Borg Warner 35 Advice

[Puddles of Oil]

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

[hidetheelephants]

Sounds about right for a non-overdrive car, they're not geared for hammering down motorways.

[shed driver]

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.

[981Boxess]

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.

[anyoldcardave]

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.

Edited by anyoldcardave on Saturday 23 March 10:22

[Puddles of Oil]

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

[981Boxess]

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.

[J__Wood]

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...

[tr7v8]

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.

[finlo]

It should be pretty obvious if it's slipping as it will get very hot very quickly.

Very simple to overhaul, when I ran V8 SD1's I could have the very similar BW 65 Striped to the bone in about 15 minutes.

[981Boxess]

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.

(also BW trained)

[tr7v8]

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.

(also BW trained)

I quite agree, a decent specialist is his best port of call

[anyoldcardave]

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.

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,

[Rob tvr S2]

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