wheel bearing hub combo flex

[dsrace]

I run wheel bearing hub combo's on my v-6 rail which is 1600 lbs to 1800 lbs wet. the bearings came off the front end of a 97 cherokee 5 on 4.5 bolt pattern thru what ever other years and I also believe they fit the v8 grand cherokee models but doesn't matter I can say this they are not 2 tappered timken even though the box said timken on it they are 2 roller bearings as far as i could tell from a website i finally found with some info on them. no I have not taken one apart but will soon. ok the reason I even ask is because when i jump my rail upon landing there is enough flex in my wheel bearing the my rotors lean over just enough that my brake pedal gets just a touch soft on the first push. but only when a hard load is put to them like jumping!  any thoughts on this guys?

[dsrace]

 ok I took a few pics to show you guys what I am talking about.   now given that when mckenzies screwed up my order at the last minute and sent me 2 piece rims that were bolted instead of welded I wasn't happy but didn't have the time to ship back and wait the supposed 4 weeks to get new ones. I then later learned that the I think cws rims were actually formerly michelle rims so that didn't make me happy and I do believe there is some actual flex in the rim itself as well. I do know that there isn't that much clearance between the nuts and my caliper with the wheel spacer on, about 1/16" and as you can see from the pic those nuts have rub my calipers at times through out a year. now when I installed these wheel bearings the book I had said 80-100ft lbs tq so that is what I did and my brakes were horrible so I switched to a 7/8" bore master cylinder and re tq'd the axle nut to 250ft lb tq with a tq wrench. that took 95-98% of the problem out but I still think there is a little flex in the wheel bearing on my heavy v6 rail. the rotor in the pic is 12.19" od and the caliper is 4 piston 1.75 pistons. now enemy is running the same wheel bearing and a 3/4" master cylinder with the same rotor but 1.38" pistons and he felt the same problems at first and started tq ing down more and got rid of most but not all I think. fast is running front brakes and imo only! I believe this may help mask this if this is what is really going on!  also my rear susp design does not have a camber curve so I wouldn't be adding load from that. I have a used bearing I picked up for mock up, I will have to cut it up later tonight and see what is really inside and post some pics.

[dsrace]

I did cut one up and this one came right off a stock axle off of a cherokee I bought from the junk yard before deciding what way to go along time ago. the housing and bearings say timken on them and there are bearing #'s too. now the jeep is a double tapered bearing so that sight I was on that sold tools to rebuild them was showing the wrong image for this wheel bearing but apperantly some of the others are rollers!

[dsrace]

now short of bearing flex there could be some flex from the carrier itself but I sure wouldn't think so. the carrier is 1086 hot 3/8" thick and the wheel bearing bolt in the middle. now after talking to enemy his brake fade is greater when hard cornering or landings and he is lighter and running smaller tires. I do not believe rim flex has anything to do with the rotor pushing the caliper pistons back in and enemy's calipers are willwood like mine except his are 1.38" pistons and he has a 3/4" bore master cylinder. my carriers are sort of boxed on the top only.

fast have you experienced some of this?

[dsrace]

I also wonder if the u-joint pulsation could be adding to something. on the mini's I have built I used the t1 chromoly 930 stubs and t1 weld in carriers all except one the first test rail but that was lighter than enemy's with even smaller wheels and a low hp honda motor and the carriers were a lot thicker.

[Ozpilot]

I also wonder if the u-joint pulsation could be adding to something. on the mini's I have built I used the t1 chromoly 930 stubs and t1 weld in carriers all except one the first test rail but that was lighter than enemy's with even smaller wheels and a low hp honda motor and the carriers were a lot thicker.

"Pad knock off" - which is the term I am used to for this - is common in a lot of circiut racing (pavement) situations.  It is common for drivers to need to give a little pump on the brake pedal with their left foot while they are still on the power but approaching a braking marker.  This brings the pads out to the disc prior to actually applying the brakes.  Pad knock off usually happens because a combination of things allow the disc to knock the pads away.

If you are only getting it after jumping maybe you could look at moving the calipers down to the "side" of the disc instead of the top.  That may mean the knock off is less and may not be noticable.  I know this is fixing the symptom rather than the problem but it may be an easier fix and you may not want to do the proper fix (if, for example, it means tightening bearings too tight etc)

[Engineer]

Hard to believe that the 3/8" would be flexing.  What offset wheels are you using? 

