BW35 Goes forward in neutral

Milo

New Member
#1
I overhauled my BW35 (did work but was noisy and in a poor state) over a year ago and it ran fine apart from after the first week it wouldn't go in reverse after a long drive in the summer so i left it to cool down then it worked ok and i later readjusted the brake band and it never occurred again. A few oil leaks had appeared and as i pulled the engine to do the core plugs a couple of months ago i had another go at leak prevention on the BW35. During this i found some flecks of metal in the sump so pulled out the front clutch and found the metal was coming from damage to the hub ( i think i probably overlooked this on the original overhaul) so i sourced a good second hand one , i measured it to be within 0.25mm same as the original and the piston that came with it had a ball instead of a reed valve so i kept the piston matching the hub. All else looked fine in the trans.

Now i fitted it, set it up and it goes forward in neutral , reverse will go if you give it some revs but doesn't like it as it seems to be fighting the forward momentum , i have readjusted and double checked everything, after a few hours only conclusion i came to was the front clutch must be stuck so i pulled out the trans and found the front clutch was not stuck, i can turn the front shaft with grips whilst holding the output shaft so it may be tight but definitely not stuck in fact the whole trans looks fine nothing seems amiss. I did try the air test , the servos worked fine but couldn't really hear the clutches engage but it did throw the front clutch hub forward when i had the pump off and the front clutch piston moves freely if air is applied directly. Not sure what to try next.
 
Last edited:

harveyp6

Well-Known Member
#2
If the front clutch is dragging it will give you the problem you have. If it was fully stuck on it would drive forwards in NEUTRAL as if it was in "D", but then in REVERSE it wouldn't go backwards, it would just lock up because you have too many things in operation at the same time, front clutch, rear clutch, and rear band. You shouldn't need to use grips on the input shaft to get it to turn. Another thing that can cause similar symptoms is if the selector pin isn't engaged correctly in the manual control valve.
 
Last edited:

Milo

New Member
#3
Is there anything that can be done for a dragging clutch ? Makes sense that this is the problem as nothing else has been changed but as i am using a slightly later model clutch hub would this be the cause as if i bought a new set of clutch plates for a later BW35 they would be the same wouldn't they.
 

harveyp6

Well-Known Member
#4
It's difficult to say what you've done, but a mismatch of parts could be the problem. Clutch friction plates are all the same, but the steels are different in the front and rear clutches, and there are different thickness pressure plates for the different size clutch packs, and different hubs, but i can't really see how you wouldn't notice that.
 

Milo

New Member
#5
The only thing i changed was the clutch hub which is slightly different, measuring inside from the clip groove to the bottom the old hub is 0.25mm longer and after fitting the plates i have to push down to get the clip on but not with any great effort. Would driving it bed it in or is this likely to cook the clutch pack.
 

harveyp6

Well-Known Member
#6
You're talking about the drum not the hub. Any drag when the clutch is not engaged will eventually overheat it. Are you sure that all the steel plates you fitted were the ones for the front clutch?
 

Milo

New Member
#9
You're talking about the drum not the hub. Any drag when the clutch is not engaged will eventually overheat it. Are you sure that all the steel plates you fitted were the ones for the front clutch?
I got it confirmed today that the front clutch housing i bought uses the same clutch pack as the one it replaced, It turns easily with pliers on the spline so only lightly binding.
 

harveyp6

Well-Known Member
#10
Well there's something going on inside there somewhere, all I can suggest is take the clutch drum assembly out again, dismantle it and see what you find. To get any forward drive at all the front clutch has to be engaged, if you have forward drive in NEUTRAL that indicates that the front clutch is applied, even if only partially.
 

Milo

New Member
#11
Turns out the clutch housing i bought was stocked as a standard one using .068" steel plates but after careful measurements i have confirmed the housing is for .053" steel plates as from the snap ring slot to the pressure plate there is a difference of .060" between the two housings. I thought a new set of .053" steel plates would be the easy option but seem hard to find as was a good clutch housing previously. Not sure if its feasible turning down the pressure plate .060".
 

Milo

New Member
#14
I think 1.3 is just rounded off from 1.3462 as Fatsco list standard as .068" and under size as .053" and JPAT list them as 1.7mm and 1.3mm . I assume the BW35 was made using the imperial system. I took the plates to my local machine shop and he said he could shave the 4 plates down converting to metric but should be close enough.
 

Milo

New Member
#15
Now the cars on the road after the local machine shop shaved the plates down to 1.3mm and all is running fine now. Admittedly would have been a bit cheaper to order from Fatsco even with customs and post but was nice to support the old skool machine shop down the road as there aren't many left now.
 
Top