Leaf springs are resilient and normally long-lasting, but can eventually deteriorate so that ride comfort becomes abysmal and the car’s safety is affected. Kim Henson describes how to remedy the situation
Leaf springs were used at the front and rear of most cars until the late 1930s, and at the rear end typically until the late 1970s on cars, later on light commercials. They can survive for many decades in normal use of the vehicle, but as time passes and mileage accumulates, leaf-springs become vulnerable to a range of potential ailments.
Part of the maintenance schedule for a leaf-sprung classic should include periodic close inspection for erosion/rusting/cracking/breakage of the leaves, excessive sagging (often the first sign of trouble), and for deterioration of the mounting pins, shackle assemblies and ‘U’ bolts.
In addition, the mountings and the spring eye bushes (usually composite metal/rubber types) need to be inspected, together with any bushes located within the ‘chassis’ structure of the car. These can wear, together with the pins (securing the ends of the springs) that sit within them, allowing unwanted excessive movement that can effectively ‘steer’ the car from the rear.
Note that in many cases, lubrication points are provided for metal bushes, so that these bushes and the pins they support can be re-lubricated regularly (ideally every 1,000 miles), thus minimising wear.
In the case of rubber bushes, the structure of each one should be assessed, and if replacement is found to be required, the bushes should be renewed in axle sets.
Such checks should be carried out at least once a year, or approximately every 12,000 miles, whichever comes first. Seriously worn/damaged components need to be renewed – again in axle sets.
Our photograph and caption sequence depicts typical procedures required to change a rear leaf spring (always renew in pairs). However, working procedures can vary, and there are often alternative approaches that can be used. It is recommended that you should always study the ‘suspension’ section of the workshop manual for your vehicle, to establish the specific method(s) recommended by the manufacturer for each aspect of the work.
New springs can be obtained from marque specialists, or sometimes through the owners’ club(s) relating to a particular make or model. Alternatively, if the basic structure of the springs is sound, specialists may be able to dismantle and renovate them. However, this will depend on their professional assessment of whether the springs are in a suitable condition for this work to be carried out. And if there’s a local blacksmith in your part of the world, they can often ‘reset’ sagged but unbroken springs – and of course you’ll be helping keep a traditional part of rural Britain in business!
When renewing leaf springs, always check all mountings and other ancillary components before starting work, and obtain all necessary spares in advance. This could avoid the car being off the road for longer than you would like.
Note that in some cases the axle is not located centrally within the length of the springs; check this aspect or the axle could possibly be fitted out-of-line…
Start by raising the vehicle and securely supporting its body on axle stands (placed under strong parts of the structure, such that the springs and their mountings can be accessed easily, and lowered from beneath the vehicle). NEVER venture beneath a vehicle supported solely by a jack or jacks.
It’s best to work on one side of the vehicle at a time; each of our photo captions refers to the components per side. Always beware of dust and debris; wear protective goggles.
TOOLS & EQUIPMENT REQUIRED
- Trolley jack(s)
- Axle stands
- Penetrating oil
- Variety of screwdrivers
- Selection of pliers/grips
- Various levers and drifts
- Copper-faced and normal hammers
- Torque wrench
HOW EASY? **
In theory this work should be straightforward and should not take more than say three hours in total to tackle both sides of the vehicle. However, in reality, it is likely that corrosion and seized pins, bolts, etc. will conspire to add hours to the job. Allow at least half a day per side.
For cheerful help with this feature, grateful thanks to John Farrow of J.& C. Motors in Bournemouth (Tel. 01202 429420).
1. After applying penetrating oil to all fasteners in advance of the work, the nuts securing the retaining plates of the swinging link/shackle assemblies (where fitted) or the mounting pin at the rear end of the spring, should be released.
2. The next step is to release the nuts (and washers, where fitted) from the ‘U’ bolts holding together the spring, axle and spring retainer plate. Beware of sudden downward movement of the spring and its retaining plate.
3. The nut securing the forward mounting pin for the spring should now be slackened but not yet removed. Apply copious quantities of penetrating oil to the pin, which can seize within the steel tube forming part of the spring eye bush.
4. Unwind the nut on the pin at the forward end of the spring, so that it covers and protects the end of the thread on the pin, then, using the MINIMUM amount of force necessary, use a copper-faced hammer to drive out the pin (remove nut in final stages).
5. In reality, the pin may be seized solid, and won’t budge. In this case gentle heat from a plumber’s blow torch can be applied to the pin, to release rust and free it. DO NOT apply heat near fuel lines, etc. Note that spring eye bushes will be destroyed by heat.
6. In theory it should be easy to remove the nuts from the two pins forming part of the swinging link/shackle assembly found at the rear end of most rear leaf springs. However, in some cases the pins may rotate with the nuts, in which case it may…
7. …be necessary to weld the offending pin(s) to the shackle assembly’s ‘fixed’ side plate. The nuts securing the removable plate to the shackle assembly can now be removed, then the plate. Now withdraw shackle assembly from spring and ‘chassis’.
8. With all fixings released, at last the leaf spring can be lowered away from under the vehicle. Take care, as springs can be very heavy (especially those fitted to light commercials, usually with more leaves than equivalent saloon models).
9. It is interesting to compare the typical profiles of new and worn leaf springs. In this case the original spring, which had been sagging when fitted to the vehicle, had much less of a curved profile than the new spring which was purchased to replace it.
10. Prepare the swinging shackle assembly components in readiness for fitting. If re-using the original assemblies, ensure that they are spotlessly clean, and that the pins are sound and rust-free. Comprehensively coat pin surfaces with anti-seize copper grease.
11. Engage the forward end of the new spring within its mounting ‘cage’ in the ‘chassis’. In this case the new springs came complete with new spring eye bushes (if not, the new bushes will need to be pushed into the spring eyes using a vice or a press).
12. Coat the entire surface of the forward mounting pin with copper-based anti-seize grease then slide/tap the pin into place to locate the spring eye in the mounting on the vehicle. Fit the retaining washer(s) and loosely attach the securing nut.
13. At the rear end of the spring, fit the pre-greased swinging shackle assembly to locate in the spring eye bush and the ‘chassis’. With brand new or re-tempered springs this can be difficult; the pronounced curvature of the spring effectively reduces its length!
14. It is often necessary to have to gently tap the swinging shackle assembly into the spring eye and ‘chassis’ bushes. However, if you meet ‘solid’ resistance, DON’T use excessive force; remove the shackle assembly and investigate/rectify the problem.
15. To help ensure that the new spring locates correctly and easily within the available width between the ‘U’ bolts, and on the mounting pad/cut-outs on the axle, use a pair of grips like this (reacting against the axle) to guide the spring into place.
16. If you are struggling to get the new spring aligned correctly with the swinging shackle assembly and the ‘U’ bolt location, it can help to use a spare trolley jack to raise or lower the nose of the axle assembly; slight movement is usually all you need.
17. When the new spring is correctly engaged at its front and rear ends, as well as at the axle, you will probably find that the rear swinging shackle assembly is angled forward like this (compared with being angled rearwards, with a worn spring!). This is normal.
18. Initially the car will ride higher than usual, but the new springs will soon settle down. The nuts/bolts should be tightened with the weight of the car on its wheels (observe torque recommendations). Re-check torques after around 100 and 500 miles.