Re: Working on Brakes (especially Rear Drums) - TJ
 

Yes, what the previous poster said about jacking up the rear end and
putting it in gear then trying to stop the tires in the air with the
brakes. It don't work for ----.

Mike

SB wrote:
>
> Jack in the air thing?
>
> "Mike Romain" <romainm@sympatico.ca> wrote in message
> news:40E1DDD0.55148A82@sympatico.ca...
> > Both.
> >
> > I can get my open rear spinning up both tires and sometimes the front as
> > well, but the drum brakes seem to be better at slowly modifying the
> > torque rather then the hit disks give.
> >
> > The valve is dynamic, it sends so much pressure to the rears, then
> > shunts the rest front, then brings it back to the rear for the final
> > stop.
> >
> > If the fronts stop really easy, no more pressure goes to the rears, if
> > the fronts stop hard, you 'can' lock the rears as you come to a stop.
> >
> > I think that's why the jack in the air thing works so well to totally
> > confuse folks.
> >
> > Mike
> > 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00
> > 88 Cherokee 235 BFG AT's
> >
> > SB wrote:
> > >
> > > Hmm....so, with the limited slip....the whole brake trick to get rid of
> the
> > > single wheel spin....will that work in 2WD? or only 4??
> > > "mabar" <mabar@NoSpamgrbonline.com> wrote in message
> > > news:TK2dncYE8b_WxXzd4p2dnA@gbronline.com...
> > > > Yep. On most cars, the front brakes do about 70% (+) of the braking.
> On
> > > the
> > > > TJ, because of the extra short wheelbase, the fronts
> > > > do MUCH more of the braking. The rears do very little of the actual
> > > braking.
> > > >
> > > > Try this test. Raise the rear wheels off the ground with a floor jack
> or
> > > > jack stands. With the engine at IDLE and with the transfer case in
> 2-wheel
> > > > drive, put the transmission in drive or 1st gear, then try to stop the
> > > rear
> > > > wheels from moving with only the foot brake. On my 6-cyl TJ with 3.73
> rear
> > > > axel ratio, it is almost impossible to stop the rears, even while
> mashing
> > > > the foot brake with all my might. Applying the parking brake will stop
> the
> > > > rears easily.
> > > >
> > > > Tom
> > > >
> > > > "SB" <chicbearsmook@hotmail.com> wrote in message
> > > > news:O94Ec.322$T6i.195@news04.bloor.is.net.cable.r ogers.com...
> > > > > Wow...do the front actually do that much?
> > > > >
> > > > > Sure feels like it the way the front dives down....
> > > > > actually shared an arse clenching experience with a dog today!
> Nosed
> > > down
> > > > > and skidded....but all's ok!
> > > > >
> > > > >
> > > > > "mabar" <mabar@NoSpamgrbonline.com> wrote in message
> > > > > news:W-OdnQ9Kgs_ZK33dRVn-sA@gbronline.com...
> > > > > > Exactly. A combination valve is also called a proportioning valve.
> It
> > > > > > distributes the braking power heavily to the front brakes and
> > > > > > much less so to the rears. On a TJ, the front brakes do the lion's
> > > share
> > > > > of
> > > > > > the braking, probably 80 to 90%.
> > > > > >
> > > > > > Tom
> > > >
> > > >

Re: Working on Brakes (especially Rear Drums) - TJ
 

Hi Bob:

Drum brakes have a "self-energizing" action while braking in forward mode.
The brake shoes actually "dig into" the drum harder when braking in forward
motion. There is no "self-energizing action" in rear motion braking on
drums. So when braking when backing down a hill for example you have almost
NO rear braking action. Applying the parking brake will help but you want to
be very careful doing that as that can easily lock up the rears which might
cause complete loss of vehicle control.

If you are in 4-hi or 4-lo on a part-time 4-wheel drive system like the TJ
or YJ, the front and rear axels are mechanically locked together and the
front brakes will actually stop the rear wheels through the drive train.
It's very important for good vehicle control on off-road hills to be in 4-
wheel drive, preferably low range. That way the engine does most of the
braking and brakes all 4 wheels through the drive train and you can just
apply gentle pressure to the brake pedal to control the descent WITHOUT
locking up the wheels and loosing control.

