Posted: Tue Mar 11, 2014 6:10 pm Post subject: brake conundrum
My brakes feel engaged continuously. After a short drive and they heat up, they definitely aren't releasing. I went to adjust the free play. The push rod is already at it's minimum (just over 7 inches). I went to reinsert the rod with the reservoir open. I can't even get the rod back over the clevis pin on the pedal. As in it appears I hit brake pressure before the pedal even moves.
Perhaps I have the wrong push rod? Other ideas?
Only two things cause the brakes to remain pressurized.
1- The master cylinder does not release all the way. You said you have adequate free play then you said you couldn't connect the rod. Confusing description of symptoms.
2-The brake line hoses are deteriorated and will allow pressure through to the brake but not back to the master cylinder. To check this just open the bleeder on each brake and see if it releases. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
I know it sounds unlikely, but I'm trying to determine if my M38 was built up with a wrong part. It's possible, perhaps unlikely, that if the wrong brake master cylinder plunger rod was too long, the brake might have been activated/locked during assembly.
From the time I got the jeep, the brake pedal feels like there is no free play and the brakes (both front that I know of) don't release after they are used. It's possible that the brakes have been engaged from the get go when I bought it. I never thought to hand roll the jeep to see if there was any drag.
I went to see if the problem was a simple adjustment of the free play and found that the plunger rod was adjusted as short as it would go, i.e. no free play adjustment available, and it was very difficult to remove off of the pedal. When I disconnected the rod from the pedal, the brakes were released and the wheels rolled easily. When I went back to put the rod in, I could feel the plunger moving fluid in the master (it geysered out of the open lid) until the rod moved inside perhaps 1/2 to 3/4 inch, then stopped hard/solid. Now the brake plunger/push rod wont go back on the brake arm. It almost fits on, but there's too much resistance with the plunger rod way inside the master cylinder. Not that it matters getting the rod on the pedal, because there would be NO free play and the brakes would again be engaged all the time.
Which begged the question whether or not the brake master cylinder push rod was the correct length.
This jeep was resurrected with almost all new working parts. The project started by my friend just back in September 2013. I didn't get a parts list when I bought it from him, but almost everything mechanical and electrical appears new, including the master, brake cylinders and lines. And the brake fluid is clear and looks new. Some things, like the brake push rod, are obviously not new. And of course I don't know if anything is correct.
I will bleed the front brakes and see if the lines are collapsed. I'm familiar with that problem because my '95 Chevy truck has already BTDT. Perhaps my Willys soft lines are NOS and deteriorated that quickly. ITMT, I'm still curious if I have the correct length brake master cylinder push rod.
I'll put a picture of the brake plunger/push rod in my gallery.
I didn't see any brake system photos in your album yet. Measure the rod length you have. Post a photo of the master cylinder as well. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Thanks again, Wes. I'll measure the MC next time I visit my Willys. I'll take another look to see if I can find a part number stamped on the MC as well.
I don't have confidence that all of my Willys' parts are correct, since I already know I have a speedo and fuel gage issue... and a few other small things that are not correct.
The brake push rod measures about 7.5 inches as short as I can get it.
The good news is that the push rod is apparently the proper length. I cracked the right front bleeder, shoved the plunger rod in and pinned it to the brake pedal. A couple pushes of the pedal to the floor bled out clean clear fluid. The bad news is that the flex lines at the wheels do not look new.
Where's a good source for a set of new (not NOS) soft lines?
A good source depends on your definition of good parts!
The simplest is to remove them and take them to your auto parts store store and lay them on the counter and tell the counter person you need new ones the same length and ID with the same end fittings.
If the counter person and the store are worth a salt they will pop open their paper catalog and select a matching part number for each.
You really should always mention your model jeep when asking for help, information or parts. The easy way is to show your model jeep in your profile in your signature line.
The M38 & M38A1 hose lengths are:
1-MC line to frt axle 11".
2-Axle to front wheel hub 2 ea 6"
3-Frame to rear axle 15" _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Thanks for the hose info. And the signature tip. When I did a search here, someone posted a long time ago to get the brake hoses new from one of the sources mentioned here. Perhaps a member? I thought it'd just be easier to order a set from someone who knows jeeps and can save me the trouble of dealing with counter drones at the local store. Although our oldest NAPA is usually helpful... but not particularly cheap.
