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freddy13
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PostPosted: Tue Apr 10, 2012 7:12 am    Post subject: Trike Brakes Reply with quote

OK, I have been wrestling with this problem for a month now. Trike is ready to ride, but I have no rear brakes.

The entire rear end and engine is from a 1970 VW Type 1.

Now for the story...I had a 9/16th bore MC (aftermarket Harley) on the rear brake system. New metal line going to the "Tee" to the rear. Everything new on the brake system except the drums and flex lines.

Went to bleed the system and got solid stream of fluid. Brakes will engage, but would not stop the trike.

I figured the MC was too small, so I put on a 1" Wilwood MC. Exact same problem as with the 9/16th MC.

I am now under the impression that the 1" MC is too large...OK, I understand the mechanics of why it would not work, but if that is the case, why doesn't the 9/16th MC work either?

Brakes will engage, but not stop the trike. (Not enough pressure it seems)
I adjusted the shoes...adjusted them until wheel stopped turning and backed them off until it free wheeled.

Same problem.

The pedal is firm, not spongy and it does not bleed off.

Adjusted the brake rod every which way but loose, no difference.

I'm lost ! LOL! Any ideas?

Could it still have air in the system? I bench bled BOTH MC's before I hooked them up.
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BL3Manx
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PostPosted: Tue Apr 10, 2012 8:03 am    Post subject: Reply with quote

You got it backwards. The equation for calculating hydraulic force is: Force = pressure X area

On the front you have kept the input force equal(your leg) and have increased the input piston area from approx .24 sq." to .78 sq", which as a result has actually reduced the output pressure by over 2/3s.

By putting a larger area master cylinder on the front you have tripled the volume of the fluid being displaced, however the output pressure has correspondingly been reduced by 2/3s, which will reduce your braking force in back an equal amount... 2/3s less.

You should put the 9/16" bore master back on and replace the wheel cylinders on back with 22.8mm Super Beetle FRONT wheel cylinders. The wheel cylinders you have are probably the original 17mm rears. The SB front wheel cylinders will increase your wheel cylinder area and thereby increase your braking force by close to double (227 vs. 445 sq mm per wheel). They're about $35 a pair. They will directly replace your present wheel cylinders.
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freddy13
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PostPosted: Tue Apr 10, 2012 9:14 am    Post subject: Reply with quote

BL3Manx,
I understand what you are saying.
Yes, the rear wheel cylinders are stock. I bought new stock ones and replaced the old ones.

Now, a question....will a stock VW master cylinder work for this application? In other words, will the stock MC work with the stock rear wheel cylinders only? It should, shouldn't it?

I do understand that since I reduced the volume of fluid, by eliminating the front wheels cylinders, that the braking will be different, but, I know other people who are using the stock MC for the rear brakes (with stock wheel cylinders) and they work.


I appreciate your time on this subject!
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BL3Manx
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PostPosted: Tue Apr 10, 2012 9:51 am    Post subject: Reply with quote

freddy13 wrote:
will a stock VW master cylinder work for this application? In other words, will the stock MC work with the stock rear wheel cylinders only? It should, shouldn't it?

I do understand that since I reduced the volume of fluid, by eliminating the front wheels cylinders, that the braking will be different, but, I know other people who are using the stock MC for the rear brakes (with stock wheel cylinders) and they work.


Yes a stock VW front master cylinder will work, however it is 19mm and your 9/16" Harley master cylinder is only 14.3 mm so the Harley master will generate 45% more pressure than a 19mm VW master cylinder and thereby 45% more braking force.

Eliminating the front brakes will have a slight effect (reduction) on how far you depress the brake pedal but will have no effect on the braking force generated by the rear brakes.

Using a stock VW master cylinder and stock VW rear wheel cylinders will work as well as they do on the back of a VW which actually is not very well at all. If you read the archives on the dune buggy forum you will see that it is very common for dune buggies (which have a more aft c.g. than a bug) to put larger than stock wheel cylinders in back to improve the rear brakes.

