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TRUCK MASTER CYLINDER UPGRADE ADVICE


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Started on adapter. Test fit reveals the need to unbolt steering box. 
two flanges and a piece of tubing. Once i get it in place will tack weld it. There will be extra tubing, will trim it after i figure out length. 

Other photo comes up upside down. So i had to delete it. 

 

 

 

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Edited by Tooljunkie
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The 3/8" aluminum flat stock arrived yesterday so sometime this week I'll use my template to make an adapter.

 

I was planning on making through holes for the Jeep MC mounting bolts but I think I'll drill and tap for 5/16-18 bolts instead.  The 3/8" plate provides enough thread engagement for a 5/16 bolt and I think it would be easier than dealing with counter sunk bolts.

 

Stay tuned.

 

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20 minutes ago, bkahler said:

Wow!  That is one tiny master cylinder!

 

Have you driven the truck yet with that setup?

 

Will be a while yet,have a few things to do with frame and front end. Want to get paint on frame and  steering And  suspension in and done. Then i can plumb in prop valve and fill with whoah juice.

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Update..used a wire coat hanger to mock up my bends. Modified a 3/16” tee to accept pressure switch. Blocked the fitting for rear line until i get different rear axle in. Not satisfied with pedal travel so far,but shoes need adjusting and i may need to reverse lines coming out of master  cylinder.thats all until next weekend. Have to empty shop and bring in some paying jobs..

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Edited by Tooljunkie
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Took the time this evening to make a mounting bracket for the Grand Cherokee MC.  Once all of the holes were in place I found an interesting dilemma.  The two holes at the top of the bracket are very slightly blocked by the MC.  This will necessitate grinding clearance spots on the MC casting.  Not a whole lot and I don't think it will interfere with the integrity of the MC but without modifying the bell housing casting by boring out the holes in the casting to remove the threads I don't see any other alternative.  For myself I'm not willing to permanently alter the bell housing so I'll modify the MC itself.

 

Sometime this week I hope to do the grinding on the MC for clearance so I can actually mount the MC to the truck and verify the brake pedal pushrod mates properly to the MC.  

 

Back when I had the original MC bolted to the truck I noticed that it appeared to sit slightly at an angle.  Tonight that became pretty obvious once I bolted the plate to the truck!  Not sure why Dodge mounted it that way but it sure looks odd.  That angle is not something I can correct by relocating holes due to the interference of the top holes with the MC.  It would just make one of the holes worse.

 

Anyway, I'm a little closer to having an MC bolted to the truck :)

 

Brad

 

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It just dawned on me, the two two bolts could be countersunk and flathead screws could be used to fasten the plate to the bell housing and then the MC would be bolted in place.  Something to think about......

 

 

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Edited by bkahler
Flathead screw discussion
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I can see where it would work to add spacers to provide clearance for adapter plate mounting.

 

However the use of a spacer would move the MC closer to the steering column in an area where clearance is at a premium.

 

One thing I had been wondering about was just how much stress the MC is actually under.  I would think if everything is aligned properly the overall stress would be minimal.

 

Considering the Grand Cherokee MC mounts with just two 5/16" bolts I wouldn't think the stress wouldn't be to much.

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the spacers would be just above the MC casting and would provide a flat surface for the bolt hex head...think of a donut with a bite taken out of it...this allows the adapter and MC to stay in the location you want it for proper clearance.

 

As for the stresses seen, the original MC had a power boost by grabbing hold of the steering wheel and puckering up something fierce, so it had to withstand something like 500# loading on a bad day...the newer MC probably doesn't see that kind of loading since the power boost made the magic happen for most folks.  I typically avoid countersinking in applications where the clamping material remaining would be less than 1.5X the thickness of the countersunk fastener...I have seen failures where bolts have pulled through material that was too thin, like a knife through butter, in high stress loading and fatigue failures.  Stress calculations for the configuration you are shooting for could be done taking into account the material properties of your mating materials, but this rule of thumb has been surprisingly accurate given that said calculations were done by well-compensated automotive engineers somewhere along the line for the Jeep MC :cool:

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8 hours ago, JBNeal said:

the spacers would be just above the MC casting and would provide a flat surface for the bolt hex head...think of a donut with a bite taken out of it...this allows the adapter and MC to stay in the location you want it for proper clearance.

 

As for the stresses seen, the original MC had a power boost by grabbing hold of the steering wheel and puckering up something fierce, so it had to withstand something like 500# loading on a bad day...the newer MC probably doesn't see that kind of loading since the power boost made the magic happen for most folks.  I typically avoid countersinking in applications where the clamping material remaining would be less than 1.5X the thickness of the countersunk fastener...I have seen failures where bolts have pulled through material that was too thin, like a knife through butter, in high stress loading and fatigue failures.  Stress calculations for the configuration you are shooting for could be done taking into account the material properties of your mating materials, but this rule of thumb has been surprisingly accurate given that said calculations were done by well-compensated automotive engineers somewhere along the line for the Jeep MC :cool:

You mentioned the loading being 500 lbs. a fair estimate, but understated. I bet its 3-5 times that amount. I think the average person can leg press near 500 lbs, so even at 1/2 that with the leverage from the pedal multilplying the force its like x10 give or take 5%. Inch lbs vs foot lbs sort of thing. This was rolling around in my head as i was building my  adapter.

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14 hours ago, JBNeal said:

the spacers would be just above the MC casting and would provide a flat surface for the bolt hex head...think of a donut with a bite taken out of it...this allows the adapter and MC to stay in the location you want it for proper clearance.

