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Power Assist Brakes
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If affordable and easy to install, would you prefer power assist brakes on your T4?
Heck Yea!
90%
 90%  [ 9 ]
No Way
10%
 10%  [ 1 ]
Total Votes : 10

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raygreenwood
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PostPosted: Sat Aug 13, 2016 12:49 pm    Post subject: Re: Power Assist Brakes Reply with quote

titan3c wrote:
Looks great-----but you mentioned a type 3 mc. Will that work OK? Are there other mc's with the front 2 hole mounts that will work on type 4?



N there are no other type 4 style cylinders that are out there. The vanagon cylinder can work with a bracket...... but thw whole object is to get rid of that bastard type 4 master cylinder. Of you notice from the sketch....on the purple plate in the trunk there is a vertical flange to be able to moujt a normal master cylinder with mounting ears.


The type 3 and 4 master cylinders....are the same diameter. ..same flu8d volume....and same stroke length for each circuit. The cars both use the same caliper in front and same brake assembly and wheel cylinder in the rear.

The cars are both similar in layout, weight and front to rear weight bias....though I think the type 4 is about 200 lbs heavier overall.

The only reason....physically....you cannot swap pistons from a type 3 master cylinder to a type 4 master cylinder is because the fluid inlet drillings are different in both castings wo the piston heads have different spacing.

The last item is calibration of the springs inside. The last experiment I need to do is to get my hands on a set of pistons complete with springs for a type 3. Then I can put them in a clear lexan tube ....with a snap ring to keep them set at factory preload.....and then mark where the piston heads are on the tube with china marker. Then use a level to push the piston stack down. In this way I can see which spring starts compressing first.

The way front to rear bias and timing is set up in dual circuit master cylinders....is by the spring preload. For instance if the primary circuit...the one the pushrod is driving against.... is supposed to actually start locking the front brakes before there is any movement of the inner piston to start acting on the rear brakes......the inner piston spring will be quite stiff.

The inner piston may bot even start moving until X amount of movement of the primary piston.....and then it may move or build force at a slower rate.

If these spring calibrations are close enough.....good to go. If they are off a bit and its as simple as swapping springs from the type 4 unit to the type 3....then good.

If the springs cannot be swapped....I can add shims or adjust to get the timing r8ht and then add an aftermarket rear pressure adjuster for ahout $50. Ray
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titan3c
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PostPosted: Mon Aug 15, 2016 4:40 am    Post subject: Re: Power Assist Brakes Reply with quote

Am I correct in understanding that in your modification a type 3 mc will work? Or a Vanagan mc would also work. Bob
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raygreenwood
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PostPosted: Mon Aug 15, 2016 7:09 am    Post subject: Re: Power Assist Brakes Reply with quote

titan3c wrote:
Am I correct in understanding that in your modification a type 3 mc will work? Or a Vanagan mc would also work. Bob


No...a vanagon master cylinder will FIT.....BUT only if you keep the MC under the dash....and only if you build a brafket for it.....and you will need both a brake balance adjuster and a rear bias adjuster because it has larger 15/16" pistons.

While it is easy to make a bracket to use a vanagon cylinder......I would only use one as a last resort if no other cylinder on the planet could be fitted. It entails totally recalibrating the brake system.

Yes.....With my modification. ...adding a relay lever and moving the cylinder to the trunk.....a type 3 cylinder will work.....but will possibly need some very minor rear brake re-bias. Otherwise the fluid volume and stroke are the same as type 4.

Once you move the MC to the trunk.....Cylinders that will bolt right up....and operate....but will require some significant recalibration......are one from late superbeetle and one from about a 1980 rabbit without power brakes.
Ray
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titan3c
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PostPosted: Mon Aug 15, 2016 8:31 am    Post subject: Re: Power Assist Brakes Reply with quote

What do you mean by rear brake rebias adjustment?
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raygreenwood
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PostPosted: Mon Aug 15, 2016 10:33 am    Post subject: Re: Power Assist Brakes Reply with quote

titan3c wrote:
What do you mean by rear brake rebias adjustment?


Reread my post two posts ago. I explained it there. In master cylinders.....the two pistons do not start moving at the same time or at the same speed due to spring pressure. This is because by design they want either the front or rear to start braking first.

Also the 411 and 412 two door and four door sedans both have adjustable rear brake pressure regulators to limit the braking pressure under hard braking to prevent rear lock up.

Brake bias is the spring and piston timing in the master cylinder......and rear breal pressure limitation is anti-skid.

The type 3 cylinder in so close to type 4 it will "work" as is.....but I have not had time as I noted.....to verify that the spring pressure bias in the cylinder is EXACTLY the same as type 4. Its important that is is as close as possible.

My brake set up right now.....is a welded on mounting tab to the pedal cluster.....that allowed me to put a master cylinder in with normal mounting ears.

DO NOT DO THAT. Its a pain ij the ass.....and still leaves you with a big mess under the dash when you go to change the MC. But at the time I did it....it allowed me to use an old type 3 cylinder I had on hand. It generally worked well.....but it was old and crapped out. At that time....all I could find tllocal that I could afford....that was close enough to modify was a super beetle cylinder.
That is how I learned first hand....that you cannot just slap in any cylinder that has the same diameter and stroke.

