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Help caliper pistons and new pads  Rating:  Rating
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 Posted: 06-14-2007 07:04 am
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Joel
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Just to let ya know.  I got tired of dinking around w/ the calipers.  It's not so easy to find extra TR7 calipers just sitting around to compare w/ what I have.  I could order another pair from elsewhere and see if they fit - but if they don't it's just more time wasted.  I don't know if I was sent the wrong calipers or if there are different TR7 calipers or what. 

So, I ordered some reman's of JH calipers from Delta at 100 bucks a pop.  About the same price as the TR7's.  If I want to get fancy w/ the pads - ala Judson?? - I can send them my pads and they'll put their own magical braking substance on them for the same price as buying their stock TR7 pads. 

Now, I'll keep ya posted on whether the car quits deciding to let one or the other front brake work and have the other take a break (pun intended) or if I have another problem.  I'm hoping that new lines and new calipers do the trick.  I already have a new master cylinder and pads. . .

I don't want to get hard on the brakes to find that she's diving one way or the other any more.  it was kinda fun once.. .




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 Posted: 06-19-2007 01:32 am
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Ron Earp
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Sorry I couldn't be of more help with the part numbers. I just ordered TR7 replacements and used them, but I can understand your reluctance to do so - none of this stuff is cheap. Remans from Delta at $100 really isn't too bad as the TR7s are remans too, in some sense.

Ron

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 Posted: 06-19-2007 06:37 am
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Joel
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Ok, so they worked fine for a day or so.  I gave them more of a workout today and the pedal is almost to the floor and no more lock up.  I'm thinking bleed them again.  But maybe there's a problem w/ the vacuum?  I'll bleed and check again.

I replaced all the lines and the front calipers (and front pads).  For 2 days or so they seemed to be MUCH better.  I could actually lock them up.  Now, no go. 

Gotta send back the TR7 calipers.  I appreciate the lead Ron.  Not your fault.  Who knows, mebbe I was sent the wrong calipers.  Mebbe there are several TR7 calipers.  Who knows.  I would try again but the savings wasn't worth the hassle. 

Now, I need to find what to change next. 

I already replaced the master cylinder.  So, new master cylinder, front calipers, lines, and pads all the way around.  Still shitty brakes. 

At least she's running pretty good!  Always something to deal w/.  That's why we own them.


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 Posted: 06-20-2007 03:19 pm
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edward_davis
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Joel,

I'm sure you've checked it already, but you might want to make sure that the PDWA is working properly, or is properly taken out of the system.  Leaks across it could cause a loss in pressure at the front calipers.  Also, and I'm sure this isn't the case, a fellow at the MG club this weekend related a story about an old Jag he'd bought and tried to drive home, only to discover the brakes were poor.  Turned out that a PO had switched the lines from the front and rear parts of the M/C, so that the front brakes were getting rear brake pressure and vice versa.  That would do it, too, but it's an extreme long shot.

Edward

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 Posted: 06-20-2007 03:39 pm
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Mark Rosenbaum
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Joel wrote: Ok, so they worked fine for a day or so.  I gave them more of a workout today and the pedal is almost to the floor and no more lock up.  I'm thinking bleed them again.  But maybe there's a problem w/ the vacuum?  I'll bleed and check again.

I replaced all the lines and the front calipers (and front pads).  For 2 days or so they seemed to be MUCH better.  I could actually lock them up.  Now, no go. 

In addition to the other suggestions provided, this could be caused by either a defective master cylinder front brake piston seal, or a leaking tipping valve (also part of the master cylinder).  If the former, you can rebuild or replace the master cylinder (and yes, even new ones can fail, though it's rare).  If the latter, tiny particles in your brake fluid are preventing the tipping valve from sealing, thus preventing your front brakes from being activated, and the cure is to bleed the brakes with copious amounts of new fluid in the hope of flushing away the debris.  If the problem is intermittent, it's almost certainly the tipping valve.

Attachment: Master cyl cross section.jpg (Downloaded 44 times)

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 Posted: 06-20-2007 04:08 pm
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DeDub
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Nice, useful sketch, Mark.   Thanks.  But that brings up a question for me: what's the tipping valve do?  I can't discern it from the drawing and I've never had a master cylinder like this apart.

Also, and on a possibly related note, since I installed the 'big brake' kit from JHPS the front brakes work so well that they overpower the rears, even with new cylinders and shoes in the rear.  The fronts now lock up way before the rears which is not the best for hot cornering.  Is there a fix for this at the master cylinder or at the PDWA on the fenderwell, any proportioning adjustment?

