post anything helpful. The image you posted makes it clear to me that the leakage I’m seeing most likely originates at the final O-ring seal BA, just before the flange Gasket. At that location, leakage will slowly drain the fluid exactly where I see it, at the bottom of the flange. That will not affect brake performance unless the fluid level is allowed to drop a long way. (Which happened over probably two years). The engineering question that puzzles me is why some of these units leak and some do not. If you surveyed all 57 and 58 Buick owners still around, how many would report seepage at that location? Is seepage past that seal related to the material used in the O ring? Are all rebuild kits the same in that regard? If I buy a rebuild kit, I will take a very close look at seal BA. It probably needs to be an absolutely perfect dimension and made of a material not degraded by DOT 3 fluid. Anything that gets past it will soak into the paper flange gasket. Overall, the complicated set of seals and metal parts shows what a mistaken design this was (quickly realized). Bill Link to comment Share on other sites More sharing options...
highcking Posted June 22, 2022 Author Share Posted June 22, 2022 Added note. I heard from Fusick - I bought the unit from them on an exchange in 2020. I installed soon after receiving. My guess is that it leaked from the start. Very hard to see the leak unless you have reason to look for it. I was fortunate in checking the fluid level … 1 Link to comment Share on other sites More sharing options...
old-tank Posted June 22, 2022 Share Posted June 22, 2022 If it is leaking past the last O-ring the other seals are compromised and /or the piston is not smooth. Watch it closely and drive to enjoy. Not likely to be a sudden failure. 1 1 Link to comment Share on other sites More sharing options...
highcking Posted June 22, 2022 Author Share Posted June 22, 2022 @Oldtank - agree. Notified Fusick, let’s see what they say, if anything. Link to comment Share on other sites More sharing options...
highcking Posted June 22, 2022 Author Share Posted June 22, 2022 See below, thinking of buying a salvage parts unit. The unit now on my car has a threaded plug where the picture shows a two-terminal sensor. What is this sensor? My wiring harness has no plug for a brake sensor. What would it be sensing? Link to comment Share on other sites More sharing options...
NailheadBob Posted June 22, 2022 Share Posted June 22, 2022 I have seen several of the pistons, pitted and not smooth for the seal to seal good as old-tank stated, on several different cars. The picture shows "AR" plunger and reaction plunger group # 4.915 and when you go to group # 4.915 it lists: piston, power brake cylinder. look at yours very close when taken apart. Bill could you post a picture of the cover of the 1958 Moraine power brake manual? I may not respond for a few days as I am headed off to the BCA Nationals in the morning. Bob Link to comment Share on other sites More sharing options...
highcking Posted June 22, 2022 Author Share Posted June 22, 2022 Link to comment Share on other sites More sharing options...
JohnD1956 Posted June 23, 2022 Share Posted June 23, 2022 4 hours ago, highcking said: See below, thinking of buying a salvage parts unit. The unit now on my car has a threaded plug where the picture shows a two-terminal sensor. What is this sensor? My wiring harness has no plug for a brake sensor. What would it be sensing? That is a brake light switch. Someone may have set up a switch in a different location, like on a bracket where it is activated by pressing the brake pedal. The parts car being an AC car, you might want to consider buying the whole car and switching the parts over to your car. Then you could go for that other MC/booster unit that blocks off the drivers side vent? Link to comment Share on other sites More sharing options...
Bill Shields Posted June 23, 2022 Share Posted June 23, 2022 John, alas it's an aftermarket AC setup that looked pretty poor, not mention the car is in Texas. For those interested, CTC Auto Ranch is parting out four or five '58 Buicks including one Super. Note that sometimes pcitures are out of date, hence they have to check to see if the power brake unit is still there. I can see one on the Super also. Link to comment Share on other sites More sharing options...
JohnD1956 Posted June 23, 2022 Share Posted June 23, 2022 Aftermarket? It looks factory to me. But if that is not a recent picture it may already be gone. I have often thought of trying to buy a factory unit for my 56 and then retrofitting a current after market system evaporator into the factory firewall box. But I have never had a 58 let alone one with a factory AC unit so if that is not a factory unit then you'd know better than I. Link to comment Share on other sites More sharing options...
Bill Shields Posted June 23, 2022 Share Posted June 23, 2022 I didn't send this picture of the evaporator/blower mounted on the transmission hump. The car has a lot of usable parts overall. 1 Link to comment Share on other sites More sharing options...
EmTee Posted June 23, 2022 Share Posted June 23, 2022 20 hours ago, old-tank said: If it is leaking past the last O-ring the other seals are compromised and /or the piston is not smooth This ^^^ I'll bet the piston is pitted or one of the O-rings got damaged during assembly. Link to comment Share on other sites More sharing options...
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