Just replaced the ARB Bushes on front suspension. Aware that the shims perform 2 functions. 1 determine castor angle 2 provide correct compression of rubber bush. I fitted a 1.5mm and a 2.5mm shim on each side of rubber bush ie 4 shims in total. On checking castor angle using the Gunson 77066 tool I got readings on O/S of 4 degrees and on N/S 4.5 degrees. My question is that the readings were on the negative scale of the instrument. Does the positive/negative scale only apply to the camber measurement. Essentially if the positive/negative scale does not apply to castor and positive castor appears on the negative scale then the castor angle is within required limits. That is positive castor angle of 4 +/- 30 mins. If not then I have a negative castor angle of circa 4 degrees which I find hard to believe as this would make the castor incorrect by 8 degrees. I doubt that any variant of the shims could correct this magnitude of error, if error it be.
In summary: does anyone have experience of this tool ie Gunson 77066 the budget priced one. The instructions are not sufficient to resolve my question.
Use of Gunson 77066 for castor angle
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mac2
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Re: Use of Gunson 77066 for castor angle
I think I can now answer my own question. I have a John Deere tractor which has a very large positive castor angle, so much so you can see its effect when steering. Placing the 77066 in position and moving the steering in the direction suggested in the instructions there was even on a small steering angle significant movement of the bubble into the scale marked negative, that is the scale furtherest from the hub.
It would appear that the pos/neg scale markings are for camber only and have no meaning for castor angle measurements.
I know the topic has been covered before but having recently 'done the ARB bushes' I can offer a few details of the experience.
1. Undoing the most forward ARB to chassis bolt can be a problem as the bolt rotates and the head is enclosed for most of its circumference in a fibreglass 'tunnel'. I tried an obstruction spanner but the crank was not in the ideal position and was no use. I bent a redundant Whitworth ring spanner having heated it red hot. As the spanner iin question was cranked rather than flat, it would not work for the other side so needed to bend another. If non cranked spanner used it should do both sides. The N/S bolt required the radiator to be drained so as to remove bottom hose to gain access. Others have tried through headlight aperture.
2 I fitted Rubber Lotus bushes to the lower arm. Using lots of red rubber grease they pressed into the arm with little difficulty using a press. Use the base of a socket that fully covers the flat area. I used a smaller socket whilst removing the old bushes and it pressed into the central bolt hole, this would, I suspecr ruin a new bush. I was surprised how easily they went in having read the horror stories of others. It does seem a big ask as the bush at its widest is 50mm and the aperture it has to pass through is 35mm. Remember to press the bushes in from the front of the arm so that the thicker part of the bush is facing forward. It helps to mark each arm beforehand.
3 Removal of the ARB is quite straightforward if the lower arms are jacked to near the horizontal, the arc followed widens the distance between the centres of the bush. I did not find the need for a ratchet strap. Refitting was made a bit easier having applied silicone grease to the bar. Remember the cup washers. Depending on the age of your car there are different shim numbers and thicknesses. Check the service notes for your car. Mine had 4 shims each side 2x1.5 ans 2x2.5mm. All must be fitted as per manual to get correct compression of bush. How many you fit in front of the bush vs the rear will determine your castor angle. The shims immediately below the nut on the ARB must slide onto the non threaded part of the bar and therefore must be concentric as the nut is tightened. This can be fiddly, I scribed a mark on the cup washer around the shim to help centralise, I found using an open end spanner best as with a socket you couldn't see they were concentric. I guessed on mine one of each on either side. I am afraid that if the measued castor angle is not as required you have to remove the whole ARB again and reshim. Nedless to say before checking the castor angle everything needs to be fully tightened.
4 Before finally torquing up the top, bottom wishbone bolts and shock absorber bolts to 50lbft, 65lbft and 50lbft respectively make sure the car is at normal ride height.
5 Checking the castor angle can easily be a diy preceedure if you have the tool. Sealey and Gunson produce a device which can be used to measure camber and castor angles eg Gunson 77066. If you look on ebay you will find exact replicas of these for about £10-12 go for one with a scale of plus 6 to minus 6. The instructions leave a little to be desired just follow the instructions for the Sealey GA45 which are obtainable off the net plus the comment at the top of this post.
It would appear that the pos/neg scale markings are for camber only and have no meaning for castor angle measurements.
I know the topic has been covered before but having recently 'done the ARB bushes' I can offer a few details of the experience.
1. Undoing the most forward ARB to chassis bolt can be a problem as the bolt rotates and the head is enclosed for most of its circumference in a fibreglass 'tunnel'. I tried an obstruction spanner but the crank was not in the ideal position and was no use. I bent a redundant Whitworth ring spanner having heated it red hot. As the spanner iin question was cranked rather than flat, it would not work for the other side so needed to bend another. If non cranked spanner used it should do both sides. The N/S bolt required the radiator to be drained so as to remove bottom hose to gain access. Others have tried through headlight aperture.
