| Author |  Topic  |
pchristy
V4 Mad
United Kingdom
511 Posts |  Posted - 28 Jul 2010 : 16:56:37  
| Grr! Spent all yesterday giving the 96 a thorough service in preparation for an imminent very long jaunt (watch this space!). She's always had a bit of vibration under braking, which I've spent ages trying to sort. Over the last year, its faded almost into non-existence. so I was more than a bit galled to discover that fitting new pads had brought it back with a vengeance!
Hit the brakes at 50, and its like driving over a cattle-grid!
It has to be a warped disk. Unfortunately, new ones seem to be unobtainable at the moment. I've tried 3 times to get new ones now - twice they turned out to be out of stock, despite the advertisers website claiming they had them, and once they never arrived - lost in the post (though I did get a full refund).
Malbrads have found a pair of good second hand ones for me. Hopefully they'll arrive before Monday so that I can get stuck in again.
Isn't it amazing how a simple service can cause such grief.....!
--
Pete
"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!" |
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Woody
V4 Guru
United Kingdom
1209 Posts | Posted - 28 Jul 2010 : 21:03:12 
| Confirm first with wheels off whether you have a warped disc. I suspect it is chatter caused by a weak/seized spring either at the bottom pivot or the top retainer which often seizes.
I would have thought a warped disc would be felt through the pedal even on slight braking and also before you changed the pads. |  |
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pchristy
V4 Mad
United Kingdom
511 Posts | Posted - 28 Jul 2010 : 22:23:16
| Hi Woody, thanks for the feedback!
I must admit to being a bit confused here. I've only experienced warped discs on vented discs, never on solid ones, but the symptoms do fit.
I'm pretty certain that the culprit is the driver's side, and I've spent most of today freeing off the caliper and greasing it with copper-ease. But nothing I've tried has worked.
Its been a long term issue since I got the car, some two years ago now, but seemed to fade with time. Fitting the new pads has brought it back with a vengeance!
It may be a variation in thickness rather than warping, but both calipers are now as free as I can get them, so there isn't really much left but the discs!
My problem is that time is now somewhat limited. I've booked up for InterSAAB in Interlaken (Switzerland), and we depart on the 11th of August! That's a fairly long jaunt for a 40 year old car, hence a careful service now! I've got some days off between now and then, but I don't have time to mess about! I will certainly bear your comments in mind when I replace the discs, and have (yet another!) go at the calipers, but I don't think I'm going to improve them any further!
--
Pete
"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!" | |
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Woody
V4 Guru
United Kingdom
1209 Posts | Posted - 28 Jul 2010 : 23:06:04
| It is more work but an option is to strip the halves of the caliper and check for wear where the fingers fit at the bottom and also whether there is significant wear at the small plate at the top.
I had this on a previous car and had a chatter under braking. I found wear at all the points mentioned and the top retainer had seized. | |
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rsimps
V4 Mad
United Kingdom
955 Posts | Posted - 29 Jul 2010 : 07:42:40
| | Also just check your caliper bolts are tight. They rattle loose, but I wouldnt think they would cause vibration. | |
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pchristy
V4 Mad
United Kingdom
511 Posts | Posted - 29 Jul 2010 : 09:25:25
| Thanks for all the feedback - all useful stuff! Malbrads have just rung back to say they've located a pair of new discs, and that I should have them tomorrow! Unfortunately I'm working until Monday now, but a friend, who is a professional mechanic, is going to give me a hand with them on Monday. We'll have a good look at the calipers whilst we are at it!
I think I can feel a pulsing on the pedal when it happens but its difficult to be sure because the vibration levels are quite high - enough to nearly shake the wheel out of your hands! The car stops fine, and in a straight line, but the vibration is quite alarming with moderate pedal pressure!
Oh, and the car has just "gone round the clock" again - probably for the 3rd or 4th time!!!
--
Pete
"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!" |
Edited by - pchristy on 29 Jul 2010 09:28:10 | |
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pchristy
V4 Mad
United Kingdom
511 Posts | Posted - 30 Jul 2010 : 09:46:55
| New discs arrived at 9 o'clock this morning!!!
Excellent service!
Never having changed the discs on a 96 before, are there any gotchas to look out for? It looks like the simply bolt onto the back of the hub. Is this right?
--
Pete
"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!" | |
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melle
V4 Fan
Netherlands
171 Posts | Posted - 30 Jul 2010 : 10:59:44
| It's as easy as just bolting them on indeed. Apply some copper grease where the disc meets the hub.
1970 Saab 96V4 "The Devil's Own V4"
1974 Saab 95V4
1977 Saab 95V4 van conversion project | |
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Borstlap
V4 Fan
Norway
139 Posts | Posted - 30 Jul 2010 : 17:15:12
| Basically it is simply bolt on, but you may have to check for excessive warp once attached. If the tolerance is too large (by heart 0.2mm) you run the risk of getting judder. You can adjust by tightening or slackening the attachment bolts.