Other people use stock VW master and wheel cylinders, but they wouldn't be a fraction as powerful if you use a Harley master (14.3mm) and front Super Beetle (22.8mm) wheel cylinders. The one down side is that you will need to keep the brake shoes closely adjusted because of the small volume of the Harley master.

Basically the way it works is

smaller master and bigger wheel cylinders = more braking force

or, bigger master and smaller wheel cylinder = less braking force

Here's an article that explains the principles http://www.pelicanparts.com/techarticles/914_BMW_calipers/brake_calc2.htm


Last edited by BL3Manx on Tue Apr 10, 2012 4:16 pm; edited 2 times in total
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freddy13
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PostPosted: Tue Apr 10, 2012 1:07 pm    Post subject: Reply with quote

OK.
I understand what you are saying, but, why didn't the Harley MC work when I had it on the trike?

The Harley MC was the first one I put on it and it did not work. I then put the bigger one on and it done the same thing.

I understand exactly what you are saying and I understand the mechanics and operation, but, I did use the Harley one first and it done the same thing. This is what is stumping me.

I have had numerous vehicles that used drum brakes. Back in the mid to late 1970's, that is all I drove...drum brake vehicles, and also replaced shoes and bled a few of those vehicles.

I will replace the wheel cylinders with the SB wheel cylinders and use the 3/4th inch MC and go from there.

Now if this doesn't work, what then? LMAO!

I have built numerous Harley's over the past 30+ years and have now built this trike and I have never had a problem like this.

Again, thanks for your time on this.
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BL3Manx
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PostPosted: Tue Apr 10, 2012 4:10 pm    Post subject: Reply with quote

A 3/4" master is the same as 19 mm. It will work fine with the 22.8mm wheel cylinders.

The 9/16" master is the same as 14.3 mm. It would work even better than the 3/4"/19 mm master.

If you tried the 9/16"/14.3mm master and "it did not work", then it was some other problem beside the size. It could be several things.

You said you haven't replaced the rubber flex hoses. You should always replace old VW flex hoses. They constrict inside when they get old and won't let the fluid past.

Also, VW master cylinders need at least 1mm freeplay when you take your foot off the pedal, before the rod pushes the piston. If you don't have the freeplay when you remove your foot, the valve to the reservoir won't open.

While you bleed the brakes, make sure the shoes are adjusted tight against the drums. Then after they're bled just back off the adjusters so the wheels turn freely but the shoes still rub a little.
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freddy13
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PostPosted: Wed Apr 11, 2012 6:49 am    Post subject: Reply with quote

I am going to replace the hoses and see if that is it.

Honestly, I do not think it is, but I won't know until I try.

I will also pick up some SB wheel cylinders and replace the stock ones.

I haven't used the stock MC...yet. I am hoping it is the hoses...

Lastly, that is the way I bled the brakes. A friend of mine told me the same thing...he is into VW's also. One thing for certain, everything but the hubs will be new. LOL!

Again, Thanks for your time.
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BL3Manx
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PostPosted: Wed Apr 11, 2012 7:51 am    Post subject: Reply with quote

freddy13 wrote:
I will also pick up some SB wheel cylinders and replace the stock ones.


Just to be clear, you want the Super Beetle FRONT wheel cylinders, not the rears.
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freddy13
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PostPosted: Wed Apr 11, 2012 3:48 pm    Post subject: Reply with quote

BL3Manx...

First of all when you say they will 'Bolt right on" Are you saying that like we used to say it in the late 1970's and 1980's????

LMAO! If you are, then ya must be and "Old Schooler" like me! LOL! I went to Mid America Motorworks http://www.mamotorworkstv.com/vw/ in Effingham, Illinois and got the parts. (That is where they have the BUGFEST and CORVETTEFEST every year) They had the front wheel cylinders for a Super Beetle and the flex hoses. I put on the hoses and then went to replace the wheel cylinders and the mounting hole was a third of a hole off. THANK GOD for twist bits! LOL! I got them mounted tho!

