Replacing MG TD front suspension bushes using modern polyurethane components

3 Jul

The front wishbone suspension bushes give the independent front suspension its ability to permit the lower spring pan to swivel on the pivot arm, and move freely up and down with the objective of absorbing road induced shocks. In practice the TD’s front independent suspension became a long standing design that was introduced with the TD in 1950, and survived the TF, the MGA, B and C and through to the final MGBV8 of 1992, albeit in an up rated format.

The original suspension bushes were made of a rubber compound, and are still available as standard replacements that have done an admirable job. However, it is no wonder that these rubber bushes can show signs of wear, they have a hard life, firmly locating the suspension components in relation to one another as well as helping to absorb vibration and noise.

Rubber bushes deteriorate over time and it is now common to use a more modern polyurethane replacement. Although the replacements are more expensive than the rubber originals they are much harder wearing and, as they are time consuming to replace, it makes sense to invest in the modern updated replacement.

John James of TTT 2 supplies Autobush quality polyurethane bushes jj(at)octagon.fsbusiness.co.uk

SuperFlex, also makes a quality product suitable for the T-Type. I understand that the bushes are not moulded but rather made from a solid rod that is accurately machined to size and therefore likely to be a good fit. SuperFlex makes the bushes in various strengths (i.e. for the MGBT V8) so it is worth ensuring you purchase the most suitable bush, the TD requires the soft version as used on the standard MGB.

For use in every day driving, visit www.superflex.co.uk – click on BMC, then MGB and select SF251-001KSS Front Wishbone Inner Kit. (Superflex, Wells. Tel: 01749 678152)

Replacing Front Suspension Bushes

Before starting the job of dismantling the suspension it is useful to ensure that you have all the correct tools and parts, it will be beneficial to have a hydraulic jack and axle stands to allow full access to the suspension. It also worth slackening the wheel nuts whilst the wheels are still on the ground so that they can be readily removed when lifted.

I found it is best to have the chassis jacked up and securely supported on the axle stands, or heavy wooden blocks, (see photo 1) in order to give safe access to all the necessary under chassis components. With the chassis jacked up you will have room to remove the un-tensioned spring that extends to 10” in length.

Photo 1

With the chassis raised on axle stand or blocks, the hydraulic jack can be re-positioned to underneath the spring pan to take the tension of the spring during dismantling (see Photos 2 and 4).

Photo 2

Photo 3 – Front Nearside suspension showing the wishbone arm bush at the inner end (left arrow) and the swivel pin nut at the right (inset) arrow.

The tension in the coil spring is considerable so great care should be taken to ensure that this energy is controlled. If the energy is released in a dangerous manner this may cause injury.

With the chassis of the vehicle firmly supported off the ground, place the hydraulic jack under the spring pan and raise the pan slightly to apply some tension in the spring but with the hydraulic damper levers clear of the rebound rubber.

The four bolts (item 30 on full page diagram) that secure the pan to the wishbones are now slackened off and the bottom link outer pan bolt (46) is now ready for removal. With this pan bolt removed from the swivel pin (45) the wheel hub/swivel assembly can be lifted up and supported by a block of wood between the shock absorber and its arm (see Photo 4 which shows Off Side suspension assembly).

Photo 4: the hydraulic jack under the spring pan (24) being lowered (in a controlled fashion) to allow the spring pan to be pushed down, gently releasing the spring tension as it expands in length.

Note: It is quite surprising how long the un-tensioned spring can be, so it is important to have the car high enough, on its stands or blocks, when lowering the wishbone assembly.

Having released the tension on the spring, push down the wishbone assembly and remove the spring. The front wishbone arm (25) can now be removed from the pan (24) by removing the 2 screws and nuts (30), that were slackened off earlier in the procedure.

Remove the front pivot arm split pin and nut (29) followed by the washer (28), this will allow the arm to be separated from the pan along with the front bush (26). Remove the rear pivot arm split pin and nut (29) followed by washer (28) allowing the removal of the spring pan, rear arm and assembly. One can now place the assemblies on the workbench for inspection noting any excessive wear.

At this stage it is worth noting that the bottom outer pin bolt has a number of important components that should be checked for integrity, during removal, including; slotted nut (37), spring washer (42), link seal, quantity two (40), support washer, quantity two (41), thrust washer, quantity two (39), one distance tube (38) and finally bottom bolt (46). Note. If the old bushes have oval holes this could be a sign that either the wishbone arm is bent or the swivel pin assembly thrust and support washers are missing.

