Borg Warner 35 Advice
Discussion
I have a 1592cc Sunbeam Alpine Automatic from 1965 fitted with a Borg Warner 35. This gearbox was really common in old classics and was put into MGs, Rovers Triumphs etc.
I have had the car for 20 years+ but I am certain that it is slower now than it used to be. At about 55-60mph it is getting quite frantic and is not pleasant on the motorway. When new this car would do over 90 mph, if I tried to do that now the engine would go bang before it got anywhere near that speed!
In top gear the drive is 1:1.The engine is in good healthy condition and I think if it was a 1600cc manual being driven at 1:1 it would be MUCH faster.
My query is whether there could be something in the automatic gearbox or torque converter that is causing a loss of power between the engine and the drive wheels. I'm thinking could it perhaps be a pump not creating enough pressure, a valve releasing incorrectly or a drive band slipping or something like that? All of the gears seem to be engaging correctly, the car pulls away in first goes to second almost immediately and then into top at about 15-20mph which is what the manuals says it should do.
I am pretty good with manual cars but automatics are quite alien to me and I would appreciate any advice or help that anyone can give.
Thank you,
Oily
I have had the car for 20 years+ but I am certain that it is slower now than it used to be. At about 55-60mph it is getting quite frantic and is not pleasant on the motorway. When new this car would do over 90 mph, if I tried to do that now the engine would go bang before it got anywhere near that speed!
In top gear the drive is 1:1.The engine is in good healthy condition and I think if it was a 1600cc manual being driven at 1:1 it would be MUCH faster.
My query is whether there could be something in the automatic gearbox or torque converter that is causing a loss of power between the engine and the drive wheels. I'm thinking could it perhaps be a pump not creating enough pressure, a valve releasing incorrectly or a drive band slipping or something like that? All of the gears seem to be engaging correctly, the car pulls away in first goes to second almost immediately and then into top at about 15-20mph which is what the manuals says it should do.
I am pretty good with manual cars but automatics are quite alien to me and I would appreciate any advice or help that anyone can give.
Thank you,
Oily
I've got the same box in my classic. The service manual calls for fluid changes every ten thousand miles (from memory, it could be more). Maybe get a specialist to give the box a good sere, depending on where you are it should be in the order of a few hundred £. Most places will have experience of the BW35 as it was so ubiquitous.
Good luck.
SD.
Good luck.
SD.
What you need to establish is if the combination of TC and the box are slipping when in top gear.
If at say 50mph you put your foot down in top, without using kickdown, are the revs increasing at the same rate as speed. If it isn’t and you have slip then that is your problem.
I would drop the pan and see what is sitting on top of it, as the bands/plates wear that is where they end up. A fluid change might help but you need the old school ATF rather than the later fancy transmission fluids. If you used the wrong type it affected the quality of the changes.
Just to add, I will assume you check fluid levels regularly, because if/when the modulator goes, as they did on BW35s, it can suck the transmission fluid out of the box leaving it short.
If at say 50mph you put your foot down in top, without using kickdown, are the revs increasing at the same rate as speed. If it isn’t and you have slip then that is your problem.
I would drop the pan and see what is sitting on top of it, as the bands/plates wear that is where they end up. A fluid change might help but you need the old school ATF rather than the later fancy transmission fluids. If you used the wrong type it affected the quality of the changes.
Just to add, I will assume you check fluid levels regularly, because if/when the modulator goes, as they did on BW35s, it can suck the transmission fluid out of the box leaving it short.
Never use Dexron fluid un a BW35/65, it destroys them very quickly, " Ford" period spec ATF is all you should use.
If you have noticed a difference, then it is not about right lol. and if it has had Dexron in it, then bank on a rebuild.
Made that mistake, once lol, on a leaky P6 V8.
If you have noticed a difference, then it is not about right lol. and if it has had Dexron in it, then bank on a rebuild.
Made that mistake, once lol, on a leaky P6 V8.
Edited by anyoldcardave on Saturday 23 March 10:22
Thanks for the replies. It has Ford ATF in it which is correct. The Rootes manual says that the fluid should NEVER be changed (but it has been previously and has not had an incorrect fluid in it, at least not for the last 20+ years). I know of people who have only had problems after changing the fluid because there is friction material suspended in tel fluid and when you change it for fresh fluid you get problems.
