5th Gear Mod

[tonyishuk]

I would welcome any comments about the mod with respect to :

 

1) Driveability off motorway

 

2) Driveability on the motorway

 

3) Effect on MPG,

 

My Rapido is 3.4 ton max weight with a 2.8 JTD. So power to weight ratio is not too much of a worry, but the jump to 5th is a real pain. I was wondering if the fuel used by over reving in 4th to get to 5th, would be offset by using extra fuel when motorway crusing. I assume the rev increase would be in the order of 500 RPM.

 

My calcs seem to say that I can still get nearly 80 mph at max revs !

 

(NOT that I intend to try it, before someone picks up on that comment !!!)

 

As always Thx in advance

 

[Guest peter]

I can't see why you would want to do it. My Rapido is 3.5 Tonnes all up and I don't have a problem. You just change up to 5th at about 45-50 mph and it still pulls like a train, and gives more MPG and less noise at cruising speeds.

[tonyishuk]

Thx for the reply

 

I take your point

 

My concerns mainly are :

 

1) Over reving the engine (although with an ecu, there should be a rev limiter). In a 2.8, there are fairly substantual lumps of metal at the end of the con rods ;-)

 

( Although I could probably do no worse than White Van Person with foot to the floor)

 

2) 45-50 mph is that sort of akward speed where you have to wait for the 5th gear to get going. Not to good if you want to do a quick (as much as one can ?) overtake.

 

 

3) The vehicle has only covered 4000 miles, so I suppose that it could do a few more before it looses up fully.

 

4) There seemed (from my rusty calcs, that there was quite a lot of MPH not usable ( both through speed limits and wind resistance) because the gearing is high.

 

5) Max BHP is at 3600 rpm, but this does seem ( to me from the sound of the engine) to be thrashing it . Maybe I scare to easily ?

 

Slightly O/T . I had a Caterham which I had the top gear modified and lowered and it made a termendous diffferernce. Previous to the mod, I could go faster on 4th than 5th ! My white van man asperations were in the making even in those days :D

 

Rgds

 

 

[mark lambert]

This may not be of help. recently read a report about 5th gear failures on 2.8 jtd pre 2002, could be due to over revving 4th gear which causes vibration in the gear box and snaps off the 5th gear teeth. If your van is pre 2002, be carefull with the high revs. I have just sold my mc louis 690 and it too suffered with the same problem of the rpm dropping very low after putting into 5th, normal behaviour i thought!

[Clive]

There are different 5th gear ratio,s available for the 2.8 JTD lump with not quite so long legs. It means you can change up earlier. Have a chat with your main dealer for details if this attracts you.

 

C.

[Mike Chapman]

Hello Tony,

 

The high 5th gear seems to be more of a problem on the 2.0 HDI than the 2.8. On a previous van we always seemed to be changing down to 4th because the engine often did not seem to have enough power to pull the higher gear. This should be less of a problem on the 2.8 but I suppose that it depends on vehicle type, weight and driving style, only you can determine if you think it is suitable for your vehicle.

 

You mention max BHP at 3600rpm but peak torque at 1800 rpm is probably just as important. You also mention that the vehicle has only covered 4000 miles and most diesels need 10000+ miles before they loosen up. Not sure what your experience of diesels is but general advice is to run them in at speed without thrashing them.

 

It is probably early days to decide whether a change of 5th gear ratio or tuning mods are required and my advice would be to stick with it for a while, put some more mileage on and if possible try and drive other models with the lower ratio to see if that suits you better.

 

Regards,

 

Mike.

[Guest starspirit]

I read somewhere (MMM?) that 5th gear failure was more of a lubrication issue than an overloading issue?

 

Maybe the gearbox needs to be good and warm before using 5th gear after which overloading is surely simply a matter of changing down before the engine labours?

 

I would have thought that the load on the gear train would be no greater when accelerating hard than when slogging up a hill in too high a gear and that neither event should cause failure?

 

My own 2.0hdi needs an early change on Motorway gradients if pace is to be maintained and dropping from 5th to 4th at just over 3000 rpm usually works whereas leaving the gear change until under 2500 rpm usually means using third as well because of the lack of torque below 300rpm.

[RonB]

Tony - Your quite right. We have had the fifth gear mod on our last two motorhomes, a 5 ton and a 4 ton, and it worked very well.

 

Fifth gear becomes much more usable with the rev band pulling well around 50-60 mpg, which is just where you want it. I mentioned in an earlier post on the subject that our mpg figures our not effected at all, no doubt due to the engine running more efficiently. The vehicles don't get breathless on motorways and we have'nt noticed any extra noise that some people seem to fear might happen. I have yet to find a downside to having the mod done and several converters are now fitting this mod as standard.

 

I did try our two local Fiat dealers when we decided to have it done but they had never heard of it! I finished up at Fiat agents Essanjay, Poole (01202 683608) who specialise in it. Its a quite simple job, changing a cog, cost around £300 and a couple of hours.