David
#19377

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 Posted: 06-20-2007 04:44 pm
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Mark Rosenbaum
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Re tipping valve.

The tipping valve shuts off the connection between the brake fluid reservoir and the bore for the master cylinder's rear piston.  When the piston is all the way to the rear (i.e. brake pedal not pressed), the valve is tipped, and open, as shown in the drawing attached to my previous post.  The valve is supposed to seal when the brake pedal is pressed and the rear piston moves forward.  When the valve seals, pressure can build up in the rear piston's bore, and this pressure is applied to (a) the front brakes and (b) the rearward face of the front piston, which operates the rear brakes. 

However, if the tipping valve fails to seal, pressure can not build up in the rear piston's bore.  Under such a circumstance, the front brakes are inoperative, and the rear brakes don't activate until the rear piston comes into physical contact with the front one, which occurs only when the brake pedal is close to the car's floor.

The most common reason for a tipping valve to fail to seal is debris in the brake fluid.  Even barely-visible particles can prevent proper operation.

Re brake balance.

The JH has no native means to alter the balance between the front and rear brakes.  The easiest way to change the balance is probably to install rear wheel cylinders having pistons of a different diameter.  Since the rear brakes came from a Vauxhall, it's reasonable to think something suitable might exist, but you'd have to research the subject.  As an alternative, you could use two master cylinders along with an adjustable mechanical linkage.  Perhaps one of our racing members could offer advice on such an arrangement.

Last edited on 06-20-2007 04:48 pm by Mark Rosenbaum

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 Posted: 06-21-2007 06:14 am
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Joel
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Update -

Since the problem I was having was what felt like intermittent failure (or sticking or something) of ONLY ONE front brake - it doesn't make sense that it would be the Tipp valve.  If it was the valve the front or the back would fail in it's entirety.   Just feeling like one front brake is working, and that flopping back and forth doesn't sound like the valve.

Anyway, I have new calipers and pads up front now.  And I put on all SS brake lines.  This was a big improvement and I have not felt any 'diving' one way or another.  So, hopefully that solved that problem.

The car still didn't stop the way I wanted it to.  So - off to someone that was supposedly more of an expert.  He took a look and declared the rear shoes to be total crap.  We put on a new set of shoes, turned the drums, bled the system.  She's stopping now!  It's the best it's ever stopped.  So, all it took was replacing the entire system!


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 Posted: 06-21-2007 01:50 pm
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edward_davis
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Sounds familiar, Joel.  I've had to do the same thing, but without as dramatic replacement: all new rubber lines/seals, and new rear shoes.  Sometimes you just have to tear out all of the old, worn out stuff and replace it with new.  If only we could do that with ourselves as well...

Edward

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 Posted: 06-21-2007 04:37 pm
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Ron Earp
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Mark Rosenbaum wrote:

The JH has no native means to alter the balance between the front and rear brakes.  The easiest way to change the balance is probably to install rear wheel cylinders having pistons of a different diameter.  Since the rear brakes came from a Vauxhall, it's reasonable to think something suitable might exist, but you'd have to research the subject.  As an alternative, you could use two master cylinders along with an adjustable mechanical linkage.  Perhaps one of our racing members could offer advice on such an arrangement.


Easiest way to do this is with a brake bias valve. These are about $50, available from Wilwood and others, and are simple to install. Just put on the rear line and it will essentially pinch the fluid down and reduce, or increase, the braking depending on how it is set.

But if you need to increase only, that is a different matter.....

Ron

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 Posted: 08-22-2007 09:41 am
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normv
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Those wanting to upgrade the front brakes the easiest way is to visit your local ebc dealer, they have at least 4 different compounds to suit the jensen, although only standards and Greens are listed in the catalogue I have also brought Yellow and Red (these are track only) you will find these pads listed for several other cars as well, including

Morgan, Lotus, Morris, Volvo, triumph, Vauxhall and others

http://www.ebcbrakes.com/automotive.html

http://www.ebcbrakes.com/Assets/2007ukautocat.pdf  (best one to use for crossover)

http://www.ebcbrakes.com/Assets/USA%202007%20automotive.xls USA catalouge


 

Also here is a link to a proportioning valve on ebay, I have used the seller several times and recomend them

http://cgi.ebay.com/ebaymotors/Wilwood-Proportioning-Valve-NEW_W0QQcmdZViewItemQQcategoryZ42605QQihZ017QQitemZ270157539588QQtcZphoto

Last edited on 08-22-2007 09:47 am by normv

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