Oddly, I bled both front brakes and the problem has gone away... perhaps temporarily. And the pedal has about normal play. So perhaps I've bought a little time.
ITMT, one or more of my drums must be egg shaped because the pedal moves in and out like it's going over a cam.
Are NOS drums still available if my drum is beyond machining?
Oddly, I bled both front brakes and the problem has gone away... perhaps temporarily.
That's not odd. Above I stated:
Quote:
2-The brake line hoses are deteriorated and will allow pressure through to the brake but not back to the master cylinder. To check this just open the bleeder on each brake and see if it releases.
You have simply confirmed this point and now you need four hoses.
I have not seen any NOS drums in a few years.
Two things I have learned over the years to not gamble with. Bad brakes and bad steering. You put yourself and other innocent bystanders at risk driving a vehicle with brake or steering problems.
I prefer to go to the counter and buy US made brand name brake hoses rather then bet of what may well be Chinese hoses from the regular jeep vendor. _________________ Wes K
45 MB, 51 M38, 54 M37, 66 M101A1, 60 CJ5, 76 DJ5D, 47Bantam T3-C & 5? M100
Joined: Dec 22, 2010 Posts: 49 Location: Victoria, B.C. Canada
Posted: Sat Mar 15, 2014 7:47 pm Post subject:
Had a similar problem when I first put my M38A1 on the road. Did all the normal checks and bled etc. It kept adding presure to the drums on each application. A mech friend suggested I check the small return hole in the bottom of the master cyl. Yup clogged tight as $&% with old dirt and gunk. Reamed out,replaced fluid and to date(after 10years) no more problems! Now where is that wood to knock on??!!
Joined: Jun 14, 2005 Posts: 110 Location: Calgary Alberta
Posted: Sun Mar 16, 2014 10:16 pm Post subject:
I had a very similar problem with my M38A1 . The previous owner said he had replaced the maste cyl.. but after a few brake applications the brakes literally stayed on. I bought the M38A1 and found the same thing, Finally I replaced the master cyl again and everything was OK. I got a rebuild kit for the one i took out and found that the piston was too long. it must have been for another application and would not move back far enough to allow the release hole to vent. _________________ SteveJ
1986 CDN Armstron MT500 dispatch Motorcycle
1986 arrow 1.75 t cargo trailer
1991 Reynolds Boughton RB44 GS TUH
1952 M38 CDN W/W (Sold)
1953 M100 CDN Trailer
1951 PE95K Genset (Sold)
Joined: Feb 16, 2007 Posts: 206 Location: Gold Coast Australia
Posted: Thu Mar 27, 2014 1:08 pm Post subject:
Firstly if you need brake hoses take your old ones to the local Parker Hannifin dealer....they will make new ones up with NEW 2014 hose with identical fittings to what was original & your new hose will be tested & DOT approved.
They will be very inexpensive & remember do not use old dated or NOS hoses. All rubber brake hose should be marked with a manufactured date + DOT approval.
Forget what you are trying to do with the pedal to master cylinder pushrod & start again.
When re-fitting the rod should be loose & NOT engage the master cylinder piston @ all before the pedal is pushed downward.
If pushrod is in contact with the piston some other adjustment [like floor seals under pedal for example] is wrong or there is not enough thread on the pushrod.
Once the pushrod is in you should then lengthen the rod adjustment so that you have about 0.025" clearance before the rod makes contact with said piston. This translates to a fraction over 0.5" foot pedal travel @ the top.
Lastly someone mentioned reaming out the small compensating or by-pass port.
This hole size is very important & it should not be reamed or drilled out [BUT cleaned if necessary] to maintain it's original dimension.
Like Steve just said if the piston can't return far enough to uncover the compensating port the brakes will drag & lock on.
That is what happens when one has no free travel also [the compensating port doesn't get uncovered properly]. _________________ John GIBBINS
ASE Master Medium/Heavy Truck & Auto Technician 2002 USA
Licensed Motor Mechanic NSW # MVIC 49593 Current
YOU CAN'T TROUBLESHOOT WHAT YOU DON'T UNDERSTAND
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