Is there a right way to put in AJP calliper seals?

I just replaced the seals and pistons on my AJP 4 pot front calliper and the breaks is worse than ever. I did think that perhaps the seals are in the "wrong way" so not returning the pistons correctly, but is that possible? How do I identify if they're the wrong way around?

Cheers

This probably won't help, but I've never had any luck rebuilding those 4 pot calipers!

I've failed twice in the past and bought new, both times I put it down to the possibility of worn bores, the alloy is fairly soft (and light)

 

I never noticed that the seals are chamfered on the inner surface, but it could be possible, so it might be worth removing them or inspecting the old ones very carefully.

 

Normally the two main reasons they stick are:

Over adjusted master cylinder actuator, so the piston in the MC can't return fully, so it pumps and pumps but can't let the fluid return, so it's worth backing off the adjuster at the lever first.

Or

The pads have worn down too much and the pistons come out too far.

This leads the pistons to twist or kink in the bores.

As they are so small they don't have to come out too far to loose support from the bores they sit in to stay square and can lead to jamming.

 

It's something I've noticed is particular to the 4 pots, it can appear that there is still some life in the pads and not fully worn out, but worn just enough for this to happen.

 

Thanks Goudrons.

The brakes weren't great so put in new pads (less than a couple of trials ago) so I think the pads are ok. I checked the fluid at the same time and it was almost gone in the master cylinder, so I put in more fluid. The brake went soft during the trial and the fluid was quite low again. This was what prompted me to replace all the seals. It holds fluid now and I've back and forward flushed the system to make sure there is no air.

The brake isn't great, coming in to the bar more than I'd like. There is a little slack (about 1/2 cm) at the brake leaver before it moves the master cylinder piston. Putting in the calliper seals was a bit tricky, so wondered if there is a trick to putting them in.

Barfy, I think there's only a difference in the width of the two seals in each piston, so you could put two thick ones in one piston and two thin ones in another, but I think you'd realise that by the time you had tried to fit all 4 Pistons. Is this on the rtl or 4rt? If you have the old style brake hose, change it for a new braided stainless one.

Hi JJ. It is for my Montesa. I have a Nissin brake master cylinder I've been meaning to put on for a while so I think it could mean a visit to the Venhill website. Perhaps I should slip a hydraulic clutch slave cylinder for the RTL into the shopping basket while I'm there???

Thanks for the bleeding tips Rich. I'll give it a go on Saturday when I can take my time over the job.

Hi. I think there's a good chance you're seal groves are corroded, so when you put new seal's in it will make it worse.

 

You'll need to strip out the pistons and seals and shape a little scraping tool from a used hacksaw blade and very carefully clean the bottom and sides of the sealing grooves of all corrosion.

Once you start picking away it will be obvious and you will be surprised how much is in there, but take your time and be careful as you don't want to remove any aluminium or damage the groove by putting a gouge on it.

 

Lots of cleaner and air line blow out and then put seals back in. I sometimes install with the thinnest smear of silicone grease to the back of the seals.

 

I can get a picture of the tool I use, if that would help

 

PB

Redhubuk - yes a picture of the tool woul be great. Thank you.

Here's an image of the tool I furnished. It's just a piece of old hacksaw blade with a notch ground out to form a tooth.

 

Cheers

 

I would advise against putting grease of any sort on the back of the seals / grooves during assembly. It will trap in the bottom of the groove and cause the seal to have a reduced inside diameter. This can cause the seal to be damaged when piston is inserter of cause seal to bind on piston in use or when attempting to bleed.

I would advise against putting grease of any sort on the back of the seals / grooves during assembly. It will trap in the bottom of the groove and cause the seal to have a reduced inside diameter. This can cause the seal to be damaged when piston is inserter of cause seal to bind on piston in use or when attempting to bleed.

 

To a certain extent that is correct, you don't want to put a toothpaste squidge amount in there, as I said thinnest of smear's and wipe off excess. it's only their to help the seals settle into a nice clean corrosion free groove. I wouldn't suggest using anything but pure silicon grease either as other greases may affect the seal material.

 

Regards