Henry Boler

As expected...

So, today I decided to try and get somewhere with these speedo problems, still no joy. Put it all together ready to test, jacked the back end up so I could run the wheels to see if the speedo would respond, would she start? ...No. 3000 miles in europe, no problems, driving almost every day the two weeks I've been home, no problems, I leave her for three days and find a valve problem!!! One of the valves isn't returning to closed position. About 8mm too low down by the looks of things. What could this be? Would I be right in assuming a dropped valve seat? I think the engine had hard seats fitted at some point before my time. Cant imagine any other ways it could break. Either way I guess the head needs to come off? Annoyed now... My other car (Vauxhall Vectra 6-Speed Auto), only has the first three gears at the moment... Joy! Henry

Dick - Thanks for keeping up with the blog! I'll definitely tell you all about it in August! Gully - We had two stops on our tour that had washing facilities, so we only had to take clothes for 33% of the time! We have just released our final post on the blog now. http://gt6ineurope.co.uk Thanks all for your support!

I tell you what, one way to make that drive better would be in a convoy! Just thought I'd let you all know, we got back home safely, the GT6 is absolutely fine! There will be a final blog post soon signing off when Ella and I get a chance!

Hi Neil, I'm glad you're reading the blog! Hopefully it'll keep you interested! This has been an incredible driving experience which no doubt I'll tell you all about in a few weeks in person! Frankfurt should be a fun trip, we stayed a night there on our way to Prague! I don't think I saw the photo, with the 5 GT6s? We have just updated the blog today, well worth a read, just to see the photos from the long day of driving! Some absolutely mind blowing scenery + GT6 going on there! Henry

Thanks for the kind words John! Doug - Haha, I have a few club members who would say the same thing, this is why we are doing the blog as mentioned! The water pump was really unexpected and began the night before we left which was a nightmare evening, knowing that the car was knackered and there was nothing we could do about it but we were driving it to Europe in the morning no matter what, having spent a lot of money on the tour so far, we couldn't just back out... The electrical fault turned out to be a blown fuse in the GPS speedos plug, so nothing of interest... It's a shame that the car's speedo died as it is new and was working brilliantly, it only managed 80 of 3000 miles! Ella says thanks to all! Her instrument is percussion, as is mine, this is how we met! Aidan - It's great to hear others are actually using the cars properly too! Since changing the water pump we've had no problems, the car is running with the temp gauge pointing at the H, but to be fair to the car, it is ridiculously hot here and I don't blame it, the heat is not causing any running issues at all though! I enjoyed the German autobahns, found out what the top speed was, managed to cross 121 mph on the flat, could not push her any further, that was a dead limit at that speed! All fun and games! Henry

Hi All, For those of you that don't already know, my girlfriend Ella and I are currently on our tour of Europe in the GT6. I was asked by a few of my TSSC Southern friends and others to consider doing a blog of the tour to act as (hopefully) an inspiration to others with the classics, and also I hope it'll be an interesting read for you all! We are currently 6 days into the tour and are currently in Bratislava! Catch up on all the fun here --> http://gt6ineurope.co.uk Henry

That's handy to know. My spare D-Type pinion was 15T, I'm assuming the one in the car is also. Henry

Haha, I just thought I had two gauges, one was knackered and one was immaculate, so I took the balance wheel out of the immaculate gauge and preserved it so that one can be made original again if needs be, and modified the bits that didn't matter instead! Both gauges are 980 TPM units, or at least, they were when new! I believe the old one was the cars original gauge but it must have been modified when the overdrive and differential were done assumably many years before I had the car. I have an extensive history file for the car, so I imagine I'll have some paperwork to confirm all of the above if I dig deep enough! Gully - To confirm, it said 980 on the housing, but had been tampered with internally. Henry

Gear worked, odometer is now correct. Balance wheel didn't work. But I got the soldering iron, power drill, laser tachometer on it and now it is bang on over the whole speed range! Success!

I've now swapped the gear and the balance spring over. Time to test!

