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-   -   JAG IRS brake shudder (http://www.clubcobra.com/forums/all-cobra-talk/120961-jag-irs-brake-shudder.html)

ollykiwi3 12-26-2014 02:30 PM
Tom-do you have any idea how much tension you have on your return springs or a measurement from the arm to the chassis securing point for the springs?
Or the length of the spring in its relaxed posi.

I only just put mine on and had to guess at the tension.maybe not enough and the pads keep contacting due to centrifugal forces during cornering?

Agreed,it needs to be looked at but still don't see how it can affect the main brakes,unless the handbrake pads are transferring material which is screwing with the coefficient?

Will keep trying

Thanks

Cobra #3170 12-26-2014 03:02 PM
Shudder
 
Quote:
Originally Posted by ollykiwi3 (Post 1331692)
Tom- thanks for your thoughts.in regard to rear brake bias and lock up,I only did that briefly for isolating the issue.brakes are back to where they should be,front locks first.

As for the handbrake test,I'm pretty sure I did that a long time ago. I don't really see the relevance as the two are independent and it only does it with foot pedal pressure.its also intermittent.very hard to repeat consistently. But the handbrake pads do keep wearing? I have return springs on the arms now,but maybe not enough.i keep having to adjust them?


Rotors are centred.
I'm going to bleed them again this weekend and see if that helps.i will be looking into the ebc Reds soon.

Cobra3170- interesting,that's kindof what the brake guy was saying.im not sure if the sensation you had was pulsating due to material build up or more like mine and being a high pitch chatter.i don't get any pedal feedback.
But another thing to look into all the same.

I did record it yesterday but too much background noise was picked up.will try again today.

Ok.thanks guys.
Did not feel it in the pedal just vehicle shudder with the rotor contamination problem. I did change to a different pad material when I switched rotors though, used carbotech pads. The stick slip occurs at a constant pressure so pedal does not pulse. You could actually see where pad material was unevenly deposited on the rotor in my case because there were dark and light spots. You can usually feel thick thin wear in the pedal so you are right that probably isn't it.

Tom Wells 12-26-2014 05:27 PM
Olly,

Can't get my car on the lift for the next couple of days maybe so here's some Googling from Jag-lovers.org:
Quote:
> I know the parking calipers are tightening and releasing,
> but evidently they are not always releasing fully.

It might not explain ALL of your symptoms, but one common problem
with the handbrakes on these cars is a misadjusted cable. By that I
mean, some nimnul has misadjusted the cable; they don't get
misadjusted on their own. The pads wear, the self-adjusters in the
caliper sieze up, and then when the lever can come all the way up
without engaging the brake, the solution is to readjust the cable.
Then when you FIX the worn pads and the siezed calipers, they still
don't work correctly because they're not being fully released when
the lever is lowered to the floor.

Full release of those handbrake calipers is imperative if you ever
want them to work correctly. The only way I know to be sure is to
get under the car and grab ONE lever and try to move it in the
release direction -- possibly pulling the other lever tighter if the
cable is in place. Each lever should be felt to be against a hard
stop. If it's not, you'll need to adjust the cable looser. The
adjustment is at the lever, where you've gotta fiddle with the
carpeting to get at it.

-- Kirbert
and
Quote:
Aahhh. I think you've hit upon it. On the car with the dragging parking
brake, I discovered that the "plate" (the U-shaped thing with the points
that go in the holes on the top of the handbrake calipers) actually bends as
the pads wear. Whereas the original condition has the arms farther apart at
the points, the dragging pad side on mine had bent past perpendicular so
that it was parallel to the side that wasn't dragging.

Which came first, the bent arm or the dragging? I'm not sure, but it would
seem that as the pads wear, the arm would have to give. Also, it's made of
rather soft metal, and I could almost straighten it by hand. I used pliers
anyway because looking at the pictures and the ones I've removed, they are
supposed to be pretty much straight down the outside edge of each side.

If you can see what you are doing, align it with the holes in the handbrake
calipers. Then reinstall it and safety wire it. I'd add that if it isn't
wide enough, it will probably act as a spring pulling the pads together a
little, until they wear enough to remove the tension.

The bent arms may have been the cause of your problems all along, so you
might want to see if you can straighten the arms and reinstall the "plate"
before dropping the calipers. I don't know if you'll be able to safety wire
it in that position, but I don't know how necessary that is. Anyone?

