brake drum gets hot brake drags

1941 - 1945, MB, GPW Technical questions and discussions, regarding anything related to the WWII jeep.
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wingnut1
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Re: brake drum gets hot brake drags

Post by wingnut1 » Sun Nov 21, 2010 6:16 am

Hi. Are you useing thickness guages to get the correct adjustment atall four drums.
Regards Bernard.
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Colin Jansen
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Re: brake drum gets hot brake drags

Post by Colin Jansen » Sun Nov 21, 2010 8:27 am

All i did with the MC was ensure 1/2 inch free play. The Drums are not getting super hot like before on the RHF but are quite warm to the touch with alot of braking all round. How hot would they normally be expected to get under heavy braking? Previously the others were all cold.
Id rather walk than not drive a Jeep

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1943 Willys MB
1943 Willys MBT
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Re: brake drum gets hot brake drags

Post by wingnut1 » Sun Nov 21, 2010 8:40 am

Hi Colin you,r supposed to use feeler / thickness guages through the slots in the edges of the drums to get the same adjustment on all 4 drums. do you have a manual.
Regards Bernard.
GPW 205133 JUNE 1944 1953 M38A1 C.D.N.

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Re: brake drum gets hot brake drags

Post by artificer » Sun Nov 21, 2010 11:22 am

The brake drums should be nearly untouchable after continual heavy braking.
Pedal free travel is actually the distance the pedal moves before the push rod touches the m/c piston. If you are underneath the vehicle & pulled the pedal downward you should feel the rod to piston contact occur @ about 1/32-1/16" of rod movement.
It is just convenient to check & say 1/2-3/4" @ the top of the pedal.
This is how I recommend you adjust Jeep brakes. Disregard the 2 bottom drawings all 4 wheels are the same as the top one.
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John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
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Re: brake drum gets hot brake drags

Post by Ian Jamieson » Sun Nov 21, 2010 2:31 pm

Colin,
on the proviso that you do indeed have the correct pedal free travel, then my money is on a failing flexi hose. I had a very similar problem a couple of years ago and after replacing the flexi hoses I had no further issues.

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Ian
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1942 Dodge WC57 Command Car.
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Re: brake drum gets hot brake drags

Post by Colin Jansen » Sun Nov 21, 2010 5:55 pm

Hi guys

Yes i do have a manual and adjusted the shoes with feeler guages as per the manual, and i have set the free play as 1/2 in until contact is made with the piston. Good to hear that the heat on all drums on excessive braking is normal. Yes i do feel one of the flexes may need replacing so have a set coming. Also have been thinking that a drum or two may be out of round and playing a part in the heat build up with the shoes being adjusted closer to the drum now.
Id rather walk than not drive a Jeep

1942 Ford GPW
1943 Willys MB
1943 Willys MBT
1943 Bantam T3
1943 Dodge WC51
1966 L5 Pack Howitzer

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Re: brake drum gets hot brake drags

Post by artificer » Sun Nov 21, 2010 6:10 pm

Drums can be oval/out of round & bell mouthed/tapered.....if there is a very slight drag it should be even thru the whole rotation of the wheel....not tight then loose throughout the rotation.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: brake drum gets hot brake drags

Post by Ian Jamieson » Sun Nov 21, 2010 6:46 pm

Hi Colin,
one of the reasons disc brakes are preferred over drum brakes is beacuse under constant braking the drums and linings would get so hot that the brakes would "fade" to the point that they were virtually useless! Discs however cool much more efficiently, but if you ever watch Bathurst you will see pit crews changing glowing brake pads with heat proof gloves. So yes, brakes can get very hot.

If you have an out of round drum you will inevitably get shudder or feed back through the brake pedal when you apply the brakes, having said that slight out of round may not manifest it-self on braking but often will when trying to adjust.

Ian
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1942 Dodge WC57 Command Car.
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Re: brake drum gets hot brake drags

Post by Jerry Hudgens » Sun Nov 21, 2010 7:48 pm

When I was in college, we analyzed the drum brake actuating mechanism and compared it to disc brakes. In reality, the drum brake provides more stopping power than the disc brakes per pound of "foot" force exerted by the driver. That is due to a feedback loop in the total mechanical circuit for the drum brakes. That is why you can get by without power boost on drum brakes but all disc brakes need power boost in order to get good stopping power. And as stated in one of the replies, the disc brakes cool much better than drum brakes and thus minimize "fading".

