Hydroboost & Master Cylinder - M1008

[Bunkerbuilder]

This is only my interpitation of why this tends to happen.

When the pedal if being pressed down without encountering much if any resistance from built up pressure its moving faster then with any resistance the bottom of the MC pistol stroke is acheeved and then the movement of fluid is stopped suddenly there seems to me that a small reversion of fluid could happen.

Pedal bounce is what I call it.

This is why I close the bleeder valve before the very end of the travel of MC piston.

Have you tried bleeding with both the engine running and not running ?

I would think not running would tend to be better as you would have more control of the pedal.

Has anyone thought of consulding the TM on this issue ?

I have the TM in the garage but never looked up this issue.

Who wants to do some reading online ?
/.25ton/TM-9-2320-289-34 CUCV Series Trucks at intermediate direct support and general support level Manual

Any idea what would cause this ? I have replaced master cylinders on a few trucks civi and military with the hydroboost setup and have had problems getting pedal. Maybe this is it ?

 

[4bogginchevys]

I'm not real computer savvy....what would it take to setup an "advanced search" option with the tm's, particularly the list posted by bunker builder. I read until i got a headache without finding more than "breaking system" or such, which listed no procedures on bleeding. I just ask because time and time again when looking for something specific I am unable to locate it....

 

[acmunro]

Brake bleeding procedure is in TM 9-2320-289-20 Pages 400-404 It covers pressure bleeding and manual bleeding. It also shows the combination valve depressor. - aka the button on the valve under the radiator. I will have to fab one of these up. To find this TM go to resources button (next to the new - "classifieds button") click - Technical Manuals - it will take you to the old site. I think the TM 9-2320-289-20 is on the 8th page of technical manuals.
http://old.steelsoldiers.com/index.php?module=pagesetter&type=file&func=get&tid=1&fid=file&pid=8

 

[abarkus]

When you replace the master the system needs to be bleed completely. you will use about a quart of dot 5 to do this. also you sometimes have to go back and do another time. it takes a lot of fluid to completely bleed a system.

 

[Bunkerbuilder]

The link you posted did not work for me but this one is the start to the procedure.

Maybe there is something we are all missing in this.

7-8. MASTER CYLINDER AND POWER BOOSTER REPLACEMENT.

Bleeding the brakes.
http://www.tpub.com/content/trucks1.25ton/TM-9-2320-289-20/css/TM-9-2320-289-20_401.htm

Brake bleeding procedure is in TM 9-2320-289-20 Pages 400-404 It covers pressure bleeding and manual bleeding. It also shows the combination valve depressor. - aka the button on the valve under the radiator. I will have to fab one of these up. To find this TM go to resources button (next to the new - "classifieds button") click - Technical Manuals - it will take you to the old site. I think the TM 9-2320-289-20 is on the 8th page of technical manuals.
http://old.steelsoldiers.com/index.php?module=pagesetter&type=file&func=get&tid=1&fid=file&pid=8

 

[4bogginchevys]

It doesn't sound like a quart has gone through the brakes lines yet. I would plan on using a whole quart and with the engine OFF....bleed bleed bleed

Edit: first off I would bleed the master where the brake lines attach(the same way you do at the wheel)
#2...adjust rear brakes up, they are directly responsible for a full feeling pedal.

 

[Bunkerbuilder]

Your statement quoted below appears to be incorrect.

Hence the name of the valve "Combination Valve" that would tend to mean it serves more than one purpose.

Disc Brake Service Needs - Classic Trucks Magazine


Engineers took the concept a step further. The "combination valve" addresses three concerns: One is the safety warning for a hydraulic circuit failure; another would be the proportioning of fluid pressure front to rear. When the brake pedal applies, and fluid pressure increases in the lines, the proportioning valve restricts hydraulic pressure to the rear wheels. The restricted ratio is an amount determined by the vehicle's design, weight distribution, and chassis dynamics. The proportioning valve compensates for weight bias. The last function of a combination valve is metering. A known issue with disc front and drum rear brakes is the lag time for the rear shoes to push through the return spring pressure and shoe-to-drum clearance before applying shoe pressure at the drum. By contrast, disc pads have no return springs and ride at the sides of the rotor. Lag time is virtually non-existent if the rotors run true
A metering valve delays hydraulic pressure to the front disc brakes. The aim is to synchronize the application of the front and rear brakes. For slick road surfaces and light braking, the metering valve helps prevent front-wheel lock up. Hard braking will push through this metering and deliver immediate front brake pressure.

that "button"doesn't have anything to do with pedal pressure, just a warning device. As I said before, back ward bleed it and then bleed it normally. If that doesn't give you real good pedal than they sold you a bad master...