I was hoping that someone might know a specific thing in the box that could cause it to lose some of the power. I am pretty certain that it used to drive faster at similar revs in the past.
I will try and get a specialist to look at it.
Oily
I was hoping that someone might know a specific thing in the box that could cause it to lose some of the power. I am pretty certain that it used to drive faster at similar revs in the past.
I will try and get a specialist to look at it.
Oily
There isn’t any downside to changing the fluid, unlike manual boxes autos are all about keeping the transmission fluid clean. So much so in fact that as they have evolved many boxes have incorporated filters in them that are changed as service items to help achieve that. Even in BW35 days they had a magnet inside to catch any stray metal particles. When the fluid is changed most of it is left inside the torque converter anyway so you are unlikely to ever change all of it.
The colour and even the smell of the fluid will give clues as to the condition of the box. Probably best to let someone familiar with them have a look at it for you, they can do a stall test on the TC, have an quick look inside the box and hopefully work out what is or isn’t going on.
The colour and even the smell of the fluid will give clues as to the condition of the box. Probably best to let someone familiar with them have a look at it for you, they can do a stall test on the TC, have an quick look inside the box and hopefully work out what is or isn’t going on.
Forty years since I looked at one so totally disregard as necessary.
Worn/slipping/badly adjusted brake bands or clutches?
Did find pdf manual at https://cdn.triumphowners.com/wp-content/uploads/2...
If you are really lucky its not the converter/gearbox and just brakes binding...
Worn/slipping/badly adjusted brake bands or clutches?
Did find pdf manual at https://cdn.triumphowners.com/wp-content/uploads/2...
If you are really lucky its not the converter/gearbox and just brakes binding...
What does the fluid look like when you dip it. It should look like cherryade, if darker/bits in it, smells burnt then the box is slipping. If it is then it'll need a rebuild. Best way to check torque converters is a stall test. The manual should tell you the stall speed. As the boxes age the seals harden then the line pressure drops & then they start to slip. If you sort it quick enough then a quick recon should be relatively cheap.
They are a very simple box, my father was BW trained on these things so some things rub off.
They are a very simple box, my father was BW trained on these things so some things rub off.
tr7v8 said:
Best way to check torque converters is a stall test. The manual should tell you the stall speed. As the boxes age the seals harden then the line pressure drops & then they start to slip. If you sort it quick enough then a quick recon should be relatively cheap.
They are a very simple box, my father was BW trained on these things so some things rub off.
Doing a stall test on anything this old is like asking your grandad to give you a piggy back upstairs, hence why I suggested getting someone more familiar with them to do it.They are a very simple box, my father was BW trained on these things so some things rub off.
(also BW trained)
981Boxess said:
tr7v8 said:
Best way to check torque converters is a stall test. The manual should tell you the stall speed. As the boxes age the seals harden then the line pressure drops & then they start to slip. If you sort it quick enough then a quick recon should be relatively cheap.
They are a very simple box, my father was BW trained on these things so some things rub off.
Doing a stall test on anything this old is like asking your grandad to give you a piggy back upstairs, hence why I suggested getting someone more familiar with them to do it.They are a very simple box, my father was BW trained on these things so some things rub off.
(also BW trained)
Puddles of Oil said:
Thanks for the replies. It has Ford ATF in it which is correct. The Rootes manual says that the fluid should NEVER be changed (but it has been previously and has not had an incorrect fluid in it, at least not for the last 20+ years). I know of people who have only had problems after changing the fluid because there is friction material suspended in tel fluid and when you change it for fresh fluid you get problems.
I was hoping that someone might know a specific thing in the box that could cause it to lose some of the power. I am pretty certain that it used to drive faster at similar revs in the past.
I will try and get a specialist to look at it.
Oily
Changing the fluid should not cause problems, friction material suspended in old fluid, is a worn out box. I was hoping that someone might know a specific thing in the box that could cause it to lose some of the power. I am pretty certain that it used to drive faster at similar revs in the past.
I will try and get a specialist to look at it.
Oily
The only things making it rev higher than usual can be slipping or not changing into top.
