Need help Identifying leak near diff

[Chirider]

First time poster, just bought a M998 yesterday. After driving it 15 miles, A few hours later I went to check for leaks and saw a a small wet mark on my driveway coming from the rear center axle area. Can you help me identify what is leaking and where it may be coming from? The origin of the fluid seems to be between the driver rear brake rotor and rear diff. The actual drip is lower (circled on 2nd photo). I tried to trace it and it is wet higher up in a narrow area. Thanks in advance!

 

[Coffey1]

Looks like the brake caliper is leaking

 

[Chirider]

Thanks for helping me. I should add that the fluid was brown and oily. Is that still consistent with a brake caliper leak?

 

[porkysplace]

Thanks for helping me. I should add that the fluid was brown and oily. Is that still consistent with a brake caliper leak?

Yes .But gear oil is brown and oily also but smells bad
Have you checked the fluid levels in the master cylinder (pre trip inspection)
Have you checked the fluid levels in the differentials ?
Have you read the -10 operators manual to do a pre trip inspection?
TM-9-2320-280-10.pdf
TM-9-2320-280-10 Operators manual for the M998 series truck. June 1991.

Other TM's you will need at some point.
TM's for the M998 series

 

[General Hood]

Follow these gentlemen's advice, and welcome to the forum from SE Oklahoma

 

[juanprado]

It is possible to have brake fluid heavily contaminated and filled with sludge so it looks dark and nasty.

Recommend you flush and bleed anyway since you will have to open system to change caliper. Just like your car or truck.

In civilian world someone could have used the wrong fluid like power stg but I doubt that is the case and that is a a real big can of worms.

Yours look like a simple caliper r&r

 

[Carrera911]

Looks the same as my rear diff. Wipe some on your finger and if it smells like sulfur or cat piss it's diff oil from the output seal to the halfshaft. I just check the level and if I ever got into water that high I'd be sure to change it before long. That seal is a major PITA to fix and requires dropping the diff as far as I know.


Sent from my iPhone using Tapatalk

 

[Coffey1]

I would pull the caliper and look at seal.
I would be willing to bet it's the culprit.

 

[ryanruck]

My truck had a leak in the exact same area on the front diff.

At first I thought it was a leaky caliper and ordered a new seal and boot kit. However, once I dug into repairing it, I saw the caliper was dry and it was actually the diff output seal.

Ordered a new output seal, had a bear of a time getting the old one out, and had to build my own seal installation tool out of an iron pipe floor flange and section of pipe (it has to fit over the output shaft).



Now I've got the actual seal installation tool that came as a set of tools but, that worked just fine.

If it is your output seal, when you go to put the new one in, grind a very slight taper on the outside edge of the seal that goes into the diff first. It will make installation much easier.

 

[Chirider]

Doesn't smell like anything nasty and it's more yellowish than brown/black. I guess it's brake fluid. I could not locate the brake fluid reservoir to check the fill line, searched the internet to no avail. Many thanks to you all?
im going to post another picture of a different fluid stain i haven't a clue as to what it is. I'll post in another thread I guess.

 

[ryanruck]

If I were you, definitely head to the link porkysplace posted for the HMMWV TMs.

They're searchable PDFs and have thousands of pages that cover just about everything you'd need to know about these trucks. The -20 series tell you how to troubleshoot and repair and the -24P have great assembly diagrams and assist in part ID.

The brake fluid reservoir is directly ahead of the brake pedal assembly on the engine side of the firewall, right against the driver's side engine bay side cover. Only put DOT 5 fluid in it! Don't mix anything else!

 

[Chirider]

Thanks a lot!

 

[Chirider]

The mechanic says the leak is from the brake caliper. He recommends both left and right to be replaced entirely. Is that normal? Not just a seal replacement? If I need to buy brake calipers where should I buy them? Thanks!

 

[juanprado]

The mechanic says the leak is from the brake caliper. He recommends both left and right to be replaced entirely. Is that normal? Not just a seal replacement? If I need to buy brake calipers where should I buy them? Thanks!

Yes, It always advisable to do pairs. Most Mechanics will not rebuild a caliper or wheel cyl as they are just parts changers nowadays not skilled technicians. Old school guys can rebuild. If rebuilt, bore needs to be honed and piston checked to make sure it is good. If replacing both calipers, might consider a full brake job with new pads and rotors and you can check that off the done list.

 

[someoldmoose]

WELCOME and hope you have a great time with your "new" machine.



Give a man a fish, he eats today. Teach a man to fix his HMMWV and he can go fishing wherever the heck he wants. Happy Motoring !

 

[infidel got me]

When in doubt-- taste it. I've done this for years (maybe that's whats wrong with me) I apprenticed under an old time mechanic and if he was not sure about a fluid (color) he would dab his finger in it and give it a taste. Usually he was right on with what it was. I've diagnosed a few like this.