poly bushes on front suspension

[Petowner]

Bought Poly bushes for all suspension , just looking at fronts and pondering over modification it looks like l need to make . Think Pet "66" is a mark2 but built with mark1 bits (how do you tell the difference?) anyway attached sketch of sizes
.
Central pin will need shortening down to fit between movable clamp on rear of front suspension that has movement from approx 29-38 mm
,poly bushes together are 38mm so fit as they are , but internal size of poly bushes is 30.5mm but wishbone area they fit is only 28-29 wide
when clamped up fully will poly bushes collapse to 28-29mm ? clamping the central pin in place?do l shorten the pin to 36mm ?
Will bushes 30.5 dimension close down to the 28-29 dimension of wishbone when clamped?
Any advice greatly appreciated

Bob

[John A. Ross]

Not long had this discussion with Peter Nunney on poly bushes.

MK 1 suspension used high pivot points, the bolts are just above valence height.
MK 2 suspension used low pivot points, the bolts were just below valence height.

Withought a drastic change you cannot really mix the two.

The MK1and Mk 2 wishbones have different sizes and I know they only sell the size for the MK 2 as I had to chop mine (a little of inner end of poly bushes and tube)

The MK 1 are narrower.

The Mk1 and Mk2 suspension have a slightly different steering rack support, front brackets and the steering rack spindle point is in a slightly different position.

I cannot recall the dates.

Looks indeed like you have early (narrow) Wishbones. i will get you dimensions for the tube from an original MK 1 bush.

The wishbone geometries cant be mixed side/side though as it can affect the camber quite a bit, one way to tell a MK 1 steering rack plate is it has fixed bolt holes while later plates have sliding / slot arrangement.

[John A. Ross]

Bob, bush below MK 1

However your slotted back brackets suggest MK 2 no idea if there was any crossover.

[Petowner]

Ah yes forgot to mention l was measuring a spare one (mounting plate) so one on car could effectively be a fixed position , not sliding bracket to take up any difference?
My concern was that l don't think poly bushes will squeeze up enough so that shouldered part of bush contacts side of wishbone , so possibly needing material off inner ends of bushes plus shortening central tube ,
need to check what is actually on car as that is what l'm going to run with .
Couldn't understand comment about under or above valence height (whats valence?)
Your bush above would fit spare plate that l have then , it's just a case of reducing central tube but would l need to mod bushes?
proof of the pudding, supposed l should fit poly bushes and see what happens if l clamp across end faces , will they compress to side of wishbone?

[John A. Ross]

Bob

Yes, Dave had a good write up on conversion at one time. The rear plate holding the steering rack puts the rack in a different position where it comes through the floor, so to change MK1 to MK2 or vice versa the steering column needs moved at floor.

The high pivot suspension (mk1) the wishbone pivot bolts are hidden by the front valence/grille like below



Found my grinder handle, my boots and gutter trim now

The later suspension brackets you can clearly see the bolts mounted lower down (sorry no pics handy, Boris is at other house at moment)

This is MK 1 suspension, narrow bushes and I had to cut the spacer AND cut the narow ends of the poly bushes so they would go in and shoulder against the end of the apertures in the wishbone correctly

John

[John A. Ross]

Bob

I found the write up from Dave at The Imp Club Forums

http://forum.theimpclub.co.uk/viewtopic.php?f=8&t=25804

For anyone reading the link is only valid for Imp Club Members as it is in the Members Only Section. It is not broken.

Not a how too Bob but summarises the differences

[John A. Ross]

Bob

Download the PDF below

https://www.hillmanimp.org/filedata/fetch?id=2135

You can see the geometry changes, the narrower bush positions means the spaceing face/face between the brackets is short and will need adjustable plate at front and back as well as a spacer.

[Dave Lane]

Differences are .
Wishbone length ( early wishbones are slightly longer )
Rear steering rack and suspension mount.
Fixed length track rod ( early one is too long - or fit adjustable both sides ).
Steering column inner and outer length (early one is too short )
Speedo cable is technically too long but could be used.

So you will need
The COMPLETE suspension from a late car
The steering column inner and outer from a late car
The shorter fixed length track rod from a late car or better still fit adjustable to both sides
Stub axles will fit either but its best to fit the greaseable later ones .
You cannot mix and match any part from a MK1 High pivot to a MK2 low pivot , NOTHING WILL FIT

So basically the whole suspension has to come off .
The four very front mounting holes by the number plate line up and are unchanged .
The four bolt holes on the rear { steering rack mount ) accessible from UNDER the car line up and are unchanged
The four bolt holes accessible from INSIDE the car DO NOT,
These will have to be welded up and redrilled .
The steering column hole needs to be welded up and moved down about an inch , its best to work out the exact position once the suspension is fitted , captive nuts for the outer column will need refitting .
That is basically it . , its best to fit the new suspension using the 8 bolts that do line up then drill the new holes through the captive nuts that dont from underneath the car , you can also work out the column hole move at the same time., then drop the suspension and sort out the welding .
Hopefully this will answer all the questions but if not just ask away

[Petowner]

Thanks Dave , will inform what l've done when l've done it
will probably end up doing what John did on thread No 5, and cut n shunt

[Hido-San]

Found the pictures ! All MK 1 wishbones so I had to cut down everything






MK 1 wishbones steering rack mount fixed bracket.

Later bones need the rack mount bracket with adjustable end, and a spacer !





Another thing to do is the bolts come through from rear of bracket which you cannot get to once it is bolted up to the body, factory must have assembled the suspension and then attached to the car.

I always weld a small bar across both head bolts so they cannot turn, that way the bones can be dropped easy enough and the bracket bolts tighteend up again easy without rear bracket access.

You McBride made a laser cut piece of steel to match the bolt heads in hex shape but for me I am happy just whacking on a bit of 1 or 1.2mm steel and blobbing the top



Another mod I did was on the adjustable track arms. A light oil coating on the arms then a couple of layers of heat shrink tubing across each arm leaves them looking smart and no need to coat them.

[Petowner]

Think my plan of attack is going to be
1 Check what length poly bushes are when compressed in wishbones
2 if needed make spacers that sit between top hat of poly bushes and side face of wishbone mounting points
3 cut down inner tubes to fit length needed

My way of thinking is that poly bushes once compressed squeeze down tightly onto inner tubes (no not the tyre ones ! Wake up at the back there)

my theory there is that don't want to modify poly bushes if l can help it , don't mind modifying steel inner tubes as l can easily replace those, and making spacer washers for poly bushes is somewhat childs play . got stainless track rods so no use for shrink rap ,but good idea..

Bob

[John A. Ross]

Bob, I think i had to trim the bushes so the shoulder/shoulder length was same as original. Few mm of each if I recall

[Petowner]

Sorted poly bushes today , assembled into wishbones and under pressure the headed bushes squeeze up to side of wishbone giving an overall width of just about 35mm so made steel tubes to overall length of 34.5mm ,can't see any problems there , more stuff to order from Bob Allen at Spares before l can start fitting , next job is to build the hubs (once l've found them) easier said than done.

Bob

[moose549]

The bushes are a fit in the arms and the stainless steel tube is meant to spin/pivot inside them so the tube wants to be 35.1 appox so the suspension plates grip it with a small amount of load on the rim of the top hats to stop forward and aft movement but allow the bushes to turn on the stainless steel tube.

[Petowner]

WHOOPS!!!! Thanks Mike , easily remedied , new stainless tubes then.
Bob