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MG MGB GT V8 Factory Originals Technical - Tramp bar mounting

Hey,
I'm in the process of fitting tramp bars to a '77 RB car and while taking measurements from the forward spring mounting poing to where the tramp bar will mount, I realized that the RB cars rear spring hangers hang lower than the CB rear spring hangers, thus the increased ride height, or part of it anyways. So we all knew that. Now my question is the following: Has anyone redrilled the forward rear spring hanger on a RB car to get a lower ride height? I was thinking that if I could do this, I could utilize the lower set of holes, the factory mounting holes, to mount the tramp bars. Any comments are welcome.
Thanks in advance.
Jake

Jake:
I think this would work but several words of caution. The forward rear spring hanger should be substantially re-enforced.
I lowered my '77 RB roadster using lowering blocks but built boxed sections for the anti-tramp bars that connect to the crossmembers between the outer sills and tunnel, plug welding them to the floor. My anti-tramp bars are longer and actually connect about half way up these boxed sections. I have fabricated a panhard rod as well.
I can send some pics of the boxed section install if you wish.
Phil
Phil O

Hi Jake

I looked into this when I did my RB to CB conversion.

With the holes drilled in the CB position (and doing that is a bad enough in itself) I found that there was not sufficient room between the spring eye and the old hole to mount a tramp bar.

Having said that - there may be someone out there who was able to squeeze one in.

Cheers
ian F



Ian Fraser

Yeah, when I lowered the ride height I did this. I did not wish to buy expensive new springs (spring for new springs ho ho!)I drilled the new holes about 46mm higher up and 2 mm further back. Others have done this as well. When drilling the new holes (in the old Chrome bumper location) be aware that the backs of the hangers are not all that symetrical, so don't try and measure from there. Hence the unintentional 2mm further back! however since the hangers on the rubber bumpers are reinforced compared to the chrome bumpers (an extra layer of metal each side) it doesn't matter. That got it down about an inch. About 6 months later I also fitted one inch lowering blocks to get the ride dead level since the rubber bumper springs are more arched than the chrome bumper and I had also taken off that big heavy rubber bumper (25kg) which had let the back up even higher.
It's easy enough to do, unbolt the front of the spring and let it up as high as you can get it to go then mark and drill. I strongly suggest you use new drill bits, a hole punch and drill a small pilot because of the awkward angle. If you enjoy pain, use an old drill bit and just go for it.
I took me about an hour to do all up,includeing removing wheels jacking up etc. I did not use an angle drive although It would have made this an easier job.
I am also going to fit antitramp bars to the old holes at some stage. Since I intent making these bars up myself I dont see a problem with fitting.I'll weld the bar offset under its' "eye". When I do this I will probably also attach/rivet a piece of reinforcing channel from the hanger to the mid section.
I might just also try it without the re-inforcing first. Alot of overengineering tends to happen in these projects.
Peter

Overengineering is one thing Im trying to avoid. I don't want to just make stuff and have it be alright just because it is too beefy for my needs.
Thanks for the input on the forward hanger, has anyone also replaced the rear mounting point for the shackles with those from a CB car as well? I found a pair of NOS pieces for a CB car and are the shackle mounting points, they put the shackles up an inch or more. Looking on my CB GT, I figure I could just weld in the CB pieces on the RB V8 after cutting out the old ones.
On the subject of engineering, does anyone know how to calculate the lateral cornering loads that the rear end sees? Ive been doing some research on it but haven't found anything really useful yet and Id like to a ballpark figure to accurately design the panhard rod.
Thanks
Jake

I'm using 15inch wheel & 60 by 95 tyres and haven't had a rubbing problem yet. The back tends to come unstuck before the tyres rub, which is a whole other problem.
To me the back shackels looked too hard to get at unless you've got the back guards off, or possibly are prepared to cut a bit out of the boot floor and repair later.
Peter

I did a RB to CB mod on the rear shackle on my rebuild.

As Peter says, it's difficult to get at, but I found it just possible with the car on a rotisserie.

You need to cut away the RB mount, but save the spacer tube (or make a new one). The CB mounting point is pressed into the channel, but not drilled.

I drilled a 1/2" pilot hole and then opened it out to the diameter of the spacer tube using a tunsten carbide die grinder cutter mounted in a 1/4" diam extension section that is normally used with a flat bit. A piece of aluminium tubing over the shaft of the extension allowed me to hold it and guide the cutter. I used an electric drill, but now I have an air die grinder and would probably use that next time.

Welding the spacer in is a bit of an act, but just possible as I was able to rotate the car to any angle.

If the suspension is lowered in this way, the RB mounting for the rear bump stop also needs to be removed. ( also check straps and shock adsorber link need to be changed)

Remove the 'peg' that holds the bump rubber. Cut away the RB pressings that have been added to the chassis channel. Weld the 'peg' back in the CB position.

Re side ways force - 1/2 of the weight of the car times 1G. However safety factor and allowance for hitting a kerb sideways will blow this away. How about whole weight of car times 5G?

HTH
Ian F



Ian Fraser

This thread was discussed between 26/02/2005 and 28/02/2005

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