The brake bias and stroke limiting pins on the inner piston were so different that while testing in a large parking lot....I almost rolled the car.

I had to put in the springs frm my 412 pistons....and trim the stroke limiting pin on the inner piston.

I should be able to test the type 3 spring and piston stack up in late september. Ray
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titan3c
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PostPosted: Tue Aug 16, 2016 4:34 am    Post subject: Re: Power Assist Brakes Reply with quote

One thing keeps bothering me Ray. With reference to your drawings: The regulator connections for the push-rods moves in an arch. This causes the push-rods to go up and down slightly. Is this movement so slight that it doesn't matter? Bob
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raygreenwood
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PostPosted: Tue Aug 16, 2016 6:53 am    Post subject: Re: Power Assist Brakes Reply with quote

titan3c wrote:
One thing keeps bothering me Ray. With reference to your drawings: The regulator connections for the push-rods moves in an arch. This causes the push-rods to go up and down slightly. Is this movement so slight that it doesn't matter? Bob


I am not sure what you are speaking of. What are regulator connections?

Are you speaking of the actual pushrod movement with regard to the disc or relay wheel?

The relay disc......is no different in movement than the top of the brake pedal......ah....wait.....I get what you mean.

Yes.....there is a slight arc....depending on how long the top of the brake pedal is above the pivot point. ..and how long you allow/want the throw to be.

This is not a problem. All brake pedal linkage is this say. This is why the bore in the outer piston is:
1. Tapered outward
2. Has a spherical bottom in the bore
3. Why the ends of the pushrods are spherical

The diameter of the relay/pivot wheel ....or you can use a pivot bar...whichever you can most easily fabricate.....and the mounting point distance from the pivot point must be calculated to set stroke length. This insures that the angular deviation of the pushrods stays within the factory range.

Ray
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titan3c
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PostPosted: Wed Aug 17, 2016 6:48 am    Post subject: Re: Power Assist Brakes Reply with quote

I was just crawling around looking under the dash to study the possibilities of this modification, and discovered there is a real mess under there.

The entire pedal cluster, and anything attached to it is badly corroded as a result of a leak in the hose from the reservoir, which I fixed sometime back.

So since I'm planning to relocate the mc, I think I better go ahead and remove the entire pedal cluster, cleaning everything and repainting. I can see that involves disconnecting the steering column. I"ve been thru disconnecting the bottom of the steering column when replacing the steering box, and it looks like I may have to take the steering column completely loose for this job.

I appreciate any advice. Bob
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titan3c
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PostPosted: Wed Aug 17, 2016 7:55 am    Post subject: Re: Power Assist Brakes Reply with quote

With reference to my previous post: Could the steering column be unbolted from the dash, and held temoorarily by a sling? Bob
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raygreenwood
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PostPosted: Wed Aug 17, 2016 9:35 am    Post subject: Re: Power Assist Brakes Reply with quote

titan3c wrote:
With reference to my previous post: Could the steering column be unbolted from the dash, and held temoorarily by a sling? Bob



Yes. You do not have to disconnect the steering column. And its not a HUGE job...but there is a bit to do. Going off memory here....its been a while.

1. It helps to mark and remove the steering wheel.
2. Slide the seat back or remove it. Disconnect the battery
3. Remove the two vertical 8mm bolts that secure the steering column bracket to the lip of the dash.
4. I think there are two more bolts that secure the lip of the pedal cluster to the dash edge

At this point the steering column drops down kind of suspended by the rubber donut joint below. This is why its easier to take the steering wheel off so you can sit in the seat and work without the wheel in the way.

5. Take the screw out that holds the fuel pump relay to the cluster and let it hang on the wires.
6. Depressurize the washer bottle. If memory serves the hoses for the washers "might" go through the square opening in the center of the pedal cluster and "may" need to be disconnected.
6. Likewise some of the wires for blinkers, brights, ignition switch etc...may be threaded through that rectangular hole. Its easy to just pull the plugs out.

7. Drain as much brake fluid from the reservoir as possible....and now pull out the feed hoses from the top of the MC...catch all the fluid in a cup...I usually use a paint can cap. Wrap the ends of the hoses up in paper towels to absorb and drips. Same process for teh steel brake lines. Then pull out the brake light plugs.

8. From memory there may be a rubber collar bushing holding the steering shaft that is bolted to the pedal cluster with two 6mm bolts. Take those out and let the bushing stay where it is.

9. There are two...possibly three or four ...if memory serves...8mm nuts on the forward end of the pedal cluster that bolt it to the firewall. Remove those....and the pedal cluster is not free. You can pull it rearwards toward toward the drivers seat.

It may try to get hung up on the bushing plate around the steering shaft. You flop the pedal cluster to the right side so the pedals are facing the left and you can pull it away from the shaft and out

NOTE:...before you start doing this...because I have not had time to get up under my dash and inspect....get down in your floor boards and take a look up under the dash. You want to see how much room you have for teh A-frames. I am 90% sure they will all fit without hitting anything critical....they are not very tall. I have not plotted the size/diameter or length of the pivot bar or wheel yet.

