Re: Historic Forest Stage Rally 124 Spider
Posted: September 18th, 2013, 7:27 pm
Well after a very long time of not doing anything on the car, I have at last got some work done, but seem to have a problem.
I have finally fitted the fuel lines through the car and mounted the pumps and filter king in the boot. The tank if finally fitted so I can now complete the rear wiring etc.
Wanting to see some external progress I decided to start fitting the front suspension. Most things started to go together well. I wanted to try my new front spring compressor. This was something shown to me by Mick Woods and was used by the works teams. Nothing too fancy just a piece of 16mm high tensile screwed rod, some long nuts, and most importantly a couple of thrust bearings. The bar passes through the shock absorber hole and a plate that is inserted in the spring. The screw is tightened and the spring compresses against its seat. The lower wishbone is then fitted and the spring released. I was most impressed. It worked really well. I think it would also work with an impact wrench or possibly an air ratchet it is that easy. When I fit the other spring, I will take a few photos. Anybody know of a hydraulic compressor that works? I have one but it wont fit.
Having fitted one spring, I decided to carry out a few basic checks on the other side. My front suspension is taken from my old rally spider. The wishbones are strengthened, and I am re fitting the Abarth front tie rods. I have attached the Abarth info sheet showing the rods. ( I would think the copyright has expired). These fit to a mounting added to the lower wishbone ( shown as point A on the diagram. ) The front is mounted to the additional front cross member added which is also the sump guard mount. All of this has been assembled onto the new car.
I assembled the wishbones on the near side without the spring. I then added the 124 hub and measured the amount of movement at a point on the edge of the lower wishbone. I then changed the hub to the 125/Argenta hub, and again took measurements. ( These fit in to the common conception that 15 mm has to be removed from the standard bump stop) So far so good.
I then attached the front tie rods. These have left and right hand threads at each end so can be adjusted. The problem is they don’t seem to work. You will see in picture 2 the how the tie rod fits to the front additional cross member and the lower wishbone. The problem is that when tightened up the lower wishbone will not move. Having slackened everything off what seems to be happening is that the pivoting arc of the tie rod is not the same as the wish bone. This now seems to be quite obvious, but what I don’t understand is that it worked on my previous rally car for 3 years. The one thing I will say is that the original rose joints always had a lot of play in them ( I was rallying on a budget and could not afford to change them so put up with the noise- this was back in 1983)
Having now studied the situation and taken a few more measurements I have come to the conclusion that the tie rod moves in an arc that is 3.5mm longer than the point it is attached to on the lower wishbone. ( See calculations sheet) . I have taken measurement and can conclude the following
Wishbone length measured from pivot centre to end of wishbone = 265mm.
Travel of suspension at this point = 150mm.
Position of mounting point for tie rod on lower wishbone from pivot point = 195 mm
Length of tie rod when connected in centre of suspension travel = 340mm
Tie rod front member mounting is in line with lower wishbone pivot point.
Now, if I bolt everything up, at the centre of suspension travel (for theoretical purposes) the tie rod would move the lower wishbone backwards or forwards by 1.75mm at 195mm from the pivot point. This movement would strain the inner wishbone mounting rubbers. (I could calculate by how much) .
My question is this how they are supposed to work? Could it be that the suspension would normally move more than this in any case?
The only difference in the suspension from my old car is that the rose joints on the tie rods are thicker. I have put the old worn rod ends on and they still show the same movement. The suspension works as there is so much play in them. The mounting point for the front cross member is the same. An interesting point is that when the sump guard is mounted, then the additional cross member is also fastened to the engine cross member, making a very stiff mounting for the tie rod/lower wishbone. Is the CS chassis different to the BS? Everything measures the same and thew parts I have seem to all fit ( wishbones, engine crossmember, antiroll bar , etc.)
The other consideration is the suspension travel /ride height on the new springs. Unfortunately this wont be known until the car is finished. However, I may need to take numerous measurements so that I know what length to set the tie rod to. After all this worry it could be that I just bolt it on when the car is finished and on the ground and it will work (as it used to) but I would rather fully understand the logic.
