Clutch and gearbox overhaul
As already
stated in my thread (My 1972 Premier President | Ownership Review)before, the clutch friction plate was found to be badly glazed although it had enough material on it. The pressure plate springs seemed fine, though the fingers were too far gone. I decided to take my time and tackle all issues one by one.
Gearbox
The gearbox itself had no issues. Shifting was fine too. However, it was leaking oil from everywhere barring the output shaft seal. The construction of the 1100 4-speed column shift gearbox is quite simple, especially as compared to the Ambassador according to my mechanic.
The gearbox is a three piece unit. The front section is just a cover which houses the release bearing and fork while also locating the starter. It enables the box to bolt onto the engine.
The centre section is what houses the cogs. 1st and 2nd gear are located on one shaft, with 3rd, 4th on another and finally reverse being located on its own shaft. There is a top cover here which is also called the inspection cover. It allows access to the gearbox internals in case some maintenance is to be done (like changing the selector shaft seals in my case)
The tail of the box is hollow. All it houses or covers is the output shaft, the shaft bearing itself, speedo pinion and the output shaft seal and flange. It is quite long considering it doesn’t really do much. I believe this has been done to reduce the effective length of the prop shaft and eliminate the need for a centre bearing carrier (something which the S1 column shift needed because the gearbox casing was too short and the prop shaft ended up being too long).
Coming to the crux of the matter, the gearbox has 3 gaskets (or packings in local lingo) and 4 oil seals.
- The input shaft seal sits inside the release bearing carrier as shown later. It prevents oil from seeping into the bell housing and wetting the clutch plates. It also sees the highest oil pressure IMO and is the first one to go in most cases
- The output shaft seal sits in the tail just behind the output flange where the prop shaft coupling bolts. It doesn’t see as much oil as the input shaft seal since there’s just enough pressure to lubricate the output shaft bearing only
- The two selector seals sit on either ends of the selector shaft which runs through the width of the entire box. They are responsible for containing any residual oil which sticks to the shaft itself and prevent it from seeping out when the shaft moves back and forth. These are located quite high up, so they again don’t see much oil
The three gaskets seal parts of the gearbox body to each other:
- One gasket goes between the front bell housing cover and centre
- The other seals the top cover to the gearbox centre body
- The third seals the tail end to the centre
It is crucial to note that the speedo pinion doesn’t use a gasket or at least it seems so. No one makes them. It is however advisable to use silicon gasket maker and seal it to prevent oil from weeping out. There is also an O-ring on top of the release bearing carrier which is present to prevent gearbox oil seep from the countershaft into the bearing carrier and then bell housing. Most mechanics remove it gingerly, but I believe it should not be done.
Dismantling the gearbox for gasket change is quite easy. The three halves are held together using 13mm nuts and spring washers. The top cover is held using 4 10mm bolts and spring washers. It is necessary to drain the oil, preferably when the box is mounted on the car itself. This can be done by removing the 17mm drain nut located underneath at the centre of the gearbox.
Input shaft seal change
After removing the 7 13mm nuts holding the front casing to the centre body, the former can be lightly pried away or tapped out and separated. This will then expose the bearing carrier bolted to the front of the centre body with the O-ring I mentioned before on top. Remove the O-ring and there are 3 14mm bolts with spring washers holding the carrier down onto the input shaft. Remove these and take the carrier out. The inside of the carrier will have the input shaft seal.
Changing the shaft seal is as easy as prying the old one out and putting a new one in. Apply some grease on the inner part of the seal where the input shaft rides to offer some lubrication.
Once the front bell housing cover is removed, the bearing carrier comes into sight. Don't miss the countershaft with its bearing below:
The O-ring on the carrier ensures that any residual oil which gets splashed around from the countershaft doesn't end up on the front of the carrier and then make its way out into the bell housing where the clutch plates sit:
Once the carrier is removed, the input shaft seal comes into sight. The old one (shown later) was as brittle as a biscuit. After removing the seal, I was perplexed to find a weep hole in the carrier itself. I think this is to allow some oil to intentionally weep onto the carrier where the release bearing slides and lubricate it. Very odd considering the O-ring shown above which is supposed to do the complete opposite:
Output shaft seal change
The output shaft seal is even easier. But it does need the output shaft flange to be removed. Since I anyway had to reseal the entire box, I decided to remove the rear section too. The rear section or tail casing is held by 6 13mm nuts and spring washers. Before that however, the prop shaft centering ring needs to be removed. It’s held onto the output shaft by a circlip. After this, there’s a toothed washer which is bent onto the main shaft nut which needs to be straightened. The shaft nut can then be removed and so can the output flange. Post this, remove the tail casing nuts and pry it out to separate it from the main body.
The end of the tail casing itself houses the output shaft seal. Simply pry the old seal out and put the new one in.