To sum this all up, it appears that the "plate" acts like a spring, bending
in as the pads wear, but having just enough give to pull the pads away from
the rotor when the brake handle is released. Ingenious engineering.

Mark

P.S. Just so everyone knows I'm not a complete idiot, in the previous
e-mail, I said to disconnect the brake lines from the rotors. Of course, I
meant calipers. Thanks to everyone for not being cruel and pointing that out
(while laughing uproariously).

-----Original Message-----
From: owner-xj at jag-lovers.org [mailto:owner-xj at jag-lovers.org]On Behalf Of Darrin hodges
Sent: Sunday, April 08, 2001 5:05 AM
To: XJ Lovers
Subject: Re: [xj] hand brake

Mark
thanks for that suggestion. my main problem was the brass
hook thingie, the original park brake pads were quite worn, im not
sure if the 'arms' on the brass thingie have been 'pushed' inwards, making
it difficult to get the hooks easily back into the holes in the calipers, so
i think ill give your idea a go and see what happens. after that i was going to
change the trans filter/fluid and reseal the exhaust joints, phew, getting worn out
just thinking about it, hopefully, ill even get to drive her before the holiday
is out!

cheers
darrin
Anyway, if you cruise over there and look, maybe one of those guys can point you in the right direction.

Tom

ollykiwi3 12-26-2014 08:57 PM
"Did not feel it in the pedal just vehicle shudder with the rotor contamination problem. I did change to a different pad material when I switched rotors though, used carbotech pads. The stick slip occurs at a constant pressure so pedal does not pulse. You could actually see where pad material was unevenly deposited on the rotor in my case because there were dark and light spots. You can usually feel thick thin wear in the pedal so you are right that probably isn't it. "

Do you recall what kind of speed it was happening? heavy load, or light braking like mine?
thanks again for your insight. where did you get the carbotech pads? what country are you in. here in NZ we are very limited to choice.

Tom- jag lovers was my next move. I heard it can be a pain to adjust these things, correctly. I have mine set so it takes one click to just get a feel of drag on the calipers. I will have to look at the brass tensioners and see what they look like. I do recall one being a bit bent.i only ever adjust the cable length as the calipers are self adjusting, and it is all working fine.although that's one hell of a complex set up.:confused:

does anyone else have a measurement for the return springs? in the relaxed state.
thanks again.

Cobra #3170 12-27-2014 10:47 AM
Brake shudder
 
Quote:
Originally Posted by ollykiwi3 (Post 1331767)
"Did not feel it in the pedal just vehicle shudder with the rotor contamination problem. I did change to a different pad material when I switched rotors though, used carbotech pads. The stick slip occurs at a constant pressure so pedal does not pulse. You could actually see where pad material was unevenly deposited on the rotor in my case because there were dark and light spots. You can usually feel thick thin wear in the pedal so you are right that probably isn't it. "

Do you recall what kind of speed it was happening? heavy load, or light braking like mine?
thanks again for your insight. where did you get the carbotech pads? what country are you in. here in NZ we are very limited to choice.

Tom- jag lovers was my next move. I heard it can be a pain to adjust these things, correctly. I have mine set so it takes one click to just get a feel of drag on the calipers. I will have to look at the brass tensioners and see what they look like. I do recall one being a bit bent.i only ever adjust the cable length as the calipers are self adjusting, and it is all working fine.although that's one hell of a complex set up.:confused:

does anyone else have a measurement for the return springs? in the relaxed state.
thanks again.
I am in the US and Carbotech is a US company I used their AX6 compound. I think any mildly aggressive compound would work and yes it was under light pedal pressure. You could also try sanding the rotors with an orbital sander and 80 grit paper to remove the old pad material and see if that makes a difference.
If it were me, I would sand the rotors as described above and put in new pads (what ever you can get) and then break them in following manufacturers recommendations. Multiple stops from a specified mph in a row then cooling then repeat for several cycles then drive with no brake application to cool to ambient temperature and then what ever else they recommend to complete the break in and get an even level of the new pad material transferred to the sanded rotors. If that doesn't work I have no other idea's :)

ollykiwi3 12-27-2014 10:43 PM
Thanks for the info.
Am going to a mates place to put car on hoist and run it up so I can see from underneath while running.

I just rebled the brakes and went for a drive.

