21 replies to this topic

[Old Bob]

OK, I have screwed up.......  Built a 1380 with all the good bits and the power now starts coming in at about 2,500 revs.  So far, so fine and while I am still running it in, the power delivery promises to be everything I had hoped for.

 

Problem is that I left the standard 3.4:1 final drive in and with a CR gearset, life isn't very pleasant in traffic - anti social might be one way to describe it!  Top speed isn't an issue so I want to drop the final drive ratio to perhaps 3.9:1 or 4.1:1

 

Question please.  How long would the job take and any helpful suggestions as the best way to proceed?

 

Thanks all.

 

Bob

[Artful Dodger]

Engine out job to change the FD ratio, you may be able to do it with it in but you would spend so much more time fannying around, it's easier to have the engine out.

Then when it's out, an hour if you know what you are doing.

Housing off
Speedo housing off
Diff out, crown wheel swapped
Pinion swapped, gears locked in two gears and torqued back up
Rebuild
Engine in:)

Probably a good days work, maybe more if you find other things to do!


Remember you need gaskets:P.

[robminibcy]

I need to do this on my engine. How do you lock / unlock the gears and tell which gears it is that need to be locked?

[Artful Dodger]

Looking on to the gearbox top down, diff towards you, look at the gear cluster. The two outer synchros (far left and far right) both need to go outward, so click the left synchro left and the right one right, this engages 1st and 4th gear, which locks the box out ad means you can torque it up:)

Don't lock them inwards, this locks 2nd and 3rd, and its not locked out proper, I did this on my SC box accidentally, and snapped a tooth on my gears :/. Had to crack detect the whole lot!! As well as buying a new gear!

[Old Bob]

Thanks for that.  I guessed it was an engine out again job but couldn't work out in my head if I would have to split the engine again.  Sometimes you can't see the wood for the trees!

 

Bob

[Teapot]

http://www.theminifo...-picture-heavy/

 

Few pics here when we changed Huey's fd to a 2.9.

 

 

 

 

[carbon]

As alternative to locking up the gearset as described above if the engine and box are still together you could instead put in top gear and then lock the flywheel using the time trusted 'used main bearing shell' special tool...

 

Avoids loading the gear teeth. Pinion bolt should be done up to 150ftlb, so the idlers won't get too hard a time.

[Artful Dodger]

^^.

Didn think of that:D

Main bearing shell does work:P better than a screwdriver!

[GraemeC]

To be honest, I'm surprised the 3.4 diff is a problem. With the power at 2.5k revs you must not be running a lairy cam so it should be reasonably tractable in 1st.
Given your other thread about a road trip I'd be wary about dropping the FDR too far as you'll be revving hard at any decent speed.

Edited by GraemeC, 29 December 2013 - 07:28 PM.

[minilee94]

^^^ normally a 3.44 is ideal for a 1380 etc

[Stiggytoo]

I have a 3.7 diff in very good condition if you are interested? 

[Old Bob]

To be honest, I'm surprised the 3.4 diff is a problem. With the power at 2.5k revs you must not be running a lairy cam so it should be reasonably tractable in 1st.
Given your other thread about a road trip I'd be wary about dropping the FDR too far as you'll be revving hard at any decent speed.

 

Sorry, probably didn't express myself clearly.  Currently the engine only starts to produce power at 2,500 revs (a 286 Kent cam) and I would like to be able to keep it comfortable around 4,500 - 5,500 for cruising.  A lower FD ratio would make it more tractable in traffic - in the crucial 15 - 25 mph range - and would attract a little less attention, while it should still be good for an acceptable road speed.

 

Bob

[Jordie]

i have run a 286 with 3.4 final drive and found it the best setup ive had, best of both.

 

If your changing the final drive ratio, you might need to change the C bracket around the pinion. I had to change mine when going from 3.44 to 3.1

[Guess-Works.com]

I'm surprised you're struggling with the 3.4 aswell.. 

 

I haven't run my 1330 for a while but when I did, it ran a 296 scatter on a GT close ratio gear kit and 3.4 final drive, power would not come in until 3.5k but was really easy to drive around town...

 

When I first built the engine, it had a 3.7 final drive, that lasted 5 days before the engine was out and it being replaced for the 3.4, I found any shorter than that was just undriveable at distance.

 

Yes it's an engine out, and I'd be wary of trying to use the clutch to hold the gearbox...

[Old Bob]

Thanks everyone.  Perhaps I am being over eager.  Engine only has about 300 miles on it so still very stiff and the competition clutch and orange diaphragm probably isn't helping in traffic either.   I should perhaps complete the full running-in to get a better idea of the available torque at low speeds before making decision.

 

Bob