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Penmaenmawr · 07-19-2013, 06:23 PM

Storage has been under cover but unheated. The occasional 40 below, average midwinter night about zero to -10. Quite mild.

Bought a gallon of Dot 3. Also ordered a master cylinder and think I'll fit it anyway, here tomorrow hopefully (and I hope it's the right one). LOOKS ...... like a straightforward job with good access. Hope I don't regret these words.

Thought I might as well bleed the existing MC since there's nothing else I can do this evening. Bled apparently fine, but then I tried the brakes and they still don't work, and no feeling of the power boost kicking back at me. Fluid levels in the MC did not go down as a result of a lot of pumping.....maybe I didn't get all the air out of it? Power steering fluid level seems fine and PS is working. Still no apparent leaks around the brake system.

Penmaenmawr · 07-19-2013, 06:40 PM

Does anyone have a part number for the master cylinder? I am worried because the picture I saw at the auto supply store, although the body looked like the same MC as mine, had a different lid. There was only one option for a 1988 P-30 with 7.4 litre V8, rear disc brakes, and 16,500 lb GVW, so it SHOULD be right. (Mine is a 1989 model 345LE)

PeterH-350LE · 07-19-2013, 08:07 PM

Quote:

Originally Posted by Penmaenmawr

Does anyone have a part number for the master cylinder? I am worried because the picture I saw at the auto supply store, although the body looked like the same MC as mine, had a different lid. There was only one option for a 1988 P-30 with 7.4 litre V8, rear disc brakes, and 16,500 lb GVW, so it SHOULD be right. (Mine is a 1989 model 345LE)

Lid and reservoir size varies, whats important is the exact measurement of where the pushrod hits the plunger of the primary piston to the mounting surface. And I mean exact to a hundreds of an inch. If its less than your old, you have to use a spacer, if its more you need a different master cylinder.

bkahler · 07-19-2013, 08:10 PM

Peter sure nailed that one. Our 310 sat in a repair shop in Little Rock for a month because they couldn't seem to get the right combination for the master cylinder mating to the hydroboost push rod.

Hopefully you'll have better luck that I did!

Penmaenmawr · 07-19-2013, 08:36 PM

Hmmm. That's a bit scary. Thanks for the heads up, it could save me a lot of trouble. Googling finds me PBR master cylinder W0133-1616833 which looks like mine, but said to be for '86 to '95 CK 3500 etc. etc. I guess that's going to turn out to be quite a few different pushrods and I'll have to be pretty lucky to get the right one!

PeterH-350LE · 07-19-2013, 08:51 PM

Quote:

Originally Posted by Penmaenmawr

Hmmm. That's a bit scary. Thanks for the heads up, it could save me a lot of trouble. Googling finds me PBR master cylinder W0133-1616833 which looks like mine, but said to be for '86 to '95 CK 3500 etc. etc. I guess that's going to turn out to be quite a few different pushrods and I'll have to be pretty lucky to get the right one!

you keep your old pushrod, its the plunger space thats critical.

bkahler · 07-19-2013, 08:52 PM

I'm pretty sure the push rod is part of the hydroboost. I believe the key is to ensure the depth of the hole in the m/c piston is the same depth on the new m/c as it is on the old m/c.

I think what happened in my case was the repair shop recieved the replacement m/c, didn't verify the depth and shipped the old one out as a core without compaing piston depth. Later after I drove out of their parking lot only to find out the brake pedal went almost to the floor and didn't really stop the motorhome did they then realized they had a problem. About ten master cylinders later they finally got the correct one. I believe they tried several different vendors trying to find the right one.

I'm sure you'll have better luck

PeterH-350LE · 07-19-2013, 09:04 PM

Quote:

Originally Posted by bkahler

I'm pretty sure the push rod is part of the hydroboost. I believe the key is to ensure the depth of the hole in the m/c piston is the same depth on the new m/c as it is on the old m/c.

I think what happened in my case was the repair shop recieved the replacement m/c, didn't verify the depth and shipped the old one out as a core without compaing piston depth. Later after I drove out of their parking lot only to find out the brake pedal went almost to the floor and didn't really stop the motorhome did they then realized they had a problem. About ten master cylinders later they finally got the correct one. I believe they tried several different vendors trying to find the right one.

I'm sure you'll have better luck

Brad, you were lucky to have no brakes, mine locked up

. And this is the scary part, which I would not believe if someone would tell me: It took over 200 miles of incremental pre-loading of the Master cylinder. Once I untighten the mounting nuts the brakes gradually released.

dadstoy · 07-19-2013, 09:10 PM

A couple years back, I replaced the master cylinder on my '82 280 (with 4 wheel disc brakes). What led me to replace it was I decided to check it one day and it was dry which surprised me. I also had no visible leaks. I was about to just fill the reservoir but first used a mirror to look into the reservoirs. See the attached pic for what I found! So time to replace. It wasn't difficult to replace, but a little time consuming. I did it all from laying underneath.