Second, I have BRAKES! I rode it around in the back 40 acres and it locked them puppies up! I still think that I need to adjust the shoes closer, but I am happy so far! Went down the road a ways and it will stop me now, but it still needs adjustment...AND/OR...it still needs the 3/4 inch MC. I still have the 1" MC on it right now. I should have the other in the next few days and it WILL go on!

Third, just how many 'clicks' on the adjusters do I need to back off when adjusting the shoes? What I done was tighten up the adjusters to where there was no free spin with the wheels. Bled both sides and then backed the adjusters off two "clicks". Before I mess with them again, I will put on the 3/4" MC and see what happens.

Fourth, I want to THANK YOU for your patience. I have been building and wrenching on Harleys for many moons and I know that sometimes an idiot comes along that does not follow instructions or cannot grasp what is happening when something is wrong. I followed instructions but could not grasp the "smaller MC + larger wheel cylinders = brakes" mechanics. You finally got it to make sense in my old brain. Also, it could have been the flex lines that were part of the problem. They are in two pieces each now! LOL!

Again, Thank You for taking the time to teach an old dog a new thing! If I knew yer address, I'd send ya money for yer favorite refreshment!

Freddy
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BL3Manx
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PostPosted: Wed Apr 11, 2012 5:06 pm    Post subject: Reply with quote

Glad to hear you hung in there and got them working.

I know what you mean about 1970s "bolt right on" equipment. I built my first buggy in 1968 and rebuilt my first motorcycle (an Indian Scout) in 1971.

Two or three clicks should be fine as long as the wheel doesn't hang up when you rotate it by hand. As the shoes wear in, they will also become more effective.

Changing from the 1" master to the 3/4" master will decrease the master piston area and increase pressure and braking force by 45%. You will have more pedal travel but as long as you keep the shoes adjusted, its no big deal.

I know a smaller master cylinder producing greater pressure is counter intuitive but its kind of like a lever. If you want to lift a heavier object using the same amount of force, you have to move the fulcrum so the object is lifted a shorter distance. A smaller master cylinder will move less fluid, but at a proportionally greater pressure.
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freddy13
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PostPosted: Fri Apr 13, 2012 9:07 am    Post subject: Reply with quote

The 3/4th MC should be here today, if the PO is at the top of their game! LOL!

If it gives me 45% more barking power, I will have to be careful hitting the brakes! LOL!

Again, Thanks!
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freddy13
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PostPosted: Sat Apr 14, 2012 11:19 am    Post subject: Reply with quote

Got the 3/4 inch MC on the trike. Holy Sheep Poop! I don't even have them bled and the brakes are FANTASTIC! Even on the first pump they are locking up the wheels!
Tomorrow I am going to get them bled and hopefully the rainstorms will be passed here in Illinois so that I can get it on the pavement and see what happens.

You were absolutely correct BL3Manx! I gained at least 45% braking power!

This old dog has learned something new!

Thanks Again!

Freddy
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freddy13
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PostPosted: Sat Apr 14, 2012 11:22 am    Post subject: Reply with quote

Also was wanting to ask....ya still have that old Indian Scout? Those old Indians are a blast to work on!
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BL3Manx
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PostPosted: Sat Apr 14, 2012 12:46 pm    Post subject: Reply with quote

It was a 1941 741 Army Scout. I still have it.

I also have a 29 101 stroker bobber, a 31 Bobber Chief, a 38 Four, a 39 Four, and a 48 648 Big Base Daytona Scout.

However, they're all pretty much works in progress(not running).
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freddy13
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PostPosted: Sat Apr 14, 2012 11:58 pm    Post subject: Reply with quote

They are fun to ride!

I have had, worked on and rode, as daily riders, a '41 FL Knucklehead, a '53 FLE (Police Special) Panhead, numerous Shovelheads (74 and 80 inchers), a 1976 Sporty and my current ride is a 1993 FLSTC Heritage Classic with custom factory paint. She has almost 100,000 miles on her now, but is still kicking along! All Original with stock bore.

