|
|
|
Hi guys !
Still a bit new to this world, I have few questions regarding the following subjects:
1)Diff
2)Brake booster
My car is a 245L from 1975 with a B20A mated to a M45. Around 125'000 miles / 200'000km
1) Rear diff:
My rear diff has in my opinion a short ratio. In 4th gear, my engine is running high in the rpm (can't give a number since I don't have a tacho) at 90km/h // 55mph. If I want to overtake, I need to go to a 65mph / 100km/h and the engine is really high in the rpm.
So, I need your expertise on that, should I swap a m47 instead (I know, that I have to find an early m47 because of the speedometer).
Or should I think about changing the ratio in my diff.
2) brake booster:
My brakes are working fine, however when hot, the brake booster makes a ticking noise when the brake pedal is not touch and when stationary. If i bend the vacuum pipe that links the brake booster valve to the engine, the ticking noise goes away. I read a lot of comment saying that the valve is the first thing to change but, in my case I am unsure if it's really useful to swap a new valve. Before installing a new brake booster, I would like to be sure that I do the right thing.
Thanks for your time !
Regards,
Tobias
|
|
-
|
|
|
Hi to all !
Thanks for your answers. I also thought that I had a M40 with my B20 until I crawl under the car and read the plate on the gearbox saying "M45". That's why I'm assuming that I have a M45.
Many of you mentioned a read end swap, which is a good idea. Actually, my rear end is making some noise when I let the accelerator pedal go and much less noise when I apply the clutch (while driving). I like the M45, so I will dig further in that route.
I would like to have your opinion on the question of the ratio: 3.9 seems to me to be the best option, the B20 is not very powerful so a 3.73 might be to much ? From your experience what's the best between the two ? I don't want to build my engine in order to have more power, I want to keep things stock.
Thanks for your input !
|
|
-
|
|
1975 was the last year the 240 was equipped with the M40, but it's likely the M45 simply took over when the M40 stocks had run out, so your's maybe one of possibly very few in the 1975 model year. The VIN won't give you any clues as the gearbox code part of it has "1" for both the M40 or the M45 (or "2" for M41 or M46). I don't know if Volvo needed to modify anything to mate the M45 to the B20, but I would expect so as it seems to me that the M45/M46 were introduced along with the (slanted) OHC versions of the redblocks.
To put things into perspective and give you an idea of rpms: I drive a 1992 245 with a 111 bhp B200F on a M47 and a 3.91:1 rear axle. On the factory 185R14 tyres, this would do an acceptable 2750 rpm at 100 km/h (62 mph) in top (5th) gear. But this isn't a fast car by any stretch of the imagination, 0-100 km/h time is 13 seconds (as specified by Volvo). Swapping to 3.54:1 would make this even worse.
A B230F on a 3.54:1 (or maybe 3.73:1) both had better acceleration (only 5 bhp more, but quite a bit more torque) and lower rpm at speed, so that engine could deal with the taller ratio.
The instruction manual lists three possible axle ratios for this model year and they were:
1) 3.54:1 (33 km/h per 1000 rpm in 4th gear, which is 1.00:1)
2) 3.73:1 (31 km/h per 1000 rpm in 4th gear)
3) 3.91:1 (30 km/h per 1000 rpm in 4th gear)
If you then calculate for 100 km/h rpm, you should have the following in 4th - and the reduction in 5th gear to:
1) 3030 rpm - 2485 rpm
2) 3225 rpm - 2645 rpm
3) 3333 rpm - 2733 rpm
So if you keep your current M45, which also has a 1.00:1 ratio in top (4th) gear, expect the rpms on the left if you swap the rear axle. >3000 rpm still sounds very "busy", but the overdrive adds quite some more reduction, as you can see.
If your B20A is only 90 bhp, like it was in my Amazon, I would consider keeping the current axle but switching - if possible - to a M46. You will need to find a shorter driveshaft too, of course.
The M47 route means cutting and welding two different bellhousings together. It can be done, but I forget if you can use your current driveshaft or not.
Edit: no you cannot. I found these pictures on a Dutch forum on mating a B20 to a M47.
The transmission mount must also be changed as the M47 is longer, but apparently the holes intended for automatic transmission mount come in handy.
|
|
-
|
|
|
Me too I have a early 245 with the B20. The late last owner changed to M41 and 3,91 axle. This combo makes the car easy on the Highway but will need a lot of shifting in the mountains. Right now I’m rebuilding the engine with a K cam and twin SU carbs, I hope I will feel the extra oomph when it’s finished.
