Q45 rebuilding brake calipers

Rebuilding Q45 Brake Calipers

By:”Ozzie”.

I had to rebuild one of my brake calipers, and thought it would make for a good article, so here it is!

The car in question here is a 1990 Infiniti Q45 (G50), but this could apply to any car, with some subtle differences. (Number of pistons per caliper, size of seals, location of some bolts etc)

Things you will need:-A car jack (preferably a hydraulic jack)
A wheel brace
10mm, 12 mm, and 17mm ring spanners
A small, long,flat head screwdriver
A G-clamp
A bench vice
Clean rags
An air compressor with an air gun attachment
A can of WD40, RP7 or other water dispersant spray
Brake fluid
A container to catch dripping brake fluid
Brake caliper rebuild kit(s) (A packet of seals for each caliper)
And a bit of patience!!

First things first…. You have to take the wheel off to get to the caliper.

As a safety precaution, you should always use jackstands, and put the wheel you remove, under the body of the car, better to crush your wheel than your legs/hands.

When working on the front (as in this case), turn the steering wheel so the disc points out from the body, as this allows better access to the bolts for removal.

First, loosen both caliper bolts with a 17mm ring spanner, without completely removing either of them.

Then, using a 12mm ring spanner, take out the brake line bolt and hang the brake line into your old container.

It will continue to drip until the reservoir empties… but don’t worry about that, we fix it later!

Now you can fully remove the caliper bolts and slide the caliper off of the disc.

Then, with the caliper held over the old container, push the piston(s) into the body of the caliper to push the fluid out.

Then, we go to the bench vice.Clamp the caliper like so….

(I used an old towel/rag to protect the caliper body, as I didn’t have any wooden blocks lying around)

Now, we apply the G-clamp to one of the pistons like so…

Around to the back now, and the the hole where the brake line bolts into is where we apply the compressed air…

The unclamped piston will be pushed out by the compressed air. Don’t apply constant pressure, do it in short bursts… otherwise your piston may go flying across the shed!!! (And no, I didn’t figure this out by mistake!)

Remove the G-clamp and take the caliper out of the vice.

Put the piston to one side for now…. The rubber boot is easy to remove, just pull it out gently, and it should come free.

Using the screwdriver, pry out the o-ring seal inside the bore of the caliper like so…

Now we clean out the caliper bore, using a clean rag and the WD40.
Get it as clean as you can, especially in the grooves where the o-ring and rubber boot go (WD40 is great for cleaning, and absorbs brake fluids worst enemy, H2O).

Use the air gun on the compressor to blow out any remaining WD40.

Get your new seals ready now, and fit the new o-ring into the groove, making sure it is completely home, and not sticking out anywhere.

Make sure you have cleaned the piston with the WD40 and the clean rag, and push it back into the caliper by hand, ensuring that it is straight. If it is a little difficult to push in by hand, you can use the G-clamp, but be sure the piston is aligned correctly with the bore in the caliper.

Now to fit the rubber boot……

Start at the back of the caliper as shown, and make sure the ridge of the boot is sitting in it’s groove (this is where the patience comes in, because it really likes to pop out!)

Slide your fingers over the top of the boot to push the seal in.
When you get to the top, you are likely to have the lip of the boot sitting out…

Using pressure from your fingers, assist the boot into the groove using the screwdriver, but be careful. The last thing you want to do is put a hole in your new seal!

Now it’s done! Make sure the seal looks uniform and even, with no high or low spots, as this indicates that the boot seal is not in the groove somewhere around the place.

Refit the caliper back onto the car, in reverse from the removal. (Caliper bolts first, then the brake line)

Top up the brake fluid reservoir (I use DOT4 fluid for the higher temp rating)

Leave the lid off of the reservoir, and go an pump the brake pedal a few times to fill the caliper….. recheck the fluid level, and top up if needed.

Now to bleed the brakes.It’s much easier with 2 people.I don’t use the plastic hose and jar method, I simply open the bleed nipple (10mm spanner)…….

…and get the other person to push down the pedal and hold it on the floor.
I then tighten the nipple, and get them to release the brake pedal all the way, then open the nipple, push to the floor and hold, tighten, release pedal…and so on, until I don’t have air coming out nipple when the pedal is pressed.

I have always used this method, and I have had no problems with air in the lines, EVER.

Re-check the brake fluid reservoir…. top up and replace the lid

Check for any leaks from the caliper or brake line.

Then re-fit the wheel and go for a test drive.

You have now rebuilt your brake caliper by yourself!

PS: A big thanks goes out to NSR_A32 (Kenny) for finding a rebuild kit and mailing it out to me, elwesso (Wes) for the air compressor tip, and GQJay (Jay) for sending me out the caliper bolts when I found out one of mine seized.