gav- Posted March 11, 2007 Share Posted March 11, 2007 took new (to me) 200tdi disco for a drive, and i am sure that the speedo is reading wrong, it feels faster and is keeping up with cars in front despite only reading between 40 and 50. comparing revs and gears with my 300tdi it looks like its doing 70 but reading 60ish. the transfer box reads 28E which is standard ratio 1.2. what other ways are there of changing the ratio, assuming the speedo is reading correctly. I mean, can you alter the ratio in the tranny box and still mount it in a 28E transfer case?(i know thats a stupid one but is it likely), is there a nother way of changing it without transfer or diff changes?/ it has me stumped, its got standard tyres on Quote Link to comment Share on other sites More sharing options...
western Posted March 11, 2007 Share Posted March 11, 2007 The speedo drive gear my be incorrect have a look here Quote Link to comment Share on other sites More sharing options...
yella 90 Posted March 11, 2007 Share Posted March 11, 2007 what size tyres are they 205's are i believe the std size for a disco 200, but i will stand to be corrected by anyone..... ? dan Quote Link to comment Share on other sites More sharing options...
Orange Posted March 11, 2007 Share Posted March 11, 2007 205/80/16 I believe are the standard ones.........part worns are rare as rocking horse excrement round here!! Trying to find one to complete an MoT set was a nightmare!! If the speedo drive gear is different from standard, it could be a parts counter mistake or it could point towards a much harder life for the transmission having had larger tyres fitted!! Quote Link to comment Share on other sites More sharing options...
Turbocharger Posted March 12, 2007 Share Posted March 12, 2007 But 205 tyres are cheap as chips anyhow - is it really worth creating an MOT set and running on 'others' anyway? Quote Link to comment Share on other sites More sharing options...
hedley Posted March 12, 2007 Share Posted March 12, 2007 205/80/16 I believe are the standard ones.........part worns are rare as rocking horse excrement round here!! Trying to find one to complete an MoT set was a nightmare!! Not trying to split hairs, but i thought the standard size was 205/75/16's, which are slightly smaller. Quote Link to comment Share on other sites More sharing options...
Orange Posted March 12, 2007 Share Posted March 12, 2007 But 205 tyres are cheap as chips anyhow - is it really worth creating an MOT set and running on 'others' anyway? The MoT set were being created cos the Machos we had weren't in any way legal from the amount of cuts and scrapes!! Nothing serious, but the inspector wouldn't have liked them!! I bought a set of 5 disco rims and 3 had tyres on. Made sense to try to find one to make a legal set for the MoT. It's all a bit academic now as I've taken that motor off the road and got myself another one that came with a nice legal set of tyres!! I wouldn't be the first to have more than one set of wheels/tyres!!! PS - Hedley - you may be right, but 205/80 sounds correct in my head!! Maybe the ones I have aren't original fitment size, then!! Quote Link to comment Share on other sites More sharing options...
BogMonster Posted March 12, 2007 Share Posted March 12, 2007 Standard fit are 205R16 (which is the same as 205/80R16 by the way) or 235/70R16, both of which are the same diameter to within a gnat's whisker. Some tyres are branded 205R16 and others are branded 205/80R16. I understand that if a tyre does not carry the /xx aspect ratio then you should assume it is /80 (though confusingly this doesn't apply to imperial sizes e.g. 7.50R16... ) and therefore it should be OK to use a mix of 205R16 and 205/80R16 on the same vehicle as long as the MOT doesn't get stuffy about different makes of tyre. As for the speedo - it shouldn't be "out" because under-reading indicates a speedo drive intended for smaller tyres, fitted to a vehicle equipped with larger tyres, so if the vehicle has a different speedo drive fitted it should actually be over-reading since 205R16s are the smallest factory tyre size. Borrow a hand held GPS like an eTrex would be my advice, they are very accurate in measuring both speed and distance on the trip meter (to check the odometer) you should quickly find out if there is a problem or not. Quote Link to comment Share on other sites More sharing options...
gav- Posted March 16, 2007 Author Share Posted March 16, 2007 is the speedo drive gear located at the speedo end or of the back of the gearbox? am running 235/70 tyres. is there a way of checking the ratio of the high transfer box without using the speedo. i was wondering if the internals of the box had been changed, or how easy is it to replace the speedo drive gear? I am looking at a 1.4 ratio box, so if i have already got one then i dont need to buy it!!! cheers Quote Link to comment Share on other sites More sharing options...
simonb Posted March 16, 2007 Share Posted March 16, 2007 is the speedo drive gear located at the speedo end or of the back of the gearbox?am running 235/70 tyres. is there a way of checking the ratio of the high transfer box without using the speedo. i was wondering if the internals of the box had been changed, or how easy is it to replace the speedo drive gear? I am looking at a 1.4 ratio box, so if i have already got one then i dont need to buy it!!! cheers Its at the transfer box end and held in by a metal fork with a 10mm bolt. Someone will post a clicky on here of the parts cat for you. Take it out and check colour of nylon gear for the type of tyres you have. There is a link on the tech forum. Quote Link to comment Share on other sites More sharing options...