I tried the handbrake only today and all was Quiet.i checked with main brakes at the same time and it chattered. So definitely not handbrake issue.yes I still need to look at that wear problem separately anyway.

Just another thing to throw in the mix,and it's something I was wondering about.
I found the stub axle splines with some wear and was wondering about spline backlash chatter.
I did find today that while driving steady at 20mph with light brake load on I could get the chatter fairly consistent BUT only going downhill or off load coasting. Not going up hil or while slight acceleration. And that seemed fairly repeatable.
Has anyone experienced spline wear like this creating problems?

ollykiwi3 12-30-2014 11:41 AM
Couldn't duplicate the issue on the hoist.
Got the brakes hot but doesn't seem to have enough load on the system to create the same problem.
Went out the driveway and one minute later it was chattering.
It's defineatly worse with the balance bar biased to front which gives better front lock up.
I'm going to look into brake line pressures at light pedal load.i have .7"for front and 5/8 for rear . Might swap them over just to see the difference. They are small but I have small pedal ratio 4:1. They work fine you just have to be working a bit harder.

DanEC 12-30-2014 03:47 PM
I believe the reason the front brake master is larger than the rear is due to the larger pistons in the front calipers that take on more of the braking application effort. If you mean you might try swapping the front and rear masters I don't think that is a good idea. Maybe I'm misunderstanding your post.

Snake2998 01-01-2015 12:55 AM
Quote:
Originally Posted by DanEC (Post 1332167)
I believe the reason the front brake master is larger than the rear is due to the larger pistons in the front calipers that take on more of the braking application effort. If you mean you might try swapping the front and rear masters I don't think that is a good idea. Maybe I'm misunderstanding your post.
In my Haynes Jag XJ6 manual the diagram shows the front caliper connected to the front MC and the rear to the rear MC but the text says exactly the opposite (or vice versa - don't have manual handy).

Don't have the car or the manual handy so can't recall what I did but it seems to work. Normally the smaller cylinder connects to the front and larger to the rear and I think that is what I did.

In fact I now have fitted much bigger discs and calipers to the car and will only know how it works when i test drive it - might reverse connection to restore rear brake balance.

DanEC 01-01-2015 06:07 AM
That sounds odd but I don't know what Jag used for front brake calipers.

Another way of looking at it is - since typically your front brakes provide over 50% of the braking effort, the pistons in the calipers are larger in the front than on the rear calipers. In order to maintain reasonable pedal effort and uniform line pressures in the two hydraulic systems for even braking, a larger diameter master cylinder would be used on the front system to match the larger pistons.

Using a large diameter master cylinder with smaller rear brake calipers and a smaller diameter master cylinder with the larger front brake calipers would no doubt provide a very interesting stopping system. Rear wheel lockup and high pedal effort would seem to be certain.

But again, I don't know what Jag did with their front brakes so maybe I'm missing something.

gunkk 01-01-2015 06:29 AM
Spline play, or any excessive elasticity between the disk and the wheel could in theory contribute to a stick-slip resonance...

strictlypersonl 01-01-2015 02:11 PM
The front caliper piston diameter is 2.375" vs the rear 1.69". In order to get 60% effort to the front (necessary balance under maximum deceleration) the front master must be larger than the rear. (There's some pad-coefficient-of-friction factored in there too. The GM pads are somewhat "stickier" than the Jags'.)

ollykiwi3 01-02-2015 02:33 PM
Quote:
Originally Posted by strictlypersonl (Post 1332475)
The front caliper piston diameter is 2.375" vs the rear 1.69". In order to get 60% effort to the front (necessary balance under maximum deceleration) the front master must be larger than the rear. (There's some pad-coefficient-of-friction factored in there too. The GM pads are somewhat "stickier" than the Jags'.)
That's all great in theory but not relavent to to my setup. Although I have xjs/xj6 callipers I don't have original masters due to no booster and small pedal ratio. I checked again and the pedal ratio is actually 2.7:1. Hence the smaller masters.
I don't recall exact size of Pistons on front ,but pretty damn sure there not 60mm. I'm still trying to get someone to tell me the sizes so I don't have to pull them apart to find out. So it's mid 80's xjs/xj12 front and s3 Xj 6 rear. I think 45-48mm. Can someone confirm.
Thanks

