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6 cyl Bristol cars Type 400 to 406 - restoration, repair, maintenance etc

403 rear axle strap bolts

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  • 1 Post By guymd

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Old 02-04-16, 07:37 PM
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Default 403 rear axle strap bolts

I've got the 403 floor completely stripped out so have good accessibility to the rear axle strap bolts. The bolt heads are badly corroded. I have soaked all 8 bolts with WD40 over several days. However, as expected, the first bolt sheared off with very little torque. Looking at the break there was not much thickness of good steel left, and I fully expect the other seven to be the same. So, I am committed to a full repair which presumably means cutting out sections of the chassis rail sides with the captive nuts and broken bolts and welding in replacements..............or does anyone have an alternative cunning plan they could share?
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Old 02-04-16, 08:53 PM
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If you think the captive nuts are likely still good, you might try drilling out the centre of a broken bolt with a sharp, well aimed bit whose diameter approaches the threads without quite touching them. Or start with a narrow bit and follow it with a wider one. Then poke at the hollowed out fringe, working from outside toward the middle with a hammer and tiny screwdriver to make it fall away from the nut. Once an edge of the bolt starts to break away, it gets easier and the bolt collapses inward. I've done this successfully myself, but not on a car. The quality of the steel may make it tough to drill.
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Old 03-04-16, 04:43 AM
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Default rear axle bolts

Suggest trying to loosen the other one with Plusgas rather than WD40 which isn't really a penetrating oil. In the US they have Kano's Kroil - wonderful name - but maybe not available in the UK. You can apparently make your own penetrating fluid with acetone and hydraulic transmission fluid - sounds exciting!
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Old 05-04-16, 10:17 AM
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I fully agree with both Guymd and Stefan so add my view in support. I have seen this many times - my advice would be to continue with the remaining screws. Some many come out especially if you apply some heat using an electric paint stripper heat gun which is possibly the safest. Make sure you shield the petrol pipe feed which, I believe, runs along the nearside chassis rail. Those that break I would then drill out using good quality HSS drills or, better still, cobalt drills in a couple of size changes. You will no doubt damage some of the existing captive nuts internal threads (I think they are 1/4 whit dia) so could try retapping first to clear the threads. If this fails,the next step is to drill and tap these out using a metric size possibly 8mm dia tapping drill size .250" (1/4) tap 8mm dia x 1.25 pitch. I suggest this as the pan head screws are probably easier to get. The alternative would be imperial 5/16" dia whit 18 TPI tapping drill 1/4 (.250). This is by far the cheapest alternative to cutting out and rewelding which would be my last resort.
PS. All drills and taps are available from Tracy Tools, Devon. Best of luck - you will prevail. You can also contact me on Pegasus@...........org.
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Old 06-04-16, 09:35 PM
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Many thanks to everyone for your help and support. I really do need to push on and get these bolts sorted out as once I have the car rebuilt the job would be several times more difficult. I will try the heat and a better penetrating fluid first and then the various drill and tap options if that fails.
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Old 07-04-16, 11:40 AM
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I suggest if there is not petrol leaking around the area and you feel it is safe , try heating the bolts to red hot with an Oxy Acetylene flame .
Allow to cool ,soak with a penetrating oil (WD40 is don't a very good product for that use) and carefully try to unwind the bolt .

In the past I have been successful using this method on other rusted bolts .

I don't want to be a pessimist but I don't like your chances of drilling out a loose captive nut with a broken bolt rusted into it ,unless you retap later with a larger hole/bolt

Geoff D
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Old 07-09-16, 09:38 PM
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Just to close this post - yesterday I got the remaining 7 bolts out using plus gas. I had not realised how much better this stuff is at releasing rusted bolts than WD40. The bolt I had previously sheared I was able to drill out using 2mm then 3mm then 4mm drills then the final 1/4 BSF drill. I then retapped the hole 1/4 BSF. I had to remove the shock absorbers to get at two of the bolts. Thanks for everyone's help.
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