I looked on line, but there were just too many choices. Probably due to thinking Napa would have one and it might be a bit less money then the real auto parts store, I tried them first. He looked it up and said it was special order and it would take about 2-3 weeks. So I walked a cross the street to a real auto parts store. I had already taken the old one off and brought it with me. The old one was a Bendix model and had a part number on it. My parts guy looked it up and said he would have it for me the next morning!

The new one is remanufactured but it is the heavy duty and correct part from Bendix and a little more expensive, but it works! Only my opinion, but don't cheap out on this part and I think it is imperative to take the old one with you to the parts store. I no longer buy anything from the Autozone type of stores and rarely buy from Napa. If you get the correct replacement, you won't have to be dealing with the push rod length issue.

Again, just my opinion, but I don't think it would be possible for the brake fluid and power steering (hydroboost) fluid to cross. Just in case your not familiar with changing master cylinders, make sure you bench bleed the master cylinder before you install it.

Penmaenmawr · 07-19-2013, 11:57 PM

Thanks PeterH and bkahler. The diagram really helped. That's a nasty picture, dadstoy! Mine looks fine by comparison.... after a quick wipe it looks like this:

It really doesn't look like there is much wrong with it, and the old fluid I sucked out was pretty respectable. Just don't know where I lost it all to.
Thanks for the tip on bench bleeding... I found a couple of good videos on it.

This is the vehicle up on jackstands:

When I get it all back together I'm tempted not to put the steel plate back.... the passenger side doesn't have one, and is no dustier than the driver side, plus it's a nuisance for getting at the MC, not to mention plugs etc.

bkahler · 07-20-2013, 01:23 PM

Quote:

Originally Posted by PeterH-Airstreamer

Brad, you were lucky to have no brakes, mine locked up

. And this is the scary part, which I would not believe if someone would tell me: It took over 200 miles of incremental pre-loading of the Master cylinder. Once I untighten the mounting nuts the brakes gradually released.

Wow! At least you didn't have to worry about any speeding tickets

bkahler · 07-20-2013, 01:32 PM

Quote:

Originally Posted by Penmaenmawr

When I get it all back together I'm tempted not to put the steel plate back.... the passenger side doesn't have one, and is no dustier than the driver side, plus it's a nuisance for getting at the MC, not to mention plugs etc.

Don't leave the steel plate off it was added by GM for a reason. It helps direct the airflow across the engine which aids in cooling.

The Argosies didn't have these panels so I'm going to be fabricating one just to get that cooling benefit.

Brad

Penmaenmawr · 07-21-2013, 04:50 PM

I was looking at a video on bench bleeding a master cylinder, and the person then fitted the MC and bled it in place. I realised that my attempt at bleeding, following the Chevy chassis manual, was totally inadequate..... basically I had been letting it dribble, and in the video the guy has it squirting wildly everywhere! So I got big plastic basin and put it under the MC, and rebled it. Five minutes later, it felt just right. There is no sponginess whatsoever, and in fact the brakes are better than they;ve ever been. I am beginning to suspect that the MC has not been checked in years (certainly not by me) and that it was down at the bottom of the reservoir before being parkied, and the succeeding year has seen it seep or evaporate or whatever to below the seal levels. I just took the 345 for a drive and everything is good.
BTW, I changed the spark plugs with the front wheels off, and that is definitely the way to do it, easiest spark plug change since the Triumph Herald.

DaveFL · 07-22-2013, 07:05 AM

Great news on having brakes fixed, since my brake repair I always test the brakes in our driveway, long enough to feel comfortable.
Maybe with your temperatures it managed to freeze dry it

and my problem of so much crap was due to humidity, either case it comes down to lack of daily use.

Penmaenmawr · 07-23-2013, 07:30 AM

Quote:

Originally Posted by DaveFL

Great news on having brakes fixed, since my brake repair I always test the brakes in our driveway, long enough to feel comfortable.
Maybe with your temperatures it managed to freeze dry it

and my problem of so much crap was due to humidity, either case it comes down to lack of daily use.

Well, I'm not sure I'm out of the woods yet, time will tell. I have read a couple of threads on other forums recently where people say it is indeed not uncommon for the hydroboost to fill with brake fluid from a leaking MC, often with little or no external sign of fluid. Here's one quote I copied:

.....also be sure to check the booster isnt full of fluid too, master will leak out the back and fill it up. a secondary siphon or a small siphon will get it out.

I did buy a replacement MC, but I'm taking it back and I'll wait until I can be quite sure I've bought the right one.