[fabr]

Personally I can see the 3/8 flexing enough.

[Nutz4sand]

Perhaps a test could be contrived.

Some kind of Epoxy that becomes brittle when dry or something like that be painted in a couple lines across the 3/8 plate in the angle you "think" it is flexing.

If the brittle pulls off the 3/8 plate or breaks acorss the line somewhere then you would know the 3/8 plate is the flex issue.

Or just build a thick plate that could be bolted to the existing hub mount to see if that stops it?

Maybe someone here could come up with a lot better way to test it?

[Enemy]

"Pad knock off" - which is the term I am used to for this - is common in a lot of circiut racing (pavement) situations.  It is common for drivers to need to give a little pump on the brake pedal with their left foot while they are still on the power but approaching a braking marker.  This brings the pads out to the disc prior to actually applying the brakes.  Pad knock off usually happens because a combination of things allow the disc to knock the pads away.

If you are only getting it after jumping maybe you could look at moving the calipers down to the "side" of the disc instead of the top.  That may mean the knock off is less and may not be noticable.  I know this is fixing the symptom rather than the problem but it may be an easier fix and you may not want to do the proper fix (if, for example, it means tightening bearings too tight etc)

Very good point Oz! Ds, I was thinking about this after I got off the phone with ya, A theory we will be able to test very soon (I hope) after I move my calipers to the front on the new carriers.

[Grimm Reaper Racing]

Do you know of anybody near you that has any strain gauges?  That would be the ideal thing to do if you wanted to perform an accurate test.

[dsrace]

"Pad knock off" - which is the term I am used to for this - is common in a lot of circiut racing (pavement) situations.  It is common for drivers to need to give a little pump on the brake pedal with their left foot while they are still on the power but approaching a braking marker.  This brings the pads out to the disc prior to actually applying the brakes.  Pad knock off usually happens because a combination of things allow the disc to knock the pads away.

If you are only getting it after jumping maybe you could look at moving the calipers down to the "side" of the disc instead of the top.  That may mean the knock off is less and may not be noticable.  I know this is fixing the symptom rather than the problem but it may be an easier fix and you may not want to do the proper fix (if, for example, it means tightening bearings too tight etc)

I understand what you are talking about and moving the calipers would require building new carriers which is not off the table yet. I would rather remedy the problem rather than mask the symptom though. I went out and looked at the box the last one came in and of course that one came from O'reilly's so I am sure it was made in china , Taiwan, cambodia or some other just get it boxed up were only making 5 cents and hour country!  that box says to tq to 180 ft lbs of tq so 250 is just a little over that. 

[dsrace]

Hard to believe that the 3/8" would be flexing.  What offset wheels are you using?

my dirt wheels are 2.5" and my paddles are 3.5" back space. I believe the dirt wheels are considered minimum offset?

[dsrace]

Personally I can see the 3/8 flexing enough.

after thinking about this alot, considering what I have heard from enemy about his, a little of what fast told me and having looked at the stock spindle off the jeep I do believe the majority of the flex is coming from the 3/8" plate! I have plenty of strength up and down and at the top some side to side but nothing from the center to the four corners at the pivot point. I was looking at this tonight and I believe if I were to make a ring apprx 1.75" tall and weld it to the carrier tightly around the flange bolting surface thus catching my inner plates and then gussets out to the four corners it might just do the trick. what do you guys think of that idea?

[dsrace]

Perhaps a test could be contrived.

Some kind of Epoxy that becomes brittle when dry or something like that be painted in a couple lines across the 3/8 plate in the angle you "think" it is flexing.

If the brittle pulls off the 3/8 plate or breaks acorss the line somewhere then you would know the 3/8 plate is the flex issue.

Or just build a thick plate that could be bolted to the existing hub mount to see if that stops it?

Maybe someone here could come up with a lot better way to test it?

I know what you are saying and not a bad idea but I already have a 3/8" thick plate welded across the top for the shock mount and I think that is why have had mild experiences with the flex as apposed to enemy's and of course the other factors! 
the plate isn't flexing enough to crack the powder coat but enough to push the pistons.