Hi all

 

Long time lurker, first time poster.

 

I have a 58 plate Mk2, 1.2 HTP. 96500 on the clock.

 

Recently I did some work on the car, replaced front pads (me), discs (me), and brake fluid change (garage).

 

I've noticed what I think is a new sound, a sort of very low level rumbling, it's very like the sound you get approaching a dual carriageway roundabout, going over the little bumps, but much quieter. It's barely noticeable, but definitely there.

I know the obvious culprit here is disc runout, which, I confess, I wasn't able to check on fitting as I didn't have the tool, but the weird thing is that it really sounds like it's coming from the back, not the front, and I haven't touched the drum brakes.

In terms of handling/performance I can't really see any change from before. The brakes are much better, obviously, and don't behave oddly. It doesn't pull one way or the other under heavy braking, fuel economy is unchanged (42-47mpg).

I took a recording of the sound (attached). You have to listen pretty hard to pick it up. It's unnoticeable at low speeds, peaks at about 35mph, and then fades out as I climb over 60mph. At 70 I can't detect it at all.

 

Should I be worried? Was I a fool to change the discs myself?

 

Any and all help appreciated.

Jon.

The Sound.mp3

Having changed the discs and pads it does sound like the caliper slide pins were not taken out and checked to see if they were free to slide in and out of the carrier, this in turn slightly holds the outer pad against the disc causing this sort of noise, the only other issue might be a wheel bearing which you can check by jacking up car let the wheel run free then grab the wheel and tyre at the top and bottom and try to rock it in and out any movement might suggest the bearing starting to fail thus the noise while driving, but check the slide pins first i have come across 2 this before BUT  PLEASE do not use cooper slip it swells the rubbers and will wreck them use silicone grease 

I really really wish I'd gotten the message about copperslip before I slathered it all over the back of the pads, which I did. I'll take the pins out and check them. How do I check for their free movement? They just screw in and out, I thought if they screw in properly then they must be in the right place, is that not true?

Copaslip is fine on the backs of the pads, but not on the pins.

Righto, thanks. Would a bit of good old fashioned Bearing Grease work on the pins?

10 hours ago, TheTallOne said:

Righto, thanks. Would a bit of good old fashioned Bearing Grease work on the pins?

 

The importance of greasing the pins is wildly exaggerated, they're chrome plated and protected by rubber bellows to prevent them sticking and they're not even a tight fit because they don't really carry any load, they're purely to keep the floating caliper aligned. The pads and the carrier take all the strain of braking.

Oh God.

 

Found the problem. The threads that the pins screw into are shredded. I must've overtightened them. God damnit.

 

Basically the pins have a bit of play as they sit in their threads.

 

What now? Tap a new thread? Lather the screws in epoxy and get them in, what?

 

I feel like an idiot.

28 minutes ago, TheTallOne said:

Oh God.

 

Found the problem. The threads that the pins screw into are shredded. I must've overtightened them. God damnit.

 

Basically the pins have a bit of play as they sit in their threads.

 

What now? Tap a new thread? Lather the screws in epoxy and get them in, what?

 

I feel like an idiot.

 

You need to helicoil the threads to repair them, they're M9 x 1.25 which is an unusual size so you need to buy a complete kit.

 

Understand that that you lack mechanical sympathy and follow the instructions carefully, don't rush and don't bodge!

 

You're not an idiot but you clearly lack experience.

There are dedicated kits on Ebay with special top hat threaded inserts, someone on the forum put up a link to one at a very good price which does both VAG and Vauxhall, so cheap that I bought one just in case although I havn't seen it yet as its in the UK.

 

Similar to this:

 

https://www.ebay.co.uk/itm/BlueSpot-16pc-Brake-Thread-Repair-Caliper-Kit-M9-X-1-25-Ford-Vauxhall-VAG-/233673109432?hash=item366800afb8

Thanks for the replies everyone, very helpful.

 

"Don't rush and don't bodge" - Rules to live by.

 

Picked up the kit from MachineMart. All done, all pins greased and tightened to the required 28Nm according to Haynes. No play in the new threads.

 

The rumble continues though. I've had all four wheels jacked up and given them a good wiggle, can't feel any play. It still sounds like it might be coming from the near side rear. That wheel turns freely by hand, there's an ever so slight scraping sound each revolution under hand turning. Is that normal? Could that be my culprit?

 

Excellent work, that scraping could well be the culprit, worth investigating further.