Occasionally sticky front caliper...rebuild or a new pair?

[AllHailKingVolvo]

Hi all,
I have an issue with the right front caliper on my 740 saloon, it has a tendency to bind a little when the car hasn’t been used for a couple of days. I’m concerned that in the current hot spell of weather, if left unchecked this could result in boiled fluid, damaged seals and god knows what else.

I’ve rebuilt quite a few racing calipers on karts etc so have a good grasp of how they work. I believe these calipers are single piston units with slide pins, am I right?

Is it worth rebuilding these with a kit, or should I just chuck a couple of new calipers at it? I’d like to save money if poss as I have a new clutch and cambelt going in this week, but by the same token i want to do it right.

Any tips would be much appreciated!

Phil

[TonyS9]

I don;t know what brake you have specifically, Its probably just a bit dirty and/or corroded. It could be worn badly but I've never seen one that didn't respond to a clean up.

Having said that its a bit messy and intensive to get it right. You could be into a whole strut overhaul. I'd definately redo the carriers at the same time. In my old age I would probably tend to replace the caliper and carriers with recon units. (940 carriers are £25 exchange from Volvo).

The 940 single piston one tend to sieze at the sliding pins, especially with low milage. I overhauled mine a few years back (all new sliding bits) and the lower pins have gone again. Still works but brake tend to pull a bit.

[Laird Scooby]

What i would do to start with Phil is to remove the slides, give them a good wire brushing and a generous smear of copper based grease*.

Also i'd use a block of wood to prevent the piston falling out, get it as far out as possible then clean round the seals and give a light squirt of WD40, push the piston back in with a G-clamp (if you have ABS, crack open the bleed nipple, attach a one-way bleed valve and let the fluid out that way, rather than forcing it back up the line) and repeat this a couple of times to make sure the piston isn't sticking. Finally bleed that part of the system to be on the safe side.

Also use a file on the edges of the pads to remove any burrs, high spots etc that may be causing the pads to stick and a light smear of copper grease on the backs and metal edges of the pads.

Finally before refitting the pads and reassembling everything, put a file through the caliper carrier so you can wedge it there, turn the hub using a screwdriver or spanner between the wheel studs to take off the lip on the edge of the disc - don't forget the other side of the disc!

Once reassembled and bled, give it a test run to see if the problem has gone, leave it a few days and another test run to check you've cured it.

If not then maybe you'll need to look deeper but i think that will sort you out.

* i mentioned copper based grease, there's now a school of thought you should only use red rubber grease/silicone grease on the slides as they have rubber covers. I've not had a problem using copper grease, i gave the above treatment to my Rover when i bought it 10 years ago and haven't needed to do anything since. That was about 22k miles ago. I also ddi the same to my current 760 (and all other cars i've owned) and not had a problem with copper grease or any comebacks on caliper problems.

[Jebus]

Agree with the give it all a good clean.


On the copper grease vs silicon, its in the Green Books for 940's from Volvo to use silicone grease so its not a new recommendation, many many many people around the world use copper grease without horrific issues, but silicone grease is easy and cheap to get hold of, does a better job at keeping things moving so its a good choice, but whatever it is you do, give them a good clean inside the carriers and use some sort of lubrication, the amount of broken sliders snapped off in the carrier I see is a daft, a quick clean and some sort of lubricant will save a lot of pain

[Laird Scooby]

Originally Posted by Jebus

Agree with the give it all a good clean.


On the copper grease vs silicon, its in the Green Books for 940's from Volvo to use silicone grease so its not a new recommendation

Out of curiosity, what do the green Books say for the 7xx series?

[Prufrock]

Originally Posted by Laird Scooby

Out of curiosity, what do the green Books say for the 7xx series?

Coincidentally I've been looking at my Green Books this morning, the Service Manual (Section 1/17) doesn't mention cooper or silicon grease at all - assuming that was the question.

J.

[Laird Scooby]

Originally Posted by Prufrock

Coincidentally I've been looking at my Green Books this morning, the Service Manual (Section 1/17) doesn't mention cooper or silicon grease at all - assuming that was the question.

J.

Thanks Jon - it was the question and you've answered it by default - if nothing else is specified then it would be fair to assume that the traditional/historic anti-seize compound would be used, in this case copper grease.

I've noticed it takes a long time (20+ years at times) for information like this to filter out to the likes of us, even if dealers are made aware at the time.

[Prufrock]

I have always used copper grease.

J.

[Laird Scooby]

Originally Posted by Prufrock

I have always used copper grease.

J.

As have the majority of us. Trouble is there are a lot of new products on the market now that weren't around when these cars were made and aren't suitable for them. People think because it's a new product it's automatically better and/or backwards-compatible with the older one, sometimes manufacturers even confirm this.

Sadly it isn't always correct and Honda faced a Class Action lawsuit in the USA over ATF for example when they introduced a new ATF and confirmed it was backwards-compatible with the older one that was discontinued.

Several fried torque convertors, irate owners and a major lawsuit later they withdrew the confirmation it was backwards-compatible.

For that reason and many similar, i'm always wary of new products being allegedly suitable for any car, not just mine!

[Prufrock]

I would always use a contemporary product if available, obviously there are exceptions. Mind you, you might have bought that tub of cooper grease 20 years ago and still have half left today !

J.