I changed the disks on the Sonett once and I was fortunate to have a neighbour with a micrometer that is used for measuring warp in race bicycle wheels. Made the job dead easy.
Alex | |
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pchristy
V4 Mad
United Kingdom
511 Posts | Posted - 02 Aug 2010 : 19:50:17
| Well, the new discs are on. The installation didn't go completely smoothly, as one of the new discs had 20 thou run-out between the disc and its mounting face! This necessitated a trip to the machine shop to get said face skimmed!
On mounting the disc in the lathe, and getting the disc running true, you could actually *SEE* the run-out on the mounting face!
Once this was sorted out, everything went smoothly, but the brakes *still* judder!
We've checked the calipers - they are free, and there are no obvious signs of wear or sticking.. The discs are true. The pads are new. We are stumped!
I'm hoping that its just a symptom of the new pads and that they will "bed in". The car stops fine, and in a straight line. The judder only occurs over 45 MPH, and under medium braking. It doesn't happen on light or heavy braking!
There is no play in the steering or ball joints!
Any suggestions gratefully received!
--
Pete
"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!" | |
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UK_Sub
Moderator
United Kingdom
1008 Posts | Posted - 02 Aug 2010 : 20:09:48
| Might be worth taking a picture of the installation - someone might spot something.
Just checking, but are the spring plates holding the brake pads in OK and are the split pins OK? | |
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melle
V4 Fan
Netherlands
171 Posts | Posted - 02 Aug 2010 : 20:26:44
| I've never encountered any warp with fresh discs, but it might be a good idea to check for it next time!
1970 Saab 96V4 "The Devil's Own V4"
1974 Saab 95V4
1977 Saab 95V4 van conversion project | |
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rsimps
V4 Mad
United Kingdom
955 Posts | Posted - 03 Aug 2010 : 07:59:12
| Its not CV joint related is it? I have had judder from brakes in reverse on the old Shed 96. That was the CV's that had alot of play in them. Is it judder or a worn drum oval at the rear? Those are the only things I can thing of.
Brembo will be doing some discs in the future, at the moment its what you can get your hands on. What make are they? | |
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pchristy
V4 Mad
United Kingdom
511 Posts | Posted - 03 Aug 2010 : 09:19:32
| UK_Sub: Yes, I used a new fitting kit, as the old spring plates seemed to be mismatched, and were pretty grotty. New split pins, too.
Richard: Yes, I was wondering about that, as you can feel a very slight shimmy under hard acceleration. However, under braking, it happens when using the free-wheel - which means that the transmission is dis-engaged? Or am I missing something here?
I originally ordered the discs from Malbrad, but they only had a pair of 2nd hand ones, which needed machining. Knowing that I was in a hurry, they managed to source some new ones, which were sent straight to me from "2-stroke to Turbo". They came in clear wrappers, and I didn't notice any manufacturer ID on them.
Luckily, my mechanic friend (ex Rolls-Royce aero engine man!) is pretty good (to put it mildly!) and spotted the poorly machined disc. Equally luckily we have a mutual friend with a very good machine shop, who fixed it for us whilst we waited! Thank God I didn't attempt this on my own!
The shimmy, or judder, seems to be much higher in frequency than the rotational speed of the wheel - its not a "once per rev" thing, although that could be triggering it. The nearest way I can describe it is that its like driving over a cattle grid a bit quick. As soon as you drop below 45 MPH, it stops as if by magic!
It does have all the hallmarks of something being loose or worn, but I'm b******d if I can find any play anywhere!
At the moment, I'm just hoping it will subside as the pads bed in! These cars were designed to run with the old asbestos pads. The newer ones are much harder, and I'm wondering if its related to this? Also, as I've said before, much of this car's history is something of a mystery, and the restorer (prior to my ownership) did some things very well, and others were appalling! But I *WILL* find it sooner or later!
--
Pete
"Duct tape is like the Force: It has a light side and a dark side, and it binds the Universe together!" | |
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Derek
V4 Mad
United Kingdom
815 Posts | Posted - 03 Aug 2010 : 10:46:43
| You might be able to eleiminate the rear drms from the "possibles" list by doing your 55mph brake test with the handbrake being pulled lightly on. Just testing the handbrake at speed, safely of course, might show something but I'd have thought you'd have tried that. Have you a usable but well worn set of pads you can try? Do you get a pull to one side or does it appear to chatter on both sides evenly?
Can you actually hear it? If so you might be able to reproduce it on the rollers. Or is it just a feeling under the foot? | |
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rsimps
V4 Mad
United Kingdom
955 Posts | Posted - 03 Aug 2010 : 12:30:20
| | What you want is a spare upright with shaft and disc, so you can change the shaft on each side. You shouldnt have problems with the pads. The other thing I have just thought of is a wheel bearing. They can give a vibration when they are on their way out, but you would expect this to happen all the time. You could try getting some new grease into them as it tends to dry out and then the brg goes. | |
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| Topic | |
Brakes