 

[4bogginchevys]

ok, I see what you mean. I was just trying to make sure that the bleed part was completely finished before going in a new direction....dont just start throwing parts at it and see where your at when the dust clears type thing.

 

[ActionStarCBRxx]

Here is the update for today.

I plugged the holes in the MC for the front/rear and pressed the pedal. No pedal pressure builds up. I then switched out my old master cylinder with the new one and plugged the holes in it. Within two pumps, I blew the plastic plugs out of the hole, and fluid shot out all over the side of the truck.

Based on that… I returned the master cylinder and they ordered me a new one.

I saw your note about the procedure for bleeding

And keep in mind when you bleed in the conventional way with 2 people you close the bleeder screw before the pedal hits the floor or you risk sucking air back into the line.

I don’t think this was happening. My helper was pushing three times, and then leaving it on the floor. Then I would open the valve and close it again. But I will keep this in mind with the next MC.

So reading your note

Are you using the correct brake fluid?
IE Silicone dot 5, not 3 or 4 or 5.1 but the silicone fluid?
And did you get the correct MC for use with Dot 5 Silicone fluid?

My stomach sank and I about puked… as I was using DOT3.

So what do I do now? Can I open all the bleeder values at each wheel and let gravity work to push it out? Any suggestions here?

Are you stating that our Master cylinders are different in design? When I ordered the MC I stated 6.2 diesel on a C35 1 ton. I thought the MC’s were used in multiple applications/multiple vehicles?


When I get the new MC, I will bench bleed it with DOT 5 and verify pedal before even connecting it to the rest of the truck.

Thanks again for all your alls help… This has been a very enlightening experience and I appreciate all the help!



K

 

[Bunkerbuilder]

I have a question before you proceed any further.

You didn’t do a rear disc conversion right ?
If you did this page looks like a good source of information.
http://www.piratejack.net/Tech-Support/Booster-Master-Cylinder-Specifcations.html

As if you did it would be a totally different master Cylinder you would be purchasing for IE disc/ disc not disc / drum as is the factory condition of the truck.

I would attempt to purchase the correct master cylinder for use with the correct DOT 5 fluid as well.

IE all of the other parts came from GM meant to use the DOT 5 not dot 3.

I say this as all of the master cylinders I have purchased over the last 2-3 years have had a tag on them to only be used with DOT 5 fluid.

I think it would be a reasonable assumption that the other components that have rubber in them, IE the calipers and wheel cylinders (if you are running the stock disc brakes on the rear axle) would also require dot 5 fluid.

Good job checking the MC the way you did.


As for your dot 3 issues I would open the bleeder screws and attach hoses to a jar for each caliper / wheel cylinder and let gravity do its thing as long as the outlet lines were disconnected from any MC you may have hooked up to them at this point. after the majority is out of the lines I would rinse the lines with clean new bottle of alcohol and then blow the lines out with DRY (you do have an air drier on your compressor right ?) clean compressed air.

Rinse and repeat is a good idea.

ETA: dont forget to rinse out your Wheel cylinders and calibers as well since they had dot 3 fluid in them.

Dont let the parts sit for a long period of time with alcohol in them as alcohol absorbs water and will make the parts with cast iron in them rust.

I say dry clean compressed air as sometimes the air gets stuff in it like water and or oil from the compressor head.

Do you have a source for the DOT 5 Silicone brake fluid?

And if you don’t where are you BTW I might have a source as I purchased a 4 gallon case of it a few years ago.

