Gearbox

[Acollin]

1966 sunbeam alpine mostly stock.

Hello all
I should have asked this question awhile back.

Now that my gearbox swap is about done— just waiting on a few small bits from Rick at SS, I thought I would try to better understand the leak in my old gearbox.

***Question: Can one see if / where a seal on a gearbox is leaking with the gearbox removed from the car?
I would like to see the leak on my old gearbox and replace the seal that I believe is leaking.

My new to me gearbox was a gift from a generous forum member who said his gearbox did not leak. I believe him— but It would have been nice to check it out. Too late now anyway!!! I will know soon enough when I get a new manifold to header gasket from Rick.

As stated in a prior post, I will review the “Quickjack” when the swap is complete.
Be well all
Andrew Collin
Sandy, Oregon

 

[puff4]

I suppose you could fill it with a light oil and *gently* pressurize it via one of the OD switch ports... but you'd need to seal off the rear housing where it connects to the drive shaft by inserting the drive shaft or some other manner.

And when I say gently... I mean no more than a couple of pounds of pressure. You don't want to blow out a seal!

 

[husky drvr]

Andrew,

You might want to review the WSM on which parts are at the front of the case where a leak might start and relevant tear down and assembly notes.

Might be as simple as an old, OE oil seal past its prime, torn or missing gasket, or possibly the sealant required on the layshaft front not there or broken down.

Just a thought,

 

[Acollin]

I believe I might have found a way to determine a certain type of leak in the front gearbox seal and I wish I would have done this simple test before I put in the new to me gear box. Still waiting on my parts with all installed except for some exhaust bits.

I tipped my old gearbox on an angle downward toward main shaft end and left it there for a day or two. A telltale puddle appeared. As I looked more closely at the area, I could see that the seal had some slight high and low spots at the gearbox sealing port. I will try to take a picture so you can see what I am looking at. The seal was not flush all-around to the case. The seal appeared to have a reasonable fit so I cannot say for certain that this was my problem, but it could very well have been.

Question: Does the gearbox need to be under pressure to leak ? My car appeared to be leaking only when driving it.

If any of you have a 4 speed synchro out of a car lying about, would you try the simple angle test and report in. Good seal or not— would be best if you could say with some certainty the seal was good or not before the test. I speculate you will learn if the seal is good or not. It will not help me but could help others— doing a test before a gearbox installation / a seal replacement job.

an aside/ some evidence: when I bought my car in 2014, the prior owner asked me if I wanted the “ drip pans” too. I said sure!! It is also clear to me from just having done the teardown/install, the gearbox had been out of the car before as I am only the 3rd owner— PO bought the car in the late 1960s. My speculation - as the PO is no longer with us - is that he probably did a clutch job and replaced the seal at the same time and it leaked from the get go. Not enough to cause a super fund site, but enough to be annoying to the point that drip pans made sense and not annoying enough to take the gearbox out again to put in a new seal.

 

[John W]

I have a 4 speed synchro out of a car (that was replaced with an overdrive years ago). I don't recall it leaking when in the car. Out of the car, before draining the oil, without the driveshaft in, the rear would leak, and the front stayed dry. I just now checked it to refresh my memory, and the rear is still wet, and the front is dry.

 

[puff4]

...
Question: Does the gearbox need to be under pressure to leak ? ....

No. Indeed, your test seems a good one.

That being said, as the car heats up, the air in the top of the gearbox also heats up ,and that expansion, if fairly rapid, has the potential to push oil out of a seal. However, as noted earlier, that expansion pressure would likely be very low - I'm guessing in the 1-1.5 PSI range.

 

[puff4]

I have a 4 speed synchro out of a car (that was replaced with an overdrive years ago). I don't recall it leaking when in the car. Out of the car, before draining the oil, without the driveshaft in, the rear would leak, and the front stayed dry. I just now checked it to refresh my memory, and the rear is still wet, and the front is dry.

The driveshaft needs to be in the transmission or the rear will leak. The rear seal in the gearbox runs against the nose of the drive shaft!

