761 Rear Axle Seal Question

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761 Rear Axle Seal Question

Postby oldspwr » Wed Sep 09, 2015 6:16 am

Since we finished the 361, the 761 hasn't been driven in the last 2 years so I decided to bring it out the garage and do a few PM things to it. When I moved it out of the garage I noticed a decent puddle under the driver side (front) rear axle wheel. I figured the wheel seal was leaking so I picked up a new Stemco grit guard.

Last night we pulled the wheels, axle, hub and drum and realized it was the same wheel seal we had replaced a few years back. For some reason it is leaking again and everything is saturated. This is actually a pretty bad leak... The seal looks to be in good shape and there are no tears in the rubber, etc. Any ideas on how to fix this? Should I put black RTV on the piece that goes on the axle? Here are a few pics...

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Re: 761 Rear Axle Seal Question

Postby Mike Pacitto » Wed Sep 09, 2015 7:03 am

Hi Tom,
I have always used silicone on the inside of the wear ring and the outside bore of the seal. I hate to ask all the stupid questions but, did you pre-lube the lip of the seal? Were the bearings tight? Were the surfaces real clean, hub and axle? These are all things I double check when we have a premature seal failure. Did you use the Stemco drive tools? We have replaced seals and had them fail the next day and could never find an obvious reason. Something else I noticed is the axle tube looks "frosted" where the bearings ride, that usually indicates a loose bearing. Clean up those surfaces with emery cloth and be sure the bearings slip easily over them. If the bearings bind up the wont torque properly.
Mike Pacitto
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Re: 761 Rear Axle Seal Question

Postby oldspwr » Wed Sep 09, 2015 7:18 am

Hi Mike...

Thanks for the reply... no stupid questions here, I appreciate your help...

- we did prelube the the rubber lip of the seal
- the bearings were in good shape (Timkens) We did clean them and reinstall them. Everything appeared to be tight. I do have the correct sockets for the nuts, etc. (4")
- we cleaned everything with brake cleaner prior to reassembly.
- I didn't have the Stemco drive tools but I used a block of wood that was cut to the diameter of the seal. I made sure the both pieces were installed square as well.

To reinstall the hub and drum, we used an ATV jack to line it up and roll it into place so as not to damage the rubber lip.

Tom




have always used silicone on the inside of the wear ring and the outside bore of the seal. I hate to ask all the stupid questions but, did you pre-lube the lip of the seal? Were the bearings tight? Were the surfaces real clean, hub and axle? These are all things I double check when we have a premature seal failure. Did you use the Stemco drive tools? We have replaced seals and had them fail the next day and could never find an obvious reason.
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Re: 761 Rear Axle Seal Question

Postby Scranton 761 » Wed Sep 09, 2015 9:12 am

Tom, from the pic the seal looks like it's doing it's job... unless you cleaned it. Is the lube coming from between the seal and the hub? I always use a light coat of something where the metal meets metal (weatherstrip adhesive, RTV, etc.). If anything it acts as a lube to prevent galling when driving it in. I haven't had a (automotive / Lt. truck) failure yet..... Big trucks are still a new game around here.

Edited 1:20PM: Sorry Mike.... Didn't initially see your "outside bore of the seal".
Last edited by Scranton 761 on Wed Sep 09, 2015 12:20 pm, edited 1 time in total.
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Re: 761 Rear Axle Seal Question

Postby oldspwr » Wed Sep 09, 2015 9:57 am

Hi Paul...

I wiped the hub off so I could inspect it for damage. The inside of the inner dual wheel had a pond of fluid in it... I won't get to it for another night or so, but I will definitely be using some where the metal to metal contact is. I will probably use hi-tach or black rtv.

Tom
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Re: 761 Rear Axle Seal Question

Postby Huskiedrive2 » Wed Sep 09, 2015 12:50 pm

Hi Tom. I agree with Mike and Paul on all counts. One other thing comes to mind, make sure to fill the cavity in the hub with gear oil just before you install the axle. Time spent turning the seal waiting for the hub to fill can also cause seal failure. Another thing to check is to make certain that the tension spring under the seal lip is not dislodged during installation. The seal will not do it's job if the spring is off the lip. Stan
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Re: 761 Rear Axle Seal Question

Postby Mike Pacitto » Wed Sep 09, 2015 1:17 pm

Hi Tom,
I think you might have damaged the face of the seal,or as Stan mentioned dislodged the spring that backs up the seal. The proper Stemco tool looks like a cup and drives on the edge the goes into the hub as well as the face. Stemco actually gives those tools free if you buy the seals. Check with the dealer that sold you the seal, or I can get you the proper driver. The tool number is right on the box. (another thing I love about Stemco )
Mike Pacitto
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Re: 761 Rear Axle Seal Question

Postby oldspwr » Thu Oct 01, 2015 2:08 pm

Ok time for a quick update on the rear axle seal...

- Mark Tolerico let me borrow all the correct tools to install the new seal along with the wear sleeve.. . (thanks Mark!)

- We thoroughly cleaned all of the oil off of the brake hardware and shoes and carefully reinstalled the drum and hub.

- When I went to adjust the brakes, we aired the truck up and I could hear air leaking from the rear axle relay valve (actually the exhaust port...).

- The air was coming from the vent in the bottom so I assumed it was bad. I went to remove the bolts from the bracket and sure enough the first bolt broke. And sure enough the other 3 broke as well.

- I could also hear air leaking from the 30/30 can on the axle we replaced the seal on. So I figured that was bad as well.

- So then I went to eBay and bought a reman Bendix 1003009 valve with horizontal ports. A week goes by and the valve shows up.

- In the meantime, Maddie turned 6 :)

- So the other day we finally get back on the 761 and installed the new relay valve. This took some time since the original bracket was cobbled together and rusty.

- After we install the new valve, guess what, air is leaking from the same spot. Damn... If I place my hand under the leak, I can watch the rear 2 cans start to apply the brakes. Hmmm...

- So I'm thinking out loud to my Dad that somehow air from the spring chamber must be leaking into the service chamber.

- Then I sat down at our trusty garage computer and did a quick Google search and found this...

"With the introduction of spring brakes, anti-compounding and 121 air brake systems, because a valve is leaking air out of its exhaust, does not mean the valve is at fault. If a spring brake is leaking from the the spring brake to the service brake side, that air will travel back up the service line and out the exhaust of the next valve back. Before replacing a valve that has air leaking from its exhaust, disconnect the delivery lines from that valve to determine if air is being fed back from some other valve or unit."

So now I need to figure out which can is bad...
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Re: 761 Rear Axle Seal Question

Postby Huskiedrive2 » Thu Oct 01, 2015 4:51 pm

That's easy Tom. Remove the two service air lines at their connection to the rear brake chambers. Charge the emergency lines by pushing in the park brake valve to release the brakes. Check to see which chamber has air coming out of the brake chamber where the service lines connect. The one with air coming out of the service port is the bad chamber.
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Re: 761 Rear Axle Seal Question

Postby Green Giant2 » Thu Oct 01, 2015 6:51 pm

Huskiedrive2 wrote:That's easy Tom. Remove the two service air lines at their connection to the rear brake chambers. Charge the emergency lines by pushing in the park brake valve to release the brakes. Check to see which chamber has air coming out of the brake chamber where the service lines connect. The one with air coming out of the service port is the bad chamber.
right on stan. same as i was thinking
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