Gearbox rear oil seal change

[stretoo]

Hello everybody.

What is the best procedure to change the gearbox rear oil seal? Box is a EJ type from a FHC 4,2 L (and is on the car). Thanks in advance for your help.

[christopher storey]

Yikes, I fear you are in trouble. It may be possible to do this in a 2+2, but in a short wheelbase car I think it is near to impossible without removing the engine and gearbox because there is insufficient clearance to move the rear cover of the gearbox backwards

[mgcjag]

Hi Stephane........had a problem on a friends 1970 S2 ots.....needed to fix the speedo drive inside the rear gearbox cover.....the cover could not be removed once the prop shaft was disconnected & to remove the prop we had to take out the IRS......could then remove the rear gearbox cover....hope this helps......Steve

[stretoo]

Thank you very much Steve. It certainly helps as it's easier to unbolt the IRS than remove the engine. I will investigate further about E types oil leaks.

Christopher: thanks for your information, I'll try to avoid removing the engine.

[stretoo]

I found this picture I have taken a few months ago. Apparently there is enough room to unbolt the propeller shaft but I don?t know how far I can push back (and/or down) it to access the flange securing nut. Before dismantling the console I would like to have your thoughts about it.

[christopher storey]

Stephane : if you also undo the propshaft to rear axle bolts , as well as the gearbox to shaft bolts, you will probably be able to drop the shaft sufficiently out of line to get at the large nut . You cannot completely remove the shaft from the car without taking out the rear suspension, but you will probably displace it enough to do your job

[stretoo]

Thanks Christopher this is a brilliant idea and it?s worth to try before unbolting the IRS. It could be useful to know the useable length to move along the splined shaft and the flange internal length. I would get an idea of how much I will have to move the propeller shaft to have a chance to remove the flange (therefore whether there is enough room to do so)*.

(*) I?m not sure it?s clear; sometimes I regret English is not my mother tongue.

[attwood]

I have successfully removed my gearbox rear oil seal from under the car without removing the IRS, although I did have to move it slightly. After removing the exhaust and the gearbox mounting it is possible to unbolt the front propshaft flange. This did not give enough clearance to remove the split pin and nut which retains the gearbox flange plate so I also disconnected the handbrake cable from the mechanism on the IRS cage and unbolted the rear propshaft flange. This allowed me to move the propshaft back a few centimetres along the handbrake side of the diff.

With this clearance I was able to remove the split pin and big nut (28mm ringspanner) from the gearbox flange plate. Unfortunately there was still not enough clearance to get the flange plate off the shaft, so I disconnected the two rear cage radius arms where they bolt to the floor of the car. By jacking under the rear of the diff the rubber mountings of the cage are flexed and the cage moved back enough to give the clearance I needed. The flange is 39mm long.

The most difficult part was undoing the four countersunk screws which retain the oil seal. These are designed to be undone using a large flat blade screwdriver and working in such a tight area with the bottom of the gearbox endplate in the way and a screwdriver which is 10 times longer than it needs to be has a high potential for going wrong! The ideal tool would be a flat screwdriver bit and a ratchet, but it would need to be a very large screwdriver bit and I have not seen one that big. I have a screwdriver with a square shaft so I was able to turn it with a spanner, but holding it tightly enough in the slot of the screw is not easy. I will be putting Allen screws back in! (5/16" UNC x 5/8" CSK).

The reason for my oil leak was clear. The oil seal was brittle and cracked and there did not appear to be a gasket behind the oil seal retaining plate, unless it is a very thin paper gasket which had become brittle and disintegrated. Not an easy job, but certainly preferable to removing the engine and box!

[stretoo]

Thank you very much Dave for these valuable information. I hope it works with S1 FHC too.

[attwood]

Small correction - the screws holding the oilseal retaining plate are slightly longer than I said previously, so the description should be 5/16" UNC x 7/8" CSK. Apparently the CSK head needs to be included in the length.

