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I'm posting this question for a fellow Stag buddy who has a BW35 Stag. Besides reducing the RPM's at speed by say 7%, what other effects does this have? Specifically he is asking about performance or pick up.
Thanks in advance. Sujit
The benefit of the 3.45 diff ratio is that cruising at 70mph becomes more relaxed, the engine is turning much slower and fuel consumption improves. I ran a 3.45 in the 2016 Round Britain event and one of the drivers achieved 38mpg.
Downside is that acceleration is reduced - 0 to 60 time is longer, but 99% of the time that is irrelevant. I notice because I do competition events and timing is critical! I have even run a 4.1 diff on a sprint event where acceleration was key. The other thing is that getting the speedo accurate can be a bit of a hit-and-miss affair.
My stag was BW35 auto and has a 3.45 TR6 diff fitted. It did lower the revs a little at motorway speeds else I really didn't notice any impact. Got off the line sharpish etc
Then I converted to a Manual J-type o/d but kept the 3.45 diff. Now I do notice the acceleration issue, needs more revs and clutch control to get it off the line quick, I guess that an advantage would be that in a straight line you have to work hard to spin up a rear wheel. The issue though is that 1st gear at idle speed the car is rolling at 10mph which is a PITA in stop start / heavy traffic.
For the limited miles that you use a stag for I would just stick to a 3.7 and spend the extra minimal amount on petrol.
Biggest issue I have found with the 3.45 is getting a diff back plate that fits the diff and can be mounted onto the stag! Triumph 2.5 estate I have been told?!? The stag 3.7 backplate fits but 2 bolt holes do not match up, fail here and the diff oil will drain out.
Stags and Range Rover Classics - I must be a loony
Changing to a 3.45 in a car with a BW 35 will re gear the car to approx. what a man od car with a 3.7 is. If changing you will need a rear cover from a Mk 1 saloon/estate or any 2000 or 2.5 Estate they are all the same as the Stag. Triumph in their wisdom changed the diff mounting for the Mk2 saloon only, not the Estate because all the Estates retained the Mk1 rear half. I have changed my Man OD to 3.45 using one of these covers, perfect fit. To correct the speedo I used a drive gear from a 2.5 J overdrive, according to TomTom the speedo is spot on at 100ks I don't know about correcting for a BW35.
Cheers Ian A
I have a 3.45 diff in the garage to fit. I am doing the rbrr in 2 months and was going to fit it for that, but I am now running out of time. It is running well with the 3.7. Also I don’t have the correct backplate, but was going to fit the current one minus the 2 bolts that don’t line up, as the majority say it is strong enough with the remaining bolts. Question is do I invest the time now or do I stick as I am?
My local Stag specialist In Poole thinks changing the diff to a 3.45 will produce economy and if touring is the main use of Stag, then that can be the cheapest way to improve mpg. Having initially replaced my diff some 4 years ago with the standard 3.7 diff because it was whining away, I was reluctant to change it again. But 70mph on the French motorways is slow and extremely noisy. The limit (when not raining) is 130kph/81 mph.
My recommendation would be to dive in and fork out the money on the Tate & Lewis ZF 4 speed conversion. If anything, it accelerates marginally quicker than through the BW 65 box, it can cruise comfortably at 70 mph at 2,500 rpm, and 80 mph is achieved at relatively quieter 3,000 rpm. The result is a marked improvement in mpg and obviously less engine wear.
I understand there are some Stags out there that have had both the T&L ZF 4 speed conversion alongside the 3.45 diff. It would be interesting for such owners to comment on this.
I understand there are some Stags out there that have had both the T&L ZF 4 speed conversion alongside the 3.45 diff. It would be interesting for such owners to comment on this.
Yes, been there, done that. I used 3.45 on the RBRR to good effect but overall I prefer the 3.7 with the ZF gearbox. Fuel consumption remains at about 30mpg
I have a 3.45 diff in the garage to fit. I am doing the rbrr in 2 months and was going to fit it for that, but I am now running out of time. It is running well with the 3.7. Also I don’t have the correct backplate, but was going to fit the current one minus the 2 bolts that don’t line up, as the majority say it is strong enough with the remaining bolts. Question is do I invest the time now or do I stick as I am?
With only nine weeks to go, I wouldn't change the diff. Spend the time making sure the car is otherwise right. My car is used for about 10,000 miles most years and still threw a wobbly on the last RBRR, that's after meticulous preperation....
I have the zf it was fitted mid December I then noticed the diff whined at 60 mph it was a 3.7 diff , so I changed to a 345 diff from Robsport the backplate fitted straight on and what a difference it’s awesome on dual carriageways ect can cruise at 70 mph at low revs and I don’t really notice any difference in torque when driving in town, the speedo does under-read by 3 mph but I have just got a speedo from a 2500 s to fit
With only nine weeks to go, I wouldn't change the diff. Spend the time making sure the car is otherwise right. My car is used for about 10,000 miles most years and still threw a wobbly on the last RBRR, that's after meticulous preperation....
I am hoping all will be fine with the car, I did the coast to coast (700 miles) in 2019, and the car does around 2000 a year. It is kept well. Difficulty is that you never know what might let go in 2000 miles over one weekend. Last time I did the rbrr in 2016 my Vitesse 2500 did not miss a beat, just hoping the stag is as reliable.
the diff has been in the garage to fit for 3 months, I just have not got round to fitting it. You’re right it’s a bit late with 9 weeks to go.
With an auto bw 35 a 3.45 diff is nice.
the torque converter helps with start up acceleration, imho it’s fine.
Also fine with a zf too.
might not be so good with manual o/d though.
There are 2 secrets to staying on top :- 1. Don't give everything away.
2.
9 weeks to go, you should change a diff in 2 days at home, an extra 2 days for changing the Quill bearing (SKF) and gusset reinforcing the Quill housing if not already done and drilling a small telltale hole in the bottom of the Quill extension that checks for a diff front seal leak.
Cheers Ian A
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