 

I'm getting old and slow and had to sit and think on about what you wrote overnight, however I think I finally get what you're trying to describe  :)

 

If I understand correctly you're looking for way to get the bracket bolted to the bell housing with out using countersunk screws which would weaken the adapter plate.  An alternative to fabricating some sort of horseshoe shaped bracket might be to grind material away on the MC as shown in red in the attached picture and using a round spacer with a longer bolt  to space the head of the bolt above the top of the MC casting.  I think a spacer with a 1/8" wall and about 1/2" in height would be sufficient.

 

 

20200128_190137xx.jpg

spacers-815198-64_1000.jpg

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I'd be hesitant to modify the MC casting, but the spacer can be modified to notch over the casting so that it rests on the adapter and the MC flange, while the bolt head contacts the other end of the spacer...you could possibly make 45° cuts on the bottom corners of the adapter to fabricate spacers out of since those areas are beyond the adapter clamping area...I have made some adapters similar to this and made spacers out of flat washers that were clipped by grinding on one side so they looked C-shaped, stacked the spacer washers for clearance, then put a full flat washer on top of that stack for bolt head contact...I've even used modified hex nuts as spacers that were the next size up from the bolt used, those worked well and could be easily replaced if necessary :cool:

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I honestly like the countersink idea better. It wont weaken it as much as you would think. 
 

you may want to consider socket head cap screws, usually much tougher than grade 8, and require less room than a 9/16” hex. Would be my choice.

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For the adapter plate I've fabricated I think it boils down to one of three options.  

 

1) Grind the MC enough to fit a socket head cap screw (no mods to adapter plate, mod to MC)

2) Countersink the plate and use flat head screws (mods to adapter plate, no mods to MC)

3) Grind the MC enough to allow clearance for a bolt to fit in the hole and use a round or horseshoe shaped spacer. (no mods to adapter plate, mods to MC)

 

There is an advantage to not modifying the MC and that is if you're on the road somewhere and the MC fails you can get one off the shelf at just about any parts store and bolt in place and you're back on your way.  If you have to modify the MC to make it fit that means it's no longer an off the shelf bolt in place affair.

 

Not using counter sunk screws means the adapter plate is stronger but negates the advantage in the paragraph above.  My preference would be option two, countersink the holes but I want to be comfortable knowing that I haven't compromised the integrity of the adapter plate.  Decisions........

 

One thing I need to keep in mind is until I bolt the assembly to the bell housing and install the brake pedal I don't know for certain that the MC is bolted in the right location on the adapter plate.  Based on all my measurements and calculations I believe it is but in the world I come from, until a change is tested you don't know for certain that it's right.  My assumption in this case is the travel of the push rod needs to be as close to center line of the MC as I can make it.  With this Cherokee MC the MC has a cylinder protruding from it that the pedal push rod has to slip into. If it's not in line with the center of the MC then I believe it could bind.

 

Thanks!

 

Brad

 

 

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When i made my adapter, the hole fits the tube nearly perfect,as well the m/c fit the tube. With tube and m/c set on plate, i used transfer punches and laid out the bolt pattern. As my master cylinder Also has the tube for the push rod i was concerned about it as well. 

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On 1/30/2020 at 10:56 AM, Tooljunkie said:

When i made my adapter, the hole fits the tube nearly perfect,as well the m/c fit the tube. With tube and m/c set on plate, i used transfer punches and laid out the bolt pattern. As my master cylinder Also has the tube for the push rod i was concerned about it as well. 

 

Does your pushrod have a snug fit in the MC bore or is there enough "slop" that being slightly off on the angle wouldn't matter?

 

On mine the pushrod is a slip fit but being off slightly could create a bind.  I'm considering turning the first inch or so of the pushrod down 0.020" or so.  I'll hold off on that action until things are actually bolted in place and I have yeah or nay evidence.

 

 

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Something else I could possibly do to address JB's concern is to double up on the plates.  I need to verify for certain but I think there is going to be more space than anticipated between the end of the MC and the steering column.  Hopefully I can generate a picture or two this weekend.

 

Brad

 

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I learned a lot this morning.  I mounted the MC on the 3/8" plate and installed the brake pedal and stuck the steering column tube in place.  You'll see in the attached pictures there might be a problem with the larger reservoir this MC has compared to the sloped model found on other MCs.  Can someone tell me how close does the pedal get to the floorboard when you apply the brakes?  Say from the top of the pedal to the sheetmetal.  

 

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Another aspect of a 3/8" adapter plate is the pushrod modifications necessary.  Both the plunger and the threaded shaft would need to be trimmed to make things fit.

 

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Here's what the clearance looks like with the 3/8" mounting plate.

 

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Depending on how far the pedal travels towards the floorboard the pedal arm below the floorboard might collide with the MC reservoir.  I do know the MC has a 1.5" piston travel so if I get the pushrod modified that might help sort things out.

 

 

Edited by bkahler
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I scrounged around in my shop and found a 3/4" thick aluminum plate so I fabricated another adapter out of it.  Ignore the shape as it was just a piece of scrap and I used what I could out of it :)  

 

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I'm happy to say it appears the template that I made seems to be accurate as all of the holes lineup without problems.

 

The same issue with pedal hitting the top of the reservoir still exists.   I need to modify the pushrod so I can find out if the tall reservoir is going to work.  

 

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The alignment of the MC bore with the pin hole in the brake pedal arm appears to be correct.  I believe that's another indication that all of my measurements seem to be accurate.

 

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With the 3/4" spacer the pushrod will need to be trimmed about 1-1/2" and little if any will need to come off the threaded shaft.

 

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I will say it's a lot harder to bore a 1-7/8" hole in 3/4" aluminum that it is 3/8"!   I might have to find a different hole saw if I end up using 3/4" plate which all things considered I do think would be a better approach.  

 

I guess the next step is to modify the pushrood......

 

Brad

 

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