Thread: Too Much Grunt

Originally Posted by BigJon

Trev - IMHO, you are asking for trouble. We recently replaced a TD5 Defender gearbox which had lunched fifth gear in a major way due to similar towing techniques (tandem axle trailer with a canvas box). This vehicle is regularly maintained (10 000km service interval, all oils replaced as required) and had done only 125 000km.

Thats a little scary but interesting! The manual does not appear to carry any warning on this, however is the construction such that fifth is weak? The thought of going all the way to Darwin in 4th gear is a bit daunting. Was there any hint of trouble before the gearbox went? noise, hard shifting etc? I have used synthetic from the moment it arrived home from the showroom floor and there is no hint of a problem. The gear box has a pump and cross drilled gears etc so I assume its built to be tuff.

Trev.

There were no warning signs that I am aware of. Mind you, it is very rarely that we get the entire story from a customer. I only know what trailer they were towing beause I happened to see it behind their rental vehicle a few days later. The 'box failed in / near Tennant Creek, some 500km north of here.

I wouldn't think that 5th gear is particularly weak. I think it is understood to be common knowledge that any overdrive gear shouldn't be used for heavy towing. We recommend that people with auto Discos (Series I and II) use 3rd rather than 4th when towing for this very reason.

Originally Posted by BigJon

There were no warning signs that I am aware of. Mind you, it is very rarely that we get the entire story from a customer. I only know what trailer they were towing beause I happened to see it behind their rental vehicle a few days later. The 'box failed in / near Tennant Creek, some 500km north of here.

I wouldn't think that 5th gear is particularly weak. I think it is understood to be common knowledge that any overdrive gear shouldn't be used for heavy towing. We recommend that people with auto Discos (Series I and II) use 3rd rather than 4th when towing for this very reason.

I'm getting more curious over treating fifth gear as an overdrive. I have always thought of it as a five speed gearbox, not a 4 speed plus overdrive. The wifes old Toyota " whatever" had an auto box with electric overdrive fitted, and this was stated as such. Should Landrover state that a Defender is a 4 speed with overdrive?

Trev.

I always thought that overdrive was when the output shaft (drive to the wheels from the transmission) revolved more slowly than the input shaft (drive to the transmission from the engine).

A search reveals:

http://en.wikipedia.org/wiki/Overdrive_%28mechanics%29

I am none the wiser.

Originally Posted by one_iota

I always thought that overdrive was when the output shaft (drive to the wheels from the transmission) revolved more slowly than the input shaft (drive to the transmission from the engine).

A search reveals:

http://en.wikipedia.org/wiki/Overdrive_%28mechanics%29

I am none the wiser.

Should that be the output shaft rotates "faster" than the input shaft. (lowering engine revs and increasing wheel speed).

"The overdrive consists of an electrically or hydraulically operated epicyclic gear train bolted behind the transmission unit. It can either couple the input driveshaft directly to the output shaft (or propeller shaft) (1:1), or increase the output speed so that it turns faster than the input shaft (1:1 + n). Thus the output shaft may be "overdriven" relative to the input shaft".

Trev.

Originally Posted by tombraider

George

More details please...

Modifications....? Tyre size? etc....

I think I know whats wrong!

Tombraider

I'm averaging a respectable 11.4 litres per hundred.
Tyres are BFG Muds 33 inch(285/75 R16)
I have the ZF auto conversion
upgraded intercooler and bruce davis chip (I beleive from a canberra landy specialist that the vehicle was used as a test bed for one of the mod chips and has realy been played with).
Bruce Davis did the original mods when he owned the rig.
Since I have owned it its had chronic overheating probs which has resulted in new radiator, water pump, welsh plugs, coolant cap, thermostat and now finaly I'm doing the head gasket (I beleive the head was the original fault but had been bodged up by the car dealer but no proof, It kept passing pressure tests over that time). I couldn't run it with the thermostat for the last year.
This weeked I will have the head off to be checked ready to put back together.

Hi there George130, re overheating..

I've just recently had my Defender TD5 head replaced, as it had a small pinhole/crack in the intake port, which was allowing the coolant to be consumed by the engine, but only when hot, and it didn't leave any telltale signs, except for a low coolant level (and all this happened in a short space of time - one 400km trip to Melbourne!)
I'd suggest have your head pressure tested again (tested hot too)
And make sure the head surface is not warped at all (apparently should be machined flat when removed)

I have been searching for the gearbox ratios to see if the fifth gear in fact meets the criteria for an "overdrive". ie it exceeds the 1:1 ratio for the input versus output shafts. The Rave disc basically says its a gearbox, (big deal), so like Iota, I am still none the wiser.

Trev.