Petrol smell in boot and speedo misreading fixes - repost
Discussion
For info / future reference. Have sorted two probs that have been bugging me with my Griff 500 (yr 2000).
1. No liquid fuel leak, just a strong petrol smell in boot after car left a few hours. Seemed to be coming from fuek gauge sender although no obvious signs that anything was wrong. Dismantled and found that the flange bolts appeared to have been overtightened. The gasket appeared to be serviceable. However cup washers had only been fitted to two of the five bolts. Apparently they were a TVR recall item and prevent fumes leaking from the bolt holes in the sender top plate. Removing two of the old bolts was a PITA - threads seized. Trimmed/hacked heads down until I could pull sender plate over them. Then stilsons to wind out the bits. Care taken to keep swarf out of tank. Resolved by replacing fuel sender gasket, bolts and nylon cup washers.
2. Speedo (Caerbont electric) was reading 15mph low at 70mph (and 7mph low at 30mph) - not helpful when approaching Gatsos! Also way off the 10% legal tolerance. Speedo has a bank of 10 dip switches to calibrate the pulses per mile setting (ppm). Found from my calculations that the 'ideal' setting based on wheel size / rotations per mile computed against the speed sender pulses would also not give me the correct speedo reading. Instead, I calculated a ppm correction factor to the current setting (based on 15mph under reading at 70mph). Result - speedo now reads accurately at 70mph and above, with 2-3 mph over indication at 30mph. Calibration info (ppm to dip switch settings) from CAI's website. This info may not be of use for cars with earlier/different speedometers.
(Reposted as first attempt was trashed by the PH system when I tried to edit it)
1. No liquid fuel leak, just a strong petrol smell in boot after car left a few hours. Seemed to be coming from fuek gauge sender although no obvious signs that anything was wrong. Dismantled and found that the flange bolts appeared to have been overtightened. The gasket appeared to be serviceable. However cup washers had only been fitted to two of the five bolts. Apparently they were a TVR recall item and prevent fumes leaking from the bolt holes in the sender top plate. Removing two of the old bolts was a PITA - threads seized. Trimmed/hacked heads down until I could pull sender plate over them. Then stilsons to wind out the bits. Care taken to keep swarf out of tank. Resolved by replacing fuel sender gasket, bolts and nylon cup washers.
2. Speedo (Caerbont electric) was reading 15mph low at 70mph (and 7mph low at 30mph) - not helpful when approaching Gatsos! Also way off the 10% legal tolerance. Speedo has a bank of 10 dip switches to calibrate the pulses per mile setting (ppm). Found from my calculations that the 'ideal' setting based on wheel size / rotations per mile computed against the speed sender pulses would also not give me the correct speedo reading. Instead, I calculated a ppm correction factor to the current setting (based on 15mph under reading at 70mph). Result - speedo now reads accurately at 70mph and above, with 2-3 mph over indication at 30mph. Calibration info (ppm to dip switch settings) from CAI's website. This info may not be of use for cars with earlier/different speedometers.
(Reposted as first attempt was trashed by the PH system when I tried to edit it)
LordGrover said:
Hmmm. Myspeedo's similarly out by a large margin since replacing the gearbox. Mine's a precat with the 'upside down' speedo though. I don't remember seeing any dip switches when I replaced the dash but if anyone has any other ideas how to resolve this I'd be very grateful.
Troogly had this problem when he had a replacement gearbox fitted. It turned out the replacement had the wrong speedo drive. He got it sorted under warranty, but you might get away with getting the speedo calibrated to the new drive.Dulfords tried several different drives but this is the best they could get. Any idea how/where to get it calibrated? Having said that it'll probably take weeks by the time it's sent, fixed and returned so I'll probably have to rely on the satnav until I get the original gearbox refurbed and put back.
Yep, I had a significantly under-reading speedo after a gearbox change. After claiming the speedo 'must have been out in the first place sir', the garage arranged for the speedo to be sent away for re-calibration (it was fine!). They then checked if the transducer was the right type (it was!). Puzzled, they then dropped the box again to look at the internal gearing for the speedo. They had fitted the wrong type! All OK now but it was about 20 mph below actual when at an indicated 70 mph.
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