What am I missing? ( apart from brain cells)
I have finally fitted the fuel lines through the car and mounted the pumps and filter king in the boot. The tank if finally fitted so I can now complete the rear wiring etc.
Wanting to see some external progress I decided to start fitting the front suspension. Most things started to go together well. I wanted to try my new front spring compressor. This was something shown to me by Mick Woods and was used by the works teams. Nothing too fancy just a piece of 16mm high tensile screwed rod, some long nuts, and most importantly a couple of thrust bearings. The bar passes through the shock absorber hole and a plate that is inserted in the spring. The screw is tightened and the spring compresses against its seat. The lower wishbone is then fitted and the spring released. I was most impressed. It worked really well. I think it would also work with an impact wrench or possibly an air ratchet it is that easy. When I fit the other spring, I will take a few photos. Anybody know of a hydraulic compressor that works? I have one but it wont fit.
Having fitted one spring, I decided to carry out a few basic checks on the other side. My front suspension is taken from my old rally spider. The wishbones are strengthened, and I am re fitting the Abarth front tie rods. I have attached the Abarth info sheet showing the rods. ( I would think the copyright has expired). These fit to a mounting added to the lower wishbone ( shown as point A on the diagram. ) The front is mounted to the additional front cross member added which is also the sump guard mount. All of this has been assembled onto the new car.
I assembled the wishbones on the near side without the spring. I then added the 124 hub and measured the amount of movement at a point on the edge of the lower wishbone. I then changed the hub to the 125/Argenta hub, and again took measurements. ( These fit in to the common conception that 15 mm has to be removed from the standard bump stop) So far so good.
I then attached the front tie rods. These have left and right hand threads at each end so can be adjusted. The problem is they don’t seem to work. You will see in picture 2 the how the tie rod fits to the front additional cross member and the lower wishbone. The problem is that when tightened up the lower wishbone will not move. Having slackened everything off what seems to be happening is that the pivoting arc of the tie rod is not the same as the wish bone. This now seems to be quite obvious, but what I don’t understand is that it worked on my previous rally car for 3 years. The one thing I will say is that the original rose joints always had a lot of play in them ( I was rallying on a budget and could not afford to change them so put up with the noise- this was back in 1983)
Having now studied the situation and taken a few more measurements I have come to the conclusion that the tie rod moves in an arc that is 3.5mm longer than the point it is attached to on the lower wishbone. ( See calculations sheet) . I have taken measurement and can conclude the following
Wishbone length measured from pivot centre to end of wishbone = 265mm.
Travel of suspension at this point = 150mm.
Position of mounting point for tie rod on lower wishbone from pivot point = 195 mm
Length of tie rod when connected in centre of suspension travel = 340mm
Tie rod front member mounting is in line with lower wishbone pivot point.
Now, if I bolt everything up, at the centre of suspension travel (for theoretical purposes) the tie rod would move the lower wishbone backwards or forwards by 1.75mm at 195mm from the pivot point. This movement would strain the inner wishbone mounting rubbers. (I could calculate by how much) .
My question is this how they are supposed to work? Could it be that the suspension would normally move more than this in any case?
The only difference in the suspension from my old car is that the rose joints on the tie rods are thicker. I have put the old worn rod ends on and they still show the same movement. The suspension works as there is so much play in them. The mounting point for the front cross member is the same. An interesting point is that when the sump guard is mounted, then the additional cross member is also fastened to the engine cross member, making a very stiff mounting for the tie rod/lower wishbone. Is the CS chassis different to the BS? Everything measures the same and thew parts I have seem to all fit ( wishbones, engine crossmember, antiroll bar , etc.)
The other consideration is the suspension travel /ride height on the new springs. Unfortunately this wont be known until the car is finished. However, I may need to take numerous measurements so that I know what length to set the tie rod to. After all this worry it could be that I just bolt it on when the car is finished and on the ground and it will work (as it used to) but I would rather fully understand the logic.
What am I missing? ( apart from brain cells)