The rear casing removed. Note how this section of the gearbox doesn't really house any gearbox components per say. It only has the output shaft, bearing and speedo pinion (mounts on the rear case) apart from the prop shaft flange:
The output shaft seal seen here. Simply needs to be pressed in and gently tapped using a rubber mallet:
The prop shaft flange in place right on top of the output shaft seal:
The flange is then secured using a toothed washer and a nut. Once the nut is tightened, one edge of the washer is hammered using a flathead screwdriver and folded over the nut to ensure it doesn't come lose (this step isn't shown here):
Post this, the centering ring for the prop shaft coupling goes into place followed by a circlip on top to secure it. That finishes the rear case assembly onto the gearbox.
Selector seal change
The two selector shaft seals are a bit tricky. These cannot be changed without pulling the selector shaft out entirely. For this, open the top cover held by 4 10mm bolts and spring washers. There are 3 springs and balls which locate below one side of the top cover. Ensure that these are either removed and kept safely or don’t fall out. Once this is done, undo the two 10mm bolts which secure the selector shaft to the arms which actuate the 3 rods which are responsible for moving the engaging forks and selecting gears. Pull the selector shaft out post this.
The two bolts circled in red need to come off in order to pull the selector shaft off. Not as easy as it sounds unfortunately:
In order to change the selector seal on the pax side, the spring and cup for the reverse gear will need to be removed. Two 10mm nuts and spring washers secure these over studs on the box. After this, the seals should be visible at both ends. Simply pry them out and press the new ones into place.
Putting everything back isn't exactly a breeze. I did get stuck here and had to take help from my mechanic. The selector shaft, arms and the three rods housing the selector forks need to be moved around a bit to secure the shaft to the arm and insert the 10mm bolts. It’s more of trial and error than anything else. Then, it was simply a matter of putting the reverse gear spring and cup back on the pax side of the box
With the main objective of this DIY achieved, the gearbox has to come back together. Start by putting the top cover back with its gasket. The gasket only goes in one way. Again, ensure that the 3 springs and balls which locate below it on the rear are in place.
The front can then come together. Install the release bearing sleeve back and secure it in place. Then install the gasket for the front cover and mate the front cover to the main body.
The rear has to go back in reverse order of dismantling. Put the rear casing in with its gasket first and secure it using the nuts. Then install the output shaft flange, toothed washer and then nut on top of it. Tighten the output shaft flange nut as much as possible and then take a flathead screwdriver to hammer the washer and lock the nut into its place. Finally, install the centering ring for the prop shaft coupling and secure it using its circlip.
With this, the gearbox is pretty much done. I did undertake a couple of more jobs which I will list below & a few extra tips which might help:
- The fulcrum and arm mechanism which allows the selector shaft to move back and forth was worn. The pin which is essentially the fulcrum has an arm with a bush inside slide onto it. The bush had worn causing excess play. This had also caused some play in the gear lever. I had the bush fixed by an experienced lathe guy
- The top cover looked like it had seen better days. My friend offered to paint it for me. Needless to say, he did a fantastic job though we couldn’t find an exact match for the stock colour
- The entire box was covered in a solidified layer of grime and gearbox oil. I had the casings washed separately using diesel and harpic before putting it back together
- I applied some anabond gasket maker on both sides of the gaskets before putting them into place and ensured the gaskets were compressed perfectly post tightening
Some mistakes made along the way and lessons learnt:
- The gearbox should have been cleaned thoroughly before dismantling. Also the top cover has a pinhole for ventilation. It has to be covered before pressure washing the box
- The top cover has a gasket which prevents oil splashing around inside the gearbox from escaping through the pinhole. My mechanic insisted I don’t install it after I ruined the new gasket while removing the top cover again (reason mentioned in the next point). He asked me to just use gasket maker and seal it. Was a mistake. Some oil does seep through that pinhole now after a spirited run
- The top cover had to be removed again as mentioned above because I had installed the selector shaft seals inside out. These only go in one way as shown in the images
The inspection cover looked worse for wear. Although its a part that cannot even be seen when the box is in place, we decided to paint it anyway. Also note the weep hole I mentioned before. It allows excess vapours to escape:
Post painting. We tried thinning red oxide with some spirit, however, it wouldn't adhere to the aluminium correctly. Finally, decided to get the closest shade and just spray paint the cover:
The old input and output shaft seals. The input shaft seal sustained a lot of damage when removing. Thankfully, all shaft seals (for both engine and gearbox) are easily available at industrial machine shops. All one needs to know is the OD, ID and thickness and finding an equivalent seal is a breeze. Gaskets can also be made at home if the need be (as I will demonstrate later in the thread):
That’s about it when it comes to the gearbox. Fortunately, everything went according to plan and nothing major came up apart from what I had thought needed to be changed.
That sums up the gearbox reseal and clean. I will document a couple of other jobs I undertook including cleaning the oil sump, oil pump strainer, installing a new main oil seal and of course, adjusting and installing the new pressure plate and clutch.
7th March 2025, 04:16
(36)
Thanks