Love the Wind!
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PostPosted: Sat Apr 28, 2012 3:47 pm    Post subject: another idea Reply with quote

I built a trike from a 73 type III and used a stock 03 harley softail master cylinder plus a 10psi reidual valve and have very good brakes. The type III's had better brakes to start with though. I used the full auto transmission, just twist and go. Cool
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MARY CHRISTY
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PostPosted: Thu Oct 03, 2013 6:10 pm    Post subject: VW Trike brake problems Reply with quote

I have been following the conversation by Freddie 13 and Manx about the brake problem/problems. It is identical to my brake problem. I have the large super beetle wheel cylinders on the rear drum wheels on my old Trike and a new Master Cylinder (3/4 bore) I have been bleeding for a long time and I think I got rid of most of the air. The brake shoes move some and will hold the wheels some, but they won't stop the wheels. I can still turn the wheels with my socket and wrench. It sounds like the problem could be the flex brake lines, since I have replaced about everything else. I noticed the shoe width is 1 3/16 instead of 1 5/8. I don't think the width would be the major problem. If I change the flex lines and the brakes start working, then I will replace the shoes with the larger width. I appreciate all the information which I have enjoyed reading. I thank you Manx and Freddie, I am glad you have yours fixed. I am new at this posting, so I hope you both see this. John Christy, Stem, N.C.
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BL3Manx
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PostPosted: Fri Oct 04, 2013 5:05 pm    Post subject: Reply with quote

I have had old flex hoses collapse internally and completely close off the flow of fluid to the wheel cylinders. Replacing them should definitely be the first thing you do.

When you bleed the brakes, if you still have a mechanical parking brake, you should have it set firmly before you bleed them, it will help get out all the air.

Before you adjust the shoes, stomp on the brakes several times, it will help the shoes settle into their best position. Then adjust the shoes firmly against the drums and then back off just enough so the wheel can be turned freely but the shoes still rub a little.

What type of rear end do you have, IRS or swingaxle? You need to be careful putting 40mm shoes in 30 mm wide drums, it can be done but its tricky and the shoes can jam against the side of the drum. It may need to have the face of the drum machined deeper or a wider spacer. Then you can get into problems with the cotter pin not clearing the nut.
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MARY CHRISTY
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PostPosted: Sat Oct 05, 2013 5:50 pm    Post subject: Reply with quote

Hello Manx, Thanks for your response. My trike is probably a 1968 or newer because the drums are 40mm width. I think it's probably a swing axle. I have no one to help me bleed the brakes, so I use a tie down strap with a ratchet. I put two new flex hoses on today and they helped some, because when I bleed both wheels, then I get about six inches of fluid into my clear plastic hose. I bled about a reservoir of fluid through the system today. I saw no bubbles, but the brakes don't completely lock. I measured the distance the pedal rod goes into the M/C and It is about 3/4 inches which is the same on my old M/C. I still have the 30mm shoes on instead of the 40mm. I think the brakes should lock even with the smaller width. It is very puzzling. Maybe, I just need to bleed them some more. Take care and have a nice weekend. John
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BL3Manx
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PostPosted: Sat Oct 05, 2013 7:50 pm    Post subject: Reply with quote

I'm sure your brake pedal has different geometry but on a bug, first you adjust the pedal stop to make absolutely sure that you have 8.25" pedal travel before the back edge of the pedal hits the body bulkhead. Then you release the pedal and adjust the pushrod length so that there is 5-7mm of pedal freeplay. Freeplay is critical. If you don't have the freeplay then the port to the reservoir doesn't open and fluid isn't drawn in.

On a trike (without a body) I'd do it in reverse order, first make sure there is 5-7 mm of pedal freeplay before the pushrod begins to depress the piston, then make sure you have full pedal travel before the pedal hits something

You can make a pressure bleeder out of one of those plastic garden pump sprayers. It sounds to me that you still have air in the system.

http://faculty.ccp.edu/faculty/dreed/campingart/jettatech/bleeder/
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