Regards Michael
|
|
-
|
|
|
When I tore my B20A down I found it did acyually have a K cam (probably not factory original) and it was very nice to drive with loads of torque. Twin SUs basically makes it sort of a B20B (sort of because IIRC a true B20B had a different cam).
It is the overdrive of the M41 that does most of the reduction in rpm at highway speeds, it's why I recommend it over just a different diff. ratio.
A tighter ratio will indeed mean less shifting, at the expense of higher rpms at speed.
|
|
-
|
|
|
Two things Grey245 -- 1. I recommended an M46 because his M45 bellhousing will bolt on to replace the slant mounted bellhousing on M46's likely to be found coming from B21-23 cars with their slant mounted bellhousings.
2. Regarding your B20A - I power my '69 144 (the Volvo From Heck) with a B20B with a later cylinder head with the 44mm intake valves, a K cam, twin SU's and a little porting. If you really want to make the engine come alive--raise the compression ration. I don't know exactly what kind of power I'm making but it's easily more than a match for a good running B20E. - Dave
|
|
-
|
|
|
Does that mean that an M41 cannot be used in this particular car without changing to the normal (for a B20) bellhousing? Or is the gearbox end of the different bellhousings in the same place and position for both M40/41 and M45/46?
|
|
-
|
|
|
To use an M40/41 he would need the B18/20 bellhousing meant for those transmissions. The gearbox mounts to those bellhousings with external bolts--from the gearbox to the bellhousing. M45/46 bellhousings mount the gearbox with bolts from inside the bellhousing. Another difference is that the bellhousing on M45/46 transmissions doubles as a bearing/seal retainer/release bearing guide, while for M40/41's that job is done by the separate part that serves as the seal housing/bearing retainer/release bearing guide. I think the front U-joint is larger with the M45/46 so the OP with an M45 could have his front driveshaft shortened the necessary amount switching to an M46. - Dave
|
|
-
|
|
|
That's a clear answer, but wether the gearbox bolts on from the outside or from the inside doesn't mean the bolt pattern is different. Looking back at my picture, it looks like the M47 also bolts on from the inside, so maybe going to an M47 isn't that complicated if you already have a M45/46 bellhousing.
In a previous post I wrote that my M47+3.91 rear axle does 2750 rpm at 100 km/h in top gear, but today I found out it's much closer to 2500 rpm despite being on slightly smaller tyres compared to the factory original 185R14 setup (now Virgos on 195/65R15 which are about 2.7% smaller in diameter).
I know for a fact that the rear axle is 3.91:1 as that's what it says on the sticker on the axle. So either that's wrong (unlikely) or the tachometer is showing the wrong rpm at that speed (yet at idle shows a correct 750 rpm).
|
|
-
|
|
|
Agreed that installing an M47 in place of an M45 would relatively straight forward (except for the connection at the driveshaft---M45-U-joint---M47-the Guido(?) type joint). But I thought the question in your last post had to do with fitting an M40/41 to the M45 bellhousing. I can't really comment about your rear axle ratio except that all the owners manuals I have for 740 and 240 models show only 3.31 -- with some offering 3.54 as an alternative. One thing I did notice is that 5th in the M47 is a tighter ratio than OD with the M46 by a few decimal points.--Dave
|
|
-
|
|
|
Thanks for clearing up the question about the transmission type, although ratio-wise they are similar and in 4th, identical. I can tell you that a change from 4.3 to 3.9 will be enough to feel a difference at cruising speed. I built my first version of my VolvOldsmobile (aluminum 215 V8) on a 1976 265 body (originally a 3.54 ratio) and later swapped in a 3.31 from a 1975 164. It made a noticeable difference at speed. Now the V8 sits in a '93 245 (an auto equipped car w/3.73) but now I have a Camaro 5-speed installed so top gear is an OD ratio. If your car truly has an M45 it would not be a stretch to find an M46 as a bolt in swap (swap to the B20A bellhousing) that would provide you with the tighter lower gears but allow lower highway rpm due to the .80 OD ratio. Going from a 4.3 to a 3.9 would give you a 10 percent drop across all the gears. Going to a 3.73 would be more effective in top with the M45 but would be a lot for the lower gears. I'd go the M46 route if possible. -- Dave
|
|
-
|
|
|