Tom

"Bob" <magicclaw@mac.com> wrote in message
news:47b769ae.0406290542.39c0c1a4@posting.google.c om...
> I'm pretty sure it's not just that.
>
> I've been getting a seat-of-the-pants feeling that my braking power
> has diminished of late; on the highway when traffic has stopped
> suddenly, I've found myself having to smash down on the brakes harder
> than before to get the jeep to stop in the same amount of time. While
> I can still lock the front up, it just doesn't seem to be as
> effective.
>
> This last weekend on the trail was my final straw: I was on a slight
> incline, and tried to go up a couple of rocks (I was in 2wd), and spun
> tires. So, I put the clutch in and hit the brake simultaneously, in
> order to put it in 4-low to get through the little bit of rocks. As
> soon as the clutch was in, the vehicle proceeded to roll back about
> 10+ feet, with me standing on the brake pedal (in retrospect, perhaps
> I should have pumped it). Either way, it was a bit freaky. The others
> in my group said my front wheels were locked up, but my rears were
> rolling, as I just rolled backward. It was like my rear brakes were
> doing nothing, and just the locking-up and subsequent dragging of my
> front wheels was all that stopped me.
>
> The braking improved a bit as the day progressed, but I decided maybe
> I'd better check and see if the brakes were (a) in good shape still
> and (b) not out of adjustment.
>

Re: Working on Brakes (especially Rear Drums) - TJ
 

Hi Bob:

Drum brakes have a "self-energizing" action while braking in forward mode.
The brake shoes actually "dig into" the drum harder when braking in forward
motion. There is no "self-energizing action" in rear motion braking on
drums. So when braking when backing down a hill for example you have almost
NO rear braking action. Applying the parking brake will help but you want to
be very careful doing that as that can easily lock up the rears which might
cause complete loss of vehicle control.

If you are in 4-hi or 4-lo on a part-time 4-wheel drive system like the TJ
or YJ, the front and rear axels are mechanically locked together and the
front brakes will actually stop the rear wheels through the drive train.
It's very important for good vehicle control on off-road hills to be in 4-
wheel drive, preferably low range. That way the engine does most of the
braking and brakes all 4 wheels through the drive train and you can just
apply gentle pressure to the brake pedal to control the descent WITHOUT
locking up the wheels and loosing control.

Tom

"Bob" <magicclaw@mac.com> wrote in message
news:47b769ae.0406290542.39c0c1a4@posting.google.c om...
> I'm pretty sure it's not just that.
>
> I've been getting a seat-of-the-pants feeling that my braking power
> has diminished of late; on the highway when traffic has stopped
> suddenly, I've found myself having to smash down on the brakes harder
> than before to get the jeep to stop in the same amount of time. While
> I can still lock the front up, it just doesn't seem to be as
> effective.
>
> This last weekend on the trail was my final straw: I was on a slight
> incline, and tried to go up a couple of rocks (I was in 2wd), and spun
> tires. So, I put the clutch in and hit the brake simultaneously, in
> order to put it in 4-low to get through the little bit of rocks. As
> soon as the clutch was in, the vehicle proceeded to roll back about
> 10+ feet, with me standing on the brake pedal (in retrospect, perhaps
> I should have pumped it). Either way, it was a bit freaky. The others
> in my group said my front wheels were locked up, but my rears were
> rolling, as I just rolled backward. It was like my rear brakes were
> doing nothing, and just the locking-up and subsequent dragging of my
> front wheels was all that stopped me.
>
> The braking improved a bit as the day progressed, but I decided maybe
> I'd better check and see if the brakes were (a) in good shape still
> and (b) not out of adjustment.
>

Re: Working on Brakes (especially Rear Drums) - TJ
 

Hi Bob:

Drum brakes have a "self-energizing" action while braking in forward mode.
The brake shoes actually "dig into" the drum harder when braking in forward
motion. There is no "self-energizing action" in rear motion braking on
drums. So when braking when backing down a hill for example you have almost
NO rear braking action. Applying the parking brake will help but you want to
be very careful doing that as that can easily lock up the rears which might
cause complete loss of vehicle control.

If you are in 4-hi or 4-lo on a part-time 4-wheel drive system like the TJ
or YJ, the front and rear axels are mechanically locked together and the
front brakes will actually stop the rear wheels through the drive train.
It's very important for good vehicle control on off-road hills to be in 4-
wheel drive, preferably low range. That way the engine does most of the
braking and brakes all 4 wheels through the drive train and you can just
apply gentle pressure to the brake pedal to control the descent WITHOUT
locking up the wheels and loosing control.