Yostumpy Posted March 16, 2007 Share Posted March 16, 2007 next time your on the m/way tuck in behind several different lorries, they max out at 60mph on the tacho so you'll know how far out your speedo is!! Quote Link to comment Share on other sites More sharing options...
gav- Posted March 16, 2007 Author Share Posted March 16, 2007 i can check the speedo using gps. I was wondering how i could check the transfer box ratio really Quote Link to comment Share on other sites More sharing options...
simonb Posted March 17, 2007 Share Posted March 17, 2007 i can check the speedo using gps. I was wondering how i could check the transfer box ratio really Somewhere on this forum is a table which gives road speed per 1000 engine revs for different Transfer/main gbox ratios and tyre sizes... or you could work it out, its not that difficult. Quote Link to comment Share on other sites More sharing options...
western Posted March 17, 2007 Share Posted March 17, 2007 It's in the Tech Archive under the gearbox info list, BUT it's not working seems to want to look on internet for a suitable program to open it. IIRC Mark90 posted it originally. Quote Link to comment Share on other sites More sharing options...
gav- Posted March 17, 2007 Author Share Posted March 17, 2007 i have an excel spreadsheet with all the ratios worked out. I am just trying to fiqure out a way of finding the transfer box ratio, without using the speedo/gps at all. i cant think of any ways so i am just going to take the gear out of the speedo drive tomorrow and have a look Quote Link to comment Share on other sites More sharing options...
dirtydiesel Posted March 18, 2007 Share Posted March 18, 2007 Standard tyres are 205R16, Which are close but not the same as 205/80 R16. If the aspect ratio isn't marked on the side wall it is actually 82 (not 80). The above is covered in a reasonable amount of dept in the mot testers handbook. Quote Link to comment Share on other sites More sharing options...
simonb Posted March 18, 2007 Share Posted March 18, 2007 i have an excel spreadsheet with all the ratios worked out. I am just trying to fiqure out a way of finding the transfer box ratio, without using the speedo/gps at all. i cant think of any ways so i am just going to take the gear out of the speedo drive tomorrow and have a look well if you don't want to do it by road and engine speed there are 4 options: 1) see if ratio sticker is still stuck on side of case below filler plug 2) remove PTO cover and input gear and count teeth. Can't remember what number of teeth the gear has for 1.2 ratio though. Also there is one type of ratio which prevents the gear being withdrawn, don't think its the 1.2 though. 3) remove bottom cover and count teeth as per 2) and also on the intermediate gear cluster, OR email Ashcrofts with box serial number! Quote Link to comment Share on other sites More sharing options...
gav- Posted March 18, 2007 Author Share Posted March 18, 2007 i have the serial number and its a 28E, which is a standard 1.4. I tried to pull out the speedo drive on the transfer box end, but couldnt be arsed with it and didnt find the gear that was mentioned above. Theres no sticker on the box, and it looks like when i drain and replace the oil, i will have a gander inside, would be wise to anyhow. Everything not as it seems though, as I appear to have 24spline diff on the rear axle on a disco, at least if i can count! Quote Link to comment Share on other sites More sharing options...
western Posted March 18, 2007 Share Posted March 18, 2007 I tried to pull out the speedo drive on the transfer box end, but couldnt be arsed with it and didnt find the gear that was mentioned above. remove the 10mm hex head bolt & U clip, then prise the housing out, & you need to twist the speedo drive gear to unmesh it with the gear inside & pull the gear where the speedo cable fits into it [don't use pliers or molegrips on the shaft part otherwise it won't be any use] to remove it from it's location Quote Link to comment Share on other sites More sharing options...
gav- Posted March 18, 2007 Author Share Posted March 18, 2007 cheers for that western, i thought it might be something like that, but couldnt be arsed to go any further with it today cheers Quote Link to comment Share on other sites More sharing options...
western Posted March 18, 2007 Share Posted March 18, 2007 Should only take 1/2 hour from start to finish at most to check the drive gear colour against the list I mentioned earleir in this thread. note the alloy housin that fits around the drive gear shaft has a 'O' ring seal on it, so the housing may jump out suddenly, as the sael passe the end of the hole & just before reassembly wipe a smear of gear oil or grease onto the seal. Quote Link to comment Share on other sites More sharing options...
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