There is a SMALL chance the relay pivot may need to be inside of the trunk like the power brake unit. I may have a few minutes do do that next week. Ray
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titan3c
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PostPosted: Wed Aug 17, 2016 10:22 am    Post subject: Re: Power Assist Brakes Reply with quote

Paragraph 9: Is the heads of these bolts accessible on the other side from underneath the car or where?

Ok, I'll measure how much top side distance available from the cluster, and also from the push-rod. Bob
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raygreenwood
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PostPosted: Wed Aug 17, 2016 10:33 am    Post subject: Re: Power Assist Brakes Reply with quote

titan3c wrote:
Paragraph 9: Is the heads of these bolts accessible on the other side from underneath the car or where?

Ok, I'll measure how much top side distance available from the cluster, and also from the push-rod. Bob


No. The bolts are carriage bolts...no heads on the outside and you cannot reach them anyway. They are behind and above the gas tank. Actually...if they were regular bolts...you could reach them through that plate under the carpet in the trunk that Lars and I were discussing.

But....what you need is a ratcheting box end wrench. Its funny...but back in my high school and college days...there was no such think as a ratcheting box end wrench...or not a good one. They are everywhere now.

It makes removing these nuts easy work....but the pain in the ass comes when you are replacing them Wink
Ray
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titan3c
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PostPosted: Wed Aug 17, 2016 12:29 pm    Post subject: Re: Power Assist Brakes Reply with quote

Am I correct in assuming these bolts are secured so they won't turn?
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raygreenwood
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PostPosted: Wed Aug 17, 2016 4:06 pm    Post subject: Re: Power Assist Brakes Reply with quote

Yes.

Ray
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titan3c
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PostPosted: Thu Aug 18, 2016 4:00 am    Post subject: Re: Power Assist Brakes Reply with quote

The corrosion is heavy on these bolts, and may be hard to break loose. Do you have a suggestion as to some product to apply to help loosen them? Bob
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raygreenwood
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PostPosted: Thu Aug 18, 2016 7:11 am    Post subject: Re: Power Assist Brakes Reply with quote

Pick the penetrating oil of your choice.

Liquid wrench.....some like PB blaster......many swear by the magic 50/50 acetone and ATF.

Whatever you use.....let it soak for a couple days and tap on them a few times and reapply.

These particular bolts......get a llt of external corrosion on them because of brake fluid. They get really crusty.

What I have started doing on bolts like this a while back.....is to wet them with full strength Jasco or similar strong phosphoric acid rust converter with a Q-tip.

When its strong like that.....it dissolves the external rust. Then spritz it with aittle water and dry it....then use the pentrating oil. Ray
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titan3c
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PostPosted: Thu Aug 18, 2016 8:15 am    Post subject: Re: Power Assist Brakes Reply with quote

Thanks for the info. BTW I just checked the space above the brake cluster. I don't think there is room for anything in there. The space is on a curveture, with hardly any room above the brake pedal arm. It looks to me like you will have to take the brake pedal push rod thru the fire wall, and go from there. That probably will be more simple anyway. Bob
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Lars S
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PostPosted: Thu Aug 18, 2016 10:24 am    Post subject: Re: Power Assist Brakes Reply with quote

I dont know if it has been covered here before but in the stock power brake setup the rod to the servo unit does not go from the top of the brake pedal but from the center of the pedal bracket,

Lars S

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PostPosted: Thu Aug 18, 2016 12:45 pm    Post subject: Re: Power Assist Brakes Reply with quote

Interesting----if I got this right there is a short arm extending up from the pivot shaft that connects to the push rod to the servo. And all this is on the inside of the bracket. Huh---my calculation is that this would put the push rod on about the same level as the connection at the top of a non-power system, which would be to the right of the bracket. Wow--- I thought I had it figured out that the push rod on the non power system was in line with the punch out on the fire wall for a power assist, and by just flipping the push rod over it would go thru the fire wall at the correct level and position as a power assist. I will have to do some more detailed and accurate checks on this. According to this picture the push rod goes thru the fire wall at the middle of the bracket. Also I wasn't sure if a different length push rod would be needed for the modification. Bob
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PostPosted: Thu Aug 18, 2016 1:22 pm    Post subject: Re: Power Assist Brakes Reply with quote

OK----I just went out and checked it out. After looking at my car, and comparing it with the pictures Lars-s has sent of the power assist system I come to this conclusion. The push rod on the power assist comes thru the fire wall in line with the center of the bracket. The push rod on the non assist of course is to the right of the bracket, but appears to be on the same level as power assist. The modification Ray is working on is feasible, but will just have to locate to accommodate the push rod location. Another thing that puzzles me is the punch out I'm thinking of is at an angle---I must not be looking at the correct punch-out but don't see another one.

Also - if making this change one chooses to use the std servo bracket under the hood he would have to change the pivot shaft on the pedal cluster also. Bob
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