Get someone who is strong to yank the steering left to right a number of times while you watch a particular area. Easier for them if the engine is running but more 'iffy' for you but hey, they should work for a beer right?
regards
Dave
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Odd shimmy at 40mph when on the brakes... help.
- Thread starter BRE Fabrications LTD
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Get someone who is strong to yank the steering left to right a number of times while you watch a particular area. Easier for them if the engine is running but more 'iffy' for you but hey, they should work for a beer right?
regards
Dave
BRE Fabrications LTD
Well-Known Member
Ok, so spent the day down at the workshop.
I checked the thickness and runout on both from discs. Drivers side runout 0.02mm, PS was 0.03mm. The disc thickness on DS varied between 31.80mm to 31.89mm. PS side varied between 31.82mm to 31.86mm.
I then checked the pistons, there are definitely signs of a sticky piston on the DS, you can see in these photos how the inner pad has worn more on one side than the other.
I worked all of the pistons in and out by way of using vice grip to clamp three pistons down and the get on the brake pedal to make the piston move. I did this with all four, they moved in and out ok. When you pump the brake pedal with no pads in the callipers is it critical for all of the pistons to move out by the same amount?
Next I rotated they tyres, checked all of the mounts (Radius Arms, Panhard, Tie Rod and Drag link) and then also checked the swivel housing bolts top and bottom, they were all tight.
I double checked the Tie Rod and drag link with a piece of angle I had, they are definitely not bent. I also had a look at the sector shaft, it doesn't look bent, but without taking the steering arm off I guess I can't bee 100%.
Next I put a crowbar in where ever I could get leverage to check for movement. The tie rods seem good and didn't show any signs of play or movement. Pan hard is good. Radius Arms are good too.
I didn't have time to get the truck to an alignment shop so I'll get it checked next weekend.
So is it possible the sticking piston could be causing the shimmy?
I managed to take a quick video clip of the shimmy.
I checked the thickness and runout on both from discs. Drivers side runout 0.02mm, PS was 0.03mm. The disc thickness on DS varied between 31.80mm to 31.89mm. PS side varied between 31.82mm to 31.86mm.
I then checked the pistons, there are definitely signs of a sticky piston on the DS, you can see in these photos how the inner pad has worn more on one side than the other.
I worked all of the pistons in and out by way of using vice grip to clamp three pistons down and the get on the brake pedal to make the piston move. I did this with all four, they moved in and out ok. When you pump the brake pedal with no pads in the callipers is it critical for all of the pistons to move out by the same amount?
Next I rotated they tyres, checked all of the mounts (Radius Arms, Panhard, Tie Rod and Drag link) and then also checked the swivel housing bolts top and bottom, they were all tight.
I double checked the Tie Rod and drag link with a piece of angle I had, they are definitely not bent. I also had a look at the sector shaft, it doesn't look bent, but without taking the steering arm off I guess I can't bee 100%.
Next I put a crowbar in where ever I could get leverage to check for movement. The tie rods seem good and didn't show any signs of play or movement. Pan hard is good. Radius Arms are good too.
I didn't have time to get the truck to an alignment shop so I'll get it checked next weekend.
So is it possible the sticking piston could be causing the shimmy?
I managed to take a quick video clip of the shimmy.
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BRE Fabrications LTD
Well-Known Member
I previously had not enough castor correction. . The drop boxes have taken the violent part away from it thankfully but I have grown to believe that there definitely something that WILL get it to mildly wobble. Big tyres do have massive leverage on the steering. But the camber in the road and slowing down has direct influence on the intensity of the wobble which is only on the passenger side.
The other day I clicked on your thread of your 12"fox slinky setup Ryan with spacers in the front too. You seam to have a tall lift and only correcting on the axle.. From my experience but dont know the exact quantity of lift? Have you sufficient castor correction?
In my experience of 80 series front axles. ..... I dont like them (sorry to offend ) 8" differential. .2 bolts in the top knuckle. .. both steering rods on the lower 4 bolts (passenger side )wtf. If I keep wheeling and running my 81 I aim to fit the far superior 60 series front axle 9.5" diff and a much stronger steering/knuckle setup.
Thats all!
Hey Iwan, I am currently running 4' of castor correction. I don't think it's related to the castor. I didn't have this issue for quite a while before it started with my current setup.
I expect you will have noticed if what you've done has helped by now but I've been having the self same issue on the Space Star. I changed both the fronts from winter to ordinary tyres and rims yesterday and the problem is gone. The shimmy was quite pronounced under braking but now it's gone. I'm guessing we've buckled a wheel on a pothole but who knows until I get them on the machine.
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Looking at your pad wear the sticky piston has left you with a 2 pot caliper on the drivers side working against a 4 pot caliper on the passenger side so front brakes want to turn the car but the rear brakes are working well so prevent it . That's my guess anyway .
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The sticking piston/s will heat the disc when you are driving around, the result is the disc is becoming warped when hot. I would put a new set of pads in, something like Brembo's, gently bed them in and see how you go. TBH, once a discs give 'pedal pulsing' then they need skimming.
regards
Dave
EDIT: Is it my imagination or are the slots in the discs, possibly rotating in the wrong direction for EBC products? Noting what looks like 'EBC Green' on the pads, and the picture below is from EBC, I know it is important to get the air flow slots direction INSIDE the disc right and if yours is all new last year and the discs are EBC? Only a thought?
regards
Dave
EDIT: Is it my imagination or are the slots in the discs, possibly rotating in the wrong direction for EBC products? Noting what looks like 'EBC Green' on the pads, and the picture below is from EBC, I know it is important to get the air flow slots direction INSIDE the disc right and if yours is all new last year and the discs are EBC? Only a thought?