Yes Master cylinders are different in well not design but materials IE the seals and piston cups in the military MC’s are made to work with the dot 5 Silicone brake fluid as the tag on the NOS MC’s I have are labeled.

ETA: this link talks about the depth of the hole in the MC where the pushroad from the booster pushes against the MC piston.

You can use an adapter for the deep hole MC when you have a short PB pushrod but if you have a long pushrod PB and you have a slallow MC hole your out of luck and need to make the combination of those parts work together.

http://www.piratejack.net/Tech-Support/Booster-Master-Cylinder-Specifcations.html

Here is the update for today.

I plugged the holes in the MC for the front/rear and pressed the pedal. No pedal pressure builds up. I then switched out my old master cylinder with the new one and plugged the holes in it. Within two pumps, I blew the plastic plugs out of the hole, and fluid shot out all over the side of the truck.
Based on that… I returned the master cylinder and they ordered me a new one.
I saw your note about the procedure for bleeding
I don’t think this was happening. My helper was pushing three times, and then leaving it on the floor. Then I would open the valve and close it again. But I will keep this in mind with the next MC.
So reading your note
My stomach sank and I about puked… as I was using DOT3.
So what do I do now? Can I open all the bleeder values at each wheel and let gravity work to push it out? Any suggestions here?

Are you stating that our Master cylinders are different in design? When I ordered the MC I stated 6.2 diesel on a C35 1 ton. I thought the MC’s were used in multiple applications/multiple vehicles?


When I get the new MC, I will bench bleed it with DOT 5 and verify pedal before even connecting it to the rest of the truck.
Thanks again for all your alls help… This has been a very enlightening experience and I appreciate all the help!



K

 

[ActionStarCBRxx]

BunkerBuilder...
Can you reply back with your source for the DOT5 fluid and the MC? I put a call into Orielly's and they will check and see if they can get me a DOT5 compatable MC.

For future reference I am going to stamp on DOT 5 ONLY on the top cover of the MC so this doesn't happen again. I did not want to go through the cylinders of each wheel... but it looks like thats what I need to do. Ugh I hate it when I cause my own problems!

The truck has the original setup of Drum/Drum.

I don't have a dryer for the compressor... but that looks like an investment I need to purchase as well. I thought I might use a storage can of air that we take on dirt bike runs, and use that air to blow down the lines. My thought was the temp off the air inside the cylinder/tank would be room temperature and any water would be on the bottom of the tank.

 

[4bogginchevys]

dot 5 should be available at ANY automotive store and the origanol lid to the master should say dot 5 only already.

 

[ActionStarCBRxx]

dot 5 should be available at ANY automotive store and the origanol lid to the master should say dot 5 only already

Can you show me a picture of what it is supposed to look like? I see some decals on ebay... want to see if they are it and where they go.

Thanks!
K

 

[Bunkerbuilder]

Drum / Drum on a M1008 CUCV ?

I was of the understanding that the M1008 only came with DISC front / DRUM rear setup.

Ill make some phone calls and try to find the fluid amd MC for you tomorrow.

When Orileys offers you DOT 5.1 Brake Fluid say thanks but no thanks IE its not the same spec at DOT 5.

I did a quick google search and came up with this.
http://www.steelsoldiers.com/deuce/44026-dot-5-brake-fluid.html

This is what I think I bought some years ago.
http://cgi.ebay.com/ebaymotors/NEW-...QQptZLH_DefaultDomain_100?hash=item2c52b4f181

NAPA Silicone Brake Fluid DOT 5 picture at link below.
http://www.steelsoldiers.com/attach...64516-dot-5-brake-fluid-napa-dot-5-gallon.jpg

NAPA Silicone Brake Fluid DOT 5
http://catalog2.genpt.com/catviewer...99999+109999&A=BFR45101_0006443459&ShowPics=1


BTW these widgets might make the job a lot easier.
Russell Speed Bleeders - SummitRacing.com

If you cant ensure that the air is dry at least drain the compressor tank a few times before you use it, IE get as much water out of it as you can.

This thread talks about moisture in the system and the reasons for making sure its not introduced, amd also talks about using DOT 5 Brake Fluid.
http://www.steelsoldiers.com/deuce/44026-dot-5-brake-fluid.html

Still working on the MC will edit this post with info as soon as I find one.