 

[husky drvr]

That being said, as the car heats up, the air in the top of the gearbox also heats up ,and that expansion, if fairly rapid, has the potential to push oil out of a seal. However, as noted earlier, that expansion pressure would likely be very low - I'm guessing in the 1-1.5 PSI range.

Not sure pressure could go that high considering the way the shift rail is formed with its top vent and no sealing for the bottom cover.

Just a thought,

 

[Acollin]

Really frustrating!
I got my last few parts from Rick at SS this morning. Put on the new header gasket, reconnected carb linkage, new copper crush washers, refilled the radiator and the gearbox. Reconnected the battery- closed hood.
Brought the car down to Earth— got in, pressed in the clutch pedal and my slave cylinder failed— pedal to the floor( got one pump) and a nice new puddle on my drip pan. While I might not have checked that the push rod had reseated, the fluid was black and appeared watery and there was a rusty muck plug in that rubber cap. I pulled the slave cylinder down and also found a scored bore. Rick at SS was my first call. New slave cylinder is on the way— maybe Saturday or more likely Monday.
A couple questions:
1) what is the preferred fluid for a series V clutch hydraulic system?
2) Rick also suggested that the slave cylinder could mount on either the front or back of the bell housing. I could not understand which way The slave cylinder should mount for my situation—something about the throw of the rod?? any advice?
Be well all
Andrew

 

[hartmandm]

Unless you have changed the fluid used in the clutch hydraulics, it is the same fluid as the brakes - DOT4 Low Moisture Absorption. I use Castrol.



Slave cylinder needs to be on the back side of the bell housing.



Mike

 

[John W]

The driveshaft needs to be in the transmission or the rear will leak. The rear seal in the gearbox runs against the nose of the drive shaft!

Guess I should have clarified my observation. As stated above, my non-synchro stock transmission had no leaks when the transmission was in the car. The front seal doesn't leak (in or out) of the car. So... since I've "stored" this transmission in all sorts of positions over the years with and without oil in it, and since the front seal has never leaked with oil IN it, then my assumption is that with the transmission out of the car, AND with the drive shaft inserted into the rear of the transmission, a simple "angle test" should reveal no leaks if the seals are good, and WOULD reveal a leak if the seals are bad (that's also assuming that pressure build up during operation wouldn't cause a leak, in which case an "angle test" wouldn't work. Hope this helps.

 

[beamdream]

Not sure pressure could go that high considering the way the shift rail is formed with its top vent and no sealing for the bottom cover.

Just a thought,

Re the shift rail vent; I once had a blocked vent which caused significant leaks from top case, plus front and rear seals. Took me forever to find the problem, couldn't work out why there was so much oil spread around the upper surface of the trans tunnel.

So yes, obviously the box will pressurise during normal operation, always worth a look at the vent hole when the box is out.

 

[husky drvr]

Re the shift rail vent; I once had a blocked vent which caused significant leaks from top case, plus front and rear seals. Took me forever to find the problem, couldn't work out why there was so much oil spread around the upper surface of the trans tunnel.

So yes, obviously the box will pressurise during normal operation, always worth a look at the vent hole when the box is out.

Thanks, good to know.

 

[jumpinjan]

Do not store a good transmission in a vertical position, please keep it level. Why? The sludge in the bottom of the transmission case will flow into the main bearings, and you should know the sludge is full of fine metallic particles.
Jan

 

[RootesRooter]

Wow. I've got a lot of shelving to reorganize. Besides turning a tranny upside down on the tail shaft and perhaps draining out the sludge, are there any cures to avoid messing up the main bearings?

Do not store a good transmission in a vertical position, please keep it level. Why? The sludge in the bottom of the transmission case will flow into the main bearings, and you should know the sludge is full of fine metallic particles.
Jan

 

[hartmandm]

Maybe using detergent oil in the gearbox and a magnetic drain plug? I guess there is some brass in there though.

Mike

 

[beamdream]

Hmmm, is this an OD box ? If so not sure I would use anything other than straight 30 oil.