Rear End Pressure
 

Rebuilt the rear-end last year and added a Mitchell overdrive.
After 3,700 miles I decided to change the lube and when I removed the plug Oil shot out as it was under quite a bit of pressure.
I never expected that although there is no pressure relief feature in the rear-end.

Also, the temperature of the front driveshaft tube was about 115 degrees after about a twenty minute drive in eighty degree weather. Is that temperature normal?
Thanks for your advice/insight.
Al

Re: Rear End Pressure
 

There is a pressure relief system as the seals are never that tight against the axle shafts. Also, there is not supposed to be a gasket between the torque tube flange and the differential housing flange.


The other thing is there really is not anything to create pressure. The R&P spinning does move the lube however it is displacing it from one area and relocating it to another. The heat from the torque tube is likely heat from the engine that is transferred by the air moving over the running engine.


Do you know what weight lube you had in the differential housing, and could it have been thin enough that it flowed freely acting as if it was under pressure??

Re: Rear End Pressure
 

I drove my 28 Phaeton 17 miles and used my heat gun on the differential. It was only a few degrees warmer than the air temp. This is on a stock unrestored rear end.

Re: Rear End Pressure
 

Running gears produce a lot of heat because of the sliding nature of tooth engagement (high friction). The gear oil transfers heat to the rear axle housings, torque tube and transmission case. Radiation and convection dissipate the heat in the housings into the outside atmosphere. The more power / torque put into the drive-train, the higher the operating temperature will go.


The side pans on the engine direct airflow alongside of the transmission which helps to keep its case temperature down. Running board aprons are also players in directing airflow past the transmission case and torque tube.


I suggest that you run a synthetic hypoid gear oil in your transmission and differential.



An overdrive will increase the amount of heat developed, so I would expect temperatures to higher than normal.



The Model "A" rear axle lacks a vent, so any moisture in the atmosphere inside of the drive-train will condensate as parts and fluids cool. A vent also reduces the atmospheric pressure inside of the drive-train, so the operating pressure would be lower.

Re: Rear End Pressure
 

The stock rear end vents pressure through the trans. I ran a Ryan OD and had leaks so added a vent on the left axle housing.

Re: Rear End Pressure
 

There is a vent hole on the rear of the transmission tower that vents the backend . The vent hole is around 3 sixteenths in diameter and located near mid way down the rear of the transmission tower below the shift lever . There is a good chance that the vent is stopped up, painted over and not visible . There has been pictures of this vent pictured here in the past by me and Mitch . Pressure can build or this vent would never been put there by Ford .

Re: Rear End Pressure
 

There was pressure the grease blew out when I removed the drain plug.
I was using STP 85-140 weight lube

Re: Rear End Pressure
 

I just replaced the STP lube with SWPCO #201 and it is thinner than the 85-140. The temp difference was about 20-25 degrees higher than ambient. By the time I changed the battery in the temp gun everything had cooled a bit. I understand some heat is normal Never thought it would be this high.
Thanks everyone for your comments.
Al

Re: Rear End Pressure
 

I did what Jim did in post 5 except lube pumped out the left side top banjo bolt tube due to the ring gear. Moved to the right top banjo bolt : drilled and tapped a small hole in the bolt and threaded in a short piece of brake tubing ( with locktite) and ran plastic tubing up the right side and up into the rt. fender brace with a differential poppet vent at the end. Some notes from other posts:OD 's or F150 trannies block any venting down the torque tube and gaskets as stated. Also, get Lubriplate 250 wt gear oil (not 140 which is approx what the vendors package), or Penrite gear lube which is closer to orig. 600 wt.for non hypoid rear ends.
Chrysler products for example generally after 1936 recommended different lubes for hypoid rear ends.

Re: Rear End Pressure
 

The rear axle & torque tube in Al's Tudor held pressure. There is a seal at the front of the torque Tube that will prevent venting through the transmission. A sealed rear bearing in the the transmission will also prevent venting.

Re: Rear End Pressure
 

I had the same experience Duke did with a banjo bolt. So driiled and tapped partially into the left axle housing about 12" from the brake backer, on a forward angle to clear the spring. Used a 10-32 bolt with the head cut off and drilled longitudally with small tubing, secured to the frame, out of the way of everything. Drilled only part way into the housing so the bolt threads bound tightly to the housing.

Re: Rear End Pressure
 

Did you remove the axle housing from the car before drilling the hole ?

Re: Rear End Pressure
 

No, I am too lazy. I drilled carefully to the point of going thru, then put grease on the drill to capture any chips. Diff oil usually does not venture out that far in the housing. In diffs that have been used for many years there is usually some grease in the housing, caused by over-zealous greasing of the wheel bearings and a faulty outer seal, many guys install that seal backwards, the lip should face outwards to direct the grease into the bearing, it is not there to keep oil in the diff.

Re: Rear End Pressure
 

I like the idea of drilling one of the upper banjo bolts and attaching a tube to it. Wouldn't like to drill a housing but I can always replace a bolt.
Thank you gents.
Al

Re: Rear End Pressure
 

I'd leave the original bolt alone, and drill an aftermarket bolt.

Re: Rear End Pressure
 

In addition to my Tudor I have a '57 Studebaker Golden Hawk, which is supposed to have a vent hole in the axle housing, on the top side. When I was restoring it, I couldn't find it, because it had been painted over. It just disappeared from view. So, to vent the axle, I drilled a small hole (1/16") in the bolt that holds the hydraulic brake system distribution block to the axle, which accomplished the same thing. I am glad I ran into this thread, because I hadn't thought about venting my Tudor's axle. Now, I plan to drill a similar hole in one of my Tudor's top banjo bolts. I think there's no need for a tube, unless one plans to drive through deep water. Thanks for the idea.

Re: Rear End Pressure
 

Like others experiences I've seen, I had lube pumping out into the tube due to the ring gear action on the top left bolt. Switched to the right top and routed the tube up to the right as stated to minimize migration..

Re: Rear End Pressure
 

Duke - that's a good point about putting the vent hole on the right side, which would avoid lube being thrown off by the ring gear. But, how did you attach a tube to the head of the bolt, into which you had drilled a hole for a vent? Bj

Re: Rear End Pressure
 

Wait a minute . Why is there a problem when it has been OK for the last 90 years? Henry had some way to make it work. I can see with an overdrive that it is not the same as Henry designed it to be. I have just rebuilt my differential so this is a timely post for me. Jack

Re: Rear End Pressure
 

Took an extra bolt per post 9, drilled a small hole, threaded end of a short piece of steel brake tubing, installed with some permanent locktite, attached plastic tubing to that. I use permatex thread seal on the bolts. I have an OD and probably a torque tube gasket which blocks any vent path.