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Old 08-07-2011, 09:23 AM   #15
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Quote:
Originally Posted by Skip426 View Post
dspowers, the system is refered to as , Hydra-boost, it assists braking with pressure from the power steering pump, if it was leaking , you would be adding p/s fluid. Good luck bleeding the brakes, with the amount of rust visible in the photos, things could get nasty. Be ready to apply a little heat to the bleeders, to get them loose, if the rubber caps are missing, take the bleeder right out and clean it with a piece of wire, before you start.
Excellent advice, new bleeder screws are cheap and normally available at any auto parts store.
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Old 08-08-2011, 06:48 PM   #16
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Need second opinion

The master cylinder that came off my HR 1982 454 7.4L Chevy P30 looks differrent from the one we had to order at auto zone mines seems to be two pieces and theres only one piece, the question is will this make any changes with the way power steering works? because there is an adapter that goes on the line that is towards the rear of the master cylinder. This line is to the power steering? Im guessing. Here are the pictures of my master cylinder/adapter.
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Old 08-08-2011, 08:55 PM   #17
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I hope this is just the picture angle and I am wrong but I sure got a bad feeling that someone has modified this sytem by eliminating the combination valve (the switch that operates the brake light on the dash). Is that black hose in the bottom picture the left front brake hose? If so, is connected to the brass "T" at the master cylinder? What is the brake line in the bottom right of the picture? (The one with the spring coil wrapped around it). WOuld sure be nice to see a picture a little bit farther out so we could see more of this setup. The 84 manual I have does not reflect a brass "T" fitting at the master cylinder.

The hydroboost unit looks simular to this:


I am fairly sure the master cylinder that mates with the Hydroboost unit should look simular to this (10,000lb hydroboost):


One that looks like this next one is used with a vacuum booster on the P30 step-van chassis (not the P32 motorhome chassis hydroboost):




My gut feeling is a P/O has installed a step van Master cylinder AND eliminated the combination valve. That master cylinder most likely would not standup to the force applied by a hydroboost unit nor provide adequate braking force for your system (ergo your leaking master cylinder). Both brake lines that come out of the master cylinder should ONLY go to the combination valve. It detects a loss of pressure in either the forward or rear brkae cirsuits. Should be located on the forward frame crossmember. The brake line with the coil around it in the bottom picture (bottom right portion) should be coming from the proportion valve. The rubber brale hose from the caliper should connect to that brake line. If the picture is fooling me then I am sorry.

Here is a master cylinder (with hydroboost) and brake line drawing from a 84 manual


BTW - the trick to using the NAPA site for the P30 motorhome chassis is to go ahead and select the P30 1 ton step-van chassis. The motorhome data is still in there. Just be sure and read the descriptions to ensure you are selecting a part that is for the motorhome or both step-van and motorhome.

Dave
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Old 08-09-2011, 12:12 AM   #18
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Better understanding!!

Here are few more pictures; the rubber hose with the T fitting has two alum lines one goes into coach the other to item in picture, the black hoes with spring goes to front brake. The problem is that the fittings didnt fit the master cylinder from auto zone so we ordered one that looks just like the picture you show, this T fitting does not fit the master cylinders we have tried and there is no way to get around it, I had this problem with fitting size that are not common or used anymore. The new cylinder is due on thursday8/11 hope it fits. any suggestions!! Thanks
The picture of the bottom or cylinder with the screws attaching it is what makes the differrence in the cylinders at auto stores. Dont know if this was modified or not.
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Old 08-09-2011, 09:39 AM   #19
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My 84 P30 manual says the style of master cylinder you have is a Bendix Mini-Master Cylinder. My original statement that it is only used on Step-vans is in error. On the Bendix Brake site (Bendix - Application Look-up) it is listed as Bendix P/N 11641 and is applicable to P30 motorhome chassis JF-9 with 4 wheel disc brakes. NAPA lists this as P/N NMC M2219 (Brake Master Cylinder Line Thread Size : 9/16"-18, 1/2"-20). Both sites list bore size as 34mm.

I suspect the extra hoses and components are either for a Auto-Parking Brake system or a Supplementary Toad Braking system. My guess is that the item you are pointing to in picture 2 of post #18 is a pressure transducer. I see there is a zert fitting in the top of it (used for bleeding air from that portion of the circuit). The other hoses going to from it I suspect are used to control a Supplementary Toad Braking system (air operated perhaps?). Does the line going into the coach by chance go to a gauge on the dash or a Supplementary Toad Braking system controller?
I am not sure but the brass "T" fitting on the master cylinder may not be stock GM. That plus the fact they used a rubber brake line to tap into it are more like aftermarket clues. I suspect it is an aftermarket tap off point for a seperate brake system. Then again it is possible it has to do with a parking brake. I recommend you trace this stuff back to understand what it is for. You will need to know all this anyway in order to properly bleed the air out of the system (each seperate fluid path should be bleed of air)

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Old 08-09-2011, 12:03 PM   #20
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Just Gotta Learn!