Jerry HUdgens

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Re: brake drum gets hot brake drags

Post by artificer » Sun Nov 21, 2010 8:00 pm

Jerry said: but all disc brakes need power boost in order to get good stopping power
With all due respect....the Suzuki Side Kick (Holden Drover or Geo Tracker) non ventilated discs on my MB are more than twice & very likely 3 times more efficient/effective than properly adjusted standard Jeep leading & trailing shoe design like on the MB/GPW's through CJ's.
This improvement with no booster just a standard 1" bore master cylinder.
Suggest "all" might be more correctly stated as "many".
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
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Re: brake drum gets hot brake drags

Post by Jerry Hudgens » Mon Nov 22, 2010 3:46 am

I agree with your statement when compared to Jeep brakes. The Jeep brake design does not have the feedback loop like say the brakes on my 1968 Mustang (Manual drum brakes). Its the floating design that has the feedback. The Jeep brake shoes are anchored at their pivot points so there is no feedback when pressure is applied to the wheel cylinder pistions. Its just straight pressure.

I was totally surprised when our professor laid out the mechanical circuit and we did the mathematical analysis. I should have saved the analysis since I bet no-one anymore can do the analysis. I know I can't. I was lucky to pass the course.

Anyway, I agree that disc brakes are much better than drum brakes. But, with the right design, the old drum brakes when cool can do some real stopping power.

Jerry Hudgens

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Re: brake drum gets hot brake drags

Post by artificer » Mon Nov 22, 2010 4:01 am

The Jeep brake design does not have the feedback loop like say the brakes on my 1968 Mustang (Manual drum brakes). Its the floating design that has the feedback.
Actually called self energising brakes they act like a wedge & wrap on with considerably greater forces than bottom anchored shoe type brakes plus most were self adjusting. Unfortunately they are also more likely to lockup & antilock brakes were not around when they were popular.
So they had a couple of advantages & some major disadvantages in the wet & snow plus brake fade & loss under heavy braking.
John GIBBINS Member Institute of Automotive Mechanical Engineers [Ret], ASE Master Medium/Heavy Truck & Auto Technician USA -2002 Licensed Motor Mech NSW MVIC 49593 Current 2015
TO DIAGNOSE, TROUBLESHOOT OR FAULT FIND ANY AUTO SYSTEM....
Understand how system parts interact with one another. GOOD parts can then be established & the NOT GOOD problem/s part/s isolated for repair or replacement.

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Re: brake drum gets hot brake drags

Post by 41jeeps » Mon Nov 22, 2010 8:00 am

A friend of mine has relined the pads with such a self energizing system.
The new linings have been made from a softer material as originally installed from the manufacturer.
He could not drive that car forward after he used the brakes.
He had to unlock the brakes by putting the car in reverse for an inch or so. :twisted:
He has had a lot of headache before he found out about the softer linings :|

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Re: brake drum gets hot brake drags

Post by Colin Jansen » Mon Nov 22, 2010 10:54 pm

Hi guys, well after going over all shoe adjustments using the process in the above diagram rather than the manual and taking account of the RHF drum being slightly out of round i think she may be solved judging by the test runs so far. She stops straight, and can lock up again and no drum is getting overly hot. With the problem in the RHF being intermittent there is always the possibility it will re surface but i am changing the flexes when they get here juat in case anyway. Cheers for all your help.
Id rather walk than not drive a Jeep

1942 Ford GPW
1943 Willys MB
1943 Willys MBT
1943 Bantam T3
1943 Dodge WC51
1966 L5 Pack Howitzer

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Re: brake drum gets hot brake drags

Post by douglasmthom » Thu Jun 07, 2012 6:25 am

I ran across this thread below which mentions the issue of free pedal travel several times. I have discovered that this is part of the problem I am having. One very valuable tool I discovered is the brake light switch which is mounted on the master cylinder. Before I began making pedal adjustments I turned on the running lights on the jeep and mounted a mirror in the back of the garage so I could see the brake light from the drivers seat. When I started pressing and releasing the brake pedal I could see that there was a lot of funky behavior associated with the free-travel adjustment.

So, along with all the other techniques mentioned, try monitoring the pressure in the master cylinder using the brake light - its just one more tool to help understand what is going on where in the system. It has helped me convince myself I had enough free travel in the pedal, but no more than necessary.
Doug Thom

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