2 I fitted Rubber Lotus bushes to the lower arm. Using lots of red rubber grease they pressed into the arm with little difficulty using a press. Use the base of a socket that fully covers the flat area. I used a smaller socket whilst removing the old bushes and it pressed into the central bolt hole, this would, I suspecr ruin a new bush. I was surprised how easily they went in having read the horror stories of others. It does seem a big ask as the bush at its widest is 50mm and the aperture it has to pass through is 35mm. Remember to press the bushes in from the front of the arm so that the thicker part of the bush is facing forward. It helps to mark each arm beforehand.
3 Removal of the ARB is quite straightforward if the lower arms are jacked to near the horizontal, the arc followed widens the distance between the centres of the bush. I did not find the need for a ratchet strap. Refitting was made a bit easier having applied silicone grease to the bar. Remember the cup washers. Depending on the age of your car there are different shim numbers and thicknesses. Check the service notes for your car. Mine had 4 shims each side 2x1.5 ans 2x2.5mm. All must be fitted as per manual to get correct compression of bush. How many you fit in front of the bush vs the rear will determine your castor angle. The shims immediately below the nut on the ARB must slide onto the non threaded part of the bar and therefore must be concentric as the nut is tightened. This can be fiddly, I scribed a mark on the cup washer around the shim to help centralise, I found using an open end spanner best as with a socket you couldn't see they were concentric. I guessed on mine one of each on either side. I am afraid that if the measued castor angle is not as required you have to remove the whole ARB again and reshim. Nedless to say before checking the castor angle everything needs to be fully tightened.
4 Before finally torquing up the top, bottom wishbone bolts and shock absorber bolts to 50lbft, 65lbft and 50lbft respectively make sure the car is at normal ride height.
5 Checking the castor angle can easily be a diy preceedure if you have the tool. Sealey and Gunson produce a device which can be used to measure camber and castor angles eg Gunson 77066. If you look on ebay you will find exact replicas of these for about £10-12 go for one with a scale of plus 6 to minus 6. The instructions leave a little to be desired just follow the instructions for the Sealey GA45 which are obtainable off the net plus the comment at the top of this post.
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mac2
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Re: Use of Gunson 77066 for castor angle
Correction... the torque for the lower wishbone to chassis is 50lbft not 60, senior moment!
Re: Use of Gunson 77066 for castor angle
Did you have to move any shims around - and so do you have any idea how much difference to the castor angle each size of shim makes?
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mac2
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Re: Use of Gunson 77066 for castor angle
On dismantling there were 2x2.5 and one 1.5mm at the front and just 1x1.5mm one to the rear.
When I measured the castor angle it was O/S +3.5 deg and N/S 4.0deg, this would have been within limits.
For no particular reason I split the shims equally front and rear1x1.5 and 1x2.5 each side. This resulted in a castor angle of O/S +4.0 and N/S 4.5 still just within limits.
It would then appear that removing a 2.5mm shim from the front resulted in an increase in castor of 0.5degree.
Placing the extra shim to the rear should not have any effect and is there to obtain correct compression of the bush, unless I am mistaken.
I suppose the main caveat would be that the rubber bush may not behave in a consistent manner comparing an old softer bush with a new one.
If these data can be believed 2.5 mm difference on front bush shimming equates to 0.5 degree. I immagine this can't be too far out as the latitude given in the castor angle spec is to within 0.5degree and there is very little scope to just keep adding or subtracting shims as only 4 can and must be fitted.
I think I was lucky in being within castor angle limits as removing/adding a shim to the front of the bush will require a complete re-dismantle
When I measured the castor angle it was O/S +3.5 deg and N/S 4.0deg, this would have been within limits.
For no particular reason I split the shims equally front and rear1x1.5 and 1x2.5 each side. This resulted in a castor angle of O/S +4.0 and N/S 4.5 still just within limits.
It would then appear that removing a 2.5mm shim from the front resulted in an increase in castor of 0.5degree.
Placing the extra shim to the rear should not have any effect and is there to obtain correct compression of the bush, unless I am mistaken.
I suppose the main caveat would be that the rubber bush may not behave in a consistent manner comparing an old softer bush with a new one.
If these data can be believed 2.5 mm difference on front bush shimming equates to 0.5 degree. I immagine this can't be too far out as the latitude given in the castor angle spec is to within 0.5degree and there is very little scope to just keep adding or subtracting shims as only 4 can and must be fitted.
I think I was lucky in being within castor angle limits as removing/adding a shim to the front of the bush will require a complete re-dismantle