Photo 5: Check the spring pan for corrosion or damage due to wear, and repair or replace as necessary. After any repairs and clean up, a fresh coat of paint (Hammerite) is a good idea as the area of the pan where the spring sits is liable to hold any water contamination from driving in the in the rain. Ensure the drain hole in the spring pan is clear.

The inner wishbone bushes (26) are now removed from the arms. I found that the old bushes were a tight fit and it was useful to employ a long nut and bolt plus a small tube and washer to press them out.

The wishbone holes should be inspected at the (outer) Swivel Pin end to ensure there are no signs of wear, if any hole is enlarged or worn the appropriate arm (25) should be replaced.

The pivot arm (21) should be checked for damage or wear. If dirt has contaminated the old bushes, this can result in pitting on the pivot arm end bearing surfaces. Give the arms a good clean and inspection. Some wear is likely as the old rubber bushes were more prone to allowing ingress of dirt. The arms can be etched primed and given a spray coat of black gloss to provide some protection. As the replacement poly bushes have a stainless steel inner sleeve (and grease) the likelihood of further damage is reduced.



(Click diagram for bigger view)

Photo 6 – the pivot arm should be checked for damage and wear

New polyurethane bushes with the stainless steel sleeve are (silicone) greased and relatively easily pressed into the wishbone arm inner holes. It is useful to be able to complete the insertion by holding the wishbone arm (with both new bushes fitted) in a vice and give the bushes a final very gentle squeeze so that only the outer rim of the bushes is exposed.

This makes the alignment of the swivel pivot bolt (46) through the two wishbone arms easier.

Grease the rear pin on the pivot arm and slide the pan assembly back on, followed by the large washer and castle nut (28 & 29).

Note. If using bushes supplied by John James it is important not to push the stainless steel sleeve into the bushes until they are fully seated on the arm as they expand! To assist fitment of the stainless steel sleeve into the bushes it may be useful to use a vice as the bushes have an outer lip which is slightly smaller than the outer diameter of the sleeve.

The rear pivot arm can now be bolted to the pan, not forgetting to fit the head of the bolts to the inside of the pan.

N.B. Do not tighten up the spring pan bolts solid but leave half a turn slack.

The front pivot arm can now be bolted to the assembly as above. Do not finally tighten until the arms are parallel to the ground.

The lower pan assembly is now pushed down vertically, the fully extended spring, with both ends smeared with grease, can be positioned between the upper Spigot disk (17) and the pan. Check that the “drain hole” in the pan is clear of the spring as mentioned above. Failure to do this will encourage corrosion to the pan. Release the wooden support to the wheel hub/swivel assembly and lower.

With the spring fully extended it can be tricky to raise the pan to re-attach it to the lower swivel bolt (46). It is therefore a good idea to remove the rubber bump stop (14) as this allows the hub unit to drop down further hence the lower pan does not need to be jacked up quite so far before locating the outer swivel bolt (46).

A bottle jack, or similar, under the outer end of the pan enables it to be jacked up slowly to allow the location of the bottom swivel (45) with the various washers and dust cap into the wishbone arms allowing the fitment of the bottom link bolt (46).

Note. I did consider using a pair of spring compressors, to reduce the length of the spring during this procedure, but I understand that they will not fit within the available space.

With the spring back in place re-attach the wheels and lower the vehicle onto the ground. Allow the newly assembled suspension components to settle back in their appropriate position before finally tightening up the four spring pan bolts (30), swivel bolt (46) and both pivot arm nuts (29).

Note that the swivel pins have also been cleaned on this vehicle!

The work on the front suspension bushes is now complete and, on this TD, the re-fitting of wings and body panels can now proceed.

Photo 7 – a finished nearside front suspension and as clean as a new pin!

Ed’s Note: Article by Jonathan Goddard with valuable contribution from John Hinds.


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One Response to “Replacing MG TD front suspension bushes using modern polyurethane components”

  1. Paul Barrow 01. Aug, 2013 at 7:41 pm #

    Hi John

    Sorry – couldn’t let the comment in the article on replacing the TD suspension bushes of “In practice the TD’s front independent suspension became a long standing design that was introduced with the TD in 1950, and survived the TF, the MGA, B and C and through to the final MGBV8 of 1992, albeit in an up rated format.” pass without comment.

    Of course it was not the TD’s front suspension at all … it is the MG Y Type’s front suspension since without the MG Y there never would have been a TD!

    :-) – Tongue in cheek, keep up the good work otherwise.

    Paul

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