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How to replace your transfer box rear oil seal - pictures

by: Auto Express team

27 Sep 2017

Go to: How to replace your transfer box rear oil seal

Mark the propshaft flanges for refitting, then remove the propshaft nuts and bolts from the front and rear flanges and remove the propshaft.
Now you will be able to slacken off the brake shoe adjuster on the backplate, undo the drum nuts and remove the brake drum.
This is the oily mess I found after removing the drum. The handbrake still worked – though it was living on borrowed time!s
Next, remove the split pin from the castellated nut. Always renew the split pin, unless, of course, it’s an emergency breakdown.
Undo the flange nut, ensuring the gearbox is in gear with the wheels chocked so that the transfer box shaft won’t rotate and the vehicle won’t roll.
Now it’s time to remove the flange from the output shaft. It might need a few obligatory gentle taps with a mallet to get it loose.
Inspect the flange’s spigot face that contacts the oil seal. If grooved, it will damage the new seal, so a new flange is needed.
Anticipate more oil loss from the catcher by having a container ready to catch it, or drain the box prior to doing the job.
The brake shoes can either be removed now, or left on the backplate until later. I removed them now, due to their oily mess.
Undo and remove the four oil catcher bolts and carefully prise off the oil catcher. I’m using a thin broad screwdriver here.
Working from above, I prised back the dust seal from the backplate, and pulled the operating rod straight out of the adjuster.
Alternatively, undo this screw connecting the operating rod to the relay lever. Mine was distorted and fiddly to undo.
Now remove the backplate from the transfer casing. Access to the operating rod is not much better if it’s still fitted.
Prise out the old oil seal with a suitable screwdriver or seal removal tool. Ensure you take care not to damage the recess face.
Thoroughly clean the casing recess of oil and dirt. Stuff clean rag around the output shaft to prevent dirt getting in as you clean the casing. An old toothbrush and white spirit works wonders. Use a solvent cleaner in the recess
I smeared Wellseal around the outer of the new oil seal before fitting it flush into the recess. Press it in gently and evenly all round.
Now you can strip, clean and lubricate the brake mechanism. A fresh coat of paint on the backplate also proved worthwhile.
We’re now ready to fit the internally lubricated expander mechanism to the brake backplate, feeding it through the aperture.
Refit the three retaining clips in their correct order, remembering the middle and top also act as retainers for the dust seal.
A new dust seal costs very little and is worth fitting, especially if the old one has hardened, split or been contaminated with oil.
Fit new brake shoes and springs (or use original good springs after cleaning) and ensure the adjuster cone is fully slackened off.
Smear both sides of a new gasket with Wellseal or your personal trusted sealant, and also the inside face of the oil catcher.
Carefully position the oil catcher and its gasket on the backplate. Time for a tea break before working underneath again? Why not.
Fit the complete backplate and shoes assembly to the transfer box and tighten the securing nuts evenly to their specified torque
If re-using the old drum, then we advise you remove the glaze from the working surface using 400 grit wet and dry paper.
Soak a new output flange felt seal in gearbox oil and fit it to the flange. The black outer might separate, so check as it is fitted.
Lubricate the flange inner face (previously checked for damage) to ease fitment into the new oil seal as it is pushed on over the shaft.
Fit the flange to the output shaft. The felt seal might need carefully reseating to ensure it is flush, using a flat screwdriver.
Refit the castellated nut and tighten it to the specified torque, then fit a new split pin with a little grease to prevent corrosion. 
The brake drum can now be refitted. Check it is seated correctly and its retaining nuts are tightened evenly and gradually.
Reconnect the operating rod to the relay lever and tighten the adjustment nut only once it has been correctly adjusted.
Adjust the expander until the drum snags, then slacken off one quarter turn. Operate the handbrake lever to centralise the shoes, and re-check.
Reconnect the propshaft. Top up the transfer box oil if the level has dropped or you drained it. Adjust the handbrake after safely testing its effectiveness. You should now be able to play a game of ‘check the fixed leak’ for som