brakes dragging?

[Gary]

yyyyyyyyyeo,

 

my 620's brakes are acting a touch strange

 

ive got 720 discs and calipers up front and standard drums on the rear

 

i think it was fine before, but now for some reason its making a light scraping noise once every turn of the wheels, as though the discs are dragging slightly for about 1/4 of the rotor each rotation. it brakes fine, ive done a couple solid stops for shits

 

ive adjusted the pedal position thing to as loose as possible - still doing it

got it back to reasonable - still doing it

ive adjusted the rear drums so they dont actually do anything - still doin it

i know front wheel bearings arent the best, ill replace them soon, sounds like the rears are making the noise also though and the bearings feel fine

 

not sure what its problem is, any ideas?

[mklotz70]

I'd jack it up and check that the bearings are not loose. Does it still make the noise when it's off the ground? How much pad do you have left? Pull the caliper off while it's off the ground and look for indications of rubbing.

 

 

I didn't quite understand the 720 discs and calipers on a 620. Are they early 720?.....which were the same as the 620 anyway.

[MikeRL411]

Warped disc?

[datzenmike]

Getting them super hot from a hard braking effort can cause transfer of brake material from the pad to the rotor. This easily happens if you stop with the rotors hot. A 'footprint' of the pad transfers to the rotor and when turning, the transferred material will grip the pad as it passes and seems like a tight spot or a warp.

 

Usually normal heat from normal use 'cures' the pads but often they are driven such that they don't heat up much and the pads remain 'green'. A sudden rare panic stop and super heating of the rotor and there is transfer. Many mechanics mistake this for an out of round rotor and have it turned which does remove the problem but for the wrong reason. Another hard stop and it returns.

 

Pads can be conditioned by driving on the highway and slowing repeatedly to heat the rotors and pads, but continue driving to cool them before stopping.

 

For now just sand them down to remove the problem

[Gary]

thanks chaps :D

 

i got em from an aus 720 dual cab, i dont think we ever got discs on our 620's (in aus) so they might be the same as your stock discs over there i dunno

 

when i swapped em over i got new discs and pads for the front, ill pull wheels off anywho for a peek. it seems to only do it when the wheel is loaded, ive jacked all wheels in the air and i cant get it to make the noise, i probably cant spin the wheel enough. ill do bearings soon and see how it goes

 

nice explanation mike, i didnt know that :) it sorta sounds like its coming from the rear but its tricky to tell with noise and such a small cab. ive done a couple hard brake tests to see if they'll be ok for my inspection, so what you're saying sounds like it could be the trick for the rears. would it be cos of old shoes? they had a bit of meat left on em but so far as i could tell they certainly werent fresh

[Pedro]

Also make sure the rotor isn't touching the control arm at any angle.

[Gary]

i got em apart today for a peek, seems the hub (more specifically, the rear bit of the lug bolts) is fouling one of the springs for the shoes

 

if i grab the hub (ie with wheel/drum off) i can pull it outward a little and move it a tiny bit from side to side. bad wheel bearings? it feels tight but kinda floating, i dunno if live axle is just like that or if its anything like independent wheel bearings where any axial play is baaaad

 

what do?

[datzenmike]

Bearing pre load may be wrong. (loose) I believe you tighten to specific amount then loosen slightly and install cotter pin.

[Gary]

i dunno :(

 

ive found the axle's end play is pretty big, 2mm or so either side (should be 0.15, according to manual) ive swapped out a diff center for a slightly better ratio, could that have anything to do with it? im not sure it would but i still havent got my head around it. needs more apart so i can see how it works

[mklotz70]

I've seen the truck diff with a block in the center of it that the axles butt up against.....did the new diff?

[Gary]

you're right, the old one did and i dont think the new one did

 

nissan calls it a thrust block, trying to swap it looks like a job for the pros to keep tolerances good :(

 

i tested bearings, with the hub off its as simple as checking the fronts. they're fine, no leaks and the like. the squeak/annoying noise was cos the hub has pulled the outer drum in close enough for an inside edge to foul a small protrusion on the shoe adjusting thing, now its also fouling one of the tension springs for the brake shoes

 

i dont really want to put the old one back in but looks like its the go

[mklotz70]

I just dug this up using google. I did this a couple of years ago. It will show you how to get the spider gears in and out of your diff. Once you get them out, you may find that the block does not fit the new diff....I don't remember. I know DatOLantern's owner had to machine a new block to solve the problem you're having.

 

http://community.ratsun.net/topic/10748-h190-spider-gear-swap/

 

 

....not sure why photobucket has changed the links over the years.....I had to go in and redo the links to the vids to get them to work....good thing ratsun lets me edit old posts :)

[Gary]

thanks for that mate :) those videos are great :thumbup:

 

i think thats decided it for me, i'll stick with the stock center until ive got time to mess about with things further. id normally have no problem making things work but as it stands im running out of time to get this car on the road proper so for now i gotta go the quick/safe option

 

later down the track i was looking at rear disc brakes anyway, i think easiest way is a whole axle swap which ive got lying around somewhere. obviously that'd also solve my diff center drama :)

 

friggin cars hey

[mklotz70]

You're more than welcome :)