 

Have fun.

 

 

[tonyishuk]

As always, many thanks for your replies.

 

Its mod I think I will try, If it does not work to well, I suppose I could always get the original gears put back in (!) A couple of hours labour is the equivlant of a tank full of deisel !

 

I'll update the thread with any news and reviews .

 

Rgdse

[sshortcircuit]

I have found 5th gear to have so much torque that it is a pleasure to drive in 5th. I often change 3rd to 5th with no problem.

 

Will be interesting to find out what your costs are and how many 10,000 of miles required to recoupe cost

[Guest starspirit]

I suspect that this is a mod you do purely for convenience as it would take years to break even, if ever, and will probably not add any value to the vehicle when selling.

 

Indeed if mentioned to a dealer it might well even detract from the value as non standard things that they can't see tend to frighten people?

[sshortcircuit]

sshortcircuit - 2007-03-18 8:42 PM

 

I have found 5th gear to have so much torque that it is a pleasure to drive in 5th. I often change 3rd to 5th with no problem.

 

Will be interesting to find out what your costs are and how many 10,000 of miles required to recoupe cost

 

I should have said the 2.8 engine has so much torque and not 5th gear.

 

Too many "nnippy sweeties"

[RonB]

I cannot see any way that this alteration could detract from the value of a motorhome Richard. It's a Fiat warranted modification if fitted post buying, a Fiat warranted option at the time of buying and standard spec in a lot of cases. In fact I think the opposite is true due to the well documented fact that Fiats fifth gear ratio is a pain in the Ar.... on the 2.8JTD.

[Guest starspirit]

Yes Ron you might think that and I might think that but cynical old me could see a dealer taking a different view - so less said the better when trading in methinks?

[MARK3]

hi, if its any use ive a year 2000 2.8 idti engine in a chiefton tandem axle and 5th gear is not used under 50mph we tow a ford KA most of the time with no probs maintaining 60mph on most hills in fifth gear avg 22-25mpg.

Gearbox problems are because of lack of oil getting to the factory add on fifth gear assembly at the extreem end of the gearbox,remember gear box lubrication is not pressure fed but submerged and splash fed,the oil recomended is a bit on the thick side so it does pay to run in 4th gear(so as no load on 5th) for about 3ish mile to enable the oil to warm up so it achieves the required viscosity to reach the 5th gear assembly.

A few years ago I was a motor vehicle technition and we had exactly the same problems with ford gear boxes they added a 5th gear asembly on to the old 4 speed this was rectified by using auto gearbox oil and drilling a higher filling plug (so it holds more oil )in the gearbox casing after rebuild(may be worth having a word with fiat technical department).

having a quick look under a 2.8jtd the fifth gear looks integral to the gearbox so should not have a problem

sorry to rabbit on regards mark.

 

 

 

 

 

[Brian Kirby]

tonyishuk - 2007-03-18 7:40 PM As always, many thanks for your replies. Its mod I think I will try, If it does not work to well, I suppose I could always get the original gears put back in (!) A couple of hours labour is the equivlant of a tank full of deisel ! I'll update the thread with any news and reviews . Rgdse

Tony

You said you found the existing 5th a bit high in practice.  Ours is a more powerful version of the engine (2.8 146hp Fiat), but has a "short" 5th.  It may, however, have a slightly higher final drive ratio - I don't know.

I find the "short" 5th is an excellent driving gear, and not just an "overdrive" type 5th for motorway cruising.  In any case we avoid motorways as far as possible - too boring!

Re running in, at 4,000 yours is less than half way there!  I reckon these small diesels need around 20,000 before they are delivering their best.  You find the engines get a bit "gruff" when they've been working harder, and the point at which that comes in gradually extends as the miles pass.  After 20K the "gruff interludes" have basically faded out altogether, and the engines rev more freely. 

However, don't be afraid to let it rev.  They are (relatively) short stroke engines and revving them (within reason) is better than "pushing" them at lower revs in a high gear.  Change down rather than just pushing the accellerator harder, and just let the engine run up its rev range freely without too much load on.  The electronics will in any case stop you doing what you're trying to do long before you could do any damage. 

From memory, the power band is between about 1,500 and 3,600 rpm, and the max revs around 4,000 rpm.  However, the torque is fairly flat from 1,500 up, and ours always seemed about "right" between 2,000 and 2,500.  Somewhere just over 2,100 was about 70 MPH, and it would still pull strongly at 80 MPH on Autoroutes.  However, even with ABS I still got a bit uneasy with 3.4 tonnes doing 80!  Not an HGV by any means, but you do sense the weight if you do need to pull up sharpish.  After all, the running gear as standard is only fit for 3.3 tonnes and, so far as I know, only the rear springs are modified for motorhome use.