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BRE Fabrications LTD
Well-Known Member
The discs are from Nitrac not EBC. But what you are saying makes sense... I could switch them rounds, I have been meaning to fit the RCV axles I have so
Could swap them around then.
What are your guys thoughts on Milner Callipers? I am toto gong with rebuilding the callipers again but looking at the costs of pistons and seals it probably won't be much more than what Miners charge for a complete calipers...
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I would have thought if they were sticking, then the force to push them out is greater than the release of pressure to draw them back? Either way, there not right for sure.
regards
Dave
Yes easy to swap and the bearings can stay in so other than a wheel bearing reset no big deal but, before you do it, check with Nitrac, as I said it is the internal vanes that cool the disc so they may be right? Anyone else know anything about Nitrac and their preferred disc rotation?
regards
Dave
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Even with the hydraulics working perfectly and all the discs machined perfectly etc etc it is still possible to get this shimmy due to non consistent material in the disc. This can cause vibration because the friction gets higher/lower with each wheel revolution even though there is steady pressure on the brake pedal. As regards thickness variation you would feel a variation of thickness in the discs with pedal going up/down. I cut my rear discs and they were out each by 0.001 inch. When they were both in phase I could feel the pedal moving up/down. Other times they would cancel each other. After about 2000 miles their faces were parallel again.
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In what position are front pistons when parked up and left to rust ? Not that i'm disagreeing at all i have the least mechanical experience on this thread i'm just throwing out a theory to a mystery we are unlikely to ever find the answer too if parts are changed until its fixed . I can picture how equal traction at 3 wheels while braking with the remaining wheel offering lower resistance could cause the shudder . The same theory might reveal itself by the rear passenger pads showing more wear because they have been working harder than the drivers side rear pads but i guess it would take a lot of miles to show that kind of wear .
How about these guys Ryan http://www.biggred.co.uk/ they seem well respected when i searched the web for forum reviews .
Rust can attack from both sides of the piston. Outside from damaged outer covers, so the piston rusts on the outside. The brake pressure pushes the pistons out, when the pressure is released, the rough rusty outside does not allow the piston to return into the calliper fully, this heats up just one side of the disc, and of course shows the odd uneven wear on the pads, the disc warps or has high spots, both give rise to pedal pulsing, this is the normal problem that occurs, and is seen quite a lot in the trade.
On the other side of the piston in the chamber sits the brake fluid, brake fluid is hygroscopic, it absorbs moisture, this collects in the lowest part of the system, wheel cylinders and callipers etc. If this is not changed then the piston starts to corrode from the inside, given Ryan resealed the pistons last year the fluid would have been changed, I was guessing the corrosion would have been on the outside, the chrome on the piston starting to lift?
If there is corrosion on the inside then the fluid must have been contaminated, or the piston condition must have been suspect at the time of install? I knew a couple of my pistons were suspect, so I replaced all four callipers for new units, with 21 years of work I deemed them toast.
regards
Dave
On the other side of the piston in the chamber sits the brake fluid, brake fluid is hygroscopic, it absorbs moisture, this collects in the lowest part of the system, wheel cylinders and callipers etc. If this is not changed then the piston starts to corrode from the inside, given Ryan resealed the pistons last year the fluid would have been changed, I was guessing the corrosion would have been on the outside, the chrome on the piston starting to lift?
If there is corrosion on the inside then the fluid must have been contaminated, or the piston condition must have been suspect at the time of install? I knew a couple of my pistons were suspect, so I replaced all four callipers for new units, with 21 years of work I deemed them toast.
regards
Dave
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BRE Fabrications LTD
Well-Known Member
Any comments or experience regarding the Milner calipers? I could rebuild them again but with new Pistons this time, but given it'll end up costing close to what the Milner units will cost is it worth the hassle?
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I've had some Milner calipers and they were fine Ryan. What's to say. Sealed chamber, fluid in, pushes piston out car stops. I know someone on here bought a pair and when they turned up they were a set of old used ones in the box. Have to think that was a bit of a freak and probably some that had been returned and accidentally put back into stock. The ones I had were really indistinguishable from OEM. What about going with Roughtrax instead.
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Why fit drilled and grooved pads on an 80?
BRE Fabrications LTD
Well-Known Member
Why not...? The original discs were in need of replacing. For similar cost to OEM I could get these.
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Frank, ever tried stopping an 80 running 37's? I can't do the math, but I have tried pressing the pedal. Just the energy stored in the spinning wheels alone makes stopping interesting at times, never mind the additional extra leverage effect of the increased diameter. My old 80 used to stop OK but it burned pads in 1000 miles. Anything you can do to improve the system when you go large is worth doing. I was running narrow 37's but Ryan's MTs look like barrage balloons
Plus they look really cool, man.
Plus they look really cool, man.
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That's the reason I had not thought of Chris, for cooling. Don't they clog with dirt and wear the pads though if you get then really muddy ?
Frank they do actually get mud in them yes. It tends to drop out after a while but it's not helpful to be honest, no. Oddly they don't seem to wear the pads faster. You'd think they were like a cheese grater but there isn't a proud edge to them as it were to actually cut. It says on the blurb that I got with them that the holes and vents allow for faster escaping of gas. I really wasn't quite sure what gas this was and how it would get trapped in there. Hey ho.