Thanks Dave Im most certain the part coming will be wrong because the picture auto parts show is too different, Yes the extra hose runs to a toad system? Another error Im making when ordering the brake parts; 4 wheels are disc and two far back wheels are drum so I say Disc and Drum? So my question can the toad system be elinminated or is that more trouble than its worth? Here are pictures of what 2nd line in coach run to and can you tell me if this is air operated? or for the drum brakes?
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Old 08-09-2011, 01:21 PM   #21
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Napa can get part overnight and I dont lose my core, cost 83.99. This project showed me lots of upgrades the need to be done, you guys make it clearer to understand and less expensive. Thanks!! Ill Be Back
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Old 08-09-2011, 02:16 PM   #22
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Quote:
Originally Posted by dspowers View Post
Thanks Dave Im most certain the part coming will be wrong because the picture auto parts show is too different, Yes the extra hose runs to a toad system? Another error Im making when ordering the brake parts; 4 wheels are disc and two far back wheels are drum so I say Disc and Drum? So my question can the toad system be elinminated or is that more trouble than its worth? Here are pictures of what 2nd line in coach run to and can you tell me if this is air operated? or for the drum brakes?
Don't be concerned about the drum brake tag axle that was an add on feature and has no bearing on ordering the new master cylinder. If the toad feature is working and you can identify what brand it is I'd leave it hooked up in case you may want to use it in the future.
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Old 08-09-2011, 02:40 PM   #23
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That aftermarket add-on control unit dates back to the 70's and earlier (Kelsey-Hayes 81740C hydraulic brake controller). It did tap into the brakeline. Apperently they were well liked but were basically superseded by modern accelerometer based units. All you should have to do is elminate the brass "T" at the master cylinder and reconnect the original brake line directly to the master cylinder. While it is easy to see how the toad system (trailer brake) connected to the motorhome brake system, I do not know how the actual toad side of that paticular system worked. You might try googling for a pdf file of the original manual. Kelsey-Hayes does mention that system on their history page (developed in the 50's ). I cannot access some of the sites that might have it from here.

GM produced both 4 wheel disc and front disc / rear drum motorhome chassis in a given year. For 84 with hydroboost at least, front disc / rear drum used the JB8 designation; 4 wheel disk used the JF9 designattion. JB5, JB6, & JB7 desgnations used a vacuum booster ratherthan Hydroboost. I think your 82 is simular. If I understand what is being said (based on JohnRR's post) you have a tag axle (4 wheels in the rear). If so then you have a base 4 wheel disc system for master cylinder purposes. The tag axle would be an Add-on with it's own seperate information not related to the toad system. Does the tag axle drum brake system hydralics connect directly to the original P30 rear disk brake system? I cannot deduce that from the pictures. I also am just making sure they did not use the "toad" system to drive the tag axle brakes. You normally have to have some form of porportion valve to mix drum and disc brakes.

To continue this type of work on your rig you really need to get the Service manual for it. GM bundled the P30 information in with pickup information (C-20/30, K-20/30) under the title Light Truck Service Manaul until the the very late 80's. They also produced a book for each year. Actually, it is a 2 volumn book set. While you can spend the $ for the paper books if you want, the best deal is the pdf version produced by Bishko (Bishko Automobile Liturature available for 1982, Chevytruck, Shop Manual).

EBAY 1982,82 Chevy truck,p30 | eBay

Just remember it is Light Truck, not S-10, S Series, Medium Duty or Heavy Duty.

1st volumn is a Remove/Replace/Service manaul
2nd Volumn is a overhual component manual.

The Bishko CD-ROM (best deal) contains all of the light truck books in pdf form (including chassis wiring).

A GM companion book (free) is http://www.bdub.net/manuals/P30/P30.pdf

Dave
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Old 08-22-2011, 04:16 AM   #24
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Perfect P/N from Napa, Thanks 83.99

Quote:
Originally Posted by Dave78Chief View Post
My 84 P30 manual says the style of master cylinder you have is a Bendix Mini-Master Cylinder. My original statement that it is only used on Step-vans is in error. On the Bendix Brake site (Bendix - Application Look-up) it is listed as Bendix P/N 11641 and is applicable to P30 motorhome chassis JF-9 with 4 wheel disc brakes. NAPA lists this as P/N NMC M2219 (Brake Master Cylinder Line Thread Size : 9/16"-18, 1/2"-20). Both sites list bore size as 34mm.

I suspect the extra hoses and components are either for a Auto-Parking Brake system or a Supplementary Toad Braking system. My guess is that the item you are pointing to in picture 2 of post #18 is a pressure transducer. I see there is a zert fitting in the top of it (used for bleeding air from that portion of the circuit). The other hoses going to from it I suspect are used to control a Supplementary Toad Braking system (air operated perhaps?). Does the line going into the coach by chance go to a gauge on the dash or a Supplementary Toad Braking system controller?
I am not sure but the brass "T" fitting on the master cylinder may not be stock GM. That plus the fact they used a rubber brake line to tap into it are more like aftermarket clues. I suspect it is an aftermarket tap off point for a seperate brake system. Then again it is possible it has to do with a parking brake. I recommend you trace this stuff back to understand what it is for. You will need to know all this anyway in order to properly bleed the air out of the system (each seperate fluid path should be bleed of air)

Dave
This part Number was a great help and perfect match!! Thanks
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Old 08-23-2011, 05:28 PM   #25
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Didn't some of the tag axle brakes use electric brakes on them and a standard brake controller like used for a TT? That would explain the T and the electric controller.
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