Making progress here. So I have taken my new speedo and my old speedo to bits, done measurements and maths and have found the fault. I said earlier that my speedo ideally needed to be 1190 TPM. Took the new speedo apart to find this; 1 start on the worm. 20 teeth on the pinion. That's a 20:1 ratio. So every 20 turns of the input gives one push on the clock gear. That has 49 teeth, so 20 * 49 = 980 TPM as expected. The old speedo; 1 start on the worm. 20 teeth on the pinion. That's a 20:1 ratio also. Every 20 turns of the input gives one push on the clock gear. However this one has a 59 tooth gear, so 20 * 59 = 1180 TPM which explains why that used to work. It is obvious now too as this gear is made of brass and clearly isn't designed for this gauge but fits fine and works. I'm going to pop that gear in my car and see what happens now! Henry

Dave Twigger confirms that it's a 5 start worm and a 15 tooth pinion. Based on that my speedo should be 1190 TPM, or whatever is closest, most likely 1184 I think is the closest.

I think I'm right in saying that if it's a 5 start worm, for me, the pinion would need to have 18 teeth to read correctly... Correct me if I'm wrong. I spoke to Overdrive Repair Services, but he wasn't too sure, he suggested the pinion would usually have 15 teeth, but sounded vague... I'll try Dave Twigger.

I wouldn't know if the J-Type parts would fit in a D-Type without looking at them both...

That's right. It'd be really nice if these parts suppliers would specify what parts are though, otherwise I have to phone them and get them to count the number of teeth on each gear etc... Henry

I was hoping there would be something like these available so fix the issue! I need a 3.64:1 to make my set up work perfectly!

Just did some maths. So my wheels do 918 turns per mile. That means the prop does 3,571.02 turns per mile. My speedo requires 980 turns per mile. Gully suggests it should require 1152 turns per mile. If Gully is correct that means the speedo drive is approx 1/3 prop speed. 1:3 (Speedo:Prop) if I've got that correct. If that's correct and I was to have the perfect speedo, it would need to be 1271 TPM unit...

The output shaft / Annulus on the overdrive is what the worm gear is attached to, so the worm gear is running at propshaft speed, which in my case is 3.89 times wheel speed, however the ratio of the worm and the pinion in the overdrive could be changed, so without changing the speed of the Annulus, the output for the speedo could be changed if an alternative gear set were available. Of course, there doesn't appear to be any alternatives, so that would have to be custom made. Does anyone know what the ratio on the speedo drive is? Without having to dismantle it, I can't count the teeth... Is it just 1:1 (Annulus:Speedo Cable)? John, reading what you said, suggests that the ratio would be 1:1, agreed? Henry

Hmm, that's interesting stuff. Pete - I'll have to run the car down the road an measure it all up when I get a chance. Gully - That sounds like the most obvious problem there then. I guess that means the car has been upgraded to overdrive at some point and has never had the speedo changed... When you say re-calibrate though, that works for the needle, but the odometer can't be recalibrated, it needs gears replacing with different ones to change the speed, will they do that too? I might have a dig and just make sure I don't have any gears lying about that might work. John - The reason I mention the overdrive is because the worm and pinion gears that set the ratio for the speedo are contained in the overdrive, so wasn't sure if they were different between cars as they are changeable. Looking at part numbers on canleys would suggest that isn't the case. I was quietly hoping that would be a neat little fix there!

A slightly different one from the norm this time. I finally have a working speedo of the correct ratio to match the GT6, it came all the way from the states! It's in lovely condition and works perfectly. However, it hasn't been very easy to calibrate the speed, and also it would appear that the odometer is over reading by about 3 miles to every 7 (as in, it says 10, I've only driven 7...). I haven't had a proper working one in the car for years so I've never been sure what has been going on. The speedo is a 980 tpm unit, which matches the old one. I changed the overdrive not so long ago, which is the part that drives the speedo. This is a Laycock D-Type unit. Are the Spitfire MKIV ones different to the GT6 MK3 ones at all, other than the output flange? I'm wondering if the speedo drive ratio could be wrong... The diff is a 3.89:1 as standard. The tyres are slightly different 175 70 13, instead of 155 80 13 or whatever the standard size is, haven't done any maths to see if that makes much difference... I'll do that now! I reckon that's negligible. Cheers, Henry

That's a step better than mine were before I made the new brackets. And with anyone in as a passenger it was awful! Keep us informed. Henry

My back wheels were exactly the same on the GT6 with JBW alloys, got fed up with the suspension ripping the balance weights off the wheels every time I had the tyres changed so I've now got 20mm spacers on the back that get the wheels out further so they don't touch any more.