[tim wood]

I know this is an old thread but I found it useful when changing my tail shaft oil seal.
A couple of points which may be useful;
I am doing mine from inside the car whilst no trim is present. A major issue seems to be gaining enough clearance to get a socket on the nut which secures the flange. I managed this by unbolting the propshaft at both ends and then by taking out the 4 bolts which hold the anti roll bar to the chassis I could wangle the prop right back with ample room.
The socket size is 1 1/8 and I had to use a 3 foot bar to loosen this.flange came off easy and then to the 4 screws. As others have said the top 3 are easy but getting to the one at the base is a struggle. I must admit I butchered this by tapping it loose with a long screwdriver lodged in the slot and a quick tap from the top.
The tip on here to use Allen headed screws when refitting is a good thought.

Tim

[politeperson]

I replaced my rear gearbox seal with the gearbox out as it was old hard, cracked and leaking.

On refitting the gearbox it still leaked because the front gearbox seal was as bad (it was probably the same age), the selector O rings were were hard and the speed o ring was hard.

Also the rear extension gasket was hard and the gearbox top cover gasket was leaking!

After I replaced all those bits (about £8 quids worth), it didn't leak.

[tim wood]

So, as part of this job I’m going to change the o ring on the speedo drive. As James notes the existing one is oil and age hardened. I’ve pulled the drive out - no problem. I’ve also taken the worm drive off the output shaft, more to clean it up really. On looking at the assembly I can’t fathom what prevents this worm drive from just spinning on the shaft. It’s not secured or fixed in any way. Unless when the entire assembly is fixed and the flange nut tightened this presses it all together?

Am I missing something?

Tim

[angelw]

Tim Wrote:

On looking at the assembly I can’t fathom what prevents this worm drive from just spinning on the shaft. It’s not secured or fixed in any way. Unless when the entire assembly is fixed and the flange nut tightened this presses it all together?

Hello Tim,
It's clamped in position when the Companion Flange Nut is tightened. The Oil Pump Drive further up the Main (output) Shaft also has no other means of driving it than clamping pressure when the nut is tightened.

Regards,

Bill

[tim wood]

Thanks Bill

[tim wood]

So, the new seal is fitted and the housing secured with countersunk Allen head screws. The flange is fitted but not fully tightened. Does anyone know the torque figure for the securing nut? I’ve checked my manuals and the knowledge base but can’t find this detail.

All I know is that I had to use my breaker bar to loosen it off !

Thanks

Tim

[angelw]

Tim Wrote:

So, the new seal is fitted and the housing secured with countersunk Allen head screws. The flange is fitted but not fully tightened. Does anyone know the torque figure for the securing nut? I’ve checked my manuals and the knowledge base but can’t find this detail.

Hello Tim,
A properly tightened fastener is one that is stretched to the extent that it acts like a very ridged spring pulling mating surfaces together. If the member is stretched past the natural elasticity of the material, this pulling effect is nullified and the member retains the stretched condition when the tightening force is removed. Accordingly, the design torque for a particular diameter and material of the component will be set within an upper and lower limit.

The nut clamping the components assembled on the Main Shaft of your Gearbox doesn't rely on the stretch of the shaft to keep it tight, but uses a split pin passing through a castellated nut and a cross hole in the shaft. Accordingly, the torque applied to this system is not overly important, save that it must be sufficiently tight to clamp component that rely on friction to drive, from turning on the shaft.

The thread diameter of the Gearbox Main Shaft is similar to that of the Differential Pinion Shaft, but with a different pitch. Therefore, I use a torque from 90lbft to 110lbft (less than the torque range specified for the pinion shaft), that will allow the split pin to be assembled with the castellated nut and the cross hole in the shaft.

Regards,

Bill

[tim wood]

Thanks Bill,
I also posted on JL and you kindly replied to that post also.
Your responses are always factual and educational and for that I’m grateful.

Job is complete now


Regards

Tim