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Finally better brake research for the v3500 pays off

camiswelding

camiswelding

1/2 ton status
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As some of you know I have been interested in better brakes on my v3500 for a year or so. The stock brakes were ok,,, but anemic at times and even though I tried all the tricks they werent up to what I thought brakes should be for our trucks.

The test truck was a 1989 v3500 3+3 crew cab dually 60/70hd 54k original miles
It has all new raybestos brakes and hardware, super stops in the front , fleet service extreme duty in the drums, new factory rotors

After driving it for 20k miles since I bought it I still thought I could do better.... trailering was always "fun" pretty much smoking the brakes on long mountains downgrades... even with careful driving....

I looked at slotted rotors and they are hard and expensive to come by for one tons and after talking to chevy people I trust didnt justify the money. The rear drums when adjusted properly give about a 20-25% bias on our trucks... even when the rear load sensing valve works properly... which for alot of older k trucks is probably never.

I have been interested in doing rear disc brakes for awhile... using chevy calipers and rotors. I looked at all the aftermarket guys,,,brembro etc and they pretty much skip our trucks because there isnt the demand due to age of the fleet.... gen 1 and 2 are getting old now and going into obsolete catagories for parts

I tried Off Road Unlimiteds "Ulitmate Master cylinder". It was a joke... it arrived (new) with a front reservoir as small or smaller than my stock one.... and they touted it as being used for 4wdb conversions with success. It didnt improve my truck one iota... and they are currently getting it back for a refund to me (as a side note they said they are phasing it out... wonder why???) It certainly imprpved their wallets,,,, we'll see if they hassle me returning it....

Then I looked at chevy 4wdb master cylinders that might match up to my hydroboost.... BINGO
I discovered that p30 motorhome and delivery van chassis from 1977-1994 had a large capacity 4wdb master that looked like it might match up to my system. The bolt holes were within tolerance... the hydroboost turned out to have the same numbers (by photo) and the port looked about the same size. The P30 was 34 mm .. the v30 series master has a bore of 1 5/16",,, hey this was good,, close enough to fit into the stock hole

I laid down roughly 170.00 ( the same or less than ORU's stuff) for a NEW raybestos 4wdb master #MC39309 and couldnt wait to try it. Nicely made with a cast iron and aluminum body and a clean plastic lid... no more funky spring trap holing on the top waiting to leak

I bench bled it and installed it... it fit like a glove...no interference... the lines from the truck had to be swapped front to rear and bolted right up. A careful bleeding of the brakes and a test run.

Real seat of the pants impression.....

I now have vastly better pedal feel
I now have a higher pedal...almost to the top.. where before I had to push a ways to get action
I checked to make sure the proportioning valve was working and tried some locked skids... no over proportioning of the rear that I was told to expect (although I havent tried high speed stops yet). I had already also purchased a chevy p30 factory proportioning valve GM #1257225.... Ill save that for the actual 4wdb conversion

This was a worthwhile investment and I can say it improves hydroboost brakes... and will make the 4wdb conversion no hassles....

I love it when it projects work better than you hope....

cam
 
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very interesting. I have a 91 V3500 3+3. The brakes are stock, and they work pretty good for me, but I do not tow with it at this time. I am going to save the part numbers you listed, and go with that setup on my truck in the future.
 
camsk5 said:
I now have vastly better pedal feel
I now have a higher pedal...almost to the top.. where before I had to push a ways to get action
Click to expand...

air in the lines or a defective master cylinder. :rolleyes:
 
Where's you get a Raybestos MC39309 for $170? Kragen/Schucks/Checker wants $270 or something nuts, and NAPA gets $279 for their fancy one.

