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Undertray Bolts


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#1 Willsy

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Posted 17 May 2019 - 07:28 PM

Hi guys I’ve had a search around the forum but found some conflicting story’s, I’m looking at getting the stainless steel complete overhaul set from speedy fasteners on eBay but would like to know if anybody that has fitted stainless steel bolts has had any corrosion issues? If I use acf-50 would I just put it on when replacing the bolts or would I need to reapply every year or so? My vx is garaged at all times and will only be used in dry weather if that makes a difference. If stainless steel is a no go what are the original bolts made from or what’s the best option? Any help would be much appreciated thanks

#2 ukcat

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Posted 18 May 2019 - 05:18 AM

Hi Stainless will be fine here. It was used for the original bolts and washers. what is your main concern is it corrosion of the alloy undertrays ?. if you look at well used vehicles used in wet conditions you will see pitting around the areas where the stainless washers have been in contact with the aluminium due to the disimilar metals causing corrosion. however you have to put everything into context as you would probably find that if normal steel bolts had been used on these vehicles they would be rusted blobs of metal (i think this was the case with some early elises). stainless on a well cared for dry use vehicle will be absolutely fine and if you are really concerned just fit some nylon washers between the stainless and the alloy

#3 hairy

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Posted 18 May 2019 - 06:54 AM

Hi - I agree with UKCAT. I have the speedy fasteners and they came ready fitted with plastic washers - it does make them quite stiff to fasten though due to the thickness.



#4 vocky

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Posted 18 May 2019 - 07:05 AM

I also use the white nylon washers between the stainless penny washers and undertrays, plus I put some copper grease on the threads



#5 oakmere

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Posted 18 May 2019 - 08:32 AM

Stainless bolts and washers + nylon washers as people have mentioned above or the tray will corrode. I have also just replaced all the spire clips as most were badly corroded but they were16 years old 😆

#6 ukcat

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Posted 18 May 2019 - 08:41 AM

If you replace the spire clips try and go for geomet or dacromet coated (same as OEM) these are a little more expensive than normal zinc plated ones but have greater corrosion resistance !!
This is assuming stainless ones arn't available which i dont think are

#7 Willsy

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Posted 18 May 2019 - 08:50 AM

Thanks a lot for everyone’s help I’ll get them ordered now then and use some nylon washers as suggested, does the act-50/copper grease last as long as they are in or do I need to top it up every so often to stop them seizing? Thanks again for your help

#8 ukcat

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Posted 18 May 2019 - 08:56 AM

Thanks a lot for everyone’s help I’ll get them ordered now then and use some nylon washers as suggested, does the act-50/copper grease last as long as they are in or do I need to top it up every so often to stop them seizing? Thanks again for your help


the best bet is to use corrosion block grease as it is thicker than acf but again its all relvant to how the vehicle is used. im sure a dry only vehicle would be fine without any grease etc. its water and salt which greatly increase the rate of corrosion

#9 Willsy

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Posted 18 May 2019 - 09:13 AM

Ok mate that’s sound thanks a lot for your help




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