Not sure how interchangable they are, bought 3 from a Ford dealer in Ireland a while back, crated, I would have thought the tail shafts are standard Ford, the bell housings and tourque converters are for 1703cc four cylinder and 2556 6 cylinder, Consul/Zephyr/Zodiac. One has gone, the one on bottom of the pile, the crate fell to bits, the 4 cylinder one is still in the crate,
I had similar symptons with my 2001 Fiat Punto where it was struggling to go much faster than 60 and I was wondering if the gearbox was not functioning as it should but it turned out to be just the head gasket needing resealing with some k-seal and it now runs great.... surely worth a try
I have a similar problem with a Singer Vogue Series 3 with Automatic Gearbox. The engine is a similar spec and type to your S4 Alpine It has a BW 35EP transmission which is probably also identical to yours. The major difference is a column change rather than (I suspect) your car having a floor change. The engine seems fine but the car, like yours would go to 90MPH max years ago does not want to exceed 60 these days.
I originally brought the car in 1990 from the first owner with a known engine fault. I had the engine rebuilt as a Greyhound reconditioned unit by Moores of Wilton (now long gone) and had the PA1AS Solex it was saddled with replaced by a Weber DCD and set up on a Dynamometer. The car passed to a friend in 2003. The friend sadly passed on earlier this year (2025) and the car returned to my possession a couple of months ago.
My next step is an Automatic Transmission expert who set the car up in 1990. The company is in Overton in Hampshire. I will let you know what he says.
If you want to try him yourself it is
Bill Knight
BK Transmissions
Unit 1 Hilltop Road
Overton RG25 3JH
Tel 01256 771577
billknight@live.co.uk
I originally brought the car in 1990 from the first owner with a known engine fault. I had the engine rebuilt as a Greyhound reconditioned unit by Moores of Wilton (now long gone) and had the PA1AS Solex it was saddled with replaced by a Weber DCD and set up on a Dynamometer. The car passed to a friend in 2003. The friend sadly passed on earlier this year (2025) and the car returned to my possession a couple of months ago.
My next step is an Automatic Transmission expert who set the car up in 1990. The company is in Overton in Hampshire. I will let you know what he says.
If you want to try him yourself it is
Bill Knight
BK Transmissions
Unit 1 Hilltop Road
Overton RG25 3JH
Tel 01256 771577
billknight@live.co.uk
I worked on several of these when I was younger. The 1600 was only 60bhp so I suspect wanting to get to 90MPH even in a manual will be unlikely.
In an Auto with pump losses etc. even less likely, even the later 1725 wasn't very quick. A mate had a late Hunter with the 1725 with a rally cam and a 28/36DCD and that accelerated well on cam but wasn't super fast at the top end. At the time I had a 1500 Cortina Mk1 and even that was super quick.
As I said earlier a stall test will check for torque converter slip but is hard on the box and if it is not well then it won't do it any good.
A specialist can check line pressure and set the bands up but slipping bands will not affect the top speed, it just affects the changes & change points.
In an Auto with pump losses etc. even less likely, even the later 1725 wasn't very quick. A mate had a late Hunter with the 1725 with a rally cam and a 28/36DCD and that accelerated well on cam but wasn't super fast at the top end. At the time I had a 1500 Cortina Mk1 and even that was super quick.
As I said earlier a stall test will check for torque converter slip but is hard on the box and if it is not well then it won't do it any good.
A specialist can check line pressure and set the bands up but slipping bands will not affect the top speed, it just affects the changes & change points.
Auto versions of many cars were given a lower ratio final drive, presumably to restore a bit of the get up and go when accelerating. A quick and easy way to improve the mph/rpm would be to source and fit a manual diff, much easier than swapping gearboxes.
Depends on what you want from the car long term.
Kim
P.s. Back in the day, I had a BW35 overhauled and the valve chest played with, along with a high stall torque converter, fitted to my Mk1 Escort which had a Daimler 2.5 V8 installed. The above mods gave it a real boost off the line. Don't know if those skills still exist though.
Depends on what you want from the car long term.
Kim
P.s. Back in the day, I had a BW35 overhauled and the valve chest played with, along with a high stall torque converter, fitted to my Mk1 Escort which had a Daimler 2.5 V8 installed. The above mods gave it a real boost off the line. Don't know if those skills still exist though.
hidetheelephants said:
ZF 4HP22/4HP24 used to be the box of choice, but it's not been made for 20+ years so availability isn't what it was. AIUI a reasonable proportion were non-ECU controlled variants which combined with 4 speeds and better efficiency made it a popular choice.
Believe there are a few Stags been converted to 4 speed ZF.Gassing Station | Classic Cars and Yesterday's Heroes | Top of Page | What's New | My Stuff