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Sierra Based 3A Body Noise


Guest iokarus

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Guest iokarus

Hi,

 

I bought a 3a (late sierra based with inboard front shocks) last year and took it out on the road today for the first time after a lot of work.

 

I noticed when i was driving it that i got a few "twang" noises as the sheet metal seemed to move about and settle out. Is this normal? The chassis has done a number of thousand miles over 12 years and has some welded reinforcements around the front and rear of the engine bay. I'm just concerned that there might be a lack of strength in the chassis.

 

Any idea whats normal?

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I have run a 3A for the past 12 years. The car is 17 years old and today passed its MOT with no problems, so big smile. The 3A is noted for some body flexing due to the stainless steel tub construction. I can honestly say that I have never had any "twang" noises as you describe. The chassis is actually very strong but cracking can happen. This is most common where the tub meets the front suspension cross member. Also its a good idea to make an anti roll bar that attaches near where the tie rods for the lower suspension arm meet the body. Also have a good look around the rear suspension mounting points.

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Do you have tie bars or an anti roll bar on the front suspension? The previous owner of my car had fitted tie bars without reinforcing the body mounting points properly which caused the side panels of the body to flex.

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I run 4angles front to rear externally under the seats joining rear tub lip to front gearbox cross member and a 2"x1" square tube between tie bar brackets.

I get the odd cluck over speed bumps ( probably the gearbox flexing on the mount) and the odd scuttle shake noise but generally not much.

Inside the passenger compartment behind the seats the rear suspension cover also bows the body side out slightly, without this the sides would be free to flex more,

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  • 4 months later...

So an update on this. I've been getting the odd pop on speedbumps as suggested above. nothing else too bad until last weekend.

 

I was driving along a slightly undulating road and walking pace and I could feel the car twisting underneath me. Basically like the seat base was moving in relation to the wheel.

 

Now I get the same thing whenever a surface lifts one of the rear wheels in relation to the others.

 

So again, how normal is this? And stress areas to check?

 

Thanks

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I have a series 3 and get no twangs or apparent movement in the chassis. I would think your chassis has a problem.

How to investigate? All over look with the naked eye for starters with lots of light paying particular attention to the floor, engine mount panels, front crossmember where it joins the body and firewall where it joins the body. Then jack each wheel in turn, good light again to see if you can detect any panels flexing. Well thats for starters at least.

 

Nigel

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Have a look at where the sierra rear suspension beam attaches to the floor and make sure it's secure. Check the rear suspension top mounting for rigidity, mine had worked loose and was twisting when we bought our car, this had caused cracks to appear at it's mounting points. Look at all the points that Longboarder has said. When looking at the front beam to monocoque welds try putting a light behind the weld and switching the garage lights off, you may see light shining through any cracks in the weld -I did!

 

Also when I bought my 3A there was no support bearing on the bulkhead for the steering column which then gave a very poor steering response (it made me feel at first as if my seat had come loose until I realised what was going on).

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I was advised by Gingerfix to run 2 tubes along the hole length of the prop tunnel from boot to scuttle

I did not do this

I did add extra plate where the diff mount bolts through the boot

As said I added angle under the floor 2 either side tying in to the gearbox cross member to the lip at the rear

Steering and pedal box are heavily reinforced with bar from steering mount to scuttle, angle inside engine bay then triangulation and boxing of the pedalbox

The roll bar was bolted through not clamped and 2 pieces of angle per side run from roll bar to rear belt mount bar and triangulated

 

This has stiffened the whole chassis

 

The original front end was so stiff as to act as 1, this with a more compliant rear means the tub will twist, changing to tie bars restored independence to all 4 corners

The last change was to bin the Zimmerides, replace with Gaz and use 120lb springs for the front not the 180lb it came with

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  • 4 months later...
Guest iokarus

So another very late update on this. I stood the car up late last year having found cracks on 3 of 4 corners of the engine bay. Seems to explain why it was flexing.

 

My car was messed around with a lot before I bought it and had a 3L Essex V6 fitted which seemed to have meant hammering the transmission tunnel and some amendments to the firewall. Needless to say I did not understand how important this was to the integrity of the cars chassis!

 

I want to get it fixed up and add some reinforcing. Would any of you have a picture of the chassis from your original build pics so that I can see how a late 3A chassis (inboard shocks) looked when it was brand new? Also, any pics of reinforcing made?

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If you sent me a message with your email address I can send all I have on the 3a chassis

I do have some pics of bare chassis tub and a few more of mods I have done

Some chassis cracked where yours have and most weld the cracks then plate over

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Hi I replied to your post some time ago but never posted pictures. Only have a few photos. I made up various reinforcing plates to tie the engine mounting "trays" to the bulkhead (I don't think I will be changing the engine type in the near future so don't need these to be able to slide and adjust). 12mm wide x 3mm thick pieces of stainless were used to form a fillet weld across the corners where the cracks were. I also cut back the bottom of the monocoque floor where the engine sits to match the sides of the trays then welded both the bottom of the monocoque to the edge of the tray - this gave the most noticeable effect of making the chassis become more rigid. A professional welder came out and did the job after I made up the plates. He was at it for about 6 hours! The square plate washers which used to mount the front nudge bar have been replaced by 1 large thick stainless plate washer each side to improve looks!

 

 

imagejpg1_zps36f2ef45.jpg

 

 

imagejpg2_zpsac0061a9.jpg

 

 

The photo below shows the front corner fillet weld and the nosecone mounting bracket which I have reinforced to tie the front crossmember to the top side of the chassis. (The shiny thing at the top is my header tank). Its a poor photo but I hope you can tell what I have had done

 

imagejpg1_zps5a76c6a5.jpg

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Forgot to say that I added reinforcement to the lower shock mounting as I was told the original folded stainless part can crack where they mount. Steel flat bar was added to the front and rear of the original section as per photo below.

 

 

Don't forget to check your rear shock mounting as well as the monocoque can crack where the mounting bolts to the front and sides

 

imagejpg1_zps07ef26c9.jpg

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Guest iokarus

I cant see in the first two pictures, but it looks like in the second 2 that you have stainless plates bolted over the seam on the top of the folded top section of the side rails. Is that right? I'm sure I have seen this on other cars, possibly a late factory addition?

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The plate is an angle that bridges the seam and has the rear of the nosecone bolted to it. The photo below shows the original bracket during my stripdown of my car before I binned the bracket and spacers and made new thicker stainless ones. The second photo shows the new brackets. These were bolted through the original mounting holes but I used 3mm stainless plates under the nuts to spread the load. You also need a packer plate between the bracket and the chassis side rails as my front crossmember sits 3 to 4mm higher than the side rails.

Rob

 

IMG_5016_zps4e674479.jpg

 

 

image_zps5e9e40a1.jpg

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