DanEC 01-02-2015 04:50 PM
Quote:
Originally Posted by ollykiwi3 (Post 1332724)
That's all great in theory but not relavent to to my setup. Although I have xjs/xj6 callipers I don't have original masters due to no booster and small pedal ratio. I checked again and the pedal ratio is actually 2.7:1. Hence the smaller masters.
I don't recall exact size of Pistons on front ,but pretty damn sure there not 60mm. I'm still trying to get someone to tell me the sizes so I don't have to pull them apart to find out. So it's mid 80's xjs/xj12 front and s3 Xj 6 rear. I think 45-48mm. Can someone confirm.
Thanks
I think Bob (Strictlypersonal) from ERA was speaking in reference to my post and addressing the size of the ERA front GM caliper which is single piston. Aren't the front Jag calipers from that time a 4-piston caliper? I believe the total area of all 4-pistons has to be considered together. But, I have a feeling this isn't really a road map to solving your issue with the rear brake chatter.

ollykiwi3 01-02-2015 06:33 PM
Quote:
Originally Posted by DanEC (Post 1332766)
I think Bob (Strictlypersonal) from ERA was speaking in reference to my post and addressing the size of the ERA front GM caliper which is single piston. Aren't the front Jag calipers from that time a 4-piston caliper? I believe the total area of all 4-pistons has to be considered together. But, I have a feeling this isn't really a road map to solving your issue with the rear brake chatter.
Right.understood.that makes sense.
I agree ,this isn't helping solve my issue.
I am a mechanical person and an engineer so I understand the theory of most of it,so what I'm really looking for is someone who has had similar experience with this issue,like a couple of the previous posts.the problem I have is I'm limited to the supply of different parts compared to you in the US,so I have to try other ideas before having to order parts from the states as its expensive for freight.
I appreciate the thoughts but we seem to keep back tracking over the same ground.
and yes they are 4pot.
Thanks again

Nick 427 03-19-2015 05:13 AM
I'm still have the same problem as yourself , once I get the brakes a little warm I can get it to shudder at will. My car has a manual transmission and on coast with the clutch pedal in or neutral it will shudder. In gear it does not. I don't believe it's a brake pad or rotor issue as I have changed both. Pads 3 times. My diff ratio is 4.27 LSD and prior to putting these gears in I didn't have any issues. Prior it was 3.31 single wheeler .
I found that when it shudders and I need to stop in a hurry (in traffic) a pull on the handbrake stops it immediately
Can this be a diff issue and not a brake issue ?

ollykiwi3 03-19-2015 11:00 AM
Thanks nick
Sounds similar.what speeds can you Get yours to do it? Mine does it from walking pace up to about 35mph.
I changed to ebc red recently and I think it slightly worse,not more violent worse,but will do it before it warms up now.

How did your stub axle splines look? Mine were quite worn. Didn't measure free play but guess 1mm at half shaft stud mount.

Mine is slightly different in that I can push through it. If I push harder on the pedal it stops shudder(more of a groan)

Do you mean if you pull on handbrake the shudder stops?

Not sure what to do next, but will visit brake specialist shop soon.

Nick 427 03-19-2015 04:38 PM
When the shudder starts is upsets the whole braking system and I either have to let go of the brake pedal and depress again or I have found as I'm braking and it's shuddering a slight lift on the handbrake stops the shudder

ollykiwi3 06-05-2016 12:11 AM
Pretty sure I have figured this thing out.
Because I never had return springs on the handbrake lever arms I was ways having to adjust the handbrake caliber and couldn't figure why it was always wearing.
I got some springs and attached them to the chassis.
I figured it was just g forces going around corners that was wearing them out, But what it was also doing was transferring handbrake pad material which was softer onto the disc making it seem even stickier and that was causing the brakes to chatter at low speed. Too grippy with not enough load.
It's been about a year now and have only heard it chatter a couple times in the early days but nothing for a long time now.
Hope this is of some help to others.
Thanks for the thoughts during this time.

Gaz64 06-05-2016 01:12 AM
Quote:
Originally Posted by strictlypersonl (Post 1332475)
The front caliper piston diameter is 2.375" vs the rear 1.69". In order to get 60% effort to the front (necessary balance under maximum deceleration) the front master must be larger than the rear. (There's some pad-coefficient-of-friction factored in there too. The GM pads are somewhat "stickier" than the Jags'.)
That is the sole reason for the larger pistons in the front.

Then the master cylinder bores can be the same, if you are using two masters.

Then it comes down to balance bar adjustment.


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