Tom

"Bob" <magicclaw@mac.com> wrote in message
news:47b769ae.0406290542.39c0c1a4@posting.google.c om...
> I'm pretty sure it's not just that.
>
> I've been getting a seat-of-the-pants feeling that my braking power
> has diminished of late; on the highway when traffic has stopped
> suddenly, I've found myself having to smash down on the brakes harder
> than before to get the jeep to stop in the same amount of time. While
> I can still lock the front up, it just doesn't seem to be as
> effective.
>
> This last weekend on the trail was my final straw: I was on a slight
> incline, and tried to go up a couple of rocks (I was in 2wd), and spun
> tires. So, I put the clutch in and hit the brake simultaneously, in
> order to put it in 4-low to get through the little bit of rocks. As
> soon as the clutch was in, the vehicle proceeded to roll back about
> 10+ feet, with me standing on the brake pedal (in retrospect, perhaps
> I should have pumped it). Either way, it was a bit freaky. The others
> in my group said my front wheels were locked up, but my rears were
> rolling, as I just rolled backward. It was like my rear brakes were
> doing nothing, and just the locking-up and subsequent dragging of my
> front wheels was all that stopped me.
>
> The braking improved a bit as the day progressed, but I decided maybe
> I'd better check and see if the brakes were (a) in good shape still
> and (b) not out of adjustment.
>

Re: Working on Brakes (especially Rear Drums) - TJ
 

Hi Bob:

Drum brakes have a "self-energizing" action while braking in forward mode.
The brake shoes actually "dig into" the drum harder when braking in forward
motion. There is no "self-energizing action" in rear motion braking on
drums. So when braking when backing down a hill for example you have almost
NO rear braking action. Applying the parking brake will help but you want to
be very careful doing that as that can easily lock up the rears which might
cause complete loss of vehicle control.

If you are in 4-hi or 4-lo on a part-time 4-wheel drive system like the TJ
or YJ, the front and rear axels are mechanically locked together and the
front brakes will actually stop the rear wheels through the drive train.
It's very important for good vehicle control on off-road hills to be in 4-
wheel drive, preferably low range. That way the engine does most of the
braking and brakes all 4 wheels through the drive train and you can just
apply gentle pressure to the brake pedal to control the descent WITHOUT
locking up the wheels and loosing control.

Tom

"Bob" <magicclaw@mac.com> wrote in message
news:47b769ae.0406290542.39c0c1a4@posting.google.c om...
> I'm pretty sure it's not just that.
>
> I've been getting a seat-of-the-pants feeling that my braking power
> has diminished of late; on the highway when traffic has stopped
> suddenly, I've found myself having to smash down on the brakes harder
> than before to get the jeep to stop in the same amount of time. While
> I can still lock the front up, it just doesn't seem to be as
> effective.
>
> This last weekend on the trail was my final straw: I was on a slight
> incline, and tried to go up a couple of rocks (I was in 2wd), and spun
> tires. So, I put the clutch in and hit the brake simultaneously, in
> order to put it in 4-low to get through the little bit of rocks. As
> soon as the clutch was in, the vehicle proceeded to roll back about
> 10+ feet, with me standing on the brake pedal (in retrospect, perhaps
> I should have pumped it). Either way, it was a bit freaky. The others
> in my group said my front wheels were locked up, but my rears were
> rolling, as I just rolled backward. It was like my rear brakes were
> doing nothing, and just the locking-up and subsequent dragging of my
> front wheels was all that stopped me.
>
> The braking improved a bit as the day progressed, but I decided maybe
> I'd better check and see if the brakes were (a) in good shape still
> and (b) not out of adjustment.
>

Re: Working on Brakes (especially Rear Drums) - TJ
 

Hey I tried it with my 88 XJ with it down on the icy ground and with the
brake pedal fully depressed the rear wheels would still spin. It would do
the same jacked up in the air also = keep spinning. This was with a
remanned master, new rear wheel cylinders, shoes & pads with all hydraulics
bled well!

My parent's 88 XJ will now lock up the rears. I had to do their rear brakes
so they would lock up. The rear wheel cylinders were "locked"/rusted up and
the wheels would keep spinning either in the air or on the emissions dyno.

I would want to check my 88 XJ's proportioning valve. Waiting to get my
'round-2-it'! lol

later,
dave AKA vwdoc1

"Mike Romain" <romainm@sympatico.ca> wrote in message
news:40E203A2.3FDF873E@sympatico.ca...
> Yes, what the previous poster said about jacking up the rear end and
> putting it in gear then trying to stop the tires in the air with the
> brakes. It don't work for ----.
>
> Mike

Re: Working on Brakes (especially Rear Drums) - TJ
 

Hey I tried it with my 88 XJ with it down on the icy ground and with the
brake pedal fully depressed the rear wheels would still spin. It would do
the same jacked up in the air also = keep spinning. This was with a
remanned master, new rear wheel cylinders, shoes & pads with all hydraulics
bled well!

