RcTek : Information & Resources for the Model Car Racer

PB Racing Shock Absorbers

The whole PB Racing range of car uses the same dampers, although the shafts used on the Dart are longer ones taken from a previous version of the 1/8th Diamond car. The older type 1/8th & 1/10th dampers had plain, non-threaded bodies, which are useful for implementing a double shock conversion on the Dart.

I have done a great deal of work on the shock absorbers and below are my observations and suggestions for building a better damper.

The Shock Absorber Parts

All of the parts are shown below and those that may need some minor alterations to ensure easy assembly and trouble free adjustment and/or maintenance are indicated.

All plastic moulded parts should have the flash (excess plastic left over from the injection moulding process) removed.

Top Alloy Cap - (#72/224 or #12/524)

PB Racing Top Alloy Cap

As they are very sharply cut, the threads on the top caps benefit from having their tops cut off as they can bind on the plastic threads of the damper body. I have found using a very sharp craft knife to shave the tops off the threads to be the most effective solution.

Trunnion Cap Moulding - (#72/223 or #12/523)

PB Racing Trunnion Cap Moulding

In direct contradiction to the original building instructions, I seal up the trunnion cap moulding holes. Although various people will disagree with this modification, my justification is that if air can flow freely in and out of the damper, then all you are really moving, especially with small suspension movements, is air.

Rubber Diaphragm - (#72/227 or 12/526)

PB Racing Rubber Diaphragm

They fit and they work, although the diaphragm from one of the Mugen 1/8th scale cars is a direct fit and has been fitted by some drivers.

Adjusting Ring - (#72/225 or #12/525B)

PB Racing Adjusting Ring

See Top Alloy Cap comments above.

Damper Body Moulding - (#72/226 or #12/525A)

PB Racing Damper Body Moulding

The adjusting ring can become tight part way down on the threads of the damper body. There is a high spot where the plastic is injected, which can be removed with a sharp craft knife

Piston Rod 39mm - (#72/228A or #12/530)

PB Racing Piston Rod

I build my rear shock absorbers using the shorter (33mm) shafts (12/529) from the 1/8th & 1/10th scale cars, as I feel that they place the piston at a better position in the body and do not fail due to running out of movement. The front shock absorbers use the standard shafts.

Some of the shafts I have used have the e-clip grooves cut at different distances apart and must have been from different production batches.

This was taken into account when I made some new pistons (see below). All shafts were polished before being assembled.

1/8″ Shaft E Clip - (#91/203 or #22/210)

PB Racing E clips

The clips are normally easy to fit (unless they go airborne!). Sometimes, though, the groove in the piston rod has been cut a little too deep, leading to a sloppy fit. Carefully closing the ends together slightly with a pair of long nosed pliers cures this problem.

1 Hole Piston - (#72/228 or #12/527)

PB Racing 1 Hole Shock Piston

See comments below.

Why You Shouldn’t Use the One Hole Pistons

After observing many pairs of dampers where the hole in the middle of the standard single hole piston had become deformed, I replaced them with a custom made two hole version.

This deformation was probably due to the fact that relatively thick oil is flowing through only one side of the piston, therefore creating an unequal lifting and pushing down of the piston.

If you Play the animated diagram on the left you will see a demonstration of what happens.

The two hole piston balances the forces out, as would the three hole piston (below left) already produced for the other PB cars.

3 Hole Shock Absorber Piston - (#12/528)

PB Racing 3 Hole ShockPiston

See comments above.

White O-Rings - (#90/800 or #22/296)

PB Racing O-rings

These o-rings are among the best I have come across so far.

Piston Rod Bush - (#72/228B or #12/531)

PB Racing Piston Rod Bush

The standard bushes were felt to be a little small in both length and diameter. New ones were made from brass to the required dimensions.

Bottom Alloy Cap - (#72/228C or #12/532)

PB Racing Bottom Alloy Cap

The core diameter of the threads inside the cap are sometimes a slightly different size to those on the damper body moulding, making fitting the cap difficult. The only solution to this is to run an appropriately sized die up the threads of the plastic moulding. See also the Top Alloy Cap comments above.

Spring Retainer - (#72/229 or #12/533A)

PB Racing Spring Retainer Moulding

Whilst it is easy and tempting to cut a slot into the spring retainer to make changing the springs easier, on the Dart this generally results in the springs escaping. This does not seem to happen on the Apollo and Black Diamond cars though.

Ball Trunnion Moulding - (#72/229A or #12/533)

PB Racing Ball Trunnion Moulding

It is easy to damage these rod ends when first threading them onto the shaft. I always partially pre-thread them with a 3mm tap.

Building the Shocks

PB Racing PB Shock Absorber Damper

After reading the above you should follow the PDF instruction sheet to arrive at an assembly that resembles the image to the left.


Although the above possibly seems a little bit extreme, there isn’t a great deal of damper for such a car as one the size of the Dart, so it really needs to be working the best it possibly can.

Related Information

I do have in my possession a quantity of non PB alloy bodied shock absorbers that have progressively wound springs that are fairly easy to fit to the Dart. I will be testing these out when time/weather permits, but have further information if you are require it.

I am also aware of a number of different types of shock absorber systems that were tried on the Dart and Diamond cars. I will try to gather the required information and seek the permissions of the relevant people to be able to publish them on-line.

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© 2001, 2009 by Darren Burnhill