this is dead

[stuarthardy]

Hi Simon

I was in the middle of replying to your problems with your 420 when I got a 'phone call and had to leave the computer. When I returned and tried to post my reply the forum demanded that I log in. I don't understand why this would be the case as I am permanently logged in.

I've decided that life is too short to be mess around with this, the World's worst, forum so I'm sorry but I was trying to help.

Regards
Stuart

[555ttg]

Hi Simon.
The 420 may have the wrong diff, for it to be running 4000rpm @ 70mph, is a bit excessive, unless it is stuck in 2nd gear. They had the BW35 'box,(I think,pls correct me if I'm wrong), not the most forgiving of auto units.
Been busy just recently, went to the USA to bring back a very early,(Oct 75 production), XJ-S. Original owner, 54000 miles, original paint and tyres!
Needs a good fettling, but runs nice and smooth, gears change and brakes are new! The interior is fabulous, with decent seats and non-sagging headliner too! Silver(faded) on Black. I've always had a soft spot for the pre-HE cars, I like the gearbox, not many people do, but it is a different car to drive than the cars with the GM 400. Anyway, it's based on the XJ saloon! Other projects taking my time are a 1969 MGB GT auto(funnily enough, it too, has the BW35), and a '73 Triumph GT6 MkIII.
Father's day here on Sunday, so Happy father's day to all over there too.
See you!

[stuarthardy]

Hi Simon

I'll try again now that I've calmed down.

I also have a 420 with autobox. It is a BW Model 8 and should have the following ratios:

1st 2.4:1
2nd 1.46:1
3rd 1:1
Reverse is 2:1

Maximum torque converter ratio is 2:1

Final drive ratio should be 3.31:1 for either auto or standard manual and 3.77:1 for an overdrive manual. Diff should have limited slip.

From memory my car does between 2000 and 2500 rpm at 70mph, so yours clearly has a problem. It is not inconceivable that your gearbox and/or final drive has been replaced with a different item. You should be able to easily identify the gearbox type and Bob Bate's excellent articles in the club magazine can help you here. I remember reading the one on the model 8 gearbox and, if I recall correctly, he even tells you how to tell the different types of 'boxes apart. I think that is a good starting point if you have access to those magazine articles. If not then I'm sure we can find a way to get you access to them.

Check to see that you are getting all 3 gears by setting off in D1 and 'feeling' for 2 gear changes, they are fairly smooth on mine and you need to be looking for them unless you're pressing on.

The other thing that is possible is that you tachometer is over-reading. Mine wavers like made and often gets stuck at higher revs than I am actually running. This is more possible than you might think because of the nature of the electronic tacho' and the infrequent use that our cars get.

I'm no expert on these matters but have come across some strange things in the course of classic car ownership.

Good luck.

Regards
Stuart

[simon4253]

Hi to you both and thanks for the replies. Sorry was out and about at the weekend as the weather was nice for a change! The 420 has a bw35 box so probably has been changed but as it has had a few owners since returning from texas the history is sparse! It does sound like the rev counter is telling the truth so will try and find tech articles on box from past issues. I don't think the diff has been apart recently but the box looks like it may have been changed when the engine was rebuilt a couple of years back.The xjs sounds good but although the bw auto is very smooth I was more impressed with the ratios in the gm400 and the economy was better as a result. I did find getting of the line in the wet was tricky but spectacular! Good luck with mgb I guess your back is better than mine? I have spent last two weeks when not doing ford mondeo (for dad!) finishing a 1956 split screen minor for a friend and a wolseley 18/85 I bought for a number plate for one of the daimlers. I blame aboring sunday and ebay!