My parent's 88 XJ will now lock up the rears. I had to do their rear brakes
so they would lock up. The rear wheel cylinders were "locked"/rusted up and
the wheels would keep spinning either in the air or on the emissions dyno.

I would want to check my 88 XJ's proportioning valve. Waiting to get my
'round-2-it'! lol

later,
dave AKA vwdoc1

"Mike Romain" <romainm@sympatico.ca> wrote in message
news:40E203A2.3FDF873E@sympatico.ca...
> Yes, what the previous poster said about jacking up the rear end and
> putting it in gear then trying to stop the tires in the air with the
> brakes. It don't work for ----.
>
> Mike

Re: Working on Brakes (especially Rear Drums) - TJ
 

Hey I tried it with my 88 XJ with it down on the icy ground and with the
brake pedal fully depressed the rear wheels would still spin. It would do
the same jacked up in the air also = keep spinning. This was with a
remanned master, new rear wheel cylinders, shoes & pads with all hydraulics
bled well!

My parent's 88 XJ will now lock up the rears. I had to do their rear brakes
so they would lock up. The rear wheel cylinders were "locked"/rusted up and
the wheels would keep spinning either in the air or on the emissions dyno.

I would want to check my 88 XJ's proportioning valve. Waiting to get my
'round-2-it'! lol

later,
dave AKA vwdoc1

"Mike Romain" <romainm@sympatico.ca> wrote in message
news:40E203A2.3FDF873E@sympatico.ca...
> Yes, what the previous poster said about jacking up the rear end and
> putting it in gear then trying to stop the tires in the air with the
> brakes. It don't work for ----.
>
> Mike

Re: Working on Brakes (especially Rear Drums) - TJ
 

Hey I tried it with my 88 XJ with it down on the icy ground and with the
brake pedal fully depressed the rear wheels would still spin. It would do
the same jacked up in the air also = keep spinning. This was with a
remanned master, new rear wheel cylinders, shoes & pads with all hydraulics
bled well!

My parent's 88 XJ will now lock up the rears. I had to do their rear brakes
so they would lock up. The rear wheel cylinders were "locked"/rusted up and
the wheels would keep spinning either in the air or on the emissions dyno.

I would want to check my 88 XJ's proportioning valve. Waiting to get my
'round-2-it'! lol

later,
dave AKA vwdoc1

"Mike Romain" <romainm@sympatico.ca> wrote in message
news:40E203A2.3FDF873E@sympatico.ca...
> Yes, what the previous poster said about jacking up the rear end and
> putting it in gear then trying to stop the tires in the air with the
> brakes. It don't work for ----.
>
> Mike

Re: Working on Brakes (especially Rear Drums) - TJ
 

How did you manage to mess up their rear brakes so they would lock up?

You need to address theirs before you worry about yours that work
right....

There 'IS' a reason that proportioning valve is in there!

Crap, in an emergency braking situation, locking the rears means instant
360's with total loss of control unless you really know what you are
doing.

Been there, done that a 'LOT' of times on purpose using the E-brake when
I used to ice race a front wheel drive Mini.

I could drive straight down a snow/ice road and just for kicks or show
in a competition hit the E-brake and do 2, 360's, let off the E-brake
and continue on in the exact same track I started from.

Mike

dave AKA vwdoc1 wrote:
>
> Hey I tried it with my 88 XJ with it down on the icy ground and with the
> brake pedal fully depressed the rear wheels would still spin. It would do
> the same jacked up in the air also = keep spinning. This was with a
> remanned master, new rear wheel cylinders, shoes & pads with all hydraulics
> bled well!
>
> My parent's 88 XJ will now lock up the rears. I had to do their rear brakes
> so they would lock up. The rear wheel cylinders were "locked"/rusted up and
> the wheels would keep spinning either in the air or on the emissions dyno.
>
> I would want to check my 88 XJ's proportioning valve. Waiting to get my
> 'round-2-it'! lol
>
> later,
> dave AKA vwdoc1
>
> "Mike Romain" <romainm@sympatico.ca> wrote in message
> news:40E203A2.3FDF873E@sympatico.ca...
> > Yes, what the previous poster said about jacking up the rear end and
> > putting it in gear then trying to stop the tires in the air with the
> > brakes. It don't work for ----.
> >
> > Mike