Thanks for clearing up the question about the transmission type, although ratio-wise they are similar and in 4th, identical. I can tell you that a change from 4.3 to 3.9 will be enough to feel a difference at cruising speed. I built my first version of my VolvOldsmobile (aluminum 215 V8) on a 1976 265 body (originally a 3.54 ratio) and later swapped in a 3.31 from a 1975 164. It made a noticeable difference at speed. Now the V8 sits in a '93 245 (an auto equipped car w/3.73) but now I have a Camaro 5-speed installed so top gear is an OD ratio. If your car truly has an M45 it would not be a stretch to find an M46 as a bolt in swap (swap to the B20A bellhousing) that would provide you with the tighter lower gears but allow lower highway rpm due to the .80 OD ratio. Going from a 4.3 to a 3.9 would give you a 10 percent drop across all the gears. Going to a 3.73 would be more effective in top with the M45 but would be a lot for the lower gears. I'd go the M46 route if possible. -- Dave
|
|
-
|
|
|
According to my 1975 US/Canada owners manual your rear axle ratio is a very tight 4.3 to 1 which translates to 16.9 mph per 1,000rpm or a little over 3500 rpm at 60 mph - which is just over half the 6,000 rpm limit of the B20 (shift to 3rd for passing). It sounds busy alright (I owned a '75 245 w/M40) but not harmful to the engine. My guess is that the OP is mistaken that his trans is an M45 - far more likely to be an M40 (but ratio wise it makes no difference). If the rpm racket is too much to live with the easiest path to lower road speed rpm would be to do a rear axle swap. A '75 244 would have a 4.1 ratio. Early 240's with the B21 have a 3.9 ratio and later 240's (with auto trans) a 3.73. Early V6 equipped 260's (with auto) have a 3.54 ratio. The later 240's with standard shift (M46) have a 3.31 but I think that would be far too long a ratio for the B20. - Dave
|
|
-
|
|
|
adding to Dave's info on rear end swap.
" Early 240's with the B21 have a 3.9 ratio and later 240's (with auto trans) a 3.73."
My 80 B21 with M45 4spd. US model with the RED 55 mph on the speedometer, which maxes on the dial at 85MPH.
When the US National 55mph speed limit was dropped, and as highway posted speeds went to 65-70, I started looking for a 5spd. The driving I95 just keeping up with the 70mph traffic...
I still have the car, but rarely take it on the interstate, excepting short trips.
So, when swaping out the rear on your 75, look for at least 3.73 rear from an auto trans donor, as a swap to a 3.9 will make no difference at highway crusing speeds, esp with the louder pushrod B20 engine
Good luck
|
|
-
|
|
|
you might choose to rebuild it and have it balanced, D cam, polish the ports, make it happy at those higher RPM.s not much harder than swapping gears and trannys, a lot more fun ..:)
|
|
-
|
|
|
good luck finding an M47 that mates with a B20.
Best relief is an Overdrive fitted tranny.
M41---fitted to B20s---you do know that the 1975 240 was the last year for the B20. From 1976 on the engines were OHC---B21, B23, B230.
Fitted to the B20- M40 4spd and the M41 with OD
The M45 4spd and the M46 with Overdrive were fitted to the the B21...series.
The M47 for the B230 began in 1987 US model(1986 elsewhere)
The speedometers get a signal from the Rear...there is no cable or speedo gear in the M47.
Since you have a M45, the easiest would be to swap in an M46--the OD version of the M45. (Check the Driveshaft length with the OD trans)
I had a 75 with a M40 4spd----and yes it is a screamer at highway speed.
But remember in the US mid 70s to well into the 80s, the National Speed Limit was 55mph, so it really didn't matter. Radar detectors were big sellers back then.
|
|
-
|
|
|
PS
There is a difference between the M40 and the M45 trans.
the M40 that was stock fitted to the B20 has a Different Input shaft than the M45 that was stock fitted to the B21.
The M40 input shaft has fewer and thicker splines than th3 M45
IF you indeed have a M45 and NOT a M40 mounted to your B20, then the Input shaft on that M45 has been changed. The M40 input shaft has fewer and thicker splines.
Same for the versions of these trannies with Overdrives attached --- M41 and M46
I know this because I have owned both a 75 and and 80 with 4spd gear boxes as well as an 87 with an M47 5spd
|
|
-
|
|
|
M41+OD had become unobtanium even 20 years ago over here, so, IIRC, something that would be done was cut two bell-housings in half en weld them into a hybrid for the newer gearbox.
I don't know how available M46+OD still is these days...
|
|
-
|
|
|
1) I would go for the M47 option as a taller diff ratio might hamper performance in every gear without giving you much relief in top gear (the M45 doesn't have an overdrive IIRC).
2) I had an Amazon that used to do exactly that. The time honoured cure was to punch a hole in the valve inside the booster with an awl and fit an inline valve in the vacuum hose between manifold and booster.
|
|
|
|
|
