T25 Diesel 5 speed upgrade....Help & advise please

[shrekwoody]

Hi

I currently keep scrolling ebay & breakers & on here but never quite sure whats best

Ive recently converted my 1990 t25 from 1700 ky to 1900 1y diesel

Looking to upgrade to 5 speed box, looking for advise on whats best to use

Any help/advice be great from all you peoples on here

Many thanks, chris

[Oldiebut goodie]

Not necessarily an upgrade! Some are worse than a 4 speed. Search the forum and Aidan's posts will give you the lowdown on the suitable boxes.

[discipleofsketch]

Yep, the fifth gear won't necessarily be any higher than the 4th gear on a 4 speed, just more steps to get there and an extra low first in a strange position!

[California Dreamin]

Cheapest option would be to fit a bigger wheel/tyre combination..A cheap pair of Merc 15inch steelies on the rears fitted with 195R15C's will get you around 7% increase in circumference and likewise drop your revs by the same at any given speed..note* not to go too mad otherwise you won't have enough power to sustain 4th gear on the flat and you will find yourself having to drop down into third at the slightest headwind or hill.

martin

[CovKid]

I'm with Martin all the way on this. Fit bigger wheels - lot easier and more noticeable results. I run on 15" Merc steels and 195x70x15c tyres - 25 offset and no spacers needed at all. Its also (generally) cheaper for commercial tyres when you go up to 15" wheels as there are far more made in that size.

I do have a 5-speed box on my petrol but 1st is virtually useless (ask any 5-speed owner) - takes you 2 foot forward before you jump into 2nd and the final ration is more or less the same as a 4-speed. What made the real difference was upping the wheel/tyre size - flies along now and slightly more economical on long runs. 1st now takes me further and I have to wait a tadge longer before I can drop into 5th so it all works as it should. Oddly, the speedo is now spot on too - checked it with satnav many times. I always think T25s look ridiculous on 14" wheels anyway - they look too small in the arches.

In fact, if you look in my garage pics, the shot of my caravelle on a beach will give you a better idea of how the wheels/tyres look. They were 65s then but I'm now on 70s.

[Plasticman]

Yep, the fifth gear won't necessarily be any higher than the 4th gear, just more steps to get there and an extra low first in a strange position!

So you folks prefer 5 th in a strange dog leg position,

[discipleofsketch]

Yep, the fifth gear won't necessarily be any higher than the 4th gear, just more steps to get there and an extra low first in a strange position!

So you folks prefer 5 th in a strange dog leg position,

I have to confess i've never driven a 5 speed T25 box so i'm just repeating what someone told me - isn't it just like an extra very low 1st gear over to the left and back?

There were a few missing words in my original reply by the way, now edited!

[discipleofsketch]

I'm with Martin all the way on this. Fit bigger wheels - lot easier and more noticeable results. I run on 15" Merc steels and 195x70x15c tyres - 25 offset and no spacers needed at all. Its also (generally) cheaper for commercial tyres when you go up to 15" wheels as there are far more made in that size.

That's interesting - so did the merc wheels fit straight on with the standard studs at the rear?. I was looking at these on Brickwerks, and the description sais they need to be removed?:-

http://www.brickwerks.co.uk/index.php/m ... 5-112.html" onclick="window.open(this.href);return false;

I do like the look of big steelies!

[CovKid]

Straight on. You just have to remove the two small drum retaining bolts (nowt to do with studs) so the wheel sits flat on the drum. There are quite a few merc steelies that fit but you want an offset around 30 (ET30). As I say, mine are 25 (ET25) which works well enough and no shortage of suitable ones on ebay. The curvature of the seats of the nuts/studs are slightly different on Merc wheels but once tightened up they're fine - or you could swap them for Merc ones if you wanted. Mine have been on 8 years.

I must admit, I wouldn't go back to the stock ones now. Van sits fractionally higher but not so you'd notice. Tyre choice for stock wheels is more limited as its an odd size these days. An experienced tyre fitter (fits tyres to artics etc) took one look at mine and recommended I go up one size. I have to say, he was right. I find it much easier to pick up tyres now as I'm well and truly in the commercial tyre bracket cos of the 15" rims.

Set I have on now are commercial ones from a Mazda Bongo of all things but they only cost £40 for all four! Its not often I come across 14" ones and thats been backed up by several tyre outlets telling me that 14" is awkward when it comes to commercial tyres. They usually have to order 14" ones in whereas you can get 15" ones anywhere - particularly part worn. It'll help with gearing no end. Forget the 5-speed box - not worth the hassle. This does a better job in my view.

https://club8090.co.uk/forum/garage.php? ... ge_id=1836" onclick="window.open(this.href);return false;

I know lots go for low-profile stuff but I've never liked the look personally and besides, I like to go over speed humps, not have to slam my anchors on.

[gary1998]

sorry for jumping on here but i asked this question before never really got an answer
1y engine with the gearbox from the 1700 ky i have 195/70/r15 all round was thinking putting
bigger tires on back how much is too much should i go 215/70 x 15 or would 195/80/r15 do

[kevtherev]

I think your question has been answered
7% increase is about it.
Because you simply do not have the power to gear up into a 1/1 ratio

Cheapest option would be to fit a bigger wheel/tyre combination..A cheap pair of Merc 15inch steelies on the rears fitted with 195R15C's will get you around 7% increase in circumference and likewise drop your revs by the same at any given speed..note* not to go too mad otherwise you won't have enough power to sustain 4th gear on the flat and you will find yourself having to drop down into third at the slightest headwind or hill.

martin

If a C rated yre has no profile indicated it will be 82.

[CovKid]

If you jump to 195 80 15s, particularly if you have a fully kitted camper, you'll be undo any benefits as noted. I could get away with 80s but mine is sprightly to say the least and I keep the weight down as far as possible. Likewise if you go wider this will also affect the overall size and ratio.

[Bigjcc55]

http://www.etyres.co.uk/tyre-size-calculator" onclick="window.open(this.href);return false;
I used this to work out what sizes I wanted to lengthen the gears slightly but keep the front ok for speedo readings.

[keytouch]

Just doing some quick calculations-

185/80/14, diameter 652mm, circumference 2048.31mm

195/70/15, diameter 654mm, circumference 2054.60mm

so 0.34% increase, I'm getting confused, where is this 7% increase? Or is that for 195/80/15s?

[discipleofsketch]

Just doing some quick calculations-

185/80/14, diameter 652mm, circumference 2048.31mm

195/70/15, diameter 654mm, circumference 2054.60mm

so 0.34% increase, I'm getting confused, where is this 7% increase? Or is that for 195/80/15s?

I'm just bumping this thread, as i've been researching this. Using the calculator at the bottom of this page here:-

http://www.brick-yard.co.uk/vehiclespec ... ltwhls.htm" onclick="window.open(this.href);return false;

If you take the R in 185R14 to be 82% rather than 80% (the default on the calculator):-

185/82/14 = 654mm diameter, which is identical diameter to 195/70/15

195/80/15 = 693mm diameter, a 5.96% increase according to that calculator

elsewhere i've had 205/75/15 recommended (688mm, therefore 5.2% increase according to that calculator)

I'm not nitpicking by the way, or an expert in this area, just curious as i'm planning a tdi conversion next year