BunkerBuilder...
Can you reply back with your source for the DOT5 fluid and the MC? I put a call into Orielly's and they will check and see if they can get me a DOT5 compatable MC.

For future reference I am going to stamp on DOT 5 ONLY on the top cover of the MC so this doesn't happen again. I did not want to go through the cylinders of each wheel... but it looks like thats what I need to do. Ugh I hate it when I cause my own problems!

The truck has the original setup of Drum/Drum.

I don't have a dryer for the compressor... but that looks like an investment I need to purchase as well. I thought I might use a storage can of air that we take on dirt bike runs, and use that air to blow down the lines. My thought was the temp off the air inside the cylinder/tank would be room temperature and any water would be on the bottom of the tank.

 

[ActionStarCBRxx]

Thanks for the info. I already read about the differences between DOT3/4/5.1 and DOT5. Tthat article was a good summary of the differences.

I had another mixup with Orielly's... they ordered me another hydroboost instead of MC. So last night I had them re-order the MC for the one that I returned defectve.

From your posting of NAPA... I found the DOT5 fluid (Orielly's didn't carry/have on hand DOT5 BTW) I also checked on a new MC at NAPAand called on that. Their MC's are built by ReyBesto's... and compatable for both DOT 3/4/5.1 and 5 so I ordered a new MC from them. The MC came to $61.00 + tax.

I found a source for a drier for the compressor here in town... I just need to get that purchased

Thanks again for the help!

 

[Asgar]

M1008 CUCV Pickup... I also changed out a master cylinder and did not get great pressure. I changed the MC, calipers, wheel cylinders and hoses and one steel line. I bled it ok, dot 5, to a hard peddle but I can push through the firm peddle to the floor and the brake warning light will come on. I can pump up and drive around but in a hard stop I can't lock up the tires, so so stopping and the brake light comes on. So, I'll just assume the MC is bad and swap that out.

Since the original MC is gone, ie, was the core swaped in, I just have the Cardone brand rebuilt MC now, does anyone know if the casting number should have been 1605 or 1925? All the parts sites list both casting numbers for the k30 / 6.2 / 1984-1985. I want to get the right version in case I messed up the first time.

Does anyone know if the MC seals will be dot 5 compatible?

Also, how normal is it to 'weep' a bit of fluid in below freezing weather from a caliper? I heard that this is a normal issue with dot 5.

Thanks, I searched the site for over an hour looking for guidance on the casting number, it would be great if someone could help me out with this.

 

[Asgar]

Still trying to find out....

For the M1008 Master Cylinder, does does anyone know if the casting number should have been 1605 or 1925? Or can someone tell me the correct Napa or other chain store part number?

 

[lindyp38]

go and carefully check all your brake lines....and connections.....to be sure there are no pin holes in your lines.....

its a possible bad line...or connection........

 

[Zero_cool]

Still trying to find out....

For the M1008 Master Cylinder, does does anyone know if the casting number should have been 1605 or 1925? Or can someone tell me the correct Napa or other chain store part number?

Nappa 1605 stamp part number ( NMC M2135 )
Nappa 1925 stamp part number ( NMC M2533 )



Does anyone know the correct one?

 

[Asgar]

I found some M1008 master cylinders listed in a lot on GL, they gave the full part numbern and contract number. Searching on line on these numbers led to a bunch of contracts to produce them. GM was one of the contractors, and the number 1925 came up in the detailed description.

Nobody ever told me what the right casting number was. I went with the 1925 only because of what I saw in the contract info. I have no idea if it is the propper one.

The first one was from autozone (cardone rebuild) and internally leaked, see my first post above. The second one was from NAPA (also cardone rebuild, just cost more) and has been installed in my M1008 for about a year now without any problems but I'm not convicened the brakes are 100%.

If you buy just the rebuild kit it says it is also compatible with dot 5 and carbone. The dot 5 (silicone) did not cause me any grief.

Good luck, if you find the 'correct' casting number or any info as to how they are different please post.