I haven't checked with the place I'd actually buy from, as they have no web presence and they're closed :)

-- A
 
camsk5 said:
The P30 was 34 mm .. the v30 series master has a bore of 1 5/16",,, hey this was good,, close enough to fit into the stock hole
Click to expand...
If I understand this right you increased the bore diameter by .026" which increased the bore area by .054 sq in.
the lines from the truck had to be swapped front to rear and bolted right up. A careful bleeding of the brakes and a test run.
Click to expand...
Note of concern, the rear piston in the master should operate the front brakes and not the rears. The rear piston is directly acted on by the pushrod while the front piston is actually driven by the compressed 'slug' of brake fluid that is between the m/c pistons. If you have a rear brake failure with the current plumbing you will have to drive the rear piston fwd until it contacts the front piston to get front brakes. With the stock plumbing you have front brakes immediately. They may not feel as firm, but there is no lost motion in the system.
Real seat of the pants impression.....

I now have vastly better pedal feel
I now have a higher pedal...almost to the top.. where before I had to push a ways to get action
I checked to make sure the proportioning valve was working and tried some locked skids... no over proportioning of the rear that I was told to expect (although I havent tried high speed stops yet). I had already also purchased a chevy p30 factory proportioning valve GM #1257225.... Ill save that for the actual 4wdb conversion
Click to expand...
With the increase in bore size your pedal effort should go up, but your line pressure will go down for the same pedal effort. How a brake pedal feels is highly subjective. Most people want a firm pedal, which is fine. A slightly soft pedal generates more line pressure for the same effort, but it's a rare driver who likes the pedal to feel that way. Every time I get back in Patch after having not driven him in a while I have to re-learn to have faith in his softer pedal. Most of the yoter heads go to the later m/c to get a firmer pedal.
The concept that a firm pedal does not equal strong brakes is not a popular one, but it is the truth. You can have both, but one does not directly imply the other.
I would be interested in b4 and after time to stop from X speed trail results or distance to stop from X speed results.
 
ntsqd said:
If I understand this right you increased the bore diameter by .026" which increased the bore area by .054 sq in.

Note of concern, the rear piston in the master should operate the front brakes and not the rears. The rear piston is directly acted on by the pushrod while the front piston is actually driven by the compressed 'slug' of brake fluid that is between the m/c pistons. If you have a rear brake failure with the current plumbing you will have to drive the rear piston fwd until it contacts the front piston to get front brakes. With the stock plumbing you have front brakes immediately. They may not feel as firm, but there is no lost motion in the system.



I would love if you would expound upon this... the ports in the p30 are the same size and line pressure (I believe) is the same. In a failure with the piston driving forward so quickly would one experience a delay of perceptable proportion. Chevrolet had the lines swapped the other way(stock non 4wdb master , (I believe) to increase line pressure to the fronts... but with the 4wdb master the line pressure was the same coming out of the M/c on both ports...proportioned by the apporpriate valve downstream. Are you sure its a "slug" of fluid or the actual piston... when I looked at the piston and the incoming ports from the reservior you can actually see a piston moving and anorrifice opening and closing....
I will do some chevy research on the safety factor of this swap and see what I come up with... and I REALLY appreciate you bringing this thought to forum




With the increase in bore size your pedal effort should go up, but your line pressure will go down for the same pedal effort. How a brake pedal feels is highly subjective. Most people want a firm pedal, which is fine. A slightly soft pedal generates more line pressure for the same effort, but it's a rare driver who likes the pedal to feel that way. Every time I get back in Patch after having not driven him in a while I have to re-learn to have faith in his softer pedal. Most of the yoter heads go to the later m/c to get a firmer pedal.
The concept that a firm pedal does not equal strong brakes is not a popular one, but it is the truth. You can have both, but one does not directly imply the other.




You are absolutely correct that higher peddle..and better perceived feel does not necessarily mean better brakes at all... that is governed by actual piston size, application force, rotor size etc etc etc. In my application I can now sense the brakes more easily... and that is very helpful, especially when towing

I would be interested in b4 and after time to stop from X speed trail results or distance to stop from X speed results.
Click to expand...




I think that worthwhile ...but I am not sure I will put the stock stuff back on if, after some further test drives, I find this working better for me,, especially with a DB conversion down the road soon

I purchased this at my local parts dealer... franklin auto parts... it did show a list of 250... net of 179... keep searching for a better parts place...

cam
 
powerbled... and new masters were in the system prior to this setup... :D
no air,,, no defects before... just anemic brakes
 
thank you thank you thank you, i have the same truck and will doing the exact same setup as you decribed. props for all the hard work. :waytogo:
 
Hey Cam,

What year P30 did that Master come off of? My brake supplier doesn't have a cross reference for Raybestos parts.

