Sever pull to the left when braking

[tsviatko]

I have not measured the disc thickness actually. I have not swapped discs either. So I guess I'll try doing that before I start repeating all the tests.

 

[Shayne]

You can pretty much see a worn disc at a glance but a warped disc might only be one mm out and you can't even tell on a motorbike when you can see it from directly above all the time . It might save you a bit of effort if you remove the side you think might be damaged first and lay it on a mirror , if it doesn't sit perfectly flush you have your answer .

 

[Chris]

You can usually tell a warped disc through the pedal, It will be related to speed and basically pump in and out as the pistons get pushed in and out as the disc oscillates. I don't mean a disc that is thicker in places, but warped like the brim of a hat. From memory the 90 doesn't have 4 pot calipers on the front. This is a common cause of disc warping as opposing pistons that have failed allow the others to 'bend' the disc. Discs can warp for other reasons of course. But you really would be able to feel that and not sure it would cause severe swerving. Older discs tend to get a ring of old crusty stuff around them making Shayne's test difficult to evaluate fully. If that is the case then a dial gauge and magnetic base would be another way with the disc still on the hub. The only other thing I can think of is mismatched discs. No batch of metal is the same - it's within tight tolerances, but never the same. If you have one genuine and one Milner, say, the actual braking charecteristcs can be widely different. I have had matched pairs of discs that are poor in terms of stopping power and some that are great. If it had a replacement disc on at some point, it could be that it's better or worse than its companion leading to the pulling effect.

C

 

[silvercruiser]

I can confirm that the colorado does have 4 pot calipers on the front, well my lwb auto does.

as all the others have said re check the pistons and see if you have any sticky/siezed ones.

 

[Chris]

Ahh, been a long time Joe. Does it really? Thanks for the correction.

OK well then that case, I would suggest that whilst even braking force might be experienced, if the inner pots were lazy on one side and the outer pots lazy on the other side, this could lead to a sort of braking steer. Overall force may be the same when measured but in actual practice could be very different.

Chris

 

[tsviatko]

It definitely looks like the brakes are part of the problem or hopefully all of the problem. I examined closely the right caliper and I found out uneven wear of the pads there. The bottom of the pad is 2mm thicker than the top. So it looks like one of the bottom pistons is stuck. That's definitely something I'd like to fix

 

[tsviatko]

Alright, it turned out to be the brakes. There were no seized pistons but one piston on the right caliper was kinda sluggish. It'd start moving after the other three hit the brake pad. That would not show on the brake force measurement since the test runs long enough for the sluggish piston to hit the pad too. However, the longer time it takes for all the pistons on the right to kick in seems to be enough to make the truck swerve to the left while braking.

So, a good test is removing the brake pads and putting something 3-4mm thinner in their place. Then have somebody slam on the brakes. If some of the pistons fail to move before the others hit the pad a reconditioning of the brake caliper would be needed.

 

[grantw]

Great news that you finally solved it