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speedo/transfer box


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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

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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!!

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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.

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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!!! :ph34r:

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!!

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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... :rolleyes: ) 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.

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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

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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.

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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.

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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

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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!

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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!

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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

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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.

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