Post up when you do a few high speed stops. Im curious if you have rear drum lock up. I won't be doing a rear disc conversion, but wouldn't mind a better master if there isn't problems with the rear locking up.

How did you determine the front and rear res. were reversed on the P30 master? I know our 1 ton masters on hydroboost set ups are reversed from 3/4 ton and 1/2 ton. I believe the smaller res. is always for the rear on rear drum / front disc brake systems. But, aren't both res. about the same size on a 4 wheel disc brake set up?

Last question. Where did you find your specs. for various master cylinders? I'm doing a project which is going to require a special master, where should I look?

Thanks for being the "Test Goat" on the ORU master!!

Eric M.
 
An update

I have a raybestos parts catalog.... in my original post I listed what year the p30 was... they also have a 15k gvw version... that one doesnt work.. the book lists this master as 1977-1994 4wdb except 15kgvw... it also shows the same part number for 93-95 p30/p30mhc with heavy duty 13x 3 1/2" drum brakes

The original v3500 has a small reservoir in front/ large in rear,,, the p30 4wdb reservoir is large both front and rear,,, but the fittings were exactly the opposite of the v3500..so all I did was bend the exisiting lines slightly... and theres plenty there to do so, to swap ends...

As was posted before by ntsqd this puts the rear brakes on the back reservoir and the fronts on the forward one... I didnt make up new lines to do it the other way to the proportioning valve but one obviously could... and if/when I go to rear discs I may do so,,, I havent looked carefully at the p30 valve comparing it to the v3500 valve yet (the v3500 is now hidden behind my ord brace) other than to say they are physically externally the same. The p30 valve may be setup to swap the lines without any further mess around

I took the truck for a ten mile test drive today... at higher speeds... I tried some panic stops and general braking. This is what I would say....

Our trucks dont have abs or other braking traction aids...so I would like to define what is known as TEN SCALE braking
1 being no brakes at all and 10 being a four wheel locked skid
The most braking one can put into our trucks efficiently is the point up to just before lock....somewhere about 9.9.... that is if we as humans could modulate it that well... so in reality anything above 8 means youre using the brakes super efficiently

I did not take any measurements... Im not going back to stock to do it... although I would have to agree this would be the best test under controlled conditions

I can say unequivocally that the brake system has better feel... I can feel that point when lock is going to occur with much greater accuracy... and because of this , for me, my system, is operating at a higher level of efficiency. While this might be a subjective test I have driven many many k trucks and this truck now stops like my lighter blazer did.
I didnt see any rear brake lockup that was not preceeded by the fronts first... My chevy dealer contact assumes this is because even if the rears were being over proportioned the weight valve compensated for it and kept the lockup to a minimum.
I did some lockups in gravel... and this was interesting... I noted the fronts had slightly... maybe by ten percent, longer skids... and I assume that is because they have more proportioning bias and should lock first... once again not very scientific but my seat pants tell me so

Im not ready to give it a complete all clear until I research the safety aspect of full brake failure and how having the front discs plumbed to the forward or front reservoir would effect a catostrophic event,,, i.e. pulling a loaded trailer max gvw panic stopping on a steep downgrade....
Chevrolet probably plumbed the p30 master differently than the drum brake rear trucks because they didnt want people swapping brake systems...and any vicarious liability chevy might endure... but this is conjecture and ill have to do some more research to see if I can find out why

But my preliminary thoughts are

this is a great mod... well worth the easy swap effort,, and if youre going for a db conversion with hydroboost it is probably the best way to go
I give it 4 thumbs for use... and a noob seal of approval for easy install

I welcome your comments

cam
 
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camsk5 said:
I think that worthwhile ...but I am not sure I will put the stock stuff back on if, after some further test drives, I find this working better for me,, especially with a DB conversion down the road soon
Click to expand...

Yeah, I wouldn't want you to do so either since you're happy with what you have.

Been my observation (no direct HB experience, yet) that with HB you can push a lot larger bore m/c than you can with a vac booster. That means you can have a high, firm pedal and still make enough pressure to have good line pressures.

Next phase is how to better reject the heat generated. The comes down to rotor mass and airflow thru the rotor.
 
Cam,

Do you know which res. (front or rear) on the P30 master is used for the front brakes on a P30 vehicle?

I'd like to give this master a try but am curious how it would work if hooked up in the same fashion as on P30 truck.

Thanks,

Eric M.
 
I dont think Im just quite ready for bling bling air scoops for the brakes...yet :D :D :D

however...if I could figure out multi piston calipers I might consider it.... :laugh:

Funny you mention the hb bore being able to push a higher line pressure.. thats exactly what my chevy man said... he said the hydroboost is so powerful that it could generate incredible psi's if not for bleed off valves and limiters. I am theorizing this setup feels so much better to me BECAUSE of a higher line pressure... even though the bore is only slightly larger doesnt it have a geometric effect? I was wondering if the size of the lines may have had an effect but at second look I dont think the additional volume would make a difference once inside a caliper or wheel cylinder... they are governed by orrifice size I would think... but higher line pressure would be another factor... and I think that would (and in my opinion ,,,has) make/made "better feeling" brakes..... as to whether the rear brake cylinder seals like it...?? but I think the effect probably isnt significant there

Im assuming that the p30 m/c plumbs with the fronts to the rear port... good question Eric.. that Ill have to ask my chevy guy to pull a brake plumbing book...


cam
 
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Looks like rockatuo does have this one for 125.00

and maybe even a reman'd off brand for like 40.00 although Im not sure of the fit or quality...its nice to have new stuff when it comes to brakes...
and heres a picture...

cam
for some reason the pic wont transfer from the rockauto site.... but its there

raybestos_.jpg
 
Putting scoops on the dust shields is what I was thinking. They do need to be set & shaped so that they blow air into the center of the rotor and not on the inboard surface.
The main advantage of multi-piston calipers is caliper body stiffness, not braking power. That stiffness translates into better pedal feel and easier modulation, but no increase in stopping power. This is assuming that total piston area doesn't change.

If you increase the m/c bore size you increase the pedal effort and the volume of fluid moved (less pedal travel per unit volume of fluid) while decreasing the line pressure for a given force on the pedal.
Using the hb unit allows you to use a larger bore and still have a reasonable pedal effort. It's sort of like cheating. :wink1:

Beware of going to a larger size tube. For most passenger cars & LD trucks the 3/16" tube is what you want. Some certain cars use 1/4", but they do it for reasons I can only speculate about. When the volume of fluid needed to move the pads or shoes to contact gets large enough, then 1/4" tube is justifyable or the fluid speed can actually generate "water hammer" in the brake system.

The downside to going to 1/4" tube is the very large increase in surface area inside the tube. All of the inside surface area tries to expand under pressure, not just the pistons. That means a much more flexy system which translates into a more mushy pedal feel. I know it doesn't seem like such a small change could do this, but it does.
An arbitrary example:

A 6' length of 3/16" tube with an assumed .040" wall thickness has an inside surface area of 0.653 sq in.
A 6' length of 1/4" tube with an assumed wall thickness of .040" has an inside surface area of 1.634 sq in.
So going to 1/4" tube from 3/16" tube (a 33% increase in OD) over a 6 foot length increases the inside surface area approx 150%
 
Thom...

Interesting factual stuff... thanks

I was kidding about the air scoops and they would be fabulous if you could figure out how to make them sano... as we know brakes can get hot and heat in brakes is death.... over 750 degrees brake fluid begins to significanly degrade..1000 and its useless.. and those temps are not unhead of in severe use

Youre the engineer.. cad design them.. Ill figure out how to build them...

Stopping a chevy HAS to be easier than stopping choo-choo trains!!!

cam
 
After putting a couple of hundred miles on this setup Im giving it the seal of approval

The master shares a minimum level between front and rear reservoirs... the brake fail light works properly... the chevy guy didnt identify any problems... if